EP4436711A1

EP4436711A1 - New surface organometallic chemistry processes for improved nh3-scr catalysts

Info

Publication number: EP4436711A1
Application number: EP21847526.7A
Authority: EP
Inventors: Phuc Hai NGUYEN; Cherif Larabi; Kai Chung Szeto; Mostafa Taoufik
Original assignee: Toyota Motor Europe NV SA; Centre National de la Recherche Scientifique CNRS; Ecole Superieure de Chimie Physique Electronique de Lyon; Universite Claude Bernard Lyon 1
Current assignee: Ecole Superieure De Chimie Physiqueelectronique De Lyon; Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1; Toyota Motor Corp
Priority date: 2021-11-22
Filing date: 2021-11-22
Publication date: 2024-10-02
Also published as: WO2023089353A1

Abstract

The present invention relates to a process for preparing a catalyst material, comprising the steps of: (a) providing a support material having surface hydroxyl (OH) groups, wherein the support material is ceria (CeO2), zirconia (ZrO2) or a combination thereof; (b) reacting the support material having surface hydroxyl (OH) groups of step (a) with a metal precursor compound containing a metal element from Group 5 (V, Nb, Ta) or Group 6 (Cr, Mo, W) in order to graft a metal element from Group 5 or Group 6 to the support material, wherein said metal precursor compound has at least one alkoxide group bound to metal atom M, the alkoxide group having a hydrogen atom bound to a β carbon atom adjacent to the α carbon atom bound to the oxygen atom linked to metal atom M in an M-O-C-C-H series of atoms; (c) heating the product obtained in step (b) under an inert atmosphere at a temperature of at least 200°C and at most 400°C. The present invention further relates to a catalyst material as may be obtained by the process set out above, and the use of the catalyst material as an ammonia selective catalytic reduction (NH3-SCR) catalyst for nitrogen oxides (NOx) reduction.

Description

NEW SURFACE ORGANOMETALLIC CHEMISTRY PROCESSES FOR IMPROVED NH3-SCR CATALYSTS

Field of the Invention

[0001] The present invention relates to the synthesis of ammonia selective catalytic reduction (NH3-SCR) catalysts for nitrogen oxides (NOx) reduction.

Background Art

[0002] Toxic NOx gases (NO, NO2, N2O) included in exhaust gases from fossil-fuel-powered vehicles or stationary sources such a power plants are required to be converted to N2 before being released to the environment. This is normally done by using different types of NOx reduction catalysts such as three-way catalysts (TWO), NOx storage reduction (NSR), or selective catalytic reduction (SCR) using ammonia as external reducing agent (NH3-SCR).

[0003] Metal oxides such as V₂O₅ are known to be good NH3-SCR catalysts. It has been suggested that the catalytic activity is achieved by the complementary features of acidity and reducibility of the surface species. Briefly, NH3 is adsorbed on a Brpnsted acid site (V⁵⁺-OH) followed by N-H activation through the adjacent V=O surface groups through a redox cycle (V⁵⁺=O/V⁴⁺-OH). The resulting surface complex reacts with gaseous or weakly adsorbed NO through Langmuir-Hinshelwood and Eley-Rideal mechanisms, respectively, to form NH2NO intermediate species which undergo decomposition into N2 and H2O. An alternate mechanism (amide-nitrosamide) involving the adsorption of NH3 over Lewis acid sites has also been proposed. Furthermore, under realistic conditions, particularly when a peroxidation catalytic convertor is placed upstream of the SCR catalytic convertor, this gives rise to formation of nitrogen dioxide which favors the SCR reaction known as fast-SCR. Indeed NO2 allows fast re-oxidation of the reduced species. However, the optimal NO2/NO ratio is one, and the presence of excess NO2 is also reduced through slower reaction leading to a lower total SCR reaction rate. Metal oxide catalysts such as V2O5 are developed mostly by synthesis routes such as impregnation, which normally produce nanoparticles of metal dispersed on support. The problem of such catalysts is the low performance, such as low NOx conversion and/or low N₂ selectivity.

[0004] Prior art catalysts have often used Cu, Fe, which are well recognized as good active sites for NH3-SCR when incorporated into zeolite materials. As regards support materials, prior art has often used SiO₂, which has high specific surface area, and may be expected to improve SCR performance by increasing the quantity of active sites.

US 9,283,548 B2 discloses catalysts of the type: MA I CeO₂ (M = Fe, Cu; A = K, Na), the synthesis route being impregnation, with chelating agents such as EDTA, DTPA being used.

J. Phys. Chem. B 2006, 110, 9593 - 9600 [Tian2006] discloses catalysts of the type: VOx I AO₂ (A = Ce, Si, Z), the synthesis route being impregnation. Applications include propane oxidative dehydrogenation (ODH). Dispersion and physisorption of the vanadium oxo-isopropoxide is achieved, rather than chemisorption.

J. Phys. Chem. B 1999, 103, 6015 - 6024 [Burchaml999] discloses catalysts of the type: Nb₂O₅ 1 SiO₂, AI₂Os, ZrO₂, TiO₂, the synthesis route being impregnation. The reference discusses surface species of isolated Nb, characterized by vibrational spectroscopy. The preparation is carried out in water, and the metal is deposited on the surface, rather than being grafted by protonolysis.

J. Phys. Chem. C 2011, 115, 25368-25378 [Wu2011] discloses catalysts of the type: VOx I CeO₂, SiO₂, ZrO₂, the synthesis route being impregnation. Iso-propanol is used as a solvent, not leading to grafting of the precursor on the surface, but instead only dispersion and physisorption of the vanadium oxo- isopropoxide. Appl. Catal. B 62, 2006, 369[Chmielarz2006] describes catalysts of the type: Fe or Cu/SiCh (3 different forms). It is widely known that Cu and Fe show good NH3-SCR performance when zeolites are used (ion-exchange synthesis). The catalyst materials were used for deNOx by NH3-SCR. Synthesis was carried out by molecular designed dispersion (MDD) using precursors Fe(acac)s, Cu(acac)2 (acac = acetylacetonate).

Science 2007, 317, 1056-1060 [Avenier 2007] describes cleavage of dinitrogen on isolated silica surface-supported tantalum(III) and tantalum(V) hydride centers [(ESi-O)2Taⁿⁱ-H] and [(ESi-O)2Ta^v-H₃].

