WO2020157696A1

WO2020157696A1 - Pyrolyzed phthalocyanine based materials for ammonia production

Info

Publication number: WO2020157696A1
Application number: PCT/IB2020/050749
Authority: WO
Inventors: Balamurugan VIDJAYACOUMAR; Mohammad Ali; Bedour AL-SABBAN; Khalid Albahily; Jean Marie Basset; Natalia MORLANES; Walid ALMAKSOUD
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2019-02-01
Filing date: 2020-01-30
Publication date: 2020-08-06
Anticipated expiration: 2021-08-01

Abstract

Catalysts for the production of ammonia are described. A catalyst can include a pyrolyzed tetraamido macrocycle / transition metal complex having a nitrogen-containing carbon matrix with the transition metal dispersed throughout. The catalyst can include a metal dopant dispersed in the pyrolyzed tetraamido macrocycle / transition metal complex.

Description

PYROLYZED PHTHALOCYANINE BASED MATERIALS FOR AMMONIA

PRODUCTION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of priority to U.S. Provisional Application No. 62/799,916, filed February 1, 2019, which is incorporated herein by reference in its entirety without disclaimer.

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0002] The invention generally concerns catalysts for the production of ammonia. In particular, the invention concerns a catalyst that includes a pyrolyzed tetraamido macrocycle / transition metal complex that includes a nitrogen-containing carbon matrix and an optional metal dopant dispersed in the nitrogen-containing carbon matrix.

B. Description of Related Art

[0003] Commercial synthesis of ammonia is performed by passing a process stream of synthesis gas (a mixture of hydrogen and carbon monoxide) and nitrogen through a catalyst arranged in one or more beds in a reactor. The nitrogen and hydrogen are present in essentially stoichiometric amounts. Commercial conditions to produce ammonia can involve a temperature between 300 °C and 600 °C and pressures above 10 MPa. Synthesis gas (a mixture of Fh and CO) is typically used as the hydrogen source. Under these process conditions, the equilibrium concentration of ammonia in a stoichiometric product gas composition is below 20% by volume in the synthesis gas stream from the reactor. A portion of the produced stream is typically recycled to the reactor, together with fresh synthesis gas, in order to provide a reasonably sufficient ammonia product yield. Prior to recycling, the product stream is cooled to separate ammonia from unreacted hydrogen, nitrogen, and inert diluents present in the synthesis gas. A fraction of the recycle gas is purged to vent inert gases. The stripped gas is then passed to a compression stage by which it is recycled to the reactor. The expense of compressing and recycling synthesis gas are important factors in the economy of ammonia production in general, and in particular when production capacities of existing ammonia synthesis loops have to be increased. Thus, the existing processes for ammonia production are energy intensive. [0004] Strategies underlying these processes for ammonia production include multi- promoted iron (Fe) based supported systems. These systems are used because the catalyst component is abundant, cheap, and convenient to handle under the reaction conditions. In view of its known advantages, Fe based catalysts still require a minimum of 400 °C and 200 atmospheres to have an appreciable extent of activity.

[0005] Various attempts to produce more efficient ammonia catalysts have been reported. By way of example, Hagen etal. (. Journal of Catalysis, 2003, Vol. 214, pp. 327-335) describes barium promoted iron, cobalt, or iron-cobalt alloys supported on carbon. These catalysts suffer in that high loadings of cobalt are necessary ( e.g ., about 20 wt.%) and high temperatures {e.g, at least 550 °C) are necessary to desorb the nitrogen from the catalyst. Furthermore, while barium promotes the synthesis of ammonia when used with cobalt, the combination of barium and iron was not effective. Other attempts to produce ammonia are described by Sehested et al. {Journal of Catalysis 188 (1999) 83-89), Hagen etal. {Chem. Commun ., 2002, 1206-1207), Jacobsen et al., (J. Am. Chem. Soc. 2001, 123, 8404-8405), Kojima, et al. {Appl. Cat. A: General 218 (2001) 121-128), Y. Gong, et al. {Nature Catalysis , 2018, 1, 178-185, Wang et al. (Nature Chemistry, 2017, 9, 64-70), and Kitano et al. {Nat. Chem. 2012, 4, 934-940).

[0006] Accordingly, the need exists for more cost effective and energy efficient ammonia production processes and catalysts.

SUMMARY OF THE INVENTION

[0007] A discovery has been made that provides a solution to at least some of the problems associated with the production of ammonia. The solution is premised on an efficient preparation and catalytic properties of transition metal {e.g, iron and/or cobalt) based catalysts for the ammonia synthesis reaction. This can be achieved via a one-step pyrolysis of a tetraamido macrocycle / transition metal complex that includes a nitrogen-containing carbon matrix. An optional metal dopant {e.g, alkali metals such as cesium (Cs) and barium (Ba)) can be incorporated into the pyrolyzed material to promote electron donation to the transition metal. The catalyst of the present invention can have transition metal {e.g, cobalt (Co) or iron (Fe)) particles, preferably nanoparticles, combined with alkali or alkaline-earth metals, supported on nitrogen-containing carbon composites. These catalysts can exhibit catalytic activities for ammonia synthesis process, with long term stability and efficient performance. As exemplified in a non-limiting manner in the Examples, the catalyst of the present invention are capable of N2 adsorption and subsequent conversion of the N2 to a NH_X species instead of a conventional catalysts which follow a N2 dissociation step to N atoms reaction pathway.

[0008] In an aspect of the present invention, catalysts for the production of ammonia are described. The catalyst can include a pyrolyzed tetraamido macrocycle / transition metal complex that includes a nitrogen-containing carbon matrix, and an optional metal dopant dispersed in the pyrolyzed tetraamido macrocycle / transition metal complex. The tetraamido macrocycle can be a phthalocyanine (Pc) or a derivative thereof, a porphyrin or a derivative thereof, an azaanulene or a derivative thereof, or a macrocycle including four (4) nitrogen atoms, preferably, a PC. The transition metal can be Fe, Co, or both. The catalyst can be a pyrolyzed FePc complex, a pyrolyzed CoPc complex, or a pyrolyzed FePc complex / CoPc complex (FeCoPc) mixture, or a combination thereof. In some embodiments, the catalyst can be a pyrolyzed FePc complex including 1 to 35 wt.% Fe, a pyrolyzed CoPc complex including 1 to 20 wt.% Co, or a pyrolyzed FeCoPc complex having a weight ratio of 1 : 1 to 20: 1, preferably 15: 1 to 10: 1. The catalyst of the present invention can have a BET surface area of at least 2 m²/g, preferably 2 m²/g to 300 m²/g, a pore size of 10 to 90 angstroms (A), preferably 10 A to 60 A, a pore volume of at least 0.01 cm³/g, preferably 0.01 to 2 cm³/g, or any combination thereof. The catalyst can have nitrogen-containing carbon material having an atomic ratio of nitrogen to carbon (N:C) from 1 to 8. The optional metal dopant can be an alkali metal or an alkaline-earth metal, or any combination thereof, preferably cesium (Cs), barium (Ba), or both. Non-limiting examples of Cs or Ba doped catalysts can include Cs pyrolyzed FePc, Cs- pyrolyzed CoPc, Ba pyrolyzed FePc, Ba pyrolyzed CoPc, Cs pyrolyzed FePc / CoPc, Ba pyrolyzed FePc / CoPc, or any combination thereof. In certain embodiments, the catalyst includes 1 to 40 wt.% of Ba, preferably 1 to 15 wt.% of Ba, more preferably 1 to 10 wt.% Ba, based on the total weight of the catalyst. A barium-containing catalyst of the present invention can have 8 wt.% Ba dispersed on a pyrolyzed Co-nitrogen-containing material. In some embodiments, the catalyst includes 1 to 15 wt.% of Cs, preferably 1 to 10 wt.% of Cs, based on the total weight of the catalyst. A Cs-containing catalyst of the present invention can have 10 wt.% Cs dispersed on a pyrolyzed Fe-nitrogen-containing material. Fe and/or Co nitrogen-containing carbon matrix of the present invention can also include iron nitrides, iron carbides, cobalt nitrides, iron metal, cobalt metal, or combinations thereof as determined by X-ray diffraction.

