Determination of kinetic parameters for the water-gas shift reaction on copper catalysts under realistic conditions for fuel cell applications

The kinetic parameters for water-gas shift reaction on Cu-