EP 2 985 077 Al describes SiC^-supported molybdenum or tungsten complexes, such as trialkyltungsten or molybdenum oxo complexes, their preparation and use in olefin metathesis.

Summary of the Invention

[0005] In order to address the problems associated with prior art products and processes in the field of ammonia selective catalytic reduction (NH3-SCR) catalysts for nitrogen oxides (NOx) reduction, the processes and products of the present invention have been developed.

[0006] The Surface Organometallic Chemistry (SOMC) approach is capable of modifying the surface of support materials by grafting organometallic precursors, i.e. forming chemical bonds between precursors and surface hydroxyl groups, and thus preserving the local structure of the grafted material to minimize the formation of diversified species on the surface of support materials that are normally created through conventional synthesis methods. This methodology can be used to synthesize metal oxide catalysts supported with different metals. A typical SOMC procedure to synthesize materials consists of three steps as follows (scheme 1):

Step 1: Preparation, example: o Support materials: ■ calcination

■ hydration

■ dehydroxylation to generate controlled concentrations of hydroxyl groups o Metal precursors:

■ Synthesis (for those that are not readily available)

• Step 2: Grafting o Allow metal precursors to react with surface hydroxyl groups of the support material in a solution, for example pentane, typically at room temperature (~ 25 °C), toluene at 110 °C and mesitylene at 164 °C o Washing and drying

• Step 3: Activation o Remove remaining organic ligands, typically by thermal treatment at around 300 °C or higher in 6 h to 16 h under vacuum or argon or nitrogen.

[0007] The present invention discloses the development of new oxide NH3-SCR catalysts with improved NOx reduction performance by using new SOMC procedures. In the present invention, unlike SOMC procedures involving a high-temperature activation step as outlined above, carbon-atom-containing organic material I organic ligands resulting from the grafting step (step 2 in the general outline above), are removed by chemical reactions at relatively low temperatures, rather than calcination in air (at higher temperatures, typically around 500°C). Without wishing to be bound by any particular theory, it is believed that a calcination procedure may alter the distribution in space of metal atoms set down on the support in the grafting process (step 2 in the general outline above), for example reducing single atom dispersion, and this may affect catalytic performance under certain conditions, for example at low temperatures. The removal of organic material / organic ligands resulting from the grafting step is made possible by the choice of metal precursor compounds, effectively building in a mechanism for removing organic material I organic ligands after the grafting step, without needing a calcination step. Without wishing to be bound by any particular theory, it is believed that the presence of a beta-hydrogen atom in the precursor compounds used in the grafting step enables an interaction such as extraction by the metal of the beta-hydrogen atom, facilitated formation of an -OH beyond and release of organic fragments without too high an activation energy being required.

[0008] Thus, in a first aspect, the present invention relates to a process for preparing a catalyst material, comprising the steps of:

(a) providing a support material having surface hydroxyl (OH) groups, wherein the support material is ceria (CeO2), zirconia (ZrO2) or a combination thereof;

(b) reacting the support material having surface hydroxyl (OH) groups of step (a) with a metal precursor compound containing a metal element from Group 5 (V, Nb, Ta) or Group 6 (Cr, Mo, W) in order to graft a metal element from Group 5 or Group 6 to the support material, wherein said metal precursor compound has at least one alkoxide group bound to metal atom M, the alkoxide group having a hydrogen atom bound to a £ carbon atom adjacent to the a carbon atom bound to the oxygen atom linked to metal atom M in an M-O-C-C- H series of atoms;

(c) heating the product obtained in step (b) under an inert atmosphere at a temperature of at least 200°C and at most 400°C.

[0009] Concerning step (c), for heating the product obtained in step (b) under an inert atmosphere, the temperature is preferably at least 250°C and at most 350°C, preferably close to or at 300°C. As mentioned above, this temperature is rather lower than a normal temperature of calcination in air, carried out at higher temperatures, typically around 500°C. An inert atmosphere, such as high vacuum (IO ⁵ mbar), or under argon or nitrogen, is used for this lower temperature treatment around 300°C. Under these conditions, alkoxide ligands, with the required beta-hydrogen atoms, bound to group 5 or group 6 metal atoms on ceria or zirconia supports, can give rise to elimination of alkenes, such as isobutene for t-butoxide ligands, as part of the catalyst preparation process.

[0010] In a second aspect, the present invention relates to a catalyst material as may be obtained by the process set out above.

[0011] In a third aspect, the present invention relates to the use of the catalyst material set out above as an ammonia selective catalytic reduction (NH3-SCR) catalyst for nitrogen oxides (NOx) reduction.

Brief description of the Schemes la and lb

R1, R2 = H, Alkyl, aryl... M = Mo, W, Cr Scheme la: schematic representation of alkoxide metal precursors reaction with ceria leading to supported intermediates that undergo catalytic species under thermal decomposition Example group VI

Scheme lb: Elimination of isobutene and t-Bu-OH from ceria bearing Group VI metal alkoxide precursor groups

Brief description of the Figures

[0012] Figure la shows improved low temperature performance of catalysts synthesized by the procedure of the present invention.

Figure lb shows DRIFT spectroscopy analysis spectra of a) ceria dehydroxylated at 200 °C, b) after grafting of [W(=0)0^tBu)₄] and c) after thermal decomposition at 300 °C under vaccum.

Figure 2 shows ¹³C CP MAS solid state NMR spectroscopies of the

[W(=0)0^tBu)₄ grafted on ceria.

Figure 3 shows physisorption isotherms of nitrogen at 77K of the material containing 3.13 wt.% of tungsten on ceria after calcination under dry air at 500 °C for 16 h.

Figure 4 shows DRIFT spectroscopy analysis spectra of a) ceria dehydroxylated at 200 °C (Ce02-2oo), b) after grafting of [W(=0)0^tBu)₄] at 110°C in toluene, and c) after thermal decomposition at 300 °C under vaccum. Figure 5 shows DRIFT spectroscopy analysis spectra of a) ceria dehydroxylated at 200 °C (Ce02-2oo), and b) after grafting of [W(=0)0^tBu)4] at 165 °C in mesitylene.

Figure 6 shows DRIFT spectroscopy analysis spectra of a) ceria dehydroxylated at 200 °C (Ce02-2oo), b) after grafting of [Nb(O^tBu)₅], and c) after thermal decomposition at 300 °C under vaccum.

Figure 7 shows physisorption isotherms of nitrogen at 77K of the material containing 3.13 wt% of niobium on ceria after calcination under dry air at 500 °C for 16 h.

