Brungs, AJ, York, AP, Claridge, JB, Marquez-Alvarez, C & Green, ML 2000, 'Dry reforming of methane to synthesis gas over supported molybdenum carbide catalysts', Catalysis Letters, vol. 70, no. 3-4, pp. 117-122.View/Download from: Publisher's site
The dry reforming of methane at elevated pressure over supported molybdenum carbide catalysts, prepared from oxide precursors using ethane TPR, has been studied. The relative stability of the catalysts is Mo2C/Al2O3 > Mo2C/ZrO2 > Mo2C/SiO2 > Mo2C/TiO2, and calcination of the oxide precursor for short periods was found to be beneficial to the catalyst stability. Although the support appears to play no beneficial role in the methane dry reforming reaction, the alumina-supported material was stable for long periods of time; this may be important for the production of pelletised industrial catalysts. The evidence suggests that the differences in the stabilities may be due to interaction at the precursor stage between MoO3 and the support, while catalyst deactivation is due to oxidation of the carbide to MoO2, which is inactive for methane dry reforming.
York, AP, Claridge, JB, Williams, VC, Brungs, AJ, Sloan, J, Hanif, A, Al-Megren, H & Green, ML 2000, 'Synthesis of high surface area transition metal carbide catalysts', Studies in Surface Science and Catalysis, vol. 130, no. B, pp. 989-994.
The synthesis of molybdenum and tungsten carbide from their oxides using the temperature programmed reaction method with methane and ethane is presented. Lower reaction temperatures are required for metal carbide formation with ethane, and the highest surface areas materials are also prepared by this method. In addition, the use of the different hydrocarbons enables synthesis of various phases of molybdenum or tungsten carbide. Thermogravimetric analysis studies demonstrate that the carbide formation mechanisms for the two transition metal carbides in ethane differ. Finally, a similar technique has been employed for the synthesis of uranium monocarbide with moderately high surface area
Claridge, JB, York, AP, Brungs, AJ & Green, ML 2000, 'Study of the temperature-programmed reaction synthesis of early transition metal carbide and nitride catalyst materials from oxide precursors', Chemistry of Materials, vol. 12, no. 1, pp. 132-142.View/Download from: Publisher's site
The synthesis of high surface area carbide and nitride materials from binary and ternary oxides of vanadium, niobium, tantalum, molybdenum, and tungsten, suitable for use as catalysts for a wide range of reactions, has been investigated via the temperatureprogrammed reaction (TPRe) method, in various gas mixtures. TPRe of oxides in CH4/H2, C2H6/H2, or NH3 yield materials with surface areas >40 m2 g-1. For the reaction with ethane or ammonia the reaction appears to proceed topotactically while that with methane does not; however, the conversion of nitrides to carbides in CH4/H2 does appear to proceed topotactically
Brungs, AJ, York, AP & Green, ML 1999, 'Comparison of the group V and VI transition metal carbides for methane dry reforming and thermodynamic prediction of their relative stabilities', Catalysis Letters, vol. 57, no. 1-2, pp. 65-69.View/Download from: Publisher's site
The group V and VI transition metal carbides have been prepared by CH4 TPR, and tested for the dry reforming of methane with carbon dioxide, at elevated pressure. Mo2C and WC were the most stable catalysts, while the group V metal carbides showed the stability order: vanadium > niobium > tantalum. Catalyst deactivation was due to carbide oxidation with CO2, while stability was associated with the reaction of metal oxide (from deactivation) with CH4, giving the metal carbide. Calculation of the Gibbs free energy for this reaction resulted in a predicted catalyst stability trend similar to that obtained experimentally
Claridge, JB, York, AP, Brungs, AJ, Marquez-Alvarez, C, Sloan, J, Tsang, S & Green, ML 1998, 'New catalysts for the conversion of methane to synthesis gas: Molybdenum and tungsten carbide', Journal of Catalysis, vol. 180, no. 1, pp. 85-100.View/Download from: Publisher's site
