EP4100159A1

EP4100159A1 - Catalytic material and use thereof

Info

Publication number: EP4100159A1
Application number: EP21703759.7A
Authority: EP
Inventors: Shik Chi Edman Tsang; Shun Shing Simson WU; Huihuang FANG
Original assignee: Oxford University Innovation Ltd
Current assignee: Oxford University Innovation Ltd
Priority date: 2020-02-07
Filing date: 2021-02-05
Publication date: 2022-12-14
Also published as: WO2021156626A1; CN115485066A; CN120205163A; GB202001706D0

Abstract

A catalytic material is described, as well as a process for making the catalytic material. Also described is a use of a catalytic material in a catalytic ammonia decomposition process. The catalytic materials comprise a metal oxide and a metal M selected from Ru, Fe, Co, Mo and mixtures of two or more thereof, and are exceptionally active in the catalytic decomposition of ammonia, even at low temperatures.

Description

CATALYTIC MATERIAL AND USE THEREOF

INTRODUCTION

[0001] The present invention relates to a catalytic material. More particularly, the present invention relates to a catalytic material suitable for use in the catalytic decomposition of ammonia. The present invention also relates to a process for preparing the catalytic material, as well as an ammonia decomposition process employing the catalytic material.

BACKGROUND OF THE INVENTION

[0002] Catalytic ammonia decomposition has long since been regarded as an important tool in the environmental clean-up of gas or liquid contamination streams. More recently, ammonia has been suggested as an interesting alternative fuel to hydrogen due to its exceptionally high energy density as well as its ease in transportation for both stationary and mobile applications¹. Catalytic decomposition of ammonia generates hydrogen, which can be used to supply combustion engines or fuel cells. In contrast to the direct use of hydrogen gas for commercial applications, which itself presents handling difficulties and has a low energy density by volume, ammonia can be liquefied at 20 °C at approximately 8 bar, thereby allowing many of the safety problems associated with transporting hydrogen gas long distances to be circumvented. Furthermore, the carbon-free decomposition of ammonia via wind power and solar power has also significantly reduced the performance of fuel cells by CO and other carbonaceous side products² originated from carbon contaminants. Consequently, ammonia has been widely employed in H2 storage and other energy applications in recent years³·⁴.

[0003] However, until now, the decomposition of ammonia to yield hydrogen in significant quantities has only been possible at high temperatures due to the thermodynamic limit of the endothermic process and a lack of efficient catalytic strategies. In recent years, a variety of metal catalysts have been exploited for decomposition of ammonia, including Ru^{5 15}, Rh¹⁶·¹⁷, Pd¹⁶·¹⁷, Pt¹², Ni⁶'^18-20, Fe¹⁹ and Co¹⁶. Furthermore, many supports, such as S1O2⁵’⁶, AI2O3⁵’⁹, zeolite¹, carbon nanotubes⁹, activated carbon⁹, C12A7¹⁰, MgO^12-14, have been investigated and have shown moderate hydrogen production rates at high temperature (> 500 °C). However, none of these approaches have shown considerable activity at lower temperature, which renders them industrially impractical. This is mainly due to the limitation of the catalytic rate-determining-steps, such as N recombination and N-H bond breaking. Changing the reaction pathway is an attractive strategy for achieving high efficiency of hydrogen production via ammonia decomposition at low temperatures. [0004] The present invention was devised with the foregoing in mind.

SUMMARY OF THE INVENTION

[0005] According to a first aspect of the present invention there is provided a catalytic material comprising: a) a metal oxide, and b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide, the magnesium oxide comprising exposed (111) facets.

[0006] According to a second aspect of the present invention there is provided a process for the preparation of a catalytic material according to the first aspect, the process comprising: a) providing a metal oxide as defined herein, b) depositing a metal M on the metal oxide, wherein M is as defined herein, and c) optionally reducing the product resulting from step b).

[0007] According to a third aspect of the present invention there is provided a catalytic material obtained, directly obtained or obtainable by the process according to the second aspect.

[0008] According to a fourth aspect of the present invention there is provided a process for the catalytic decomposition of ammonia, the process comprising the step of contacting ammonia with a catalytic material comprising: a) a metal oxide comprising: i) magnesium oxide comprising exposed (111) facets, or ii) cerium oxide, or iii) magnesium oxide comprising exposed (111) facets and cerium oxide; b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof.

[0009] Suitably, the catalytic material used in the fourth aspect of the invention is the same as the catalytic material of the first aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Throughout the entirety of the description and claims of this specification, where subject matter is described herein using the term “comprise” (or “comprises” or “comprising”), the same subject matter instead described using the term “consist of” (or “consists of” or “consisting of”) or “consist essentially of” (or “consists essentially of” or “consisting essentially of”) is also contemplated.

[0011] Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0012] Features described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any of the specific embodiments recited herein. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0013] Unless otherwise specified, where the quantity or concentration of a particular component of a given product is specified as a weight percentage (wt.% or %w/w), said weight percentage refers to the percentage of said component by weight relative to the total weight of the product as a whole. It will be understood by those skilled in the art that the sum of weight percentages of all components of a product will total 100 wt.%. However, where not all components are listed (e.g. where a product is said to “comprise” one or more particular components), the weight percentage balance may optionally be made up to 100 wt% by unspecified ingredients.

Catalytic material

[0014] In a first aspect, the invention provides a catalytic material comprising: a) a metal oxide, and b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide, the magnesium oxide comprising exposed (111) facets.

[0015] The inventors have surprisingly found that the present catalytic material is particularly active in the catalytic decomposition of ammonia, even at relatively low temperatures. In particular, the catalytic material is capable of achieving hydrogen formation rates of 27.0 mmol g_cat ^'1 min^-1 at a weight hourly space velocity (WHSV) of 30,000 ml_ g_cat ^'1 h ¹ at only 400"C. Without wishing to be bound by theory, the inventors believe that these results are at least partly attributable to the nature of the metal oxide support material, the polar facets of which may exhibit superior proton conduction properties and hence facilitate the removal of protons from the surface of the metal M. Furthermore, it is interesting to note that the catalytic material allow for the decomposition of ammonia to hydrogen without production of nitrogen oxides, thereby representing an industrially attractive approach for CO^free hydrogen production for practical applications.

[0016] The metal oxide comprises magnesium oxide, wherein the magnesium oxide comprises exposed (111) facets. The (111) facet of magnesium oxide is polar as it comprises alternating layers of positively charged Mg²⁺ and negatively charged O² ions, such that the outermost surface has a net charge. This is in contrast to the non-polar (110) and (100) facets of magnesium oxide, the facets of which contain an equal mixture of both Mg²⁺ and O² ions, such that the outermost surface is net neutral. Without wishing to be bound by theory, the inventors believe that the polar (111) facets of magnesium oxide gives rise to notably enhanced proton mobility, which enhances bond activation and proton removal during the ammonia decomposition reaction. Suitably, (111) facets form at least 10% of the exposed surfaces of the magnesium oxide. The amount of (111) facet in the magnesium oxide can be determined, for example, by integration of the characteristic peaks in nuclear magnetic resonance. More suitably, (111) facets form at least 20% of the exposed surfaces of the magnesium oxide. Even more suitably, (111) facets form at least 30% of the exposed surfaces of the magnesium oxide. Yet more suitably, (111) facets form at least 40% of the exposed surfaces of the magnesium oxide. Yet even more suitably, (111) facets form 40-50% of the exposed surfaces of the magnesium oxide. Most suitably, (111) facets form 44-48% of the exposed surfaces of the magnesium oxide.

[0017] One process employed by the inventors yields magnesium oxide in which (111) facets form approximately 46% of the exposed surfaces of the magnesium oxide. However, the inventors have shown that the presence of significant quantities of the (111) facet has a notable beneficial effect on the catalytic properties of the material, such that magnesium oxides having an even higher quantity of (111) facet can be even more catalytically active. Thus, in any of the embodiments discussed above, (111) facets may form up to 60%, 70%, 80%, 90% or 100% of the exposed surfaces of the magnesium oxide. Such increased quantities of (111) facets may, for example, be present in magnesium oxide particles having an octahedral form, in which all 8 facets are (111) facets.

[0018] The magnesium oxide is suitably in the form of nanoparticles (i.e. particles in which the maximum dimension is less than 1 micron). The average particle size of the nanoparticles (based on the maximum dimension of each particle) is suitably 50-500 nm, more suitably 100-250 nm. The nanoparticles can have a variety of forms, but are often provided as sheets (e.g. hexagonal sheets) having upper and lower (111) facets and a thickness of 1-20 nm, suitably, 2-15 nm. Alternatively, the nanoparticles can have the aforementioned octahedral form.

[0019] It will be appreciated that term “magnesium oxide” used throughout the entirety of this specification encompasses the corresponding hydrolysed or partially hydrolysed forms that may be present, particularly at the surface of the magnesium oxide, especially after the hydrogen reduction treatment of the material.

[0020] Suitably, the magnesium oxide has a periclase crystal structure.

[0021] The metal M is typically applied to the metal oxide by chemical vapour deposition, wetness impregnation or ball milling. Therefore, it will be understood that the metal M is distributed (i.e. dispersed) across the surface of the metal oxide.

[0022] The metal M may be present in the catalytic material as an oxide (e.g. ruthenium oxide), or in metallic form (e.g. ruthenium metal), or both. If the catalytic material has not undergone reduction treatment, at least some of the metal M will be present as an oxide. If the catalytic material has underdone reduction treatment, at least some of the metal M will be present in a metallic form. In an embodiment, greater than 90 wt% (or alternatively all) of the metal M is present as an oxide. Alternatively, greater than 90 wt% (or alternatively all) of the metal M is present in metallic form.

[0023] The average particle size of the metal M (whether it is present as an oxide or in metallic form) is suitably 0.5-100 nm. The average particle size of the metal M can be determined, for example, by transmission electron microscopy. More suitably, the average particle size of the metal M is 2-20 nm.

[0024] In an embodiment, the metal M is selected from the group consisting of Ru, Fe and a mixture thereof. In a particularly preferred embodiment, the metal M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo. In a particularly preferred embodiment, the metal M is only Ru.

[0025] In another embodiment, the metal M is a mixture of Co and Mo.

[0026] In an embodiment, the catalytic material comprises:

0.01-30.0% w/w of the metal M, and 40.0-99.9% w/w of the metal oxide.

The quantity of metal M refers to the amount of elemental M, which can be determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The metal M may be present as an oxide or in metallic form. Suitably, the catalytic material comprises: 0.01-20.0% w/w of the metal M, and 40.0-99.9% w/w of the metal oxide.

More suitably, the catalytic material comprises:

0.01-15.0% w/w of the metal M, and 55.0-99.9% w/w of the metal oxide.

Even more suitably, the catalytic material comprises:

0.5-10.0% w/w of the metal M, and 70.0-99.5% w/w of the metal oxide.

Yet more suitably, the catalytic material comprises:

1.5-7.0% w/w of the metal M, and 80.0-98.5% w/w of the metal oxide.

Yet even more suitably, the catalytic material comprises:

2.5-6.0% w/w of the metal M, and 85.0-97.5% w/w of the metal oxide.

Most suitably, the catalytic material comprises:

2.8-4.5% w/w of the metal M, and 88.0-97.2% w/w of the metal oxide.

[0027] The catalytic material may additionally comprise a promotor, Q. The inclusion of a promoter notably increases the activity of the catalytic material. The promotor, Q can be incorporated into the catalytic material by wet impregnation, the steps of which will be familiar to one of skill in the art. Suitably, the promotor, Q is selected from the group consisting of Cs, K, Ba, and mixtures of two or more thereof. More suitably, Q is selected from the group consisting of Cs, K and a mixture thereof. Most suitably, Q is Cs.

[0028] Where the catalytic material comprises a promotor, Q, the molar ratio of metal M to Q (i.e. M:Q) may be 1 :(0.1 -3). Suitably, the molar ratio of M:Q is 1 :(0.5-1.5). More suitably, the molar ratio of M:Q is 1:(0.75-1.25).

[0029] The catalytic material may additionally comprise an acidic zeolite. The catalytic material may comprise 0.01-50.0% w/w of the acidic zeolite. Suitably, the catalytic material comprises 0.01-20.0% w/w of the acidic zeolite. In a particular embodiment, the catalytic material is ZSM-5.

[0030] In an embodiment, the metal oxide consists essentially of or consists of magnesium oxide having any of the definitions appearing hereinbefore.