Figure 8 shows DRIFT spectroscopy analysis spectra of a) ceria dehydroxylated at 200 °C (Ce02-2oo), b) after grafting of [Nb(O^tBu)s] at 110°C in toluene, and c) after thermal decomposition at 300 °C under vaccum.

Figure 9 shows DRIFT spectroscopy analysis spectra of a) ceria dehydroxylated at 200 °C (Ce02-2oo) and b) after grafting of [Nb(O^tBu)₅] at 164 °C in mesitylene.

Detailed description of the invention

[0013] Catalysts produced according to the present invention may show high NOx conversion in NH3-SCR reactions. Among advantageous features of the present invention are:

- a process of grafting (chemical reactions between precursors and surface) rather than impregnating;

- grafted metals with atomic scale dispersion rather than nano-particles;

- a support which is thermally pre-treated (dehydroxylation), resulting in a desired anchoring point (OH), and where grafting yields well-dispersed surface species, thereby preventing sintering of the active metal center.

[0014] In the present invention, new NH3-SCR catalysts with suitable combinations of a metal selected from transition metal groups such as V, Nb, Ta, W, Mo and Cr and a support material selected from CeO2, ZrO2 or their mixtures such as CeCh-ZrCh are disclosed. These catalysts are prepared by new SOMC procedures using various organometallic metal precursors.

[0015] Conventional oxide catalysts normally consist of large metal particles supported on oxides. The active sites are ill-defined. The catalysts disclosed in the present invention may provide nearly 100% atomic scale dispersion of metal. Such highly dispersed metal sites are believed to not only simply give higher density of active sites but also to change the catalytic mechanism of NH3-SCR, in which NH3 adsorbed on metal sites can actively react with NOx adsorbed on surface of support. In other words, in the new catalysts, interaction between the metal and the support material is promoted, thus enhancing the catalytic performance.

[0016] In the present invention, it has been observed that catalyst materials prepared with a chemical activation step to remove organic material I organic ligands resulting from the grafting step, wherein a group 5 or group 6 metal is attached to a ceria and/or zirconia support during said grafting step using complexes I organometallic compounds of such group 5 or group 6 metals, may show higher NH3-SCR catalytic activity in certain circumstances, and notably in a temperature range of 100°C to 200°C. Although the absolute catalytic performance in this temperature range may be low (compared to catalytic output at higher temperatures), the relative increase that catalysts of the present invention may offer, with respect to catalysts prepared by high- temperature calcination for the activation step, is rather significant in the practial context of exhaust gas catalysts, since emissions generated during the so-called cold-start period, where working temperatures may well be in this low range of 200°C or lower, actually contribute significantly to overall emissions.

[0017] Appropriate support materials in the form of ceria (CeCh) and/or zirconia (ZrCh) can be obtained from commercial suppliers. For example, ceria can be obtained from suppliers such as SOLVAY and typically has a specific surface area of about 250 m²/g. [0018] In an advantageous embodiment to provide a certain controlled concentration of OH groups on the support material, in order to provide the material in step (a) of the process of the invention, hydration of the oxide support material (as received in a typical commercial sample) may be carried out in a first instance using moisture, followed by dehydroxylation through heating under reduced pressure. The concentration of OH groups is notably influenced by the temperature of the treatment. In a generally appropriate process for treating a ceria (CeO2) support material, a pressure of about 10'⁵ mbar, at a temperature of 200 °C for typically 16 h constitute advantageous treatment conditions. The concentration of OH groups on the support material can for example be determined by chemical titration through reaction with AI('BU)3 - the latter reacts quantitatively with surface hydroxyl groups releasing one equivalent of isobutane per OH group.

[0019] Preferred support materials in the present invention are ceria (CeO2) or ceria-zirconia (CeO2 - ZrO2) supports. Concerning the mixed ceriazirconia (CeO2 - ZrO2) support, the amount of ZrO2 can be in the range 20-80 wt%, preferably between 30-60 wt%. A higher content of ZrO2 may in practice decrease the concentration of OH groups. CeO2 and CeO2-ZrO2 are not known in the prior art as good support materials for SCR catalysts - these materials normally have lower specific surface area (SSA) than SiO2.

[0020] In a preferred embodiment of the present invention, the support material provided in step (a) contains at least 0.3 mmol and at most 2.0 mmol OH groups/g of the support material, preferably at least 0.5 mmol and at most 1.3 mmol OH groups/g of the support material.

[0021] Concerning the functionalization (grafting) stage (b), generally appropriate solvents include apolar solvents, such as in particular hydrocarbon solvents. Specific example of solvents include: pentane, hexane, heptane, toluene, xylenes, and mesitylene. In terms of reaction conditions for grafting, temperatures may range from room temperature up to reflux conditions and the reaction time may appropriately be from 1 hour to 60 hours.

[0022] A preferred group of metal precursor compounds to be sue din grafting step (b) of the process of the present invention is a Group 5 metal complex of metal Mi having the following structure: wherein metal Mi is Ta, Nb or V, and each R group is independently a hydrogen atom, an alkyl group or an aryl group, and most preferably all R groups are hydrogen atoms and/or methyl groups, or said metal precursor compound is a Group 6 metal complex of metal M₂ having the following structure: wherein metal M2 is W, Cr or Mo, and each R group is independently a hydrogen atom, an alkyl group or an aryl group, and most preferably all R groups are hydrogen atoms and/or methyl groups.

[0023] In preferred embodiments of the present invention, the metal precursor compound bears one or more tert-butoxide or iso-propoxide groups, particularly preferably tert-butoxide groups.

[0024] Among preferred metal precursor compounds to be used are ones containing a metal element from Group 5 (V, Nb, Ta) that are monomeric species selected from the group consisting of:

Ta(OCMe2Et)s, Ta(OMe)(iso-PrO)4, Ta(OEt)(iso-PrO)4, Ta(iso-PrO)s, Ta(OMe)(tert-BuO)4, Ta(OEt)(tert-BuO)4, Ta(iso-PrO)(tert-BuO)4, Ta(tertBuO)s, Ta(OEt)(OCMe₂Et)₄, Ta(isoPrO)(OCMe₂Et)₄, NbO(tert-BuO)₃, NbO(tert-BuO)₃. V(O^tBu)₄, VO(OiPr)₃, and VO(OiPr)₄.