[0009] In another aspect of the present invention, methods of producing ammonia from nitrogen (N2) and hydrogen (Fh) are described. A method can include contacting a gaseous reactant stream that includes N2 and H2 with any one of the catalysts of the present invention under conditions sufficient to produce gaseous ammonia (NH3). Reaction conditions can include a ratio of H2:N2 of 2: 1 to 5: 1, preferably 3 : 1, a temperature of 250 °C to 550 °C, a pressure of 1 to 10 MPa, or any combination thereof. The method can also include activating the catalyst at a temperature of 400 to 530 °C prior to contacting the catalyst with the reactant stream. In some embodiments, the catalyst can include Cs and the activation temperature can be 400 °C to 530 °C, preferably 475 °C to 495 °C. In embodiments where the catalyst includes Ba, the activation temperature can be 500 °C to 530 °C, preferably 510 °C to 520 °C.

[0010] In yet another aspect of the present invention, methods of producing the ammonia catalyst of the present invention are described. A method can include pyrolysis of a tetraamido macrocyclic / transition metal complex material at a temperature of 550 °C to 800 °C under an inert atmosphere to form the pyrolyzed tetraamido macrocyclic / transition metal complex that includes the nitrogen-containing carbon matrix (pyrolyzed PC material), and optionally impregnating the pyrolyzed PC material with a metal dopant precursor material. The pyrolyzed PC material can be cooled under an inert atmosphere and then passivated. In a preferred embodiment, the tetraamido macrocyclic / transition metal complex can include at least one of pyrolyzed iron phthalocyanine (FePc) or pyrolyzed cobalt phthalocyanine (CoPc).

[0011] In the context of the present application, 20 embodiments are described. Embodiment l is a catalyst for the production of ammonia, the catalyst comprising: a pyrolyzed tetraamido macrocycle / transition metal complex comprising a nitrogen-containing carbon matrix; and an optional metal dopant. Embodiment 2 is the catalyst of embodiment 1, wherein the tetraamido macrocycle is a phthalocyanine (Pc) or a derivative thereof, a porphyrin or a derivative thereof, or an azaanulene or a derivative thereof, or any macrocycle containing at least 4 complexing nitrogen atoms. Embodiment 3 is the catalyst of embodiment 2, wherein the tetraamido macrocycle is a phthalocyanine (Pc). Embodiment 4 is the catalyst of any one of embodiments 1 to 3, wherein the transition metal is iron (Fe), cobalt (Co) or both, and the transition metal is dispersed throughout the nitrogen containing carbon matrix. Embodiment 5 is the catalyst of any one of embodiments 1 to 4, wherein the catalyst includes the metal dopant and the metal dopant comprises an alkali metal or an alkaline-earth metal, or any combination thereof, preferably cesium (Cs), barium (Ba), or both. Embodiment 6 is the catalyst of embodiment 5, wherein the catalyst is Cs-FePc, Cs-CoPc, Ba-FePc, Ba-CoPc, Cs-FePc-CoPc, Ba-FePc-CoPc, or any combination thereof. Embodiment 7 is the catalyst of embodiment 6, wherein the catalyst comprises 1 to 15 wt.% of Cs, preferably, 1 to 10 wt.% of Cs, based on the total weight of the catalyst. Embodiment 8 is the catalyst of embodiment 7, wherein the catalyst has 10 wt.% Cs dispersed on a Fe-nitrogen-containing material. Embodiment 9 is the catalyst of embodiment 5, wherein the catalyst comprises 1 to 40 wt.% of Ba, preferably, 1 wt.% of Ba, based on the total weight of the catalyst. Embodiment 10 is the catalyst of embodiment 9, wherein the catalyst is 8 wt.% Ba dispersed on a Co-nitrogen-containing material. Embodiment 11 is the catalyst of any one of embodiments 4 to 10, wherein catalyst is a pyrolyzed FePc complex, a pyrolyzed CoPc complex, or a pyrolyzed FePc complex /CoPc complex (FeCoPc) mixture, or a combination thereof. Embodiment 12 is the catalyst of embodiment 11, wherein the catalyst is a pyrolyzed FePc complex including 1 to 35 wt.% Fe, a pyrolyzed CoPc complex including 1 to 20 wt.% Co, or a pyrolyzed FeCoPc complex having a weight ratio of 1 : 1 to 20: 1, preferably 15: 1 to 10: 1. Embodiment 13 is the catalyst of any one of embodiments 1 to 12, wherein the catalyst has a BET surface area of at least 2 m²/g, preferably 2 m²/g to 300 m²/g, a pore size of 10 to 90 angstroms (A), preferably 10 A to 60 A, a pore volume of at least 0.01 cm³/g, preferably 0.01 to 2 cm³/g, or any combination thereof. Embodiment 14 is the catalyst of any one of embodiments 1 to 13, wherein the nitrogen- containing carbon material has an atomic ratio of nitrogen to carbon (N:C) from 1 to 8. Embodiment 15 is the catalyst of any one of embodiments 4 to 14, wherein the nitrogen- containing carbon material further comprises iron nitrides, iron carbides, cobalt nitrides, iron metal, cobalt metal, or combinations thereof as determined by X-ray diffraction.

[0012] Embodiment 16 is a method of producing ammonia from nitrogen (N2) and hydrogen (Eh), the method comprising contacting a gaseous reactant stream comprising N2 and Eh with any one of the catalysts of embodiments 1 to 15 under conditions sufficient to produce gaseous ammonia (NFE). Embodiment 17 is the method of embodiment 16, wherein the ratio of Fh:N2 is 2: 1 to 5: 1, preferably 3 : 1, and the conditions comprise a temperature of 250 °C to 550 °C, a pressure of 1 to 10 MPa, or any combination thereof. Embodiment 18 is the method of any one of embodiments 16 to 17, further comprising activating the catalyst prior at a temperature of 400 to 530 °C prior to contacting the catalyst with the reactant stream, and, optionally, the catalyst comprises Cs and the activation temperature is 400 °C to 530 °C, preferably 475 °C to 495 °C, or wherein the catalyst comprises Ba and the activation temperature is 500 °C to 530 °C, preferably 510 °C to 520 °C.