[0031] In an alternative embodiment, the metal oxide comprises both magnesium oxide having any of the definitions appearing hereinbefore, and cerium oxide. The inclusion of cerium oxide alongside magnesium oxide notably improves the catalytic properties of the catalytic material, irrespective of the particular morphology of the cerium oxide. [0032] When the metal oxide comprises both magnesium oxide having any of the definitions appearing hereinbefore, and cerium oxide, the catalytic properties of the catalytic material are improved significantly when the cerium oxide comprises exposed (100) facets. When compared with the polycrystalline form, the cube and rod morphologies of cerium oxide contain an increased quantity of polar (100) facets. Therefore, the cerium oxide suitably comprises exposed (100) facets. More suitably, (100) facets form at least 20% of the exposed surfaces of the cerium oxide. The amount of (100) facet in the cerium oxide can be determined, for example, by integration of the characteristic peaks in nuclear magnetic resonance. Even more suitably, (100) facets form at least 40% of the exposed surfaces of the cerium oxide. Yet more suitably, (100) facets form at least 60% of the exposed surfaces of the cerium oxide. Yet even more suitably, (100) facets form at least 80% of the exposed surfaces of the cerium oxide. Still more suitably, (100) facets form at least 85% of the exposed surfaces of the cerium oxide. Most suitably, (100) facets form 88- 96% of the exposed surfaces of the cerium oxide. Theoretically, (100) facets can form a maximum of 50% of the exposed surfaces of cerium oxide having rod morphology. In contrast, (100) facets theoretically form all of the exposed surfaces of cerium oxide having cube morphology.

[0033] In an embodiment, the cerium oxide is present as a mixture of cube and rod morphologies.

[0034] In an embodiment, the cerium oxide is present predominantly (or entirely) as the cube morphology.

[0035] The cerium oxide is suitably in the form of nanoparticles (i.e. particles in which the maximum dimension is less than 1 micron). The average particle size of the nanoparticles (based on the maximum dimension of each particle) is suitably 5-50 nm, more suitably 10-30 nm. The nanoparticles can have a variety of forms, but are often provided as the aforementioned rod and/or cube forms.

[0036] When the metal oxide comprises both magnesium oxide having any of the definitions appearing hereinbefore, and cerium oxide having any of the definitions appearing hereinbefore, the weight ratio of magnesium oxide to cerium oxide may be 1 :(0.1-10.0). Suitably, the weight ratio of magnesium oxide to cerium oxide is 1:(0.25-4.0). More suitably, the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0). Even more suitably, the weight ratio of magnesium oxide to cerium oxide is 1 :(0.75-1.25). Most suitably, the weight ratio of magnesium oxide to cerium oxide is 1 :(0.90-1.10).

[0037] In an embodiment, the metal oxide is provided as a mixture of discrete particles of magnesium oxide and discrete particles of cerium oxide, each of which having any of the definitions appearing hereinbefore. In such an embodiment, discrete, single phase particles of each oxide are prepared separately prior to being mixed with one another. Therefore, the metal oxide may be viewed as a physical mixture of magnesium oxide and cerium oxide. The metal M may be separately deposited on each metal oxide, prior to combining the two M-loaded metal oxides. Alternatively, the metal M may be deposited on both metal oxides after they have been combined.

[0038] In an alternative embodiment, the metal oxide is provided as a plurality of particles, at least some of those particles comprising a mixture of magnesium oxide and cerium oxide, each of which having any of the definitions appearing hereinbefore. In such an embodiment, magnesium oxide and cerium oxide are co-synthesised to yield mixed phase particles (i.e. a population of particles, at least some of which are not single phase), onto which the metal M is then deposited. Such metal oxides may be viewed as a chemical mixture of magnesium oxide and cerium oxide.

[0039] The following paragraphs outline particular, non-limiting embodiments of the catalytic material.

[0040] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-30.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1 :(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-20.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 0.5-100 nm.

[0041] In an embodiment, the catalytic material comprises: a) 55.0-99.9% w/w of a metal oxide, and b) 0.01-15.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1:(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-20.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore. The average particle size of the metal M may be 0.5-100 nm.

[0042] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-15.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0043] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-125), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-8.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0044] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-30.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-125), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-20.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore. The average particle size of the metal M may be 0.5-100 nm.

[0045] In an embodiment, the catalytic material comprises: a) 55.0-99.9% w/w of a metal oxide, and b) 0.01-15.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[0046] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[0047] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-125), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-8.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore. The average particle size of the metal M may be 2.0-20 nm.

[0048] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[0049] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[0050] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide.

[0051] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[0052] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[0053] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide.

[0054] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-30.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0055] In an embodiment, the catalytic material comprises: a) 55.0-99.9% w/w of a metal oxide, and b) 0.01-15.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.25-4.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1:(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-20.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0056] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0). The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1 :(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-15.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0057] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1 :(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-8.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0058] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-30.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0059] In an embodiment, the catalytic material comprises: a) 55.0-99.9% w/w of a metal oxide, and b) 0.01-15.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.25-4.0).

The average particle size of the metal M may be 2.0-20 nm.

[0060] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-125), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-15.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0061] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0062] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0063] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0064] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

[0065] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0066] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0067] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0). The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1 :(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-8.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0068] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-30.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0069] In an embodiment, the catalytic material comprises: a) 55.0-99.9% w/w of a metal oxide, and b) 0.01-15.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.25-4.0).

The average particle size of the metal M may be 0.5-100 nm.

[0070] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0071] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0072] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-30.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.1-10.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-125), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-20.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 0.5-100 nm.

[0073] In an embodiment, the catalytic material comprises: a) 55.0-99.9% w/w of a metal oxide, and b) 0.01-15.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.25-4.0).

The average particle size of the metal M may be 0.5-100 nm.

[0074] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0075] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0076] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0077] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1(0.50-2.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1(0.75-125), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-15.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore. The average particle size of the metal M may be 2.0-20 nm.

[0078] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 10% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0).

The average particle size of the metal M may be 2.0-20 nm.

[0079] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.1-10.0).

The average particle size of the metal M may be 0.5-100 nm.

[0080] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1 :(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-15.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0081] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises magnesium oxide having (111) facets that form at least 30% of the exposed surfaces of the magnesium oxide, and cerium oxide having (100) facets form at least 40% (suitably at least 80%) of the exposed surfaces of the cerium oxide, suitably wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0).

The catalytic material may further comprise a promotor, Q (such as Cs), such that the molar ratio of M:Q is 1:(0.75-1.25), and/or an acidic zeolite (such as ZSM-5) in an amount of 0.01-8.0% w/w, wherein the promotor, Q, and the acidic zeolite have any of the definitions appearing hereinbefore.

The average particle size of the metal M may be 2.0-20 nm.

[0082] It will be appreciated that in any of the foregoing particular, non-limiting embodiments, the metal oxide may have any of the alternative definitions outlined hereinbefore.

[0083] It will be appreciated that in any of the foregoing particular, non-limiting embodiments, the metal M may have any of the alternative definitions outlined hereinbefore.

Preparation of catalytic material

[0084] In a second aspect, the invention provides a process for the preparation of a catalytic material according to the first aspect, the process comprising: a) providing a metal oxide as defined herein, and b) depositing a metal M on the metal oxide, wherein M is as defined herein, c) optionally reducing or partially reducing the product resulting from step b). [0085] As discussed hereinbefore, the metal M of the catalytic material may be present as an oxide or in a metallic form or both, depending on whether catalytic material is provided in a non- reduced state or a reduced/partially reduced state. In an embodiment, the process further comprises an optional step c) of reducing or partially reducing the product resulting from step b). Optional step c) may comprise heating the product of step b) at a temperature of 200-600°C under a reducing atmosphere for 0.5-10 hours. Suitably, optional step c) comprises heating the product of step b) at a temperature of 300-500°C under a atmosphere of 1-20 vol% hydrogen (e.g. 3-8 vol%) in helium for 2-6 hours.

[0086] The metal M may be deposited on the metal oxide by chemical vapour deposition, wet impregnation or ball milling. Suitably, the metal M is deposited on the metal oxide by chemical vapour deposition. Suitably, the amount of metal M used is such that the resulting catalytic material has a quantity of metal M discussed hereinbefore in respect of the first aspect.

[0087] In an embodiment, the process further comprises the step of depositing a promotor, Q as defined hereinbefore on the product resulting from step b). Such a step occurs prior to optional step c). The promotor, Q is suitably deposited on the product resulting from step b) by wet impregnation. Suitably, the amount of Q used is such that the resulting catalytic material has a quantity of Q discussed hereinbefore in respect of the first aspect.

[0088] In an embodiment, the process further comprises the step of mixing the product resulting from step b) with an acidic zeolite, as defined hereinbefore. Such a step occurs prior to optional step c). Prior to having been mixed with the product resulting from step b), the acidic zeolite may undergone heat treatment at a temperature of 200-500°C for 1-8 hours, and optionally then dried in a vacuum oven.

[0089] The process may use both of a promotor, Q, and an acidic zeolite. Suitably, the promotor, Q, is deposited on the product resulting from step b), after which the resulting product (including Q) is then mixed with the acidic zeolite.

[0090] The process may use pre-made magnesium oxide comprising exposed (111) facets.

[0091] Alternatively, the process includes steps for preparing the magnesium oxide. In an embodiment, step a) comprises preparing magnesium oxide comprising exposed (111) facets by hydrothermal synthesis. Suitably, an aqueous solution comprising a magnesium salt (e.g. magnesium chloride) and a suitable surfactant (e.g. benzoic acid) is treated with a base (e.g. NaOH) and then subjected to hydrothermal conditions to yield a solid product that is then calcined to yield magnesium oxide comprising exposed (111) facets.

[0092] In an embodiment, the metal oxide provided in step a) consists of magnesium oxide comprising exposed (111) facets. [0093] In an alternative embodiment, the metal oxide provided in step a) comprises both magnesium oxide and cerium oxide, wherein the magnesium oxide comprises exposed (111) facets. As discussed hereinbefore in relation to the first aspect of the invention, the cerium oxide may comprise exposed (100) facets. The cerium oxide comprising exposed (100) facets used in step a) may be pre-made, or may be prepared by hydrothermal synthesis. In such embodiments, the mixture of magnesium oxide and cerium oxide provided in step a) may be provided as a physical mixture, a chemical mixture, or a mixture of both. In embodiments comprising both magnesium oxide and cerium oxide, the relative quantities of the two oxides in the resulting product are suitably as described hereinbefore in relation to the first aspect.

[0094] A physical mixture may be prepared by mixing pre-prepared samples of magnesium oxide and cerium oxide. The resulting physical mixture may therefore comprise a mixture of discrete single-phase particles of magnesium oxide and discrete single-phase particles of cerium oxide

[0095] A chemical mixture may be prepared by subjecting a mixture of magnesium oxide precursors and cerium oxide precursors to conditions sufficient to yield a mixture of the magnesium oxide and cerium oxide. For example, an aqueous mixture comprising a magnesium salt (e.g. magnesium chloride) and a cerium salt (e.g. cerium nitrate) may be treated with a base (e.g. NaOH) and then subjected to hydrothermal conditions to yield a solid product that is then calcined to yield a chemical mixture of magnesium oxide and cerium oxide. The resulting chemical mixture may therefore comprise a plurality of mixed-phase particles (i.e. a population of particles, at least some of which are not single phase).

[0096] In a particular embodiment, the process further comprises a step of mixing (e.g. physically mixing) the catalytic material (i.e. the product resulting from step b), or step c) if employed, or any intervening steps) with a further catalytic material. Suitably, the further catalytic material comprises: a metal oxide, wherein the metal oxide is: magnesium oxide having any of those definitions appearing hereinbefore in respect of the first aspect, or cerium oxide having any of those definitions appearing hereinbefore in respect of the first aspect, or both magnesium oxide and cerium oxide, either or both of which having any of those definitions appearing hereinbefore in respect of the first aspect, and a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof. The further catalytic material may additionally comprise a promotor, Q, and/or an acidic zeolite. The magnesium oxide, cerium oxide, metal M, promotor, Q, and acidic zeolite of the further catalytic material (and their respective quantities) are suitably as defined hereinbefore in respect of the first aspect of the invention. In particular, suitable and preferred definitions of the magnesium oxide, cerium oxide, M, Q and acidic zeolite in the context of the first aspect of the invention are also suitable and preferred definitions of the magnesium oxide, cerium oxide, M, Q, and acidic zeolite of the further catalytic material.