[0025] Also among preferred metal precursor compounds to be used are ones containing a metal element from Group 6 (Cr, Mo, W) that are monomeric species selected from the group consisting of:

M(=O)(OR)4 or (R-C=)M(OR)₃, wherein M is Mo or W, and R = ethyl, isopropyl, or tertiobutyl;

WO(OCMe₃)₃(tbac) acetylacetonate (tbacH);

MoO(O^tBu)₄; and

CrO(O^tBu)4;

Also among preferred metal precursor compounds to be used are dimeric complexes selected from the group consisting of:

Nb2O(tert-BuO)s;

MoChCO-tert-Bu ;

MoO2(O-iPr)₂;

(RO)₃W=C-C=W(OR)₃, wherein RO is OCMe₃, OCMe₂CF₃, or OCMe₂Et; and

(OR)₃M=M(OR)₃, wherein M = Mo or W, and R is tert-Bu or iso-Pr. [0026] Catalyst materials of the present invention can interact with gas reactants in a catalytic process. In certain embodiments the catalyst materials may be applied to an inert substrate such as a metal plate, corrugated metal plate, or honeycomb. Alternatively, the catalyst material may be combined with other solids such as fillers and binders in order to provide an extrudable paste that may be transformed into a porous structure such as a honeycomb.

[0027] A catalytic converter based on catalyst materials of the present invention may appropriately include the catalyst material disposed on a supporting element such that passages are made available for the passage of exhaust gases, and the supported catalyst material may appropriately be housed in a metal casing. The metal casing is generally connected with one or more inlets such as pipes for transferring exhaust gases towards the catalyst material.

[0028] In order to function in NH₃-SCR catalysis, the catalytic converter is appropriately connected with a source of ammonia in order for the latter to come into contact with exhaust gas. The ammonia can be provided as anhydrous ammonia, aqueous ammonia, urea, ammonium carbonate, ammonium formate, or ammonium carbamate. In some embodiments, an ammonia storage tank is used to contain the ammonia source.

[0029] An SCR system can be integrated into various systems that require NOx reduction. Applications include engine systems of a passenger vehicle, truck, utility boiler, industrial boiler, solid waste boiler, ship, locomotive, tunnel boring machine, submarine, construction equipment, gas turbine, power plant, airplane, lawnmower, or chainsaw. Catalytic reduction of NOx using catalyst materials according to the present invention is therefore of general interest in situations where fossil fuels are used for power generation, not just for transportation but also in power generation devices, and domestic appliances using fossil fuels. [0030] Within the practice of the present invention, it may be envisaged to combine any features or embodiments which have hereinabove been separately set out and indicated to be advantageous, preferable, appropriate or otherwise generally applicable in the practice of the invention. The present description should be considered to include all such combinations of features or embodiments described herein unless such combinations are said herein to be mutually exclusive or are clearly understood in context to be mutually exclusive.

Experimental section - Examples

[0031] The following experimental section illustrates experimentally the practice of the present invention, but the scope of the invention is not to be considered to be limited to the specific examples that follow.

A/ Preparation of catalysts based on supported Nb and W on ceria

1. Preparation of (=Ce-O)₂W(=O)₂.(₂₀0) with low loading of W

(3.8 wt. W%) in two steps

1.1 Preparation of W(=O)O^tBu)₄/CeO2-(200) with low loading of W (3.8 wt. W%) at room temperature

[0032] [W(=0)0^tBu)₄] was synthesised from (W(0CI₄), as reported in the literature (Organometallics, Vol. 1, No. 1, 1982).

[0033] A mixture of a desired amount of [W(=O)OtBu)₄] and Ce0₂(2oo) (4 g) in pentane (20 ml) was mixed at 25 °C for 4 h. After filtration, the solid [W(=O)O^tBu)₄]/CeO₂ was washed three times with 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr) (Scheme 2) and characterized by DRIFT, NMR, ICP.

Erreur ! Source du renvoi introuvable.: Grafting Of W(=O)(O^lBu)₄ on ceria at room temperature in pentane

1.1.1 Characterization of [W(=O)O^tBu)4]/CeO2 by DRIFT spectroscopy

[0034] The grafting reaction of [W(=0)0^tBu)₄] on ceria to form [W(=O)O^tBu)₄]/CeO2-(200) is monitored by DRIFT spectroscopy (Figure lb). After the reaction and the removal of the excess complex, the bands between 3400 and 3700 cm ¹ attributed to a different vibration mode of v(CeO-H) at 3747 cm S completely disappeared. New broad bands at 3100-2850 and 1620- 1400 cm ¹ ranges are observed. These peaks are characteristics of aliphatic v(C-H) and b(C-H) vibrations of the physisorbed tertiobutanol, produced during the grafting reaction and chemisorbed tertiobutoxide ligands to surface tungsten (Figure lb). The DRIFT spectrum of the resulting material (Figure lb) shows a partial consumption of the other OH vibration bands, located between 3700 and 3600 cm ¹, while a new broad band appears, resulting from the interaction of some OH groups with tungsten alkoxide ligands. These confirms the chemical reaction between surface hydroxyl groups of ceria with tunsgten tertiobutoxide precursor by protonolysis and formation of ‘BuOH. 1.1.2 Characterization of the intermediate [W(=O)O^tBu)₄]/CeO2 by elemental analysis

[0035] Mass balance measurement carried out on this material [W(=O)O^tBu)4]/CeO2 showed the presence of 3.8 wt% and 2.9 wt% of W and C respectively (C/W = 11.6). This strongly suggests that the structure of the tungsten fragments is based on bipodal bis-tertiobutoxide species on the surface of the ceria (cf. Scheme 2), assuming that one ‘BuOH remains physisorbed on the ceria. The ethanol produced during the grafting was not evaluated, as it remains strongly bonded to the surface.

