Kinetic Study of the Reverse Water-Gas Shift Reaction over CuO/ZnO/Al_2O_3 Catalyst at Low Temperature

摘要

The kinetics and reaction mechanism of the reverse water-gas shift reaction (RWGS) over CuO/ZnO/Al_2O_3 catalysts were studied using a differential reactor.The experiments were carried out at 523 K and 2.9-5.7 atm.Effect of reactants composition on the reaction rate was checked by changing P_(CO_2)~(0) and P_(H_2)~0.When the P_(CO_2)~0 and P_(CO_2)~0 were low,the reaction rate was dependent on partial pressure of both reactants and there was a strong dependency on P_(H_2)~0.At high P_(CO_2)~0 and P_(H_2)~0,reaction order with P_(H_2)~0 was zero,and order with P_(CO_2)~0 was 0.23.The data was analysed using rate equations based on power law,Langmuir-Hinshelwood mechanism,and surface redox mechanism in which Cu was considered as an active site.The reaction rate derived from surface redox mechanism matched well with the reaction rate derived from power law,and the calculated r_0 values,based on surface redox mechanism,was in good agreement with the experimental values.Also,a linear relationship between P_(CO)~0 and reaction rate indicated that the surface redox mechanism was operative under these conditions.Therefore,it was conclued that the RWGS at 523 K proceeds by surface redox mechanism via oxidation and reduction of the Cu active site.