[0097] Suitably, the metal oxide of the further catalytic material is cerium oxide comprising exposed (100) facets.

[0098] Particular non-limiting examples of the further catalytic material are outlined in the following paragraphs.

[0099] In an embodiment, the further catalytic material comprises: a) 40.0-99.9% w/w of cerium oxide, wherein (100) facets form at least 20% of the exposed surfaces of the cerium oxide, b) 0.01-20.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof,

[00100] In an embodiment, the further catalytic material comprises: a) 80.0-98.5% w/w of cerium oxide, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo.

[00101] In an embodiment, the further catalytic material comprises: a) 88.0-97.2% w/w of cerium oxide, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru.

[00102] Suitably, the further catalytic material further comprises a promotor, Q (e.g. Cs), and/or an acidic zeolite (e.g. ZSM-5) in an amount described hereinbefore in relation to the first aspect.

[00103] The use of a further catalytic material is particularly suitable when the metal oxide provided in step a) of the process consists of magnesium oxide comprising exposed (111) facets. For example, the process may comprise: a) providing a metal oxide consisting of magnesium oxide comprising exposed (111) facets, wherein (111) facets form at least 40% of the exposed surfaces of the magnesium oxide, b) i) depositing a metal M on the metal oxide, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo and wherein the amounts of metal oxide and M are such that the catalytic material comprises:

80.0-98.5% w/w of the metal oxide, and b) 15-7.0% w/w of the metal M, b) ii) depositing a promotor, Q, on the product resulting from step b) i), wherein Q is Cs and the molar ratio M:Q is 1(0.5-15) c) optionally reducing or partially reducing the product resulting from step b) ii), d) mixing the catalytic material resulting from step b) ii) (or c)) with a further catalytic material, wherein the further catalytic material comprises:

80.0-98.5% w/w of cerium oxide, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide, and

1.5-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo.

Either or both of the catalytic material and further catalytic material may also comprise an acidic zeolite, as defined hereinbefore, and/or a promotor Q, as defined hereinbefore.

[00104] Where a further catalytic material is used, the catalytic material resulting from step b) (or c)) is mixed with the further catalytic material such that, in the resulting product, the weight ratio of the metal oxide provided in step a) (e.g. magnesium oxide) to the metal oxide of the further catalytic material (e.g. cerium oxide) is 1(0.1-10.0). Suitably, in the resulting product, the weight ratio of the metal oxide provided in step a) (e.g. magnesium oxide) to the metal oxide of the further catalytic material (e.g. cerium oxide) is 1(0.25-4.0). More suitably, in the resulting product, the weight ratio of the metal oxide provided in step a) (e.g. magnesium oxide) to the metal oxide of the further catalytic material (e.g. cerium oxide) is 1(0.50-2.0). Even more suitably, in the resulting product, the weight ratio of the metal oxide provided in step a) (e.g. magnesium oxide) to the metal oxide of the further catalytic material (e.g. cerium oxide) is 1(0.75-125). Most suitably, in the resulting product, the weight ratio of the metal oxide provided in step a) (e.g. magnesium oxide) to the metal oxide of the further catalytic material (e.g. cerium oxide) is 1(0.90- 1.10).

[00105] In a third aspect, the invention provides a catalytic material obtained, directly obtained or obtainable by the process according to the second aspect.

[00106] It will be understood that features of the second and third aspects of the invention (e.g. the metal oxide, M, Q, acidic zeolite and respective quantities thereof) may have any of those definitions appearing hereinbefore in relation to the same features of the first aspect of the invention. Suitable, preferred and optional definitions of the first aspect of the invention are also contemplated as suitable, preferred and optional definitions of the second and third aspects of the invention.

Catalytic decomposition of ammonia

[00107] In a fourth aspect, the invention provides a process for the catalytic decomposition of ammonia, the process comprising the step of contacting ammonia with a catalytic material comprising: a) a metal oxide comprising: i) magnesium oxide comprising exposed (111) facets, or ii) cerium oxide, or iii) magnesium oxide comprising exposed (111) facets and cerium oxide; b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof.

[00108] The (111) facet of magnesium oxide is polar as it comprises alternating layers of positively charged Mg²⁺ and negatively charged O² ions, such that the outermost surface has a net charge. This is in contrast to the non-polar (110) and (100) facets of magnesium oxide, the facets of which contain an equal mixture of both Mg²⁺ and O² ions, such that the outermost surface is net neutral. Without wishing to be bound by theory, the inventors believe that the polar (111) facets of magnesium oxide gives rise to notably enhanced proton mobility, which enhances bond activation and proton removal during the ammonia decomposition reaction. Suitably, (111) facets form at least 10% of the exposed surfaces of the magnesium oxide. The amount of (111) facet in the magnesium oxide can be determined, for example, by integration of the characteristic peaks in nuclear magnetic resonance. More suitably, (111) facets form at least 20% of the exposed surfaces of the magnesium oxide. Even more suitably, (111) facets form at least 30% of the exposed surfaces of the magnesium oxide. Yet more suitably, (111) facets form at least 40% of the exposed surfaces of the magnesium oxide. Yet even more suitably, (111) facets form 40-50% of the exposed surfaces of the magnesium oxide. Most suitably, (111) facets form 44- 48% of the exposed surfaces of the magnesium oxide.

[00109] One process employed by the inventors yields magnesium oxide in which (111) facets form approximately 46% of the exposed surfaces of the magnesium oxide. However, the inventors have shown that the presence of significant quantities of the (111) facet has a notable beneficial effect on the catalytic properties of the material, such that magnesium oxides having an even higher quantity of (111) facet can be even more catalytically active. Thus, in any of the embodiments discussed above, (111) facets may form up to 60%, 70%, 80%, 90% or 100% of the exposed surfaces of the magnesium oxide. Such increased quantities of (111) facets may, for example, be present in magnesium oxide particles having an octahedral form, in which all 8 facets are (111) facets.

[00110] The magnesium oxide is suitably in the form of nanoparticles (i.e. particles in which the maximum dimension is less than 1 micron). The average particle size of the nanoparticles (based on the maximum dimension of each particle) is suitably 50-500 nm, more suitably 100-250 nm. The nanoparticles can have a variety of forms, but are often provided as sheets (e.g. hexagonal sheets) having upper and lower (111) facets and a thickness of 1-20 nm, suitably, 2-15 nm. Alternatively, the nanoparticles can have the aforementioned octahedral form.

[00111] Suitably, the magnesium oxide has a periclase crystal structure.

[00112] The cerium oxide may comprise exposed (100) facets. When compared with the polycrystalline form, the cube and rod morphologies of cerium oxide contain an increased quantity of polar (100) facets. Therefore, the cerium oxide suitably comprises exposed (100) facets. More suitably, (100) facets form at least 20% of the exposed surfaces of the cerium oxide. The amount of (100) facet in the cerium oxide can be determined, for example, by integration of the characteristic peaks in nuclear magnetic resonance. Even more suitably, (100) facets form at least 40% of the exposed surfaces of the cerium oxide. Yet more suitably, (100) facets form at least 60% of the exposed surfaces of the cerium oxide. Yet even more suitably, (100) facets form at least 80% of the exposed surfaces of the cerium oxide. Still more suitably, (100) facets form at least 85% of the exposed surfaces of the cerium oxide. Most suitably, (100) facets form 88- 96% of the exposed surfaces of the cerium oxide. Theoretically, (100) facets can form a maximum of 50% of the exposed surfaces of cerium oxide having rod morphology. In contrast, (100) facets theoretically form all of the exposed surfaces of cerium oxide having cube morphology.

[00113] In an embodiment, the cerium oxide is present as a mixture of cube and rod morphologies.

[00114] In an embodiment, the cerium oxide is present predominantly (or entirely) as the cube morphology.

[00115] The cerium oxide is suitably in the form of nanoparticles (i.e. particles in which the maximum dimension is less than 1 micron). The average particle size of the nanoparticles (based on the maximum dimension of each particle) is suitably 5-50 nm, more suitably 10-30 nm. The nanoparticles can have a variety of forms, but are often provided as the aforementioned rod and/or cube forms.

[00116] In an embodiment, the metal oxide comprises, consists essentially of or consists of magnesium oxide comprising exposed (111) facets. [00117] In an embodiment, metal oxide comprises, consists essentially of or consists of cerium oxide.

[00118] In an embodiment, metal oxide comprises, consists essentially of or consists of magnesium oxide comprising exposed (111) facets and cerium oxide.

[00119] The metal M is typically applied to the metal oxide by chemical vapour deposition, wetness impregnation or ball milling. Therefore, it will be understood that the metal M is distributed (i.e. dispersed) across the surface of the metal oxide.

[00120] The metal M may be present in the catalytic material as an oxide (e.g. ruthenium oxide), or in metallic form (e.g. ruthenium metal), or both. If the catalytic material has not undergone reduction treatment as part of the manufacturing process, at least some of the metal M will be present as an oxide. If the catalytic material has underdone reduction treatment as part of the manufacturing process, at least some of the metal M will be present in a metallic form. In an embodiment, greater than 90 wt% (or alternatively all) of the metal M is present as an oxide. Alternatively, greater than 90 wt% (or alternatively all) of the metal M is present in metallic form.

[00121] A reduction treatment may also be applied directly before ammonia decomposition (irrespective of whether a reduction treatment has been used as part of the manufacturing process). Therefore, in an embodiment, prior to contacting the catalytic material with ammonia, the catalytic material is heated at a temperature of 200-600°C under a reducing atmosphere for 0.5-10 hours. Suitably, prior to contacting the catalytic material with ammonia, the catalytic material is heated at a temperature of 300-500°C under an atmosphere of 1-20 vol% hydrogen (e.g. 3-8 vol%) in helium for 2-6 hours.

[00122] The average particle size of the metal M (whether it is present as an oxide or in metallic form) is suitably 0.5-100 nm. The average particle size of the metal M can be determined, for example, by transmission electron microscopy. More suitably, the average particle size of the metal M is 2-20 nm.

[00123] In an embodiment, the metal M is selected from the group consisting of Ru, Fe and a mixture thereof. In a particularly preferred embodiment, the metal M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo. In a particularly preferred embodiment, the metal M is only Ru.

[00124] In another embodiment, the metal M is a mixture of Co and Mo.

[00125] In an embodiment, the catalytic material comprises:

0.01-30.0% w/w of the metal M, and 40.0-99.9% w/w of the metal oxide. The quantity of metal M refers to the amount of elemental M, which can be determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The metal M may be present as an oxide or in metallic form. Suitably, the catalytic material comprises:

0.01-20.0% w/w of the metal M, and 40.0-99.9% w/w of the metal oxide.

More suitably, the catalytic material comprises:

0.01-15.0% w/w of the metal M, and 55.0-99.9% w/w of the metal oxide.

Even more suitably, the catalytic material comprises:

0.5-10.0% w/w of the metal M, and 70.0-99.5% w/w of the metal oxide.

Yet more suitably, the catalytic material comprises:

1.5-7.0% w/w of the metal M, and 80.0-98.5% w/w of the metal oxide.

Yet even more suitably, the catalytic material comprises:

2.5-6.0% w/w of the metal M, and 85.0-97.5% w/w of the metal oxide.

Most suitably, the catalytic material comprises:

2.8-4.5% w/w of the metal M, and 88.0-97.2% w/w of the metal oxide.

[00126] The catalytic material may additionally comprise a promotor, Q. The inclusion of a promotor notably increases the activity of the catalytic material. The promotor, Q can be incorporated into the catalytic material by wet impregnation, the steps of which will be familiar to one of skill in the art. Suitably, the promotor, Q is selected from the group consisting of Cs, K, Ba, and mixtures of two or more thereof. More suitably, Q is selected from the group consisting of Cs, K and a mixture thereof. Most suitably, Q is Cs.

[00127] Where the catalytic material comprises a promotor, Q, the molar ratio of metal M to Q (i.e. M:Q) may be 1 :(0.1 -3). Suitably, the molar ratio of M:Q is 1:(0.5-1.5). More suitably, the molar ratio of M:Q is 1:(0.75-1.25).

[00128] The catalytic material may additionally comprise an acidic zeolite. The catalytic material may comprise 0.01-50.0% w/w of the acidic zeolite. Suitably, the catalytic material comprises 0.01-20.0% w/w of the acidic zeolite. In a particular embodiment, the catalytic material is ZSM-5.