1.1.3 Characterization of the intermediate [W(=O)O^tBu)4]/CeO2 by Solid State NMR

[0036] The characterization of the resulting material [W(=O)O^tBu)4]/CeO2 was performed by ^XH and ¹³C CP MAS solid state NMR spectroscopies. The ^XH MAS and ¹³C CP MAS NMR data show the presence of tungsten tert-butoxy fragments, as reflected by the ^XH and ¹³C peaks at 1.4 and 26 ppm, respectively (Figure 2). On the MAS NMR spectrum, the shoulder on the low field side of the main peak (about 2.5 ppm) is assigned to the residual, interacting Ce-OH. It is to be noted that there is an absence of a signal belonging to quaternary carbon atoms. From these combined spectroscopic and analytical elements, it can be concluded that the reaction of [W(0^tBu)4] with the ceria surface dehydroxylated at 200 °C proceeds by W-0 cleavage with concomitant ‘BuOH formation, leading to a bipodal surface species (Scheme 2). The released ‘BuOH remains physisorbed to the surface catalyst as confirmed by the observation of a signal ca. 80 ppm in the ¹³C CPM NMR spectrum attributable to the free ‘BuOH. 1.1.4 Characterization of [W(=O)O^tBu)₄]/CeO2 (sample 3.8 wt% W) by BET

[0037] The BET surface area measured for the resulting material (Figure 3) was found to be ca. 183 ± 9 m²/g, closely approximate to the one found for the neat ceria calcined under the same conditions, which was ca. 207±10 m²/g. This would mean that the crystal structure is preserved and the grafting as well as the calcination process induce no particle sintering. Moreover, the pore volumes showed a slight decrease from 0.7 cm³/ g to ca. 0.6 cm³/g due the presence of organometallic fragments that occupy a certain amount of the volume.

1.2 Preparation of (=CeO)2W(=O)2 by heat treatment at 300°C of W(=O)O^tBu)₄/CeO2 intermediate

[0038] This step consists of the conversion of the supported complex W(=O)O^tBu)₄/CeO2 to supported W oxo species on ceria.

[0039] 1 g of W(=O)O^tBu)4/CeO2 was introduced into a glass reactor and heated to 300 °C under high vacuum (IO^-5 mbar) for 2 h. The volatiles were collected in liquid nitrogen trap and analysed by gas chromatography. GC analysis of the gas released after heating revealed the presence of ‘BuOH and isobutene. DRIFT analysis of (=CeO)2W(=O)2 reveals the disappearance of the alkyl vibrational bands (3000-2800 cm^-1), accompanied by re-appearance of isolated Ce-OH groups between 3750 and 3400 cm^-1. Unfortunately, the characteristic W=O vibration is masked by the network vibration of the support in the IR spectrum, even by using the Raman spectroscopy. 2. Preparation of (=Ce-0)2W(=0)2-(2oo) with higher loading of W (6.9 wt. W%) at 110°C

2.1 Preparation of W(=O)O^tBu)4/CeO2 - oo) with loading of W (6.9 wt. W%) at 110°C

[0040] A mixture of a desired amount of [W(=0)(0^tBu)₄] and CeCh oo) (4 g) in toluene (20 ml) was mixed at 25 °C for 4 h. After filtration, the solid [W(=0)(0^tBu)₄] /Ce02-(2oo) was washed three times with 10 ml of toluene and with 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr) (Scheme 2) and characterized by DRIFT, NMR, ICP.

Scheme 2: Grafting of W(=O)(O^lBu)₄ on ceria at 110 °C in toluene

2.1.1 Characterization of (=CeO)2W(=O)2 by DRIFT spectroscopy

[0041] The grafting reaction of [W(=0)0^tBu)₄] on ceria to form [W(=O)O^tBu)₄]/CeO2-(200) is monitored by DRIFT spectroscopy (Figure 4). After the reaction and the removal of the excess complex, the bands between 3400 and 3700 cm ¹ attributed to different vibration modes of v(CeO-H) at 3747 cm ¹, completely disappeared. New broad bands at 3100-2850 and 1620-1400 cm ¹ ranges were observed. These peaks are characteristics of aliphatic v(C-H) and b(C-H) vibrations of the physisorbed tertiobutanol, produced during the grafting reaction and chemisorbed tertiobutoxide ligands to surface tungsten (Figure 4b). The DRIFT spectrum of the resulting material (Figure 4b) shows a partial consumption of the other OH vibration bands, located between 3700 and 3600 cm ¹, while a new broad band appears, resulting from the interaction of some OH groups with tungsten alkyl ligands. These confirms the chemical reaction between surface hydroxyl groups of ceria with tunsgten tertiobutoxide precursor by protonolysis and formation of ‘BuOH.

2.1.2 Characterization of the intermediate [W(=O)O^tBu)₄]/CeO2 by elemental analysis

[0042] Mass balance measurement carried out on this material [W(=O)O^tBu)4]/CeO2 showed the presence of 6.9 wt% and 5.1 wt% of W and C respectively (C/W = 11). This strongly suggests that the structures of the tungsten fragments are bipodal bis-tertiobutoxide species on the surface of the ceria (Scheme 2), assuming that one ‘BuOH remains physisorbed on the ceria. The tertiobutanol produced during the grafting was not evaluated, as it remains strongly bonded to the surface (Scheme 2).

2.1.3 Characterization of [W(=O)O^tBu)₄]/CeO2-(200) (sample 6.92 wt.°/o W) by BET

[0043] The BET surface area measured for the resulting material is ca. 170 ± 9 m²/g inferior to the neat ceria calcined under the same conditions, which was ca. 207±10 m²/g. This would mean that the increase of the loading of W leads to the decrease of the surface area of the support. Moreover, the pore volumes showed a slight decrease from 0.7 cm³/ g to ca. 0.6 cm³/g due the presence of organometallic fragments that occupies a certain amount of the volume. 2.2 Preparation of (=CeO)2W(=O)2 by heat treatment at 300°C of W(=O)O^tBu)4/CeO2 intermediate (loading of W = 6.9 %) This step consists of the conversion of the supported complex CeO2 to supported W oxo species on ceria. 1 g of CeO2 was introduced into a glass reactor and heated to 300 °C under high vacuum (IO^-5 mbar) for 2 h. The volatiles were collected in liquid nitrogen trap and analysed by gas chromatography. GC analysis of the gas released after heating revealed the presence of isobutene. DRIFT analysis of W(=O)O^tBu)4/CeO2 reveals the disappearance of the alkyl vibrational bands (3000-2800 cm^-1), accompanied by re-appearance of isolated Ce-OH groups between 3750 and 3400 cm^-1 (Figure 4c). Unfortunately, the characteristic W=O vibration is masked by the network vibration of the support in the IR spectrum, even when using Raman spectroscopy.

3. Preparation of bis-oxo tungsten species (=CeO)2W(=O)2 in one step with loading of W (10 wt. W%) at 165 °C

Scheme 3: Representation of grafting reaction of W=O(O^lBu)₄ complex with ceria at 165 °C in mesitylene; includes the grafting of the W based complex followed by the thermal decomposition of the resulted surface fragments as represented in the scheme above.

