Reaction selectivity to hydrocarbons and solid-state carbon over molybdenum sulfide-based shift catalyst

• We study the reaction selectivity of Co–Mo-based shift catalyst.
• Side reactions are confirmed to be Fischer–Tropsh reaction and Boudouard reaction.
• Fischer–Tropsh reaction is enhanced at high temperature, high pressure, low steam supply, and long residence time.
• Boudouard reaction is enhanced a low temperature, high pressure, and low steam supply.
• The 2 side reactions are nearly suppressed when as long as here is presence of water partial pressure.

IGCC-CCS process is one application of a cobalt-molybdenum (Co–Mo)-based water-gas shift catalyst (sour shift catalyst). In this process, it is necessary for the shift reaction to progress efficiently with a small amount of steam in order to suppress CO2 emissions and to increase production efficiency. However, if the amount of steam used in the shift reaction is decreased, there is a possibility that the selectivity of side reactions represented by hydrocarbon production and carbon deposition increases. Therefore, we investigated the effects of various operating parameters regarding the selectivity and reaction mechanism of the side reactions with a reduced steam supply in the shift reaction for Co–Mo-based shift catalyst. Among the side reactions accompanying the shift reaction, the reaction of hydrocarbon production progresses due to the Fischer–Tropsch reaction and increases at a high temperature, high pressure, low steam supply, and long residence time. Moreover, the reaction of carbon deposition in the catalyst progresses due to the Boudouard reaction, which produces carbon directly from the CO source and the deposition increases at a low temperature, high pressure, and low steam supply. Furthermore, the selectivity of the shift reaction of the Co–Mo-based catalyst is high in the co-existing steam conditions, and the shift reaction progresses even if there is a small amount of steam in the reaction gas.

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