[00129] The following paragraphs outline particular, non-limiting embodiments of the catalytic material used in the fourth aspect of the invention.

[00130] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[00131] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00132] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00133] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[00134] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00135] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00136] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[00137] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00138] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00139] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[00140] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00141] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00142] In an embodiment, the catalytic material comprises: a) 40.0-99.9% w/w of a metal oxide, and b) 0.01-20.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 80% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 0.5-100 nm.

[00143] In an embodiment, the catalytic material comprises: a) 80.0-98.5% w/w of a metal oxide, and b) 15-7.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 80% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00144] In an embodiment, the catalytic material comprises: a) 88.0-97.2% w/w of a metal oxide, and b) 2.8-4.5% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises cerium oxide comprising exposed (100) facets, wherein (100) facets form at least 80% of the exposed surfaces of the cerium oxide.

The average particle size of the metal M may be 2.0-20 nm.

[00145] It will be appreciated that in any of the foregoing particular, non-limiting embodiments, the metal oxide may have any of the alternative definitions outlined hereinbefore in relation to the first or fourth aspect of the invention. [00146] It will be appreciated that in any of the foregoing particular, non-limiting embodiments, the metal M may have any of the alternative definitions outlined hereinbefore in relation to the first or fourth aspect of the invention.

[00147] In a particularly suitable embodiment, the catalytic material used in the fourth aspect is the same as the catalytic material of the first or third aspect.

[00148] It will be understood that features of the catalytic material used in the fourth aspect of the invention (e.g. the metal oxide, M, Q, acidic zeolite and respective quantities thereof) may have any of those definitions appearing hereinbefore in relation to the same features of the first aspect of the invention. Suitable, preferred and optional definitions of the first aspect of the invention are also contemplated as suitable, preferred and optional definitions of the fourth aspect of the invention.

[00149] The catalytic process may be performed under batch conditions or under continuous flow conditions.

[00150] The ammonia that is contacted with the catalytic material may be in the form of a liquid or a gas. Water (in liquid or gas form) may also be present.

[00151] In one embodiment, the ammonia is in the form of a liquid and the catalytic process is performed under batch conditions. The liquid ammonia is suitably present as an aqueous solution of 10-50 vol% ammonia.

[00152] In another embodiment, the ammonia is in the form of a gas and the catalytic process is performed under continuous flow conditions over a fixed bed of the catalytic material.

[00153] The catalytic process may suitably be conducted in the presence of molecular oxygen. The inventors have surprisingly found that the thermodynamic limits for ammonia decomposition can be overcome by the addition of a quantity of O2 to partially consume hydrogen at steady state. In an embodiment, the molar ratio of NH3:C>2 is 1 :0.01 to 1:0.75. More suitably, the molar ratio of NH3:C>2 is 1 :0.05 to 1 :0.43. Molecular oxygen is suitably co-fed into the reaction alongside ammonia. More suitably, the catalytic process is performed under continuous flow conditions and molecular oxygen is co-fed into the reaction alongside gaseous ammonia. The gaseous ammonia may be provided at a pressure of 0.001 to 100 bar.

[00154] The catalytic process may be conducted at a temperature of 150-900°C. Suitably, the catalytic process is conducted at a temperature of 200-750°C. More suitably, the catalytic process is conducted at a temperature of 250-550°C. Even more suitably, the catalytic process is conducted at a temperature of 350-500°C. Most suitably, the catalytic process is conducted at a temperature of 425-475°C. [00155] The catalytic process is suitably conducted at a WHSV of 5000-35000 ml_ g_cat ¹ h ¹. More suitably, the catalytic process is conducted at a WHSV of 8000-32000 ml_ g_cat ¹ h ¹.

[00156] The following numbered statements 1 to 116 are not claims, but instead serve to define particular aspects and embodiments of the claimed invention:

1. A catalytic material comprising: a) a metal oxide, and b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof, wherein the metal oxide comprises magnesium oxide, the magnesium oxide comprising exposed (111) facets.

2. The catalytic material of statement 1 , wherein (111) facets form at least 10% of the exposed surfaces of the magnesium oxide.

3. The catalytic material of statement 1 , wherein (111) facets form at least 20% of the exposed surfaces of the magnesium oxide.

4. The catalytic material of statement 1 , wherein (111) facets form at least 30% of the exposed surfaces of the magnesium oxide.

5. The catalytic material of statement 1 , wherein (111) facets form at least 40% of the exposed surfaces of the magnesium oxide.

6. The catalytic material of statement 1 , wherein (111) facets form 40-50% of the exposed surfaces of the magnesium oxide.

7. The catalytic material of any preceding statement, wherein (111) facets form greater than 90% of the exposed surfaces of the magnesium oxide.

8. The catalytic material of any preceding statement, wherein the magnesium oxide is provided as nanoparticles. 9. The catalytic material of statement 8, wherein the nanoparticles have an average size of 100-250 nm.

10. The catalytic material of any preceding statement, wherein the metal M is selected from the group consisting of Ru, Fe and a mixture thereof.

11. The catalytic material of any preceding statement, wherein the metal M is Ru.

12. The catalytic material of any preceding statement, wherein the catalytic material comprises:

0.01-30.0% w/w of the metal M, and 40.0-99.9% w/w of the metal oxide.

13. The catalytic material of any preceding statement, wherein the catalytic material comprises:

0.01-15.0% w/w of the metal M, and 55.0-99.9 % w/w the metal oxide.

14. The catalytic material of any preceding statement, wherein the catalytic material comprises:

1.5-7.0% w/w of the metal M, and 80.0-98.5% w/w of the metal oxide

15. The catalytic material of any preceding statement, wherein the catalytic material comprises:

2.5-6.0% w/w of the metal M, and 85.0-97.5% w/w of the metal oxide.

16. The catalytic material of any preceding statement, wherein the metal M is distributed across the surface of the metal oxide.

17. The catalytic material of any preceding statement, wherein the metal M has an average particle size of 0.5-100 nm.

18. The catalytic material of any preceding statement, wherein the metal M has an average particle size of 2.0-20 nm. 19. The catalytic material of any preceding statement, further comprising a promotor, Q.

20. The catalytic material of statement 19, wherein Q is selected from the group consisting of Cs, K, Ba, and mixtures of two or more thereof.

21. The catalytic material of statement 19, wherein the Q is selected from the group consisting of Cs, K and a mixture thereof.

22. The catalytic material of statement 19, wherein Q is Cs.

23. The catalytic material of any one of statements 19 to 22, wherein the molar ratio of M:Q is 1 :(0.1 -3).

24. The catalytic material of any one of statements 19 to 22, wherein the molar ratio of M:Q is 1 :(0.5-1.5).

25. The catalytic material of any one of statements 19 to 22, wherein the molar ratio of M:Q is 1 : (0.75-1.25).

26. The catalytic material of any preceding statement, further comprising an acidic zeolite.

27. The catalytic material of statement 26, wherein the acidic zeolite is ZSM-5.

28. The catalytic material of statement 26 or 27, wherein the catalytic material comprises

0.01-50.0% w/w of the acidic zeolite.

29. The catalytic material of statement 26 or 27, wherein the catalytic material comprises 0.01-20.0% w/w of the acidic zeolite.

30. The catalytic material of any preceding statement, wherein the metal oxide consists of magnesium oxide.

31. The catalytic material of any one of statements 1 to 29, wherein the metal oxide comprises both magnesium oxide and cerium oxide, wherein the magnesium oxide comprises exposed (111) facets. 32. The catalytic material of statement 31 , wherein the cerium oxide comprises exposed (100) facets.

33. The catalytic material of statement 32, wherein (100) facets form at least 20% of the exposed surfaces of the cerium oxide.

34. The catalytic material of statement 32, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

35. The catalytic material of statement 32, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide.

36. The catalytic material of statement 32, wherein (100) facets form at least 80% of the exposed surfaces of the cerium oxide.

37. The catalytic material of statement 32, wherein (100) facets form at least 85% of the exposed surfaces of the cerium oxide.

38. The catalytic material of any one of statements 31 to 37, wherein the cerium oxide is present as a mixture of cube and rod morphologies.

39. The catalytic material of any one of statements 31 to 37, wherein the cerium oxide is present predominantly (or entirely) as cube morphology.

40. The catalytic material of any one of statements 31 to 39, wherein the cerium oxide is provided as nanoparticles.

41. The catalytic material of statement 40, wherein the nanoparticles have an average size of 10-30 nm.

42. The catalytic material of any one of statements 31 to 41 , wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.1-10.0).

43. The catalytic material of any one of statements 31 to 41 , wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.25-4.0). 44. The catalytic material of any one of statements 31 to 41 , wherein the weight ratio of magnesium oxide to cerium oxide is 1:(0.50-2.0).

45. The catalytic material of any one of statements 31 to 41 , wherein the weight ratio of magnesium oxide to cerium oxide is 1 :(0.75-1.25).

46. The catalytic material of any one of statements 31 to 45, wherein the metal oxide is provided as a mixture of discrete particles of magnesium oxide and discrete particles of cerium oxide.

47. The catalytic material of any one of statements 31 to 45, wherein the metal oxide is provided as a plurality of particles, at least some of those particles comprising a mixture of magnesium oxide and cerium oxide.

48. A process for the preparation of a catalytic material as defined in any preceding statement, the process comprising the steps of: a) providing a metal oxide as defined in any preceding statement, b) depositing a metal M on the metal oxide, wherein M is as defined in any preceding statement, and c) optionally reducing the product resulting from step b).

49. The process of statement 48, wherein in step b), the metal M is deposited on the metal oxide by chemical vapour deposition, wetness impregnation or ball milling.

50. The process of statement 48 or 49, wherein the process further comprises depositing a promotor, Q on the product resulting from step b), wherein Q is as defined in any one of statements 19 to 25.

51. The process of any one of statements 48, 49 or 50, wherein the process further comprises mixing the product resulting from step b) with an acidic zeolite, wherein the acidic zeolite is as defined in any one of statements 27 to 29.

52. The process of any one of statements 48 to 51 , wherein the metal oxide provided in step a) consists of magnesium oxide comprising exposed (111) facets.

53. The process of statement 52, wherein the magnesium oxide is as defined in any one of statements 2 to 9. 54. The process of any one of statements 48 to 51 , wherein the metal oxide provided in step a) comprises both magnesium oxide and cerium oxide, wherein the magnesium oxide comprises exposed (111) facets.

55. The process of statement 54, wherein the metal oxide is as defined in any one of statements 2 to 9 and 32 to 47.

56. The process of any one of statements 48 to 51 , wherein the process further comprises the step of mixing the catalytic material with a further catalytic material, wherein the further catalytic material comprises: a metal oxide, wherein the metal oxide is: magnesium oxide as defined in any one of statements 1 to 9, or cerium oxide as defined in any one of statements 31 to 41, or both magnesium oxide as defined in any one of statements 1 to 9 and cerium oxide, as defined in any one of statements 31 to 41 a metal M as defined in any one of statements 1 and 10 to 18.

57. The process of statement 56, wherein the metal oxide of the further catalytic material is different from the metal oxide of the catalytic material.

58. The process of statement 56 or 57, wherein the metal M of the further catalytic material is identical to the metal M of the catalytic material.

59. The process of statement 56, 57 or 58, wherein the further catalytic material further comprises: a promotor, Q as defined in any one of statements 19 to 25, optionally wherein the promotor, Q of the further catalytic material is identical to the promotor, Q of the catalytic material, and/or an acidic zeolite as defined in any one of statements 27 to 29, optionally wherein the acidic zeolite of the further catalytic material is identical to the acidic zeolite of the catalytic material.

60. The process of any one of statements 56 to 59, wherein the further catalytic material comprises: a) 40.0-99.9% w/w of cerium oxide, wherein (100) facets form at least 20% of the exposed surfaces of the cerium oxide, b) 0.01-20.0% w/w of a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof,

61. The process of any one of statements 56 to 59, wherein the further catalytic material comprises: a) 80.0-98.5% w/w of cerium oxide, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide, and b) 15-7.0% w/w of a metal M, wherein M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo.

62. The process of any one of statements 56 to 59, wherein the further catalytic material comprises: a) 88.0-97.2% w/w of cerium oxide, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide, and b) 2.8-4.5% w/w of a metal M, wherein M is Ru.