[0013] Embodiment 19 is a method of producing the ammonia catalyst of any one of embodiments 1 to 15, the method comprising: pryolyzing a tetraamido macrocyclic / transition metal complex material at a temperature of 550 °C to 800 °C under an inert atmosphere to form the pyrolyzed tetraamido macrocyclic / transition metal complex material comprising a nitrogen-containing carbon matrix of any one of embodiments 1 to 15, and optionally impregnating the pyrolyzed complex material with a metal dopant precursor material. Embodiment 20 is the method of embodiment 19, further comprising cooling the pyrolyzed tetraamido macrocyclic / transition metal complex material under an inert atmosphere and passivating the cooled composite, wherein the tetraamido macrocyclic / transition metal complex material comprises at least one of iron phthalocyanine (FePc) or cobalt phthalocyanine.

[0014] Other embodiments of the invention are discussed throughout this application. Any embodiment discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each embodiment described herein is understood to be embodiments of the invention that are applicable to other aspects of the invention. It is contemplated that any embodiment or aspect discussed herein can be combined with other embodiments or aspect discussed herein and/or can be implemented with respect to any method or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0015] The following includes definitions of various terms and phrases used throughout this specification.

[0016] An“aliphatic group” is an acyclic or cyclic, saturated or unsaturated carbon group, excluding aromatic compounds. A linear aliphatic group does not include tertiary or quaternary carbons. Non-limiting examples of aliphatic group substituents include halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, amide, nitrile, acyl, thiol and thioether. A branched aliphatic group includes at least one tertiary and/or quaternary carbon. Non-limiting examples of branched aliphatic group substituents include alkyl, halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, amide, nitrile, acyl, thiol and thioether. A cyclic aliphatic group is includes at least one ring in its structure. Polycyclic aliphatic groups may include fused, e.g., decalin, and/or spiro, e.g., spiro[5.5]undecane, polycyclic groups. Non-limiting examples of cyclic aliphatic group substituents include alkyl, halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, amide, nitrile, acyl, thiol and thioether.

[0017] An“alkyl group” is linear or branched, substituted or unsubstituted, saturated hydrocarbon. Non-limiting examples of alkyl group substituents include alkyl, halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, amide, nitrile, acyl, thiol and thioether.

[0018] An“aryl” group or an“aromatic” group is a substituted or unsubstituted, mono- or polycyclic hydrocarbon with alternating single and double bonds within each ring structure. Non-limiting examples of aryl group substituents include alkyl, halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, amide, nitrile, acyl, thiol and thioether.

[0019] A “heteroaryl” group or a “heteroaromatic” group is a mono-or polycyclic hydrocarbon with alternating single and double bonds within each ring structure, and at least one atom within at least one ring is not carbon. Non-limiting examples of heteroaryl group substituents include alkyl, halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine, amide, nitrile, acyl, thiol and thioether.

[0020] The terms“about” or“approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0021] The terms “wt.%,” “vol.%,” or“mol.%” refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0022] The term“substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0023] The terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.

[0024] The term“effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0025] The use of the words“a” or“an” when used in conjunction with any of the terms “comprising,”“including,”“containing,” or“having” in the claims, or the specification, may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and “one or more than one.” [0026] The words“comprising” (and any form of comprising, such as“comprise” and “comprises”),“having” (and any form of having, such as“have” and“has”),“including” (and any form of including, such as“includes” and“include”) or“containing” (and any form of containing, such as“contains” and“contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0027] The catalysts of the present invention can“comprise,”“consist essentially of,” or “consist of’ particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phrase“consisting essentially of,” in one non limiting aspect, a basic and novel characteristic of the catalysts of the present invention are their abilities to catalyze formation of ammonia from nitrogen and hydrogen.

[0028] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0030] FIG. 1 shows a calibration curve to convert the signal of ammonia monitored in the Mass-Vac spectrometer into NFb concentration in the reactor outlet.

[0031] FIGS 2A-2D shows catalytic performances of the phthalocyanine-derived catalysts for the ammonia synthesis reaction at reaction conditions of 200 mg of catalyst, flow rate 40 mL min^-1, molar N2:H2 = 1 :3, and a weighted hourly space velocity (WHSV) of 12000 mL g^-1 h-. FIG. 2A: NFb-synthesis rate (m mol g^-1 h^-1) as a function of the pressure at 400 °C. FIG. 2B: NFb-synthesis rate as a function of the temperature at 10 bar. FIG 2C: specific activities (m mol gmetai ¹ h at 400 °C and 10 bar. FIG. 2D: time dependence of the catalytic activities versus time on stream (for stability testing) in the range 400-520 °C and 30-70 bar (3 to 7 MPa).

[0032] FIG. 3 shows catalytic performance of the 2 wt.% Cs-FePc catalyst of the present invention and commercial Fe-KMl for the ammonia synthesis reaction at reaction conditions of 200 mg of catalyst, flow rate 40 mL min^-1, molar N2:H2 = 1 :3, with a WHSV of 12000 mL g^-1 h^-1, pressure of 1-70 bar (0.1 MPa to 7 MPa), and a temperature of 400 °C.

[0033] FIGS. 4A-4D shows kinetic parameters of the pyrolyzed phthalocyanine catalysts for the ammonia synthesis. FIG. 4A: Arrhenius plots of in the temperature range 250-450 °C, at 10 bar. Dependences of ML-synthesis rate on the partial pressures of N2 (FIG. 4B), Fh (FIG. 4C) and ML (FIG. 4D) at 400 °C and 10 bar. (Qvof¹, total flow rate).

[0034] FIGS. 5A and 5B shows catalytic performance of the pyrolyzed phthalocyanine catalysts for the ammonia synthesis reaction at reaction conditions of 200 mg of catalyst, flow rate 40-120 mL min^-1, mole N2:H2 = 1 :3, with a WHSV of 12000-40000 mL g^-1 h^-1, pressure of 10 bar (1 MPa), temperature of 400 °C. FIG. 5A shows the influence of the space velocity at 10 bar (1 MPa) and 400 °C, and FIG. 5B shows the percentage of ammonia in reactor outlet.

[0035] FIGS. 6A-6D shows best-fit results for the experimental reaction rates for 10 wt.% Cs-FePc catalyst with respect to the rate equations derived considering different rate determining steps of N2 activation (FIG. 6 A), NH formation (FIG. 6B), NH2 formation (FIG. 6C) and ML formation (FIG. 6D).

[0036] FIG. 7 shows X-ray diffraction (XRD) patterns of the for the phthalocyanine catalysts of the present invention after pyrolysis and after the ammonia synthesis reaction.

[0037] FIG. 8 shows DF-STEM imaging of the pyrolyzed catalysts of the present invention showing single atoms of metals distributed on the support in addition to the metal nanoparticles.