High-surface-area molybdenum and tungsten carbide materials, synthesised by the temperature programming reduction of the relevant metal oxide with methane/hydrogen, are highly efficient catalysts for the conversion of methane to synthesis gas, via the steam reforming, dry reforming, or partial oxidation processes. The activities of the carbides were found to be comparable to those of elemental iridium and ruthenium (well known to be active noble metal catalysts for the reforming of methane), and the conversion and product distribution were in accord with those calculated from the thermodynamic equilibria. At ambient pressure the carbides deactivated, in all the processes, due to the oxidation of the catalyst to MO2, while operation at elevated pressure (8 bar) resulted in stabilisation of the carbide and no catalyst deactivation for the duration of the experiments (72 h). HRTEM analysis showed that no macroscopic carbon was deposited on the catalysts during the catalytic reactions. The deactivation rate of the carbides reflected the strength of the oxidant used: oxygen > water ? carbon dioxide. A deactivation mechanism, via the insertion of O* resulting in oxide terraces is discussed, and two possible mechanisms for the production of synthesis gas by the methane dry reforming reaction over metal carbides are proposed: noble metal type and redox type
York, APE, Claridge, JB, MarquezAlvarez, C, Brungs, AJ & Green, MLH 1997, 'Group (V) and (VI) transition metal carbides as new catalysts for the reforming of methane to synthesis gas.', ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, vol. 213, pp. 85-FUEL.
York, AP, Claridge, JB, Marquez-Alvarez, C, Brungs, AJ, Tsang, S & Green, M 1997, 'Synthesis of early transition metal carbides and their application for the reforming of methane to synthesis gas', Studies in Surface Science and Catalysis, vol. 110, pp. 711-720.
Binary and ternary group V and VI transition metal oxides were converted to their carbides using temperature programmed reduction (TPR). When ethane was substituted for methane in the TPR, transmission electron microscopy indicated that the oxide-carbide transformation proceeded topotactically. The carbides synthesised were tested as catalysts for methane reforming with carbon dioxide (dry reforming), giving carbon monoxide and hydrogen (synthesis gas) as the main products; of the binary carbides, only molybdenum and tungsten were active and stable, displaying activities comparable to supported noble metal catalysts. No carbon deposition was observed on post-catalytic carbide samples. Molybdenum and tungsten carbides were also active for methane reforming with air (partial oxidation) and water (steam reforming). No synergistic effects were evident in the ternary carbides, and only those with a high ratio of Mo/W to group V metal exhibited significant catalytic activity and stabilit
York, AP, Claridge, JB, Brungs, AJ, Tsang, S & Green, ML 1997, 'Molybdenum and tungsten carbides as catalysts for the conversion of methane to synthesis gas using stoichiometric feedstocks', Chemical communications Chemcomm, vol. 1, pp. 39-40.View/Download from: Publisher's site
Molybdenum and tungsten carbides are extremely active and stable catalysts for the dry reforming, partial oxidation and steam reforming of methane to synthesis gas using stoichiometric feedstock; no bulk carbon deposition was observed
York, AP, Claridge, JB, Marquez-Alvarez, C, Brungs, AJ & Green, ML 1997, 'Group (V) and (VI) transition metal carbides as new catalysts for the reforming of methane to synthesis gas', American Chemical Society. Division of Fuel Chemistry. Preprints of Symposia, American Chemical Society, San Francisco, pp. 606-609.
High surface area group V and VI transition metal carbides, synthesised by temperature programmed reduction of the metal oxides with methane/hydrogen, have been tested as catalysts for the dry reforming of methane with carbon dioxide and partial oxidation of methane with air. Mo2C and WC were stable and highly active catalysts for these reactions at elevated pressure, while they deactivated at ambient pressure. The product distribution obtained was close to that predicted by the thermodynamic equilibrium, except that no carbon formation was observed on the catalyst surface. The carbides of niobium and tantalum deactivated, even in the dry reforming reaction at elevated pressure, due to their greater tendency towards oxidation.