63. The process of any one of statements 56 to 62, wherein the metal oxide provided in step a) of the process consists of magnesium oxide comprising exposed (111) facets.

64. A catalytic material obtained, directly obtained or obtainable by the process of any one of statements 48 to 63.

65. A process for the catalytic decomposition of ammonia, the process comprising the step of contacting ammonia with a catalytic material comprising: a) a metal oxide comprising: i) magnesium oxide comprising exposed (111) facets, or ii) cerium oxide, or iii) magnesium oxide comprising exposed (111) facets and cerium oxide; b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof.

66. The process of statement 65, wherein the metal oxide comprises, consists essentially of or consists of magnesium oxide comprising exposed (111) facets.

67. The process of statement 65, wherein the metal oxide comprises, consists essentially of or consists of magnesium oxide comprising exposed (111) facets and cerium oxide. 68. The process of statement 65, wherein the metal oxide comprises, consists essentially of or consists of cerium oxide.

69. The process of statement 65, 66 or 67, wherein (111) facets form at least 10% of the exposed surfaces of the magnesium oxide.

70. The process of statement 65, 66 or 67, wherein (111) facets form at least 20% of the exposed surfaces of the magnesium oxide.

71. The process of statement 65, 66 or 67, wherein (111) facets form at least 30% of the exposed surfaces of the magnesium oxide.

72. The process of statement 65, 66 or 67, wherein (111) facets form at least 40% of the exposed surfaces of the magnesium oxide.

73. The process of statement 65, 66 or 67, wherein (111) facets form 40-50% of the exposed surfaces of the magnesium oxide.

74. The process of statement 65, 66 or 67, wherein (111) facets form greater than 90% of the exposed surfaces of the magnesium oxide.

75. The process of any one of statements 65 to 57 or 69 to 74, wherein the magnesium oxide is provided as nanoparticles.

76. The process of statement 75, wherein the nanoparticles have an average size of 100- 250 nm.

77. The process of any one of statements 65 or 67 to 76, wherein the cerium oxide comprises exposed (100) facets.

78. The process of any one of statements 65 or 67 to 76, wherein (100) facets form at least 20% of the exposed surfaces of the cerium oxide.

79. The process of any one of statements 65 or 67 to 76, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide. 80. The process of any one of statements 65 or 67 to 76, wherein (100) facets form at least 60% of the exposed surfaces of the cerium oxide.

81. The process of any one of statements 65 or 67 to 76, wherein (100) facets form at least 80% of the exposed surfaces of the cerium oxide.

82. The process of any one of statements 65 or 67 to 76, wherein (100) facets form at least 85% of the exposed surfaces of the cerium oxide.

83. The process of any one of statements 65 or 67 to 76, wherein the cerium oxide is present as a mixture of cube and rod morphologies.

84. The process of any one of statements 65 or 67 to 76, wherein the cerium oxide is present predominantly (or entirely) as cube morphology.

85. The process of any one of statements 65 or 67 to 84, wherein the cerium oxide is provided as nanoparticles.

86. The process of statement 85, wherein the nanoparticles have an average size of 10-30 nm.

87. The process of any one of statements 65 to 86, wherein the metal M is selected from the group consisting of Ru, Fe and a mixture thereof.

88. The process of any one of statements 65 to 86, wherein the metal M is Ru.

89. The process of any one of statements 65 to 88, wherein the catalytic material comprises:

0.01-30.0% w/w of the metal M, and 40.0-99.9% w/w of the metal oxide.

90. The process of any one of statements 65 to 88, wherein the catalytic material comprises:

0.01-15.0% w/w of the metal M, and 55.0-99.9 % w/w the metal oxide. 91. The process of any one of statements 65 to 88, wherein the catalytic material comprises:

1.5-7.0% w/w of the metal M, and 80.0-98.5% w/w of the metal oxide

92. The process of any one of statements 65 to 88, wherein the catalytic material comprises:

2.5-6.0% w/w of the metal M, and 85.0-97.5% w/w of the metal oxide.

93. The process of any one of statements 65 to 88, wherein the metal M is distributed across the surface of the metal oxide.

94. The process of any one of statements 65 to 93, further comprising an alkali metal Q.

95. The process of statement 94 wherein the alkali metal Q is selected from the group consisting of Cs, K, Ba and mixtures of two or more thereof.

96. The process of statement 94, wherein the alkali metal Q is selected from the group consisting of Cs, K and a mixture thereof.

97. The process of statement 94, wherein the alkali metal Q is Cs.

98. The process of any one of statements 94 to 97, wherein the molar ratio of M:Q is 1 :(0.1 -

3).

99. The process of any one of statements 94 to 97, wherein the molar ratio of M:Q is 1 :(0.5- 1.5).

100. The process of any one of statements 94 to 97, wherein the molar ratio of M:Q is 1 :(0.75-1.25).

101. The process of any one of statements 65 to 100, further comprising an acidic zeolite.

102. The process of statement 101 , wherein the acidic zeolite is ZSM-5. 103. The process of statement 101 or 102, wherein the catalytic material comprises 0.01- 50% w/w of the acidic zeolite.

104. The process of statement 101 or 102, wherein the catalytic material comprises 0.01- 20% w/w of the acidic zeolite.

105. The process of any one of statements 65 to 104, wherein the process is performed under batch conditions.

106. The process of any one of statements 65 to 104, wherein the process is performed under continuous flow conditions.

107. The process of any one of statements 65 to 106, wherein the ammonia is gaseous ammonia.

108. The process of any one of statements 65 to 106, wherein the ammonia is liquid ammonia.

109. The process of any one of statements 65 to 108, wherein the ammonia is contacted with the catalytic material in the presence of molecular oxygen.

110. The process of statement 109, wherein the molar ratio of NH3:C>2 is 1:0.01 to 1:0.75.

111. The process of statement 109, wherein the molar ratio of NH3:C>2 is 1:0.05 to 1:0.43.

112. The process of any one of statements 65 to 111, wherein the ammonia is contacted with the catalytic material at a temperature of 150-900°C.

113. The process of any one of statements 65 to 111 , wherein the ammonia is contacted with the catalytic material at a temperature of 250-500°C.

114. The process of any one of statements 65 to 113, wherein the ammonia is provided at a pressure of 0.001 to 100 bar.

115. The process of any one of statements 65 to 114, wherein the ammonia is contacted with the catalytic material in the presence of steam. 116. The process of any one of statements 65 to 115, wherein the catalytic material is as defined in any one of statements 1 to 47 and 64.

EXAMPLES

[00157] One or more examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:

Fig. 1 shows transmission electron microscopy of (a) MgO(111), (b) MgO(110), (c) MgO(100) supports. Lattice spacings are calculated from the measurement of 10 fringes.

Fig. 2 shows X-ray diffractograms of MgO(111), MgO(110), MgO(100) supports.

Fig. 3 shows (a,b) HAADF-STEM of 3 wt%-Ru/MgO(111); inset of (b) local fast fourier transform pattern of (b).

Fig. 4 shows (a) ¹H NMR, (b) trimethylphosphine oxide (TMPO) assisted ³¹ P MAS NMR measurement of MgO(111), MgO(110) and MgO(100).

Fig. 5 shows in-situ Fourier Transform IR measurement over (a) Ru/MgO(111), (b) Ru/MgO(110) samples after exposure of H2 for 15 minutes (Normalised difference spectra of in-situ spectra from background spectra). Spectra were obtained by collecting 32 scans with a resolution of 4 cm^-1 and are presented in absorbance unit. Powder of samples were pressed into pellets and loaded onto the sample holder. The sample was then flushed with He for 30 minutes to clean the surface under 200 °C. After collecting background spectra, N2 gas was passed through the sample holder for 15 minutes at 20 mL min ¹ and in-situ sample spectra were recorded. After 15 minutes, H2 gas was then passed at 20 mL min ¹ and in-situ spectra were recorded. The presented spectra are the difference spectra of the in-situ spectra from the background spectra.

Fig. 6 shows Operando Ambient-Pressure XPS. (a,c) 01s spectra for Ru/MgO(111) and Ru/MgO(110) respectively under consecutive switching between Ar and H2 gas at 350 °C. Spectra were measured at a photon energy of 980 eV. (b,d) Depth profiling 01s spectra using variable photon energy under H2 at 350 °C. “5 atomic layers” is corresponding to a penetration depth of 21.3 A with photon energy (PE) of 980 eV; “6 atomic layers” is of a depth of 26.2 A with PE 1280 eV; “8 atomic layers” is of a depth of 35.5 A with PE 1880 eV.

Fig. 7 shows (a) current-voltage test of Ru/MgO catalysts at 25 °C, (b) Current-voltage test of Ag- Ru/MgO catalysts at 150 °C.

Fig. 8 shows size distributions of ceria nanoparticles in different morphologies (a) cubes (b) rod length and their corresponding TEM images of CeC>2. Fig. 9 shows (a) exit wave restored from HR-TEM images showing ceria cubes with predominately polar (100) surfaces, overlaid with the expected model crystal structure; (100) FFT of the HR-TEM image (b) HRTEM image showing ceria rods with predominately non-polar (110) surface overlaid with the expected model crystal structure; (110) FFT of the HRTEM image.

Fig. 10 shows thermodynamic equilibrium for ammonia decomposition as a function of temperature under atmosphere pressure.

Fig. 11 shows catalytic performance of ammonia decomposition over Ru-based catalysts with different MgO supports. Reaction conditions: T = 400 °C, WHSV = 15000 ml_ g_cat ^'1 h ¹, 1 atm.

Fig. 12 shows NH3 conversion as a function of WHSV over Ru/MgO(111) catalyst at 350, 375, 400, and 425 °C.

Fig. 13 shows NH₃ conversion as a function of reaction temperature over Ru/MgO(111) and CsRu/MgO(111) catalyst at a WHSV of 30000 ml_ g_cat ^'1 h ¹.

Fig. 14 shows Arrhenius plots of reaction rate (ln(r)) versus 1/T for NH₃ decomposition over Ru/MgO(111) and Cs-Ru/MgO(111) catalysts.

Fig. 15 shows NH₃ conversion and H₂ yield of CsRu/MgO(111) with different O₂ contents. Reaction conditions: WHSV = 4000 ml_ g_cat ^'1 h ¹, 1 bar.

Fig. 16 shows Comparison of (a) H2 formation rate and (b) H2 yield over Ru/MgO(111), Ru/CeO₂(100) and Ru/CeO₂(100)-MgO(111) with a WHSV of 30000 ml_ g_cat-¹ IT¹ at 250 and 300 °C.

1. Preparation of catalysts

1.1. Preparation of MgO facets

[00158] MgO nanosheets with exposed (111) facets (denoted as MgO(111)) were synthesized by using the hydrothermal method with the aid of benzoic acid as surfactant. In brief, 2.0 g MgCh and 0.12 g benzoic acid were dissolved in 60ml_ deionized water with sonication treatment at room temperature. The obtained mixture was stirred for 10 minutes. 20ml_ of 2M NaOH solution was then added drop wise into the mixture, forming a white precipitate. The slurry was subsequently transferred to a 100ml_ autoclave and gradually heated to 180 °C and maintained for 24 hours. The Mg(OH)2 phase precursor was obtained after filtration followed by washing with water and drying at 80 °C under vacuum overnight. MgO(111) nanosheets were obtained after calcination in compressed air at 500 °C for 6 hours.

[00159] Commercial MgO (denoted as Com-MgO) was purchased from Sigma Aldrich. [00160] MgO(110) with preferential exposed (110) facets was prepared starting from a commercial MgO with reconstruction. Typically, 500 mg commercial MgO was boiled in water for 5 h, followed by drying at 120 °C overnight. Then the obtained powders were calcined under vacuum at 500 °C for 6 h.

[00161] MgO(100) with preferential exposed (100) facets was obtained by traditional thermal decomposition of Mg(NC>3)2 precursor directly at 500 °C for 5 hours.

[00162] Octahedron MgO(111) was prepared by a surface reconstruction method by cleaving MgO nanocubes in a pH-controlled solution. Typically, MgO nanocubes, which were used as a base precursor with predominant (100) facets, were prepared by the combustion of Mg ribbons in ambient conditions under controlled air flow. The smoky crystals were collected by a glass plate under Ar environment to prevent surface etching in moisture, which were then dissolved in a carefully pH-controlled aqueous solution. For the production of (111 ) facet, the MgO nanocubes were allowed to age for 7 days at ambient temperature at a pH 1 solution where the surfaces were slowly cleaved until it exposed an octahedron structure (with all the 8 exposed facets as (111)). The obtained crystals were then calcined under vacuum to remove the surface hydroxyl groups resulting in the formation of clean octahedron MgO(111) structure.