[0045] A mixture of a desired amount of [W(=O)(O^tBu)4] and Ce0₂(2oo) (4 g) in mesitylene (20 ml) was mixed at 165 °C °C for 4 h. After filtration, the solid (=CeO)₂W(=O)2 was washed three times with 10 ml of mesitylene and with 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr) and characterized by DRIFT, NMR, ICP.

3.1 Characterization of ( CeO)₂W(=O)₂ by DRIFT spectroscopy

[0046] The grafting reaction of [W(=0)0^tBu)4] on ceria to form (=CeO)₂W(=0)2-(2oo) at 165 °C is monitored by DRIFT spectroscopy (Figure 5). After the grafting reaction and the removal of the excess complex, compared to the grafting temperature below 110°C , the bands between 3400 and 3700 cm ¹ attributed to different vibration modes of v(CeO-H) partially disappeared. Peaks with very low intensities characteristic of isobutyl fragments v(C-H) and b(C-H) between 3100-2850 and 1620-1400 cm ¹ ranges are observed (Figure 5b). These imply that the grafting of [W(=O)O^tBu)4] at high temperature is accompanied by thermal decomposition of tertiobutoxide ligands yielding W-bis- oxo species (=CeO)2W(=O)2 chemisorbed on ceria with elimination of isobutene (Scheme 3).

3.2 Characterization of (=CeO)2W(=O)2by elemental analysis

[0047] Mass balance measurement carried out on this material [W(=O)O^tBu)4]/CeO2 showed the presence of 10 wt.% of W. The absence of C on the resulting surface species strongly suggests that the grafting at 165 °C is accompanied by thermal decomposition of tertiobutoxide tungsten fragment to hydroxyl ligands and oxo ligands with formation of isobutene and tertiobutanol (Scheme 3).

3.3 Characterization of ( CeO)₂W(=O)₂ (sample 10 wt.%W) by BET

[0048] The BET surface area measured for the resulted material is ca. 98 ± 9 m²/g inferior to the neat ceria calcined under the same condition, which was ca. 207±10 m²/g. This would mean that the increase of the loading of W to 10 wt% showed a decrease in the surface area of the support due the presence of high concentration of tungsten oxo fragments that occupies a certain amount of the volume. Due to the absence of alkyl group on the surface, this catalyst has been used for SCR of NOx without thermal treatment.

4. Preparation of (=CeO)2Nb(=O)(OH) with low loading of Nb (1.49 wt. Nb%) at room temperature

4.1 Preparation of (=CeO)2Nb(=O)(OH) with low loading of Nb (1.49 wt. Nb%) at room temperature [0049] [Nb(O^tBu)₅] was synthesised from (NbCUCTHF ), as reported in the literature (Polyhedron, 2015, 90, 99-103).

Scheme 4: Grafting Of Nb(O^lBu)₅ on ceria at room temperature

[0050] A mixture of a desired amount of [Nb(O^tBu)s] and CeCh oo) (4 g) in pentane (20 ml) was mixed at 25 °C for 4 h. After filtration, the solid [Nb(O^tBu)s]/CeO2 was washed three times with 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr) and characterized by DRIFT, NMR, ICP.

4.1.1 Characterization by DRIFT spectroscopy of [Nb(O^tBu)₅]/Ce0₂-(2oo)

[0051] The grafting reaction of [Nb(O^tBu)s] on Ceria to form [Nb(O^tBu)₅] /Ce02-(2oo) is monitored by DRIFT spectroscopy (Figure 6). After the grafting reaction and the removal of the excess complex, the bands between 3400 and 3700 cm ¹ attributed to different vibration mode of v(CeO-H) at 3747 cm ¹ completely disappeared. New broad bands at 3100-2850 and 1620- 1400 cm ¹ ranges are observed. These peaks are characteristics of aliphatic v(C-H) and b(C-H) vibrations of the physisorbed tertiobutanol, produced during the grafting reaction and chemisorbed tertiobutoxide ligands to surface tungsten (Figure 6b). The DRIFT spectrum of the resulting material (Figure 6b) shows a partial consumption of the other OH vibration bands, located between 3700 and 3600 cm-1, while a new broad band appears, resulting from the interaction of some OH groups with tungsten alkoxide ligands. These confirms the chemical reaction between surface hydroxyl groups of ceria with tunsgten tertiobutoxide precursor by protonolysis and formation of ‘BuOH.

4.1.2 Characterization of the intermediate [Nb(O^tBu)₅]/CeO2 by elemental analysis

[0052] Mass balance measurement carried out on this material [Nb(O^tBu)s]/CeO2 showed the presence of 1.49 wt% and 2.69 wt% of Nb and C respectively (C/Nb = 14). This strongly suggest that the structure of the niobium fragments are bipodal bis-tertiobutoxide species on the surface of the ceria (Scheme 2), assuming that one ‘BuOH remains physisorbed on the ceria. The tertiobutanol produced during the grafting was not evaluated, as it remains strongly bonded to the surface.

4.1.3 Characterization of [Nb(O^tBu)₅]/CeO₂ (sample 1.49 wt°/o Nb) by BET

[0053] The BET surface area measured for the resulting material (Figure 7) was found to be ca. 185 ± 10 m²/g, closely approximate to the the one found for the neat ceria calcined under the same condition, which was ca. 207±10 m²/g. This would mean that the crystal structure is preserved and the grafting as well as the calcination process induce no particle sintering. Moreover, the pore volumes showed a slight decrease from 0.7 cm³/ g to ca. 0.6 cm³/g due the presence of organometallic fragments that occupy a certain amount of the volume. 4.2 Preparation of (=CeO)2Nb(=O)(OH) by heat treatment at 300°C of [Nb(O^tBu)s]/CeO2 intermediate

[0054] This step consists of the conversion of the supported complex (=CeO)2Nb(=O)(OH) to supported Nb oxo species on ceria. 1 g of [Nb(O^tBu)s]/CeO2 was introduced into a glass reactor and heated to 300 °C under high vacuum (IO^-5 mbar) for 2 h. The volatiles were collected in liquid nitrogen trap and analysed by gas chromatography. GC analysis of the gas released after heating revealed the presence of ‘BuOH and isobutene. DRIFT analysis of (=CeO)2Nb(=O)(OH) (scheme 7) reveals the disappearance of the alkyl vibrational bands (3000-2800 cm^-1), accompanied by re-appearance of isolated Ce-OH groups between 3750 and 3400 cm^-1 (Figure 6c). Unfortunately, the characteristic Nb=O vibration is masked by the network vibration of the support in the IR spectrum, even by using the Raman spectroscopy.