[0038] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DFTATLFD DESCRIPTION OF TTTF INVENTION

[0039] A discovery has been made that provides a solution at least some of the aforementioned problems associated with the production of ammonia. The solution is premised on an efficient preparation and catalytic properties of transition metal nitrogen containing carbon materials for the ammonia synthesis reaction. In particular, the catalyst can include Co or Fe dispersed in a nitrogen containing carbon matrix. Addition of optional alkali or alkaline- earth metals can promote electron transfer to the transition metal during ammonia synthesis.

[0040] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Catalysts

[0041] The catalysts of the present invention can include a transition metal nitrogen- containing carbon material. In some embodiments, alkali and/or alkaline-earth metals can be supported on or dispersed throughout the transition metal nitrogen-containing carbon materials of the present invention. The catalyst can have any shape or size. The catalyst can have a surface area of at least 2 m²/g, or at least any one of, equal to any one of, or between any two of 2, 10, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275 and 300 m²/g as determined using Brunauer-Emmett-Teller (BET) analysis. Pore sizes of the catalyst can be 10 to 90 angstroms (A), preferably 10 A to 60 A, or at least any one of, equal to any one of, or between any two of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, and 90 A. A pore volume of the catalyst can be at least 0.01 cm³/g, preferably 0.01 to 2 cm³/g, or at least any one of, equal to any one of, or between any two of 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2 cm³/g. The catalyst can include at least one of: 1) a surface area of at least any one of, equal to any one of, or between any two of 2, 10, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275 and 300 m²/g as determined using Brunauer-Emmett-Teller (BET) analysis; 2) a pore sizes of at least any one of, equal to any one of, or between any two of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, and 90 A; and/or 3) a pore volume of or at least any one of, equal to any one of, or between any two of 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2 cm³/g.

[0042] The catalyst can include a nitrogen-containing carbon matrix. The nitrogen- containing carbon matrix can be derived by pyrolysis of a tetraamido compound / transition metal complex which is discussed in more detail in the preparation of the catalyst section. The atomic ratio of nitrogen to carbon (N:C) in the carbon support can range from 1 to 8 or at least any one of, equal to any one of, or between any two of 1, 2, 3, 4, 5, 6, 7, and 8. Without wishing to be bound by theory, it is believed that when an alkali metal or alkaline-earth metal is used, the nitrogen-containing carbon support participates in the catalysis reaction by facilitating the electron donation from the alkali metal or alkaline-earth metal to the transition metal. [0043] The catalyst material can include 1 to 35 wt.% of a transition metal, or at least any one of, equal to any one of, or between any two of 1, 5, 10, 15, 20, 25, 30, and 35 wt.% of a transition metal based on the total weight of the catalyst. The transition metal can be dispersed throughout the pyrolyzed tetraamido compound / transition metal complex. Preferably, the transition metal is dispersed throughout the nitrogen-containing carbon matrix. More preferably, the pyrolyzed tetraamido compound / transition metal complex comprises, consists essentially of, or consists of the nitrogen-containing carbon matrix and the transition metal is dispersed throughout the matrix. Transition metals include metals from Columns 3 to 12 of the Periodic Table. Non-limiting examples of transition metals include chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), ruthenium (Ru), cobalt (Co), rhodium (Rh), nickel (Ni), palladium (Pd), copper (Cu), silver (Ag), and zinc (Zn), and any combination or mixture or alloy thereof. In a particular aspect, the transition metal can include Fe, Co, or a mixture thereof. The metal can be in a metallic form, oxide form, nitride form, carbide form, or combinations thereof. For example, the catalyst can include iron metal, iron nitrides, iron carbide, cobalt metal, cobalt nitride, cobalt carbide, iron oxide, cobalt oxide, or combinations thereof. The transition metal can be in the form of particles that have a size of 1 nm to 50 nm, or 2 nm to 25 nm, or at least any one of, equal to any one of, or between any two of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, and 50 nm.

[0044] The catalyst can optionally include Columns 1 and/or 2 metals, also referred to as alkali or alkaline-earth metals. Non-limiting examples of alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or combinations thereof. Alkaline- earth metals can include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), or combinations thereof. The catalyst can include 1 wt.% to 40 wt.% or at least one of, equal to one of, or between any two of 1, 5, 10, 15, 20, 25, 30, 35, and 40 wt.% of alkali metal and/or alkaline-earth metal based on the total weight of the catalyst. In some instances, the catalyst includes a total of 1 wt. % to 40 wt.% of Ba and/or Cs based on the total weight of the catalyst. The alkali and/or alkaline-earth metal can be supported on the pyrolyzed tetraamido compound / transition metal complex. More preferably, the pyrolyzed tetraamido compound / transition metal complex comprises, consists essentially of, or consists of the nitrogen-containing carbon matrix and the transition metal is dispersed throughout the matrix with the alkali- or alkaline- earth metal impregnated in the matrix. B. Preparation of Catalysts of the Present Invention

[0045] The catalysts of the present invention can be made by pyrolysis of a tetraamido macrocycle / transition metal complex. A tetraamido macrocycle is a macrocycle that includes at least four (4) nitrogen atoms, of which 4 of the nitrogen atoms are capable of complexing with a metal atom. Non-limiting examples of tetraamido macrocycle compounds can include Pc or a derivative thereof, a porphyrin or a derivative thereof, or an azaanulene or a derivative thereof. Non-limiting illustrations of tetraamido macrocyclic / transition metal complexes are shown below as structures I through III.

In each structure, M is the transition metal, preferably Co or Fe, and R can be one or more substituents on the ring system. In some embodiments, R is a hydrogen or an aliphatic group, substituted aliphatic group, an aromatic group, a substituted aromatic group, or combinations thereof. In some embodiments, R is H, methyl, ethyl, phenyl, or substituted phenyl groups. Tetraamido macrocycles / transition metal complexes can be made using known organometallic synthetic methodology or purchased from commercial vendors such as MilliporeSigma (U.S.A.).

[0046] A method of producing the catalyst of the present invention can include pryolyzing a tetraamido macrocyclic / transition metal complex material under an inert atmosphere at conditions sufficient to form the pyrolyzed tetraamido macrocyclic / transition metal complex material of the present invention that include nitrogen. The material can be a composite having the transition metal dispersed throughout the complex or composite.

[0047] The tetraamido macrocyclic / transition metal complex material can be single compound ( e.g FePc or CoPc) or a mixture of compounds (e.g, a mixture of FePc and CoPc). The mixture can be physically mixed using grinding, ball mixing or any other type of physical mixture to produce a homogeneous mixture. The mixture of tetraamido macrocyclic / transition metal complex material can include any amount of two or more tetraamido macrocyclic / transition metal complex material. By way of example, a mixture can include 0.1 to 99.9 wt.% FePc or 0.1 wt.% to 99.9 wt.% CoPc, or any range or value there between. In a preferred aspect, a 8: 1 to 10: 1 weight ratio or about a 9: 1 weight ratio of FePc to CoPc can be ground together prior to pyrolysis.

