Synthesis, characterisation, and evaluation of supported cobalt molybdenum nitride for Fischer-Tropsch reaction

摘要

Fischer-Tropsch Synthesis (FTS) is known as the most practical way to convert natural gas to hydrocarbon products including synthetic fuel depending on the catalysts and operating conditions. Australia has 25% of world's natural gas resources hence Australia's crude oil dependency can be reduced extensively by developing catalysts that will facilitate the technique of converting natural gas to synthetic fuel.Molybdenum nitride has been employed in this study for FTS because of its superior mechanical strength, stability, exceptional resistance to carbon deposition & suifur poisoning. In particular, molybdenum nitride is endowed with similar electronic properties to those of noble metals. Other transition metal nitrides such as Co nitride and Co-Mo nitride were also investigated in this study. The physicochemical attributes of nitride catalysts were examined by BET surface area, particle dispersion, acid site strength & concentration, and surface elemental composition. Gas to solid nitridation kinetic was thermogravimetrically monitored. CO hydrogenation activity was measured in a fixed bed reactor using various syngas compositions and temperatures at atmospheric pressure. The effect of nitridation conditions on catalytic properties of nitrides was investigated via 23 factorial design. It has revealed that nitridation parameters; temperature, nitriding gas composition (H2:NH3) and nitridation reaction time were all significantly influencing catalyst properties. The optimal nitridation condition was 973 K, H2:NH3=1: 1, and 4 hours of nitriding time which gave higher alkene selectivity. 20 wt% M02N/Ah03 was found to be the better FT catalyst compare to catalysts with lower Mo loading and other inorganic oxide supports. Nitridation kinetic studied by thermogravimetric analysis showed that successful nitridation of transition metal oxide precursor was dependent of nitridation temperature and hydrogen concentration. Co-Mo nitride has several forms of nitride species, COS.47N, C03M03N, MoN, and Mo2N. It was shown that COS.47N was the most active component favouring the CO hydrogenation rate and alkene selectivity. Mechanistically-based kinetic models suggested that methanation over Co nitride occurs mainly via surface carbon while surface oxygenated intermediates were accountable for methanation over Co-Mo nitride and Mo nitride.