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EP-4735166-A1 - METHOD OF PRODUCING A CATALYST STRUCTURE COMPRISING MOLYBDENUM CARBIDE, AND CATALYST STRUCTURE COMPRISING MOLYBDENUM CARBIDE

EP4735166A1EP 4735166 A1EP4735166 A1EP 4735166A1EP-4735166-A1

Abstract

The present invention relates to a method of producing a catalyst structure comprising molybdenum carbide on a porous carrier compound, comprising preparing a mixture comprising a porous carrier compound and a molybdenum oxide; shaping the mixture into a porous green body by a 3D-printing technique; and carburizing the porous green body by exposing the mixture to a reducing atmosphere comprising a carbon-comprising gas at a temperature between 650 °C and 1000 °C, thereby converting at least a portion of the molybdenum oxide into molybdenum carbides and obtaining a catalyst structure having an elevated temperature; cooling the catalyst structure having an elevated temperature to room temperature in an atmosphere which is inert with respect to molybdenum oxide, thereby obtaining the catalyst structure; wherein the concentration of molybdenum oxide in the mixture is such that a ratio of the molybdenum content in the mixture to the BET surface area of the porous carrier compound in the mixture is equal to or lower than 2.5 * 10-5 mol Mo /m², wherein the molybdenum content in the mixture is measured by ICP-OES and the BET surface area is measured by multi-point BET analysis of a N2 adsorption isotherm. The invention further relates to a catalyst structure obtained by the methods of the invention.

Inventors

  • PAJARES, Arturo
  • VANGENEUGDEN, DIRK

Assignees

  • Vito NV

Dates

Publication Date
20260506
Application Date
20240627

Claims (20)

  1. 1. Method of producing a catalyst structure comprising molybdenum carbide on a porous carrier compound, comprising the steps of: preparing a mixture comprising a porous carrier compound and a molybdenum oxide, shaping the mixture into a porous green body by a 3D-printing technique, carburizing the porous green body by exposing it to a reducing atmosphere at a temperature between 650 °C and 1000 °C, thereby converting at least a portion of the molybdenum oxide into molybdenum carbide and obtaining a catalyst structure having an elevated temperature, and cooling the catalyst structure having an elevated temperature in an atmosphere which is inert with respect to molybdenum oxide, thereby obtaining the catalyst structure, characterized in that: the reducing atmosphere comprises a carbon-comprising gas, and the concentration of molybdenum oxide in the mixture is such that a ratio of the molybdenum content in the mixture to the BET surface area of the porous carrier compound in the mixture is equal to or lower than 2.5 * 10' 5 molMo/m 2 , wherein the molybdenum content in the mixture is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) and the BET surface area is measured by multi-point BET analysis of a N2 adsorption isotherm.
  2. 2. Method according to claim 1 , wherein the molybdenum oxide comprises one or a combination of MoOa and MOO2, the method further comprising: impregnating a porous carrier compound with a precursor of the molybdenum oxide, drying the impregnated porous carrier compound, and calcining the dried impregnated porous carrier compound, thereby converting the molybdenum oxide precursor into the molybdenum oxide and obtaining the mixture, preferably wherein the molybdenum oxide precursor comprises one or a combination of (NH4)6Mo?O24.nH2O, where n is between 0 and 4, X2MOO4, wherein X is potassium or sodium, molybdenum chloride, a molybdenum alkoxide or a molybdenum oxalate.
  3. 3. Method according to any one of the preceding claims, wherein the molybdenum oxide concentration in the mixture is such that a ratio of the molybdenum content in the mixture to the BET surface area of the porous carrier compound in the mixture is equal to or lower than 1 * 10' 5 molMo/m 2 .
  4. 4. Method according to any one of the preceding claims, wherein the molybdenum oxide concentration in the mixture is such that a ratio of the molybdenum content in the mixture to the BET surface area of the porous carrier compound in the mixture is equal to or lower than 2.5 * 10' 6 molMo/m 2 .
  5. 5. Method according to any one of the preceding claims, wherein the molybdenum oxide concentration in the mixture is such that a ratio of the molybdenum content in the mixture to the BET surface area of the porous carrier compound in the mixture is between 5 * 10' 8 molMo/m 2 and 2.5 * 10' 5 molMo/m 2 .
  6. 6. Method according to any one of the preceding claims, wherein the molybdenum oxide concentration in the mixture is such that a ratio of the molybdenum content in the mixture to the BET surface area of the porous carrier compound in the mixture is between 1 * 10' 7 molMo/m 2 and 2.5 * 10' 6 molMo/m 2 .
  7. 7. Method according to any one of the preceding claims, wherein the carburization temperature and the concentration of molybdenum oxide in the mixture are such that the molybdenum carbide comprises cubic b-MoC and/or hexagonal q-M03C2, as identified from the X-ray diffraction (XRD) analysis by means of the powder diffraction database of the International Center for Diffraction Data (ICDD), wherein the molybdenum carbide comprises at least 30 % by weight, preferably at least 50 % by weight, of cubic b-MoC and/or hexagonal q-M03C2, based on the total weight of molybdenum carbide in the catalyst structure.
  8. 8. Method according to any one of the preceding claims, wherein at least 20 %, preferably at least 50 %, of the molybdenum oxide is converted into molybdenum carbide.
  9. 9. Method according to any one of the preceding claims, wherein carburization of the mixture is performed at a temperature between 700 °C and 900 °C.
  10. 10. Method according to any one of the preceding claims, wherein the carbon- comprising gas comprises one or a combination of a C1-C4 alkane and/or CO.
  11. 11. Method according to claim 10, wherein the carbon-comprising gas comprises methane.
  12. 12. Method according to any one of the preceding claims, wherein the reducing atmosphere comprises hydrogen.
  13. 13. Method according to claim 12, wherein the molar ratio of the carbon-comprising gas and hydrogen is between 100:1 and 1 :100.
  14. 14. Method according to claim 12 or claim 13, wherein the molar ratio of the carbon- comprising gas and hydrogen is between 10:1 and 1:10.
  15. 15. Method according to any one of the preceding claims, wherein the porous carrier compound comprises a metal oxide, a doped metal oxide, a silicate, alumina, silica, or combinations of two or more thereof.
  16. 16. Method according to claim 15, wherein the doped metal oxide is a metal oxide doped with yttrium, cesium, zirconium, or a combination of two or more thereof.
  17. 17. The method according to any one of the preceding claims, wherein the inert atmosphere comprises helium, argon and/or nitrogen.
  18. 18. The method according to any one of the preceding claims, wherein the mixture further comprises a binder.
  19. 19. The method according to claim 18, wherein the binder comprises an organic binder, more preferably methylcellulose.
  20. 20. The method according to claim 18, wherein the binder comprises an inorganic binder, preferably AIOOH.