[0048] The pyrolysis conditions can include a temperature of 500 to 800 °C or at least one any one of, equal to any one or between any two of 500, 525, 550, 575, 600, 625, 650, 675, 700, 725, 750, 775, and 800 °C. The pressure can be atmospheric. Inert atmosphere can be a chemically unreactive (inert) gas such as nitrogen or argon. The pyrolysis can be performed until determined to be complete or from 1 to 24 hours or 2 to 10 hours or about 6 hours. The pyrolyzed tetraamido macrocyclic / transition metal complex material can be cooled under inert gas atmosphere to 20 °C to 35 °C (e.g, room temperature). After cooling the pyrolyzed material can be passivated by flowing an inert gas containing 1% oxygen over the pyrolyzed material for a desired amount of time or from 1 to 24 hours or 2 to 10 hours or about 6 hours. The passivated pyrolyzed material that includes the transition metal dispersed throughout the nitrogen containing carbon matrix can be a porous material having the pore size, surface area, and pore volume previously described.

[0049] Optionally a metal dopant can be added to the pyrolyzed material using impregnation methodology. Impregnating can include preparing an aqueous solution of the metal dopant precursor material (e.g, an alkali metal dopant precursor material or an alkaline- earth metal dopant precursor material). Non-limiting examples of metal precursors include a metal nitrate, a metal amine, a metal chloride, a metal coordination complex, a metal sulfate, a metal phosphate hydrate, metal complex, or any combination thereof. Metal precursor compounds can be purchased from any chemical supplier such as Sigma-Aldrich (St. Louis, Missouri, USA), Alfa-Aeaser (Ward Hill, Massachusetts, USA), and Strem Chemicals (Newburyport, Massachusetts, USA). The aqueous solution can include water, metal dopant precursor, and an optional impregnating aid (e.g, citric acid or nitric acid). In a preferred aspect, the metal dopant precursor material can be barium nitrate or cesium nitrate. The amount of metal dopant precursor can be determined based on the final amount of metal dopant to be added (loaded) on the catalyst pores. An amount of the aqueous solution equal to the pore volume of the catalyst can be contacted with the pyrolyzed tetraamido macrocyclic / transition metal complex material at temperatures from 20 °C to 100 °C or any value or range there between. Contact time can be from 0.5 hours to 24 hours or any value or range there between. The impregnated material of the present invention can be dried to remove excess water at a temperature of 100 °C to 120 °C for 1 to 24 hours.

C. Ammonia Production

[0050] Certain asepcts of the invention are directed to production of ammonia by catalytic conversion of a nitrogen/hydrogen gas mixture in the presence of a pyrolyzed tetraamido macrocyclic / transition metal complex catalyst as described above. The process can include passing a feed stream containing nitrogen and hydrogen through a reactor and contacting the feed stream with a pyrolyzed tetraamido macrocyclic / transition metal complex material catalyst of the present invention under ammonia-forming conditions to generate a product stream having a greater ammonia-concentration than the feed stream. In certain instances, the feed stream and/or catalyst can be preheated or equilibrated prior to introduction into the reactor. In a further aspect, the reactor is a fixed bed or tubular reactor.

[0051] The reaction can include contacting nitrogen (N2) and hydrogen (H2) at a molar ratio of about 5: 1, 4: 1, 3 : 1, 2: 1, 1 : 1 with the catalyst of the present invention at ammonia forming conditions. Ammonia forming conditions can include temperature, pressure, space velocity and the like. Reaction temperatures can range from a temperature of 250 °C to 550 °C or be at least any one of, equal to any one of, or between any two of 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525, and 500 °C. The reaction pressure can range from 1 to 10 atm (0.10 MPa to 1. MPa) or be at least any one of, equal to any one of, or between any two of 0.1, 0.15, 0.175 and 1 MPa to produce ammonia (NTb). In some embodiments, the catalyst can be activated: (i) prior to contact with N2 and H2 at a temperature of 250 to 550 °C; (ii) at the reaction temperature; (iii) prior to contacting the catalyst with the reactant stream; or (iv) at least any one of, equal to any one of, or between any two of 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525, and 500 °C.

[0052] In one aspect, a system can include a separator for separating the ammonia from by-products, the separator having an inlet connected to the reactor for receiving the ammonia and by-products, a first outlet connected to an ammonia storage tank for collecting the ammonia, and a second outlet connected to a recycle loop for re-circulating by-product back to the inlet of the reactor.

EXAMPLES

[0053] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

(Synthesis of Fe(II)Pc or Co(II)Pc Catalysts of the Present Invention)

[0054] All materials were prepared by pyrolysis of metal phthalocyanines Fe(II)Pc and Co(II)Pc, purchased from MilliporeSigma (U.S.A.) and used without further purification. A certain amount of metal phthalocyanine was positioned in a porcelain boat placed in a tubular oven under nitrogen. The temperature was increased to 735 °C (heating rate: 2 °C min^-1) and maintained at that temperature for 6 h. After the pyrolysis the oven was cooled to room temperature under the nitrogen atmosphere and the sample is passivated with 1% O2 in nitrogen for 6 h.

Example 2

(Synthesis of Mixed FePc and CoPC Catalysts of the Present Invention)

[0055] The catalyst containing FePc and CoPc, was prepared by grinding a mixture of Fe(II)Pc and Co(II)Pc (9: 1, mass ratio Fe(II)Pc: Co(II)Pc) together for 20 minutes in a mortar, before the pyrolysis step and passivating step described above in Example 1.

Example 3

(Synthesis of Ba or Cs doped FePc, CoPC, and

FePc/CoPc Catalysts of the Present Invention)

[0056] The materials obtained after the pyrolysis of the phthalocyanine precursors, were impregnated with aqueous solutions of cesium nitrate or barium nitrate at a temperature of about 21 °C. The Cs loading (2-10% wt.) and that of Ba (8% wt.).

Example 4

(Preparation of Comparative Sample of Fe, Co,

Fe/Co Metals on a Carbon Support with Cs Doping)

[0057] A comparative sample of iron, cobalt or both metals supported on carbon was prepared using classical impregnation method and then promoted with cesium (2 wt.% Cs / 10 wt.% Fe or Co on carbon). To obtain the carbon support, commercially available activated carbon was heated under a nitrogen atmosphere at 950 °C (heating rate: 5 °C min^-1) for 12 h, followed by cooling to ambient temperature, washing with water to remove the dusty fraction, and drying at 100 °C overnight. The material thus prepared was impregnated with aqueous solutions of iron nitrate, cobalt nitrate or both (co-impregnation), dried and calcined in air at 220 °C (heating rate of 2 °C min^-1) to convert the salts into their oxides. The dried sample was impregnated with aqueous solutions of cesium nitrate to obtain a material with 2% wt. Cs and 10 wt.% Fe or Co.

Example 5

(Characterization of Materials)

[0058] The samples were analyzed to characterize the physical and structural properties of the catalysts. Table 1 lists the structural properties of the catalyst.