[00163] High surface-area MgO(111) (HS-MgO(111)) was prepared by using the magnesium hydroxycarbonate precursor. Magnesium nitrate was first dissolved in water at 60 °C (11 w/w % solution. Meanwhile, in a separate flask, sodium carbonate was dissolved in water at 60 °C (11 w/w % solution) followed by the addition of sodium hydroxide (40 w/w% of NaOH in the solution). The mixture was then heated to boiling temperature and then cooled down to ambient temperature. Filtration was performed and the supernatant solution was heated to 60 °C. The resultant solution was added slowly to the magnesium nitrate solution prepared above to form a magnesium carbonate precipitate. The precipitate was then collected by filtration following by washing in cold water and centrifugation for three times. The resultant solid was dried at a 80 °C oven. HS-MgO(111) was obtained by calcination at 500 °C for three hours.

1.2. Preparation of Ru-loaded MgO

[00164] Supported Ru/MgO materials were prepared by chemical vapor deposition via impregnation under inert atmosphere. Briefly, quantified Ru3(CO)i2 was dispersed in tetrahydrofuran (THF) solution and then desired amount of MgO supports were added. The obtained mixture was sonicated for 6 h, followed by removal of solvent. The resultant orange powders were treated at 70 °C under vacuum for 12 h where light grey powders were finally obtained. Then, these chemical precursors were heated and vaporized and deposited on MgO before reaching 350 °C with 2 °C/min for 5 h under Ar gas flow. Thus, supported Ru/MgO(110), Ru/MgO(100), Ru/Com-MgO were successfully synthesized. For Ru/MgO(111), Mg(OH)2 with exposed polar surface was used as precursor. The loading of Ru was similar as described above.

1.3. Preparation of Ru-loaded CeC -MgOd H)

[00165] Polar CeC>2 (100) as a cube form and CeC>2 with predominant non-polar (110) surface as a rod form were synthesized preferentially by hydrothermal synthesis of cerium nitrate in sodium hydroxide at 180 °C and 100 °C, respectively²⁰. Ru deposition on these oxides was prepared by chemical vapor deposition via impregnation under inert atmosphere as previously mentioned in the case of MgO(111).

[00166] A physical powder mixture of Ru/CeC>₂(100) + Ru/MgO(111) was pre-mixed and grinded in a same pot accordingly.

[00167] Co-synthesised CeC>₂(100)-MgO(111) and CeC>₂(110)-MgO(111) supports were prepared by the hydrothermal synthesis of ceria oxides at 180 °C and 100 °C, respectively but with an appropriate quantity of magnesium oxide precursor added, see above (resulting in CeC>2: MgO in 1 :1 weight ratio). In brief, the oxide precursors were added in 10 ml_ of 0.45 M cerium nitrate aqueous solution and dispersed by sonication and then add the mixed solution drop by drop to the 80 ml_ specific concentration NaOH solutions (NaOH = 6 M for rods and cubes). After stirring for 30 min, the mixture was added to a 200 ml_ Teflon-lined stainless-steel autoclave. The sealed autoclave was then transferred to a temperature-controlled oven (T = 373 K for CeC>₂(110), 453 K for CeC>₂(100)) and held there for 24 h. After cooling, the precipitates were filtered, washed with deionized water and dried at 353 K under vacuum for 12 h. After that, RU₃(CO)₁₂ was dispersed in tetrahydrofuran (THF) solution and then desired amount of CeC>₂(100)-MgO(111) and CeC>₂(110)-MgO(111) precursors were added. The obtained mixture was sonicated for 6 h, followed by removal of solvent. The resultant orange powder was treated at 85 °C under vacuum for 24 h until the light grey powder was obtained. Finally, this powder was heated at 350 °C with 2 °C/min for 4 h under 5%H₂/N₂ gas flow.

1.4. Preparation of CoMo bimetallic nanoparticles

[00168] The CoMo nanoparticles were prepared by one pot synthesis of cobalt nitrate salt and ammonium heptamolybdate salt followed by calcination under ammonia. Briefly, quantified cobalt nitrate hexahydrate and ammonium heptamolybdate with mole ratio of Co:Mo = 1 :1 were dissolved in water and stirred for 3 hours. The mixture was then dried at 100 °C overnight followed by calcination at 400 °C in 2 hours under dry air. The resultant product was then heated under pure ammonia at 700 °C at 1 °C/min for 3 hours. After cooling down to room temperature, the product was passivated in 0.1% O2 in N2 to avoid overoxidation.

1.5. Preparation of CoMo-loaded H)

[00169] The CoMo nanoparticles obtained from 1.4 was loaded to the CeC>₂(100) -MgO(111) (with synthesis procedure following that of 1.3) with theoretical loading of 25 weight% via ball milling method for 30 minutes.

1.6. Preparation of Cs-promoted Ru-loaded samples

[00170] The Cs promoted Ru-based catalysts were prepared by wet impregnation of Ru catalysts with CsNCh solution. This was followed by drying at 70 °C overnight.

1.7. Incorporation of ZSM-5 into Ru-loaded samples

[00171] The ZSM-5 is first pre-treated at 350 °C under air for 4 hours followed by evacuation at 80 °C overnight. The product is then physically mixed with the Ru-loaded metal oxides at a ratio as described above.

2. Catalytic ammonia decomposition

2.1. Continuous flow fixed-bed reactor

[00172] The ammonia decomposition was carried out in a continuous flow fixed-bed reactor with a computer-controlled auto-sampling system. Typically, 50 mg of catalyst was loaded in the centre of the quartz tube sandwiched with quartz wools. Prior to the reaction, the catalyst was pretreated at 350 °C under 5%H₂/He gas flow for 4 h. The gas was switched to N H3 stream and then the catalyst bed was adjusted to the target reaction temperature. ForC promoting ammonia decomposition, calibrated quantities of O2 gas flow was introduced during the reaction. All the activity tests were conducted in the temperature range of 250-500 °C with varied weight hourly space velocity (WHSV) under atmosphere pressure. After the stabilization, the gas composition was analyzed by an online gas chromatography (Agilent 7890 A) equipped with TCD detector and a HayeSep Q column. A blank test was conducted in a reactor where quartz powders were used instead of the Ru-MgO catalysts. No ammonia conversion was observed within the experimental temperature range. [00173] For the evaluation of catalytic effect under water flow, the fixed-bed reactor was coupled with a liquid pump where the performance was measured by titration. Firstly, acid solution (0.5M) was prepared before the reaction and a blank test without catalyst was carried out to double check the gas flow of ammonia. The pretreatment of the catalysts follows the procedures mentioned above. Then the performance of the catalysts without water addition was measured after reaction stabilization. After this water at pre-defined flow rate was introduced into the system where the activity is measured.

2.2. Liquid-phase batch reactor

[00174] The ammonia decomposition in ammonia water was carried out in a batch reactor at elevated temperature. Typically, 20 mg of catalyst was reduced fresh and placed inside the batch reactor. Subsequently 20 ml_ of 33% ammonia in water was added to the reactor. Helium was then flushed to the reactor for 3 times to expel the air inside and then 10 bar of He was injected (to facilitate for GC measurement later). The temperature was then raised to different temperatures at 5 °C/min. After the reaction the hydrogen and ammonia quantity was analyzed by an online gas chromatography (Agilent 7890 A) equipped with TCD detector and a HayeSep Q column. The hydrogen formation rate was then calculated by backward-titration to the ammonia water solution.

3. Results and discussion

[00175] All the MgO supports with preferential exposed surface facets were successfully synthesized and are characterized by transmission electron microscopy (Fig. 1), where the lattice spacings agree well to the literature values^{21 22}. X-ray diffraction also confirms the periclase nature of the MgO (Fig. 2). After impregnation, the majority of the Ru species are found to be atomically dispersed on the MgO(111) support despite a high Ru weight% loading. As displayed in Fig. 3, the Ru species are found to be singly anchored on the highly-ordered MgO(111) facet which is presumably due to the high stabilization energy offered by the polar support.

[00176] In order to investigate the surface properties of MgO(111) nuclear magnetic resonance (NMR) was performed. ¹H MAS NMR was adopted to assess the H⁺ affinity of the surface oxygen anion sites on different pure MgO supports prepared. As shown in Fig. 4a, all MgO supports with residue H⁺ show two chemical shifts with one resonance at around 0.7 ppm and the other resonance at 5.43 ppm for MgO(111), 4.78 ppm for MgO(110) and 4.74 ppm for MgO(100). The first peak at around 0.7 ppm is the resonance of proton from isolated hydroxyl group (i.e. Mg- OH) and physical-adsorbed water ²³, while second peak at lower field can be assigned to the bridging hydroxyl proton (i.e. Mg-O(H)-Mg). A significant shift from around 4.7 ppm for both nonpolar (100) and (110) surfaces to 5.4 ppm for polar (111) surface is attributed to the preferential adsorption of proton induced by local electric field from surface polarity as observed in the case of ZnO ²³.

[00177] This polarity-induced preferential proton adsorption was further confirmed by probe- assisted ³¹ P MAS NMR ²³. The adsorption of Lewis base molecule, trimethylphosphine oxide (TMPO), is expected to interact with surface cations (i.e. Mg²⁺ or H⁺) and reflect their corresponding chemical states by shifts in ³¹ P NMR. As shown in Fig. 4b, the adsorption of TMPO on bridging hydroxyl proton is indeed highly dependent on the surface polarity of the exposed MgO facet that a clear shift from 43 ppm of MgO(100) and MgO(110) to 45.8 ppm of MgO(111) can be observed (physical adsorption of TMPO at ~41 ppm). However, no interaction between TMPO and surface Mg²⁺ can be seen for three MgO supports presumably due to the easy hydroxylation of Mg²⁺ to Mg-OH that the interaction with TMPO is too weak to give ³¹ P chemical shift ²⁴.

[00178] Fourier-transformed Infra-red spectroscopy (FTIR) was then used to examine the surface properties of the MgO(111) support under a dynamic reducing atmosphere at 200 °C. To further ascertain the relationship between protons and the bridging O² on the polar (111) surface, in-situ Fourier Transformed IR measurement on Ru supported on the faceted MgO was carried out. Fig. 5a displays the spectra where hydrogen gas was passed onto the anhydrous Ru/MgO samples at 200°C for 15 minutes. Here, the broad peak at 3300 cm^-1 was assigned to the -OH stretching region, which is stemmed from the adsorbed protons on the bridging O² of MgO(111). The dramatic difference in its intensity between the polar (111) facet and the other 2 facets has again shed light on the superb affinity for H and mobility of the bridging O² of this polar support phase to remove the H from Ru metal to the support surface in H2. The comparatively much smaller but progressive increase in the OH intensity upon exposure to N2 to Ru/MgO(111) or H2 to Ru/MgO(110) is due to the moisture from the gas streams.

[00179] Thus, the NMR and FTIR both shed light on the fast hydrogen adsorption on the polar MgO(111) support. Operando XPS was then used to probe the coverage as well as the extent of hydrogen spillover on the polar MgO(111). As seen in Fig. 6, the 01s spectra of Ru/MgO(111) can be resolved as [OH] and [0² ~Mg] component at approximately 531.6 eV and 529.6 eV respectively. The sample was first heated to 350 °C under H2 to remove the surface RuO_x and was then switched to Ar for the first measurement. A noticeable [OH] peak was observed under Ar which was presumably due to the residual H to stabilize the unstable O² surface. It is interesting to note a significant increase in the [OH] component from 13.6% to 26.3% when the gas was switched to H2, which could be inferred as the hydrogen spillover from Ru surface to the O² surface. This increase in surface H⁺ on polar MgO(111) also agrees well with the chemisorption experiment. When the gas was subsequently switched back to Ar, the [OH] component decreased correspondingly, indicating the reversibility of such phenomenon where the surface protons migrated back to the Ru. In contrast, a broad peak was observed for Ru/MgO(111) where the line broadening was attributed to the charging effect. This also revealed the difference in the nature of conductivity of the material where charge can be channeled away in polar MgO(111) whilst retained in the non-polar MgO(110). When the gas was switched between H2 and Ar, there was no noticeable difference between the spectra for Ru/MgO(110). In order to probe the depth and distance that the surface H⁺ can travel, depth profiling of the 01s spectra was performed at various photon energy using synchrotron XPS (Fig. 6b, 6d). It is worthwhile to note the decrease of the relative [OH] signal with increasing information depth (i.e. more of the signal coming from deeper layers) is consistent with the H⁺ being located mostly near the surface, suggesting that the surface H⁺ mainly travel across the oxygen surface horizontally. In contrast, there was no noticeable change in the 01s spectra for Ru/MgO(110) in various depths, which is consistent with little or no surface H⁺ on this sample.

