A Study On Low-Temperature Water-Gas Shift Reaction Over Molybdenum Carbide Catalysts

Water gas shift reaction (WGS, CO+H2O=CO2+H2,△H0298k=-41.4kJ/mol) is the oxidation of CO with the same amount of H2O, and effectively produce hydrogen. So, it has a wide range of application in hydrogen production. In recent years, the low temperature WGS reaction has attracted more attention due to the development of fuel cell power system. CO concentration in H2beyond10ppm are irreversibly poisoning of the PEM fuel cell anode Pt catalyst, WGS reaction is important in generating more hydrogen and lowering the CO content.In this paper, β-Mo2C, a-MoC1-x and metal promoted molybdenum carbide catalysts were prepared by temperature-programmed reaction. Their catalytic performance was investigated for WGS reaction in laboratory scale, and characterized by XRD, BET, CO Chemisorption and TPSR. Some results were obtained as follows:(1) The effect of pretreatment on catalytic activity of β-Mo2C was studied. It was found that pretreatment in15%CH4/H2led to higher activity of β-Mo2C than the one pretreated in pure H2. And the in-situ synthesized β-Mo2C without any passivation showed the highest activity for WGS reaction. Characterization results indicate that re-carburization of the oxidized surface in15%CH4/H2should be responsible for the enhanced activity.(2)α-MoC1-x catalyst was synthesized and tested for WGS reaction. By comparison with P-M02C, it was found that a-MoC1-x was more active in low temperatures. But it deactivated gradually with time on stream. Correlated with the characterization results, it was proposed that the deactivation was due to surface oxidation of the molybdenum carbide and the decrease in surface area.(3) Addition of Ni, Co, Fe produced β-Mo2C phase during the TPRe process. In contrast, the loading of Cu and Au mainly resulted in the a-MoC1-x phase. It was proposed that the loading of Au and Cu to MoO3drove MoO3reduction into a topotactic transformation through a MoOxCy intermediate phase. Among them,3%Au/MoC1-x catalyst showed the highest low-temperature activity for WGS reaction, the CO conversion reached100%at150℃. Due to the addition of Au, the stability of molybdenum carbide was also enhanced.