[0059] High-angle annular darkfield scanning transmission electron microscopy (HAADF- STEM) was performed using a Titan Themis-Z microscope from Thermo-Fisher Scientific by operating it at the accelerating voltage of 300 kV. Prior to the analysis, the microscope was set to scanning TEM (STEM) mode to acquire atomic number (Z) sensitive STEM images with an attached a high-angle annular dark-field (HAADF) detector. From the data, it was determined that small-sized Fe and Fe-Co nanoparticles are highly dispersed onto the nitrogen-doped carbon support material. The size of the metal particles is mainly distributed in the range of 5-25 nm.

[0060] The chemical composition of the catalysts was determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis on a Thermo-Electron 3580. The iron loading was around 18 wt.% and cobalt was 8 wt. %, and Fe and Co in the ratio 9: 1 had an Fe content of 13.33 wt.% and Co content of 3.58 wt.%.

[0061] X-ray diffraction (XRD) measurements were performed on a D8 Advance diffractometer from Bruker with Bragg-Brentano geometry using CuK_ai,2 radiation. For the identification of the phase composition, the program module“Pattern Fitting” implemented in STOE’ s WinXPOW software was used. X-ray diffraction (XRD) patterns for the samples after pyrolysis and after the ammonia synthesis reaction are shown in FIG. 7. Iron nitrides (Fe_xN) and iron carbides (Fe3C) were observed by XRD.

[0062] Energy Dispersive X-ray (EDX) elemental mapping was performed using a high throughput X-ray energy dispersive spectrometer (EDX) was also utilized in conjunction with DF-STEM imaging to acquire STEM-EDS spectrum-imaging datasets. During the acquisition of these datasets, at every image-pixel, a corresponding EDS spectrum was also obtained for generating simultaneously the elemental maps of O, C, Cs, Fe, and Co. From the EDX it was determined that nitrogen was present in the carbon support and the Cs were around the Fe nanoparticles. Surprisingly, it was also observed single atoms of metals were distributed on the support together with the metal nanoparticles (FIG. 8). Without wishing to be bound by theory, it is believed that the single atoms contributed to the catalytic activities for the production of ammonia.

[0063] Specific surface areas and pore volumes were determined with a Micromeritics ASAP 2010 adsorption analyzer at liquid nitrogen temperature. Before measurements, the materials were degassed at a temperature of 150°C for 10 h. The total pore volume was calculated by using the adsorbed volume at a relative pressure of 0.97. The BET surface area was estimated in the relative pressure range of 0.06-0.2. Nitrogen adsorption-desorption isotherms and pore-size distributions of the catalysts were analyzed, after the pyrolysis treatment and after the reaction, and high surface areas and pore volumes were observed (Table 1). The surface area was also analyzed after the ammonia synthesis reaction with no significant changes observed. For the sample 2% Cs-FePc, 230.0 m²g^-1 (pore size 37.8 A), and for the sample FeCoPc, 210.3 m²g^-1 (pore size 36.3 A).

Table 1

Example 6

(Production of Ammonia)

[0064] Activity measurements of ammonia synthesis were carried out in a stainless-steel flow reactor supplied with stoichiometric Fh + N2 mixture equipped with a temperature and pressure controllers, a pressure indicator, a back pressure regulator and appropriate valves. The flow rate of hydrogen and nitrogen was controlled by Brooks mass flow-controllers. The pressure and temperature were kept constant using the correspondent controllers. The catalyst (200 mg) was positioned in the reactor, and a total flow of Fh and N2 of 40 ml min^-1 was used for the experiments, keeping the H2:N2 ratio 3: 1. The reactor outlet was connected to the Mass- Vac Spectrometer for continuous monitoring of the NFb mass signal (Mass = 17). Argon (Ar, 0.6 ml min^-1) was used as reference for the calibration of the instrument. [0065] Prior to measurements, the samples were reduced in a H2:N2 stream with a total flow of 40 ml min^-1, at 485 °C for 36 h (Cesium- promoted iron catalysts) and at 520 °C for 48 h (Barium-promoted cobalt catalyst) (heating rate 4°C min^-1). Activation at higher temperature than those indicated resulted in a decrease of the catalytic performance for the iron-based catalysts. The signal of ammonia was monitored during the activation pre-treatment until this signal was constant, after that the catalysts are considered under the steady-state conditions.

[0066] The reaction temperature was varied in the range between 400-550 °C, and the pressure from atmospheric to 70 bar (0.7 MPa). During the experiments, each set of conditions was kept constant for 1 h to ensure a stable performance was reached and to analyze the ammonia in the reactor outlet using the online connected Mass-Vac Spectrometer. From the concentration of ammonia in the outlet gas, the reaction rate was determined and expressed in NFL pmol g^-1 h^-1.

[0067] The ammonia signal monitored by the mass-Vac was converted into the concentration of ammonia in the outlet gas by the calibration curve previously obtained for the instrument, using Ar inert gas as reference. The calibration curve (FIG. 1) was obtained for gas mixtures of known concentration of ammonia in N2:H2 (3 : 1) mixtures. And the calculation procedure in order to convert the signal monitored in the mass spectrometer to the moles of NFL and to the ammonia synthesis rate, is described as follows:

1) The signal for the ammonia in Torr was converted into ppm of NFL using the calibration curve (FIG. 1)

2) Then ppm of ammonia was converted into flow rates in mL/min and mol/min using next equations:

3) mL NFL (NTP)/min = ppm NFL x 1.10 ⁶ x total flow rate (mL/min)

4) moles NFb/min = (mL NFL (NTP)/min / 1000 mL) x 1 atm / [0.082 atm L/mol/K x 293.15 K]

5) NFL rate (pmol g^-1 h^-1) = (moles NFL/min x 60 min/h x 1.10⁶ pmol/mol) / mass catalyst (g)

[0068] The N2 and Fh reaction orders measurement were carried out with a total flow rate of 60 ml min^-1 of mixed gas (N2, Fh, Ar), at constant total pressure (10 bar) and temperature (400 °C). For the N2 order measurement the Fh flow rate was 45 ml min^-1 kept constant, and the flow rate of N2 is changing while keeping (N2 +Ar) in 15 ml min^-1. For the Fh order measurement the N2 flow rate was 15 ml min^-1 kept constant, and the flow rate of Fh was changed while keeping (Fh +Ar) at 55 ml min^-1. The reaction order of NFb was obtained by changing the flow rate of syngas in the range 40-120 ml min^-1, while keeping a constant N2 and H2 partial pressure (FhilNk ratio 3 : 1.). All the kinetic measurements were conducted under conditions far from equilibrium.

[0069] The catalytic activity and stability with time on stream are shown in FIGS. 2A-2D and compared with the performance of an iron-based commercial catalyst (fused magnetite KM1, Haldor-Topsoe) tested here as a reference material, which is widely used catalyst for the Haber-Bosch process. FIGS. 2A and 2B show the pressure and temperature dependence of the catalytic activity, respectively. The catalysts 2 wt.% Cs-FePc, 8 wt.% Ba-CoPc, 2 wt. %Cs- FeCoPc and 10 wt.% Cs-FePc, were very efficient in the ammonia synthesis reaction and led to a higher activity than did the commercial catalyst, Fe-KMl . The catalysts showed 2-fold increase in the catalytic performance (at 400 °C and 0.1-3 MPa) compared to the commercial benchmark iron-based catalyst (Fe-KMl).