[00180] Given the ability for H⁺ to travel across MgO(111) surface, proton conductivity was then measured via the current-voltage test under a hydrogen atmosphere. As shown in Fig.7, Ru/MgO(110) and Ru/MgO(100) shows similar and comparable resistance whereas Ru/MgO(111) shows a much lower resistance across the range. It is worthwhile to note that the difference between the spectra is even more significant at the negative bias. This could be inferred as the greater mobility of the positive charge carrier, namely proton in this case, on the MgO(111) surface. To merge the grain boundary and enhance the surface mobility of charges on the MgO supports, Ag powder is introduced into the sample pellet and pre-reduced under flowing hydrogen at 350 °C. Fig.7b demonstrates the high temperature test (150 °C) and similar trend is again observed. A strikingly low resistance of Ru/MgO(111) due to H⁺ conductivity is observed which is stemmed from the enhanced proton mobility travelled across the polar MgO(111) surface. In conclusion the above characterizations have pointed to the excellent proton transport ability of the MgO(111) surface facilitated by Ru nano-interface, which can therefore enhance the bond activation via migration of adsorbed H species from metal surface to MgO(111) support .

[00181] Similarly, polar CeC>2 (cube) and non-polar CeC>2 (rod) were characterized by TEM and HR-TEM as depicted in Figures 8 and 9.

[00182] Ammonia decomposition has been regarded as an attractive process to produce CO_>r free H2 because the ammonia is thermodynamically unstable at high temperatures. This reaction is a mildly endothermic process that involves successive cleavage of N-H bonds and recombination of N and H. Although it can begin to decompose at low temperatures as shown in Fig. 10, the equilibrium conversion of ammonia is 98-99% at 425 °C with the practical conversion highly dependent on both catalysts and temperatures. It still remains challenging to efficiently produce hydrogen at low temperatures with high weight hourly space velocity. This is due to the limitation of rate-determining step of N recombination for ammonia decomposition, especially at low temperatures (300-500 °C). High strength of the metal-N bond usually in the range of 500- 630 kJ mol^'1 results in great difficulties in activation of metal-N bond formed. The key solution is promoting the electron transfer from the support or additives to the antibonding orbital of transient metal-N in the reaction. Based on the catalyst synthesis and characterizations, it is believed that Ru/MgO(111) displays a high capability for proton conductivity, which is beneficial for removal of proton during the breaking of N-H bond. To this regard, electrons can be enriched on the metal sites and transfer to weaken the metal-N bonds, promoting the ammonia decomposition at low temperatures.

[00183] Having checked the thermodynamic feasible performance, ammonia decomposition was carried out in the continuously fixed-bed reactor over our Ru-based catalysts. As shown in Fig. 11, Ru-based catalysts with different MgO supports display preference on ammonia decomposition under 400 °C with a weight hourly space velocity (WHSV) of 15000 ml_ g_cat ¹ h ¹. Ru/MgO(111) gives the highest activity of 82.4% among these samples. In contrast, Ru/MgO(110) shows only 43.2% NH3 conversion under the same conditions even though the samples have similar surface area. This is presumably due to the different surface properties of MgO (111) and (110) as described above. The MgO (111) facet covers with O-terminations, which may provide great number of basic surface sites, which is beneficial for electron donating and proton conducting. In contrast, the interlaced Mg²⁺ and O² on the (110) surface results in relative lower conversion. The Ru/MgO(100) displays the lowest activity with 19.8% NH₃ conversion. For comparison, Ru/Com-MgO without any preferred exposed facets of polycrystalline commercial MgO shows 24.3% conversion of ammonia, slightly higher than that of Ru/MgO(100). Therefore, MgO supports with different exposed facets provide different surface configurations and they play an important role for efficient conversion of NH₃.

[00184] The effect of WHSV was investigated under different reaction temperatures over Ru/MgO(111). Fig. 12 depicts the NH₃ conversion as a function of WHSV. It can be seen that with the increase of WHSV the ammonia conversion decreases, which might be due to the decrease of residence time of NH₃ on active sites. This indicates that relatively low WHSV is beneficial for NH₃ conversion. It is worth noting that the NH₃ conversion decreases slower under 425 °C than those of low reaction temperatures as the increase of WHSV. Therefore, above 92% conversion can also be obtained at 425 °C with a WHSV of 30000 ml_ g_cat ¹ h^'1 (Fig. 12). A comparison of different Ru loading was also investigated as listed in Table 1. Due to the chemical deposition for Ru loading used, the actual loading is expected to be lower than that of recipe loading. Understandably, the activity increases with the increase of Ru loading and the activity reach full conversion with a WHSV of 30000 mL g_caf¹ h ¹ at 450 °C. Therefore, 5% experimental loading was used for synthesis of catalysts unless otherwise stated.

Table 1 Catalytic performance of Ru/MgO(l 11) with different Ru loading.

Catalyst Experimental Actual NEE conv. Error in loading / wt% loading³ / /% conv / % wt%

Ru/MgO(l 11) 5 3.4 99.9 1.2

2 NA 46.1 2.4 1 NA 31.1 0.5

0.5 NA 24.1 0.2

³ Determined by ICP-OES analysis. Reaction conditions: T = 450 °C, WHSV = 30000 mL g_cat ^_1 h ¹, 1 atm.

[00185] Thus, it should be noted that comparison of activity over different catalysts should be made at the same temperature and WHSV (contact time). The higher temperature and lower WHSV will render higher ammonia conversion accordingly.

[00186] Due to the effect of electron donation, alkali ions have been demonstrated as effective promoters for supported Ru-based catalysts. Here, cesium was applied as the promoter to modify the Ru/MgO(111) catalyst (Ru/Cs molar ratio is 1/1). As depicted in Fig. 13, it can be seen that the catalytic performance shows a S-type curve and the conversion increases with the increase of temperature, which is in agreement with the mild endothermic reaction for NH3 decomposition. The ammonia conversion activity shows a great enhancement in the range of 325 to 400 °C. For Ru/MgO(111), the NH3 conversion achieves the thermodynamic equilibrium at 450 °C with a high WHSV of 30000 mL g_caf¹ h ¹, which is superior to previous reports for un-promoted Ru-based catalysts. The performance of CsRu/MgO(111) displays a similar trend with that of Ru/MgO(111); however, the incorporation of Cs significantly increases the NH3 conversion for the Ru/MgO(111) catalyst. It reaches almost the complete conversion at 425 °C with a WHSV of 30000 mL g_cat ¹ h

¹, which is higher than that of Ru/MgO(111) sample (92%). More than 30% enhancement for NH3 conversion can be achieved under the same reaction conditions between 350 and 400 °C.

Notably, the enhancement is more obvious at lower reaction temperatures.

[00187] Given that the apparent activation energy (Ea) is a critical parameter directly related to the catalytic performance, Arrhenius plots were used to derive the Ea for ammonia decomposition

(Fig. 14). Compared to those Ru/MgO materials reported with the E_a of 100-120 kJ/mol¹⁰, Ru/MgO(111) shows a much lower E_a of 77.5 kJ/mol, giving rise to an excellent performance. Modification of Ru/MgO(111) with Cs not only promotes the activity but also results in a decline in apparent energy, giving a 47.5 kJ/mol. The enhanced activity of Cs modified Ru/MgO(111) catalyst could be attributed to a change in the electronic property of the metallic Ru. A comparison of Ru catalysts in the literature is listed in Table 2. The NH3 conversion of Ru/MgO(111) is 99.9% at 450°C, which is superior to most of catalysts reported in literature. H2 formation rate was calculated based on the weight of catalyst regardless of Ru content and it shows the highest of H2 formation rate of 33.5 mmol g^_1 min ¹. By further optimising the exposure of the polar (111) facet, Ru/octahedron-MgO(111) displays complete conversion at a lower temperature of 400 °C (Entry 11 in Table 3). A higher surface-area MgO(111) support was also prepared by the calcination of a magnesium hydroxycarbonate precursor (Entry 12 in Table 3). Overall, The Ru/MgO(111) and Cs promoted Ru/MgO(111) are alternative materials for highly-efficient ammonia decomposition. Although Ru/MgO(111) based catalysts give an outstanding catalytic performance in ammonia decomposition, it still remains a great challenge to achieve high H2 production under low reaction temperatures, which limits the commercial applications especially coupling with proton exchange membrane fuel cell for mobile applications.

Table 2 NH₃ conversion over Ru catalysts at 450 °C and atmospheric pressure (WHSV: 30000 mL g_cat ^_1 h ¹).

Catalyst Preparation method Ru / NH₃ ¾ formation ¾ formation Ref. wt% conv. / % rate / mmol rate / mmol g_cat ¹ min ¹ gRu ¹ min ¹

R11/AI₂O3 Impregnation 10 31.5 11.5 115 [5]

Ru/SiCL Impregnation 10 34.5 11.4 114 [5]

Ru/MCM-41 Impregnation 5 42.4 14.2 284 [6]

Ru@Zr02 Deep purple 3 ca. 40 13.4 447 [7]

Ru/CNTs Impregnation 5 43.7 14.6 292 [8]

Ru/MgO Impregnation 4.8 30.8 10.3 215 [9]

Ru/Ti02 Impregnation 4.8 27.2 9.1 190 [9]

R11/AI₂O3 Impregnation 4.8 23.3 7.8 163 [9]

Ru/AC Impregnation 4.8 28.7 9.6 200 [9]

Ru/C12A7:e ^a CVD 2.2 70.0 11.7 532 [10]

Ru/C12A7:e ^b CVD 2.2 ca. 99.9 16.7 759 [10]

Ru/BHA^C Impregnation 2.74 ca. 20.8 13.9 507 [11]

Ru/MgO Polyol reduction 2.8 41.3 13.8 493 [12]

Ru/MgO^d DP method 3.5 52.7 21.2 606 [13]

K-Ru/MgO^d DP method 3.5 87.0 35.6 1017 [13]

Ru/MgO-MIL^e Pyrolysis 3.1 ca. 70.0 11.7 377 [14]

Ru-Cs/MgO-MIL^e Pyrolysis 3.1 ca. 97.2 16.3 526 [14]

Ru/c-MgO DP method 4.7 80.6 27.0 565 [15]

Ru/MgO(l 11) CVD 3.4 99.9 33.5 985 This work ^aCVD: Chemical Vapor Deposition; conditions: WHSV = 15000 mL g ¹ h ¹, T = 400 °C; ^bconditions: WHSV = 15000 mL g ¹ h ¹, T = 450 °C; ^CBHA: Barium hexaaluminate, conditions: WHSV = 60000 mL g ¹ h ¹; ^dDP: Deposition-Precipitation method, conditions: WHSV = 36000 ml g ¹ h ¹, K/Ru= 1/2; Conditions: WHSV = 15000 mL g ¹ h ¹, T = 450 °C. [00188] Here, it has surprisingly been found that cerium oxide is also a good candidate as a support for Ru in the ammonia decomposition, which might undergo a redox pathway to cleave N-H bond. Interestingly, different morphologies of ceria supporting Ru gave virtually 100% conversions under the WHSV at 450 °C, which suggests an even higher activity than MgO(111) under comparable testing conditions. However, a proper comparison can be made at lower temperature of 400 °C before the complete conversion of ammonia. As seen from Table 3, Ru/CeC>₂ (100) cube appears to give higher activity than corresponding CeC>₂(110) of rod form as well as polycrystalline CeC>2 nanoparticle with no specific facet exposure. Thus, it is clear that the use of polar facets in the cases of MgO(111) and CeC>₂(100) as supports for Ru can significantly enhance the ammonia decomposition. .