Description

METHOD OF PRODUCING A CATALYST STRUCTURE COMPRISING MOLYBDENUM CARBIDE, AND CATALYST STRUCTURE COMPRISING MOLYBDENUM CARBIDE Technical field [0001] The present invention is related to a method of producing a catalyst structure comprising molybdenum carbide on a porous carrier compound. The present invention is further related to a catalyst structure comprising molybdenum carbide on a porous carrier compound. Background art [0002] Over the past decades, CO2 utilization has received renewed attention due to the CO2 emissions rising. Converting CO2 from detrimental greenhouse gas into value-added chemicals and fuels provides an alternative to the transition to a low carbon economy. However, the activation of CO2 and its hydrogenation to alcohols and hydrocarbons are challenging tasks because CO2 is a thermodynamically stable and chemically inert molecule. A possible solution is reducing CO2 into CO first, for example via the Reverse Water Gas Shift (RWGS) reaction. The produced CO can then be used as feedstock to produce several chemical compounds. [0003] The conversion of CO2 into CO is advantageously performed in the presence of a catalyst. Traditional catalysts include noble metal-based catalysts. [0004] Recently, transition metal carbides (TMCs) have been investigated as alternative to the conventional noble metal-based catalysts because of their similar catalytic properties. Several TMCs have been found that can activate CO2 and split H2, making them a feasible catalyst for the reduction of CO2. In particular, molybdenum carbide shows a better catalytic performance compared to other TMCs, with MoC and M02C being the most studied. [0005] US 6,207,609 discloses a method of producing M02C as powder by reacting ammonium molybdate with hydrogen and carbon monoxide at a temperature higher than 300 °C and lower than 850 °C, thereby reducing the ammonium molybdate (decomposing it into molybdenum oxides), and then directly carburizing the molybdenum oxides to M02C. [0006] US2021/0322960 discloses a one-step method for synthesizing a supported transition metal carbide catalyst. A mixture comprising a support such as AI2O3, a transition metal precursor and a solid carbon source is first calcined in a reducing atmosphere at a temperature between 200 °C and 500 °C, followed by carburization in a reducing atmosphere at a temperature between 700 °C and 900 °C, and cooling in a protective atmosphere and passivation. When the transition metal is molybdenum, the carbide is present as M02C. [0007] The catalytically active phases of the foregoing methods are mainly present in the form of M02C with a relatively large crystal size (>10 nm). A disadvantage of the foregoing methods is that it is difficult to control the phase of the molybdenum carbide formed and the size of the crystals, and thus of the catalyst structure obtained. [0008] Evaluation of alumina-supported Mo carbide produced via propane carburization for the Fischer-Tropsch synthesis, Dai-Viet N. Vo et al., Fuel 93 (2012), pp. 105-116, discloses a method for producing particles of a Mo carbide on a y-alumina support by impregnation of y-alumina with (NF jeMoyCh^FW. The impregnated slurry is then dried, crushed and sieved to particles having a size of 140 pm to 230 pm. These particles are then subjected to carburization at a temperature between 450 °C and 700 °C in the presence of C2H6/H2 and C3H8/H2. The carburization is a two-stage process involving the transformation of Mo oxide to the MoCi-x carbide via an intermediate oxycarbide phase. The obtained carbide catalysts were found to contain both FCC a-MoCi-x and HCP p-MoCi-x. [0009] Highly active, selective and stable reverse water gas shift catalyst based on high surface area MoC/y-A^Os synthesized by reverse microemulsion, Guanjie Sun et al., Topics in Catalysis (2021) 64, pp. 414-430, discloses a method for producing a catalyst structure comprising MoC and M02C as active phases, by forming a reverse micro-emulsion comprising alumina and molybdenum oxide precursors. A gel-like precipitate was formed of MOO3/Y-AI2O3 which was dried to provide a powder. The powder was subjected to carburization at 800 °C in the presence of F^CF . The obtained catalysts were found to contain both M02C and MoC. [0010] Supported nanostructured MoxC materials for the catalytic reduction of CC>2 through the Reverse Water Gas Shift Reaction, A. Pajares et al., Nanomaterials 2022, 12, 3165, discloses a carbothermal reduction method of producing MoxC-based catalysts supported on for example Y-AI2O3 by adding urea as a solid carbonaceous source to a solution of M0CI5 and contacting the resulting viscous solution with Y-AI2O3 powder. The resulting solid was dried at 333 K, treated with argon at 1073 K for 3 hours, then cooled down to room temperature under argon and exposed to air without passivation to form MOxC/AhCh. The obtained carbide catalyst was found to contain p- [0011] Methane steam reforming on supported and nonsupported mol