[0070] The catalyst 10 wt.% Cs-FePc shows similar catalytic performances to the Cesium- promoted C03M03N, (See, Table 3) around 14000 m mol g^-1 h^-1 at 400 °C and 0.3 MPa, which in turn is reportedly not only better than the iron-based catalyst, but also better than the commercial graphite supported ruthenium (See, Table 3).

[0071] The reaction rate over 2 wt.% Cs-FePc, 8 wt.% Ba-CoPc, 2 wt.% Cs-FeCoPc and 10 wt.% Cs-FePc catalysts showed an approximately linear response to the pressure increase (FIG. 2A). For 2 wt.%Cs-FePc it underwent a near sevenfold rise to 20000 m mol g^-1 h^-1 when the reaction pressure is increased from 0.1 MPa to 0.7 MPa at 400 °C (See, FIG. 3).

[0072] While FePC and CoPc catalyzed the production of ammonia, the reaction rate increased when promoted with an alkali metal or alkaline-earth metal (FIG. 2A). Without wising to be bound by theory, it is believed that the promotion proceeded via electron transfer from the alkali metal or the alkaline-earth metal to the Fe surface. As a result, the barrier for nitrogen dissociation (the most commonly assumed rate limiting step in ammonia synthesis) was decreased. Consequently all NH_X species, including adsorbed NFb molecule, were less strongly chemisorbed. This lead to a higher amount of free sites for N2 dissociation, thus the catalytic activity increased compared to no promotion.

[0073] As a control experiment, iron supported on carbon and promoted with an alkali- metal (2 wt.% Cs-10 wt.% Fe/Carbon) was subjected to the conditions above. The catalyst of the present invention has better activity for ammonia synthesis reaction (FIG. 2A). This result confirmed the use of the phthalocyanine template was absolutely necessary to attain the most active structure for this process and to boost the catalyst performance.

[0074] When the catalytic performance was evaluated by the specific activity (FIG. 2C) the reaction rate per gram of metal over the 8 wt.% Ba-CoPc catalysts was about 20 times that of commercial catalyst Fe-KMl . Also, iron-based catalysts activity was more than 10 times that of the commercial catalyst Fe-KMl .

[0075] The catalyst stability under reaction conditions appeared are shown in the FIG. 2D. No deactivation phenomena was observed during the long-term stability test performed for 100 h with 2 wt.% Cs-FePc and 8 wt.% Ba-CoPc. The ammonia synthesis rate remained constant under several reaction conditions in the range 400 to 520 °C and 0.3-0.7 MPa. Methanation reactions of hydrogen and the pyrolyzed Pc was not observed at the reaction temperatures.

[0076] Kinetic Studies: The kinetic parameters were obtained for 2 wt.% Cs-FePc, 8 wt.% Ba-CoPc, 2 wt.% Cs-FeCoPc and 10 wt.% Cs-FePc (Table 2, and FIGS. 4A-4D) and can be compared with the values reported for selected catalysts from the literature (Table 3). Apparent activation energies were calculated from the Arrhenius plots (FIG. 4A). The value for the apparent activation energy was close to 42 kJ mol^-1 for the 10 wt.% Cs-FePc catalyst. N2 dissociation was assumed to be the rate limiting step, thus, the low value meant that globally this step was favored as compared to the one for the commercial catalyst Fe-KMl (70 kJ mol^-1). But this large difference of apparent activation energy suggested another rate determining step which would not be N2 dissociation. Because this value was close to that one observed for other intermetallic catalysts (LaCoSi) (41.9KJ/mol, Table 3), in which the formation of NH_X species was determined as the rate-limiting step, this reaction mechanism is believed to be applicable. (See, Table 2).

Table 2

Table 3

1. Sehested et al ., Journal of Catalysis 188 (1999) 83-89. 2. Hagen et al. , Chem. Commun ., 2002, 1206-1207. 3. Kojima, et al, Applied Catalysis A: General 218 (2001) 121-128. 4. Y. Gong, et al. , Nature Catalysis , 2018, 1, 178-185. 5. Wang e al. , Nature Chemistry , 2017, 9, 64-70. 6. Kitano e/ a/., /Va/. Chem. 2012, 4, 934-940. 7. Hagen e/ al, J. Catal. 2003, 214,

327-335.

[0077] The order with respect to N2 is given in the FIG. 4B and Table 2. For conventional heterogeneous catalysts, N2 reaction orders are close to unity (0.8-1.0), because the overall reaction is limited by the rate of N2 cleavage (Table 2). For the catalyst of the present invention (10 wt.% Cs-FePc catalyst) a significant decrease in the order with respect N2 as compared to commercial catalyst Fe-KMl. Also, this decrease was dependent on the amount of alkali or alkali earth metal content (the higher the dopant content, the lower was the order with respect to nitrogen). This decrease of the order showed that in the steady state, the surface became more populated with“dissociated” nitrogen.

[0078] No ammonia was detected when only hydrogen was introduced, which confirmed that gas-phase N2 molecules were activated over these catalysts of the present invention. The reaction order with respect to H2 over all the catalysts was found to be close to 2 (FIG. 4C and Table 2). A similar value was reported for the commercial iron-based catalyst, Fe-KMl. The positive H2 order indicated that the problem of hydrogen poisoning, which arises from the strong adsorption of hydrogen on the metal surface, was not observed in these catalytic systems of the present invention.

[0079] The reaction order with respect to NTb is around -2 for the iron-based catalyst of the present invention (FIG. 4D and Table 1). This observation suggested that NHx species populated the catalyst surface more densely than N and H atoms, which is also seen with the commercial catalyst and other reported bimetallic ammonia synthesis catalysis (See Table 3).

[0080] The cobalt-based catalyst (8 wt.% Ba-CoPc) of the present invention had an ammonia reaction order of -0.2, suggesting cobalt-based catalysts were less poisoned by the increasing concentration of ammonia. The results corroborated that the cobalt catalyst was kinetically less sensitive to the content of ammonia in the gas phase than the iron-based one. For that reason, ammonia synthesis rate was less affected by the changes in the space velocity, due to the differences in the ammonia concentration levels, while the iron-based catalysts are more sensitive (FIGS. 5A and 5B). This is essential for the industrial practice, where the low inhibition of the reaction rate by the ammonia product is an important factor of the catalyst usefulness.