[00189] Excitingly, the incorporation of CeC>₂(100) into MgO(111) is somehow creating a beneficial synergy to yet further enhance the ammonia decomposition rate. In Table 3, the cosynthesis of Ru/CeC>2 (100)-MgO(111) by the hydrothermal method shows interestingly higher activity than that of the physical mixture of Ru/CeC>2 (100) + Ru/MgO(111). It is noted that Ru/CeC>₂(100)-MgO(111) (Entry 7) gives 80.5% conversion at the 27.0 mmol g_caf¹ min ¹ H2 formation rate. In comparison, the physical mixture (the mass ratio of two catalysts is the same as the co-synthesised one) shows lower activity. To further enhance the hydrogen formation rate, an acidic zeolite, ZSM-5, was added to the optimized Ru/CeC>₂(100)-MgO(111), the Bronsted acid site of which have been shown to capture ammonia at elevated temperatures. As a result, the local ammonia concentration effect around the catalyst was anticipated. This can render the H2 formation rate to 30.4 mmol g_cat ¹ min ¹ at 400 °C.

Table 3 N¾ conversion over different Ru-based catalysts at 400 °C and atmospheric pressure.

Entry Catalyst T / °C WHSV / NH₃ H₂ Ref. mL g ¹ h conv. / formation

¹ % rate / mmol gcat^"1 min ¹

1 Ru/c-MgO 400 30000 ca. 43.5 14.6 [15]

2 Ru/MgO(l 11) 400 30000 68.9 23.1 This work

3 Ru/Ce0₂-NPs 400 30000 55.6 18.6 This work

4 Ru/Ce0₂-Rod 400 30000 66.7 22.3 This work

5 Ru/Ce0₂-Cube 400 30000 79.1 26.5 This work

6 Ru/CeO₂(100)+ Ru/MgO(l 11) 400 30000 50.2 16.8 This work

7 Ru/CeO₂(100)-MgO(l 11) 400 30000 80.5 27.0 This work

8 CsRu/CeO₂(100)-MgO(l 11) 400 30000 94.6 31.7 This work

9 ZSM-5+ Ru/CeO₂(100)-MgO(l 11) 400 30000 92.4 30.4 This work

10 ZSM-5+ CsRu/CeO₂(100)-MgO(l 11) 400 30000 99.9 33.5 This work

11 Ru/Octahedron-MgO(l 11) 400 30000 99.9 33.5 This work

12 Ru/HS-MgO(l 11) 400 30000 62.7 21.0 This work [00190] In addition, it is key to develop a novel process for low-temperature NH3 decomposition whilst keeping a considerable H2 space-time yield/purity. As stated, the endothermicity of the decomposition reaction can limit thermodynamics and kinetics for the conversions of ammonia to hydrogen and nitrogen. Motivated by this need, a small amount of O2 was introduced in the reaction of ammonia in order to partially combust some of formed H2 to H2O to alter the overall enthalpy of the decomposition reaction. As a result, the decomposition reaction to produce H2, N₂, and H2O, may drive the original endothermic reaction into thermal neutral or slight exothermic reaction (oxidation decomposition) dependent on stoichiometry and nature of catalysts at steady state. However, the introduction of oxygen can concomitantly consume H2, resulting in the decrease of theoretical H2 yields. It is therefore important to balance the ammonia conversion and the O2 content to sustain high yields of H₂ production. Fig. 15 demonstrates the NH₃ conversions and H2 yields of CsRu/MgO(111) with different O2 contents. The theoretical H2 yield (at complete NH₃ decomposition under 300 °C) decreases with the increase of O2 content (with an assumption that O2 reacts selectively with H2 to produce H2O), which are still higher than the experimental measured H₂ yields indicative of incomplete NH₃ conversions. Also, the measured H2 yields and ammonia conversions are indeed higher at higher temperatures approaching towards thermodynamic values. It is interesting to see that the ammonia conversion under the kinetic controlled regime increases with increasing O2 content. Thus, the presence of O2 on surface can clearly assist some fundamental pathways for ammonia decomposition reaction. However, no formation of nitrogen oxides was detected. It was also noted that the H2 yield displays a volcano-type curve at 250 °C (less pronounced at 300 °C) with increasing O2 content at an optimal value just before O2 in in excess. This suggests excess O2 (incomplete O2 conversions) on surface appears to compete with the active sites for ammonia decomposition. H2 formation rates were calculated and are shown in Fig. 16. We introduced 8.26% of O2 content to drive the overall DH of reaction to 0 kJ/mol (NH₃ + 0.09 O2 = 1.32 H₂ + 0.5 N₂ + 0.18 H2O DH = 0 kJ/mol), where theoretical optimal value of 88% H2 yield can be achieved without any input of energy.

[00191] The CeC>2 (100) material as support for Ru appear to outperform those of MgO(111) presumably the redox feature to induce N-H heterolytic cleavage and the proton conductivity on its surface is clearly facilitated. Excitingly, the co-synthesized mixture of Ru/CeC>₂(100)- MgO(111) from hydrothermal method shows a more superior performance at the two different temperatures. To this end, the effectiveness of this composite catalyst for the oxidative ammonia decomposition was evaluated by introducing a small amount of O2. Experimentally, as seen from the Fig. 16, it can be observed that the H2 formation rate has a remarkable enhancement at 250 and 300 °C, respectively over Ru/MgO(111) and Ru/CeC>₂(100). Therefore, using small amount of O2 during the reaction is clearly beneficial for H2 production in oxidative decomposition of ammonia.

[00192] The effectiveness of this catalyst for ammonia decomposition was also evaluated in aqueous phase in a batch process (Table 4). As a result, 20 mg Ru/MgO(111) was pre-reduced under 5% hE at 350 °C for 6 hours and loaded fresh into the stainless steel batch reactor. 20.0 mL of 33% NH₃ in H₂O was then transferred to the reactor. 5 bar of He was injected and expelled for 3 times to remove the air / nitrogen inside. 10 bar of He was injected such that the outlet gas can be injected into GC for measurement after the reaction. The reaction was allowed to take place at 250 °C for 17.5 hours. The outlet gas was injected into GC to ascertain that H2 was produced and back titration was carried out to determine the amount of ammonia reacted.

Table 4 Decomposition of ammonia solution over Ru/MgO(l 11) in a batch reactor kept at 250 °C for

17.5h.

Catalyst Experimental Actual loading³ NEE conv. Average rate/ loading / wt% / wt% /% mmolg 'min ¹

Ru/MgO(l 11) 5 3.4 35.5 8.9

Determined by ICP-OES analysis. Reaction conditions: T = 250 °C. 17.5 hours

[00193] In addition, the performance of Ru/MgO(111) under the effect of water at high temperature was evaluated (Table 5). It is exciting to find that the water-inhibition effect is low despite its known detrimental effect to typical catalysts. At a ratio of NhEiEEO = 2:1 , the catalytic activity dropped only slightly whereas at high water ratio of NhEiEEO = 1:2, more than 60% of the activity can still be maintained.

Table 5 Decomposition of ammonia over Ru/MgO(l 11) with water in a fixed bed reactor at 400 °C with the WHSV of 30000 mL g ¹ h ¹.

Liquid water flow / mmol min ¹ Activity change / %

0 0

0.27 -13.8

1.11 -39.5 [00194] Catalytic performance of bimetallic CoMo nanoparticles supported on CeO2(100)- MgO(111) has also been performed to demonstrate the effect of non-precious metals when compared to Ru (Table 6).

Table 6 Decomposition of ammonia over CoMo/CeO₂(100)-MgO(l 11) at various temperature and

WHSV.

Temperature/ WHSV/ N¾ conversion / ¾ formation rate /

°C mL g_cat ¹ h ¹ % mmol g_Cat ¹ min ¹

550 30,000 22.0 7.4

600 30,000 62.1 20.9

600 15,000 76.5 25.7

[00195] The catalytic performance under high temperature and high WHSV has also been examined for the catalyst (Table 7). It is surprising to find that complete conversion can still be achieved even at 620 °C and a WHSV of 300,000 ml_ g^_1 h ¹. A reference using Johnson Matthey Fe catalysts has been included which attains a conversion at 51% under the same reaction condition.

Table 7 Decomposition of ammonia under high temperature (620 °C) and high WHSV (300000 mL g ¹ h ') over Ru/CeO₂(100)-MgO(l 11) and Johnson Matthey Fe catalysts.

Catalyst N¾ conversion / ¾ formation rate /

_ % _ mmol min ¹

Ru/CeO₂(100)-MgO(l 11) 100.0 334.8

JM Fe catalysts_ 50 9_ 170 4

[00196] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims. REFERENCES

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Claims

2. The catalytic material of claim 1 , wherein (111) facets form at least 30% of the exposed surfaces of the magnesium oxide.

3. The catalytic material of claim 1 or 2, wherein the metal M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, preferably wherein the metal M is only Ru.

4. The catalytic material of claim 1, 2 or 3, wherein the catalytic material comprises: 0.01-30.0% w/w of the metal M, and

40.0-99.9% w/w of the metal oxide, preferably wherein the catalytic material comprises:

2.5-6.0% w/w of the metal M, and 85.0-97.5% w/w of the metal oxide.

5. The catalytic material of any preceding claim, wherein the metal M has an average particle size of 0.5-100 nm.

6. The catalytic material of any preceding claim, further comprising a promotor, Q, wherein Q is selected from the group consisting of Cs, K, Ba, and mixtures of two or more thereof.

7. The catalytic material of claim 6, wherein the molar ratio of M:Q is 1 :(0.1 -3).

8. The catalytic material of any preceding claim, wherein the metal oxide consists of magnesium oxide.

9. The catalytic material of any one of claims 1 to 8, wherein the metal oxide comprises both magnesium oxide and cerium oxide, wherein the magnesium oxide comprises exposed (111) facets.

10. The catalytic material of claim 9, wherein the cerium oxide comprises exposed (100) facets.

11. The catalytic material of claim 10, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

12. The catalytic material of any one of claims 9, 10 and 11, wherein the metal oxide is provided as a mixture of discrete particles of magnesium oxide and discrete particles of cerium oxide (e.g. a physical mixture of magnesium oxide and cerium oxide), or the metal oxide is provided as a plurality of particles, at least some of those particles comprising a mixture of magnesium oxide and cerium oxide (e.g. a chemical mixture of magnesium oxide and cerium oxide).

13. A process for the preparation of a catalytic material as claimed in any preceding claim, the process comprising the steps of: a) providing a metal oxide as defined in any preceding claim, b) depositing a metal M on the metal oxide, wherein M is as defined in any preceding claim, and c) optionally reducing the product resulting from step b).

14. A process for the catalytic decomposition of ammonia, the process comprising the step of contacting ammonia with a catalytic material comprising: a) a metal oxide comprising: i) magnesium oxide comprising exposed (111) facets, or ii) cerium oxide, or iii) magnesium oxide comprising exposed (111) facets and cerium oxide; b) a metal M selected from the group consisting of Ru, Fe, Co, Mo, and mixtures of two or more thereof.

15. The process of claim 14, wherein the metal oxide comprises, consists essentially of or consists of cerium oxide.

16. The process of claim 14 or 15, wherein (111) facets form at least 30% of the exposed surfaces of the magnesium oxide.

17. The process of any one of claims 14, 15 and 16, wherein the cerium oxide comprises exposed (100) facets.

18. The process of any one of claims 14 to 17, wherein (100) facets form at least 40% of the exposed surfaces of the cerium oxide.

19. The process of any one of claims 14 to 18, wherein the metal M is Ru and optionally one or more selected from the group consisting of Fe, Co and Mo, preferably wherein the metal M is only Ru..

20. The process of any one of claims 14 to 19, wherein the catalytic material comprises: 0.01-15.0% w/w of the metal M, and

55.0-99.9 % w/w the metal oxide.

21. The process of any one of claims 14 to 20, wherein the process is performed under batch conditions or under continuous flow conditions.

22. The process of any one of claims 14 to 21 , wherein the ammonia is contacted with the catalytic material in the presence of molecular oxygen, preferably wherein the molar ratio of ammonia to molecular oxygen is 1 :0.01 to 1 :0.75 .

23. The process of any one of claims 14 to 22, wherein the ammonia is contacted with the catalytic material at a temperature of 150-900°C, preferably at a temperature of 250-500°C.

24. The process of any one of claims 14 to 23, wherein the ammonia is contacted with the catalytic material at a pressure of 0.1 to 100 bar.

25 The process of any one of claims 14 to 24, wherein the catalytic material is as defined in any one of claims 1 to 12.