Scheme 5: Thermal treatment Nb(O^lBu)5/CeO2 intermediates at 300 °C under vacuum 5. Preparation of (=CeO)2Nb(=O)(OH) with loading of Nb (3 wt. Nb°/o) at 110°C

5.1 Preparation of [Nb(O^tBu)₅]/CeO2 with loading of Nb (3 wt. Nb°/o) at 110 °C

Scheme 6: Grafting Of Nb(O^lBu)₅ on ceria at 110°C in toluene

[0055] A mixture of a desired amount of [Nb(O^tBu)s] and CeCh oo) (4 g) in toluene (20 ml) was mixed at 110 °C °C for 4 h. After filtration, the solid [Nb(O^tBu)s]/CeO2 was washed three times with 10 ml of toluene and with 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr) and characterized by DRIFT, NMR, ICP.

5.1.1 Characterization of [Nb(O^tBu)₅]/CeO2(200) (3 wt.%) by DRIFT spectroscopy

[0056] The grafting reaction of [Nb(OtBu)₅] on ceria to form [Nb(O^tBu)s]/Ce02(2oo) is monitored by DRIFT spectroscopy (Figure 8). After the grafting reaction and the removal of the excess complex, the bands between 3400 and 3700 cm ¹ attributed to different vibration modes of v(CeO-H) at 3747 cm ¹ completely disappeared. New bands at 3600-3400 cm ¹ accompagned with signals in the 3100-2850 and between 1620-1400 cm ¹ ranges were observed, these peaks are characteristic of OH groups, aliphatic v(C-H) and b(C-H) vibrations of the physisorbed tertiobutanol, produced during the grafting reaction and chemisorbed tertiobutoxide ligands on surface (Figure 8b). These confirms the chemical reaction between surface hydroxyl groups of ceria with niobium tertiobutoxide precursor by protonolysis and formation of ‘BuOH.

5.1.2 Characterization of the intermediate [Nb(OtBu)s]/CeO2(200) (3 wt%) by elemental analysis

[0057] Mass balance measurement carried out on this material [Nb(O^tBu)s]/Ce02(2oo), showed the presence of 3 wt% and 1.8 wt% of W and C respectively (C/W = 9). This strongly suggest that the structure of the tungsten fragments are bipodal bis-tertiobutoxide species on the surface of the ceria (Scheme 2), assuming that a small quantity of ‘BuOH remains physisorbed on the ceria. The tertiobutanol produced during the grafting was not evaluated, as it remains strongly bonded to the surface (Scheme 6).

5.1.3 Characterization of [Nb(O^tBu)₅]/Ce02(2oo) (3 wt.%) by BET

[0058] The BET surface area measured for the resulted material is ca. 185 ± 9 m²/g inferior to the neat ceria calcined under the same condition, which was ca. 207±10 m²/g. This would mean that the increase of the loading of Nb has no effect on the surface area of the support. Moreover, the pore volumes showed a slight decrease from 0.7 cm³/ g to ca. 0.6 cm³/g due the presence of organometallic fragments that occupies a certain amount of the volume. 5.2 Preparation of (=CeO)2Nb(=O)(OH) by heat treatment at 300°C of [Nb(OtBu)s]/CeO2 intermediate (3 wt%)

[0059] This step consists of the conversion of the supported complex [Nb(O^tBu)s]/CeO2(200) to supported Nb oxo hydroxy species on ceria (Scheme 7). 1 g of [Nb(O^tBu)₅]/Ce02(2oo) was introduced into a glass reactor and heated to 300 °C under high vacuum (IO^-5 mbar) for 2 h. The volatiles were collected in liquid nitrogen trap and analysed by gas chromatography. GC analysis of the gas released after heating revealed the presence of isobutene. DRIFT analysis of [Nb(O^tBu)₅]/Ce02(2oo reveals the disappearance of the alkyl vibrational bands (3000-2800 cm^-1), accompanied by re-appearance of isolated Ce-OH groups between 3750 and 3400 cm^-1 (Figure 8c). Unfortunately, the characteristic Nb=O vibration is masked by the network vibration of the support in the IR spectrum, even by using the Raman spectroscopy.

6. Preparation of (=CeO)2Nb(=O)(OH) with loading of Nb (4.47 wt. Nb°/o) at 165°C

Scheme 7: Grafting of [Nb(O^lBu)₅] on ceria at 165 °C in in mesitylene toluene [0060] A mixture of a desired amount of [Nb(O^tBu)₅] and CeCh oo) (4 g) in mesitylene (20 ml) was mixed at 165 °C for 4 h. After filtration, the solid (=CeO)2Nb(=O)(OH) was washed three times with 10 ml of mesitylene and with 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr) and characterized by DRIFT, NMR, ICP.

6.1 Characterization of (=CeO)2Nb(=O)(OH) by DRIFT spectroscopy

[0061] The grafting reaction of [Nb(O^tBu)s] on ceria to form (=CeO)2Nb(=O)(OH) at 164°C is monitored by DRIFT spectroscopy (Figure 10). After the grafting reaction and the removal of the excess complex, the bands between 3400 and 3700 cm ¹ attributed to different vibration modes of v(CeO-H) at 3747 cm ¹ completely disappeared. The intensity of bands characteristic of isobutyl fragments v(C-H) and b(C-H) between 3100-2850 and 1620-1400 cm ¹ ranges are very low (Figure 10b). These results confirms that the grafting of [Nb(OtBu)₅] at high temperature is accompanied by thermal decomposition of tertiobutoxide ligands to Nb-mono-oxo-hydroxo species chemisorbed on ceria and elimination of isobutene (Scheme 7).

6.2 Characterization of the intermediate (=CeO)2Nb(=O)(OH) by elemental analysis

[0062] Mass balance measurement carried out on this material (=CeO)2Nb(=O)(OH) showed the presence of 4.47 wt% of Nb. The absence of C on the resulting surface species strongly suggests that the grafting at 164 °C is accompanied by thermal decomposition of tertiobutoxide niobium fragment to hydroxy and oxo ligands with formation of isobutene and tertiobutanol. 6.3 Characterization of (=CeO)2Nb(=O)(OH) (sample 4.47 wt.%Nb) by BET

[0063] The BET surface area measured for the resuling material is ca. 105 ± 10 m²/g lower than the neat ceria calcined under the same condition, which was ca. 207±10 m²/g. This would mean that the increase of the loading of Nb to 4.47 wt.% showed a decrease in the surface area of the support due the presence of high concentration of niobium oxo hydroxo fragments that occupies a certain amount of the volume. Due to the absence of alkyl group on the surface, this catalyst was used for SCR of NOx without thermal treatment.

7. Preparation of the catalysts based on supported Nb and W on ceria using classical SOMC method (grafting and calcination)

7.1 Preparation of NbOx/CeOa by grafting of [Nb(OEt)₅]2 followed by calcination

Scheme 8: Example preparation of the catalysts NbOx/ceria by grafting of [Nb(OEt)₅]₂ followed by calcination at 500°C [0064] A mixture of a desired amount of [[Nb(0Et)s]2 and CeCh oo) (4 g) in toluene (20 ml) was mixed at 25 °C for 4 h. After filtration, the solid [Nb(OEt)₅]2CeO2-(200) was washed three times with 10 ml of toluene and 10 ml of pentane. The resulting powder was dried under vacuum (IO^-5 Torr). [Nb(OEt)₅]2/CeO2-(200) was characterized by DRIFT, solid state NMR, ICP.

[0065] The intermediate product [Nb(OEt)s]2/CeO2-(200) was calcined using glass reactor under continuous flow of dry air at 500 °C for 16 h. The recovered material NbOx/ CeCh- oo) prior to catalytic testing was characterized.

7.2 Preparation of WOx/CeOa by grafting of [W(O)(OEt)₄]2 followed by calcination

[0066] A mixture of [W=O(OEt)4]2 (0.625 g, 1 mmol) and 6 g CeCh- oo) in toluene (30 mL) was stirred at 25 °C for 12 h. After filtration, the obtained solid [W=O(OEt)4]2/CeO2 was washed three times with toluene in order to extract the unreacted complex and then with pentane to remove toluene. The resulting yellow powder was dried under vacuum (IO ⁵ Torr). [W=O(OEt)₄]2/CeO2 was characterized by ICP, DRIFT, solid state NMR.

[0067] The material [W=O(OEt)4]2/CeO2 was calcined using glass reactor under continuous flow of dry air at 500 °C for 16 h. The recovered material prior to catalytic test was characterized.

Catalytic activity test conditions

[0068] Pellet samples of approximate 33 mg were prepared under 1 ton pressure and put into a quartz reactor (diameter 4.5 mm). A mixture of gas consisting of NO 300 ppm, NH3, 350 ppm, O2 10%, H2O 3%, CO2 10%, He (balance), was sent through a catalytic bed at the rate of 300 mL/min. The reactor was heated from room temperature to 600°C with a heating rate of 10 °C/ min. The system was kept at 600°C for 10 min before cooling down to room temperature. Gas composition at the outlet was monitored during the heating up and cooling down by a combination of FTIR, MS and chemiluminescence. The catalytic activity of the materials are depicted in Figure 1.

Claims

32 Claims

1. Process for preparing a catalyst material, comprising the steps of:

2. Process according to claim 1, wherein said metal precursor compound is a Group 5 metal complex of metal Mi having the following structure: 33 wherein metal Mi is Ta, Nb or V, and each R group is independently a hydrogen atom, an alkyl group or an aryl group, and most preferably all R groups are hydrogen atoms and/or methyl groups, or said metal precursor compound is a Group 6 metal complex of metal M2 having the following structure: wherein metal M2 is W, Cr or Mo, and each R group is independently a hydrogen atom, an alkyl group or an aryl group, and most preferably all R groups are hydrogen atoms and/or methyl groups.

3. Process according to claim 1 or 2, wherein the metal precursor compound bears one or more tert-butoxide or iso-propoxide groups, preferably tert-butoxide groups.

4. Process according to any of claims 1 to 3, wherein the metal precursor compound contains a metal element from Group 5 (V, Nb, Ta) and is a monomeric species selected from the group consisting of:

Ta(OCMe2Et)₅, Ta(OMe)(iso-PrO)₄, Ta(OEt)(iso-PrO)₄, Ta(iso-PrO)₅, Ta(OMe)(tert-BuO)₄, Ta(OEt)(tert-BuO)₄, Ta(iso-PrO)(tert-BuO)₄, Ta(tertBuO)s, Ta(OEt)(OCMe₂Et)₄, Ta(isoPrO)(OCMe₂Et)₄, NbO(tert-BuO)₃, NbO(tert-BuO)₃. VCC^Buk VO(OiPr)₃, and VO(OiPr)₄.

5. Process according to any of claims 1 to 3, wherein the metal precursor compound contains a metal element from Group 6 (Cr, Mo, W) and is a monomeric species selected from the group consisting of:

M(=O)(OR)4 or (R-C=)M(OR)₃, wherein M is Mo or W, and R = ethyl, isopropyl, or tertiobutyl; (tbac) acetylacetonate (tbacH); and

6. Process according to claim 1 or 3, wherein the metal precursor compound is a dimeric complex selected from the group consisting of:

Nb2O(tert-BuO)s;

MoChfO-tert-Bu ;

MoO2(O-iPr)₂;

(RO)₃W=C-C=W(OR)₃, wherein RO is OCMe₃, OCMe₂CF₃, or OCMe₂Et; and

(OR)₃M=M(OR)₃, wherein M = Mo or W, 3H313480 0021 JP DIV 1/JHD/PH/SB-SOMis tert-Bu or iso-Pr.

7. Process according to any of claims 1 to 6, wherein the support material provided in step (a) contains at least 0.3 mmol and at most 2.0 mmol OH groups/g of the support material, preferably at least 0.5 mmol and at most 1.3 mmol OH groups/g of the support material.

8. Process according to any of claims 1 to 7, wherein in step (c) of heating the product obtained in step (b) under an inert atmosphere, the temperature is at least 250°C and at most 350°C, preferably of 300°C.

9. Catalyst material as may be obtained by the process according to any of claims 1 to 8.

10. Use of the catalyst material according to either of claim 9 as an ammonia selective catalytic reduction (NH₃-SCR) catalyst for nitrogen oxides (NOx) reduction.