[0081] The rate-determining step (RDS) for NFb synthesis over 10 wt.%Cs-FePc catalyst, was further examined by comparing the experimental reaction rates and calculated rates. The rate equations were established based on the Langmuir-Hinshelwood mechanism. The rate determining step (RDS) for ammonia synthesis was examined by fitting the modeled rate equations to a set of obtained reaction rates. The rate equations were expressed by the Langmuir-Hinshelwood mechanism. The following sequence of elementary steps can be expressed for the overall reaction:

H₂(g) ® H₂(ad) H₂(g) ® H₂(ad), (1)

N₂(g) ® N₂(ad)N₂(g) ® N₂(ad), (2)

H₂(ad) ® 2H(ad)H₂(ad) ® 2H(ad), (3)

N₂(ad) ® 2N(ad)N₂(ad) ® 2N(ad), (4)

N(ad) + H(ad) ® NH(ad)N(ad) + H(ad) ® NH(ad), (5)

NH(ad) + H(ad) ® NH₂(ad)NH(ad) + H(ad) ® NH₂(ad), (6)

NH₂(ad) + H(ad) ® NH₃(ad)NH₂(ad) + H(ad) ® NH₃(ad), (7)

NH₃(ad) ® NH₃(g)NH₃(ad) ® NH₃(g), (8) where (g) and (ad) denote gas-phase and adsorption species, respectively. Among these steps, steps (4)-(7) control the overall rate of reaction due to the large activation energy. The partial pressure of NTb (PNTb) was omitted when it was sufficiently small compared with PN2 and PTb at the outlet. Under the reaction conditions employed, PNTb of the obtained experimental rates were much smaller than PN2 and PTh at the outlet, and the equilibrium value, which reasonably satisfied the applicable condition of the calculated equations derived with elimination of the PNH3 term and the reverse reaction. The final rate equations are as follows:

r =

where k4, ks, k₆, k7, are the rate constant of the forward reactions 4-7, and Ki is the equilibrium constant in step i. Equations (9)-(12) are expressed based on the assumption that steps (4)-(7) are the RDS, respectively. In order to examine the RDS for ammonia synthesis, the derived equations were separately fitted into sets of experimental rates using a least squares method and evaluated to determine which equations best described the experimental rates. The best fitting of modelled rates to the experimental rates is shown in FIGS. 6A-D. The fitting was poorer when the activation of N2 was supposed to be the RDS. In contrast, when the formation of NH, NTb and NTb were the RDS, the fitting was significantly improved, which revealed highest R.2 value of 0.96 for NTb (FIG. 6D). These fittings indicated that it was rational to consider that the RDS for ammonia synthesis over these catalytic systems derived from metal phthalocyanines of the present invention could be any formation steps of NH_X species rather than the N2 dissociation step, as previously contemplated.

[0082] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

1. A catalyst for the production of ammonia, the catalyst comprising:

a pyrolyzed tetraamido macrocycle / transition metal complex comprising a nitrogen- containing carbon matrix; and

an optional metal dopant.

2. The catalyst of claim 1, wherein the tetraamido macrocycle is a phthalocyanine (Pc) or a derivative thereof, a porphyrin or a derivative thereof, or an azaanulene or a derivative thereof, or any macrocycle containing at least 4 complexing nitrogen atoms.

3. The catalyst of claim 2, wherein the tetraamido macrocycle is a phthalocyanine (Pc).

4. The catalyst of any one of claims 1 to 3, wherein the transition metal is iron (Fe), cobalt (Co) or both, and the transition metal is dispersed throughout the nitrogen containing carbon matrix.

5. The catalyst of any one of claims 1 to 4, wherein the catalyst includes the metal dopant and the metal dopant comprises an alkali metal or an alkaline-earth metal, or any combination thereof, preferably cesium (Cs), barium (Ba), or both.

6. The catalyst of claim 5, wherein the catalyst is Cs-FePc, Cs-CoPc, Ba-FePc, Ba-CoPc, Cs-FePc-CoPc, Ba-FePc-CoPc, or any combination thereof.

7. The catalyst of claim 6, wherein the catalyst comprises 1 to 15 wt.% of Cs, preferably, 1 to 10 wt.% of Cs, based on the total weight of the catalyst.

8. The catalyst of claim 7, wherein the catalyst has 10 wt.% Cs dispersed on a Fe-nitrogen- containing material.

9. The catalyst of claim 5, wherein the catalyst comprises 1 to 40 wt.% of Ba, preferably, 1 wt.% of Ba, based on the total weight of the catalyst.

10. The catalyst of claim 9, wherein the catalyst is 8 wt.% Ba dispersed on a Co-nitrogen- containing material.

11. The catalyst of any one of claims 4 to 10, wherein catalyst is a pyrolyzed FePc complex, a pyrolyzed CoPc complex, or a pyrolyzed FePc complex /CoPc complex (FeCoPc) mixture, or a combination thereof.

12. The catalyst of claim 11, wherein the catalyst is a pyrolyzed FePc complex including 1 to 35 wt.% Fe, a pyrolyzed CoPc complex including 1 to 20 wt.% Co, or a pyrolyzed FeCoPc complex having a weight ratio of 1 : 1 to 20: 1, preferably 15: 1 to 10: 1.

13. The catalyst of any one of claims 1 to 12, wherein the catalyst has a BET surface area of at least 2 m²/g, preferably 2 m²/g to 300 m²/g, a pore size of 10 to 90 angstroms (A), preferably 10 A to 60 A, a pore volume of at least 0.01 cm³/g, preferably 0.01 to 2 cm³/g, or any combination thereof.

14. The catalyst of any one of claims 1 to 13, wherein the nitrogen-containing carbon material has an atomic ratio of nitrogen to carbon (N:C) from 1 to 8.

15. The catalyst of any one of claims 4 to 14, wherein the nitrogen-containing carbon material further comprises iron nitrides, iron carbides, cobalt nitrides, iron metal, cobalt metal, or combinations thereof as determined by X-ray diffraction.

16. A method of producing ammonia from nitrogen (N2) and hydrogen (Fh), the method comprising contacting a gaseous reactant stream comprising N2 and Fh with any one of the catalysts of claims 1 to 15 under conditions sufficient to produce gaseous ammonia (MB).

17. The method of claim 16, wherein the ratio of Fh:N2 is 2: 1 to 5: 1, preferably 3: 1, and the conditions comprise a temperature of 250 °C to 550 °C, a pressure of 1 to 10 MPa, or any combination thereof.

18. The method of any one of claims 16 to 17, further comprising activating the catalyst prior at a temperature of 400 to 530 °C prior to contacting the catalyst with the reactant stream, and, optionally, the catalyst comprises Cs and the activation temperature is 400 °C to 530 °C, preferably 475 °C to 495 °C, or wherein the catalyst comprises Ba and the activation temperature is 500 °C to 530 °C, preferably 510 °C to 520 °C.

19. A method of producing the ammonia catalyst of any one of claims 1 to 15, the method comprising: pryolyzing a tetraamido macrocyclic / transition metal complex material at a temperature of 550 °C to 800 °C under an inert atmosphere to form the pyrolyzed tetraamido macrocyclic / transition metal complex material comprising a nitrogen- containing carbon matrix of any one of claims 1 to 15, and optionally impregnating the pyrolyzed complex material with a metal dopant precursor material.

20. The method of claim 19, further comprising cooling the pyrolyzed tetraamido macrocyclic / transition metal complex material under an inert atmosphere and passivating the cooled composite, wherein the tetraamido macrocyclic / transition metal complex material comprises at least one of iron phthalocyanine (FePc) or cobalt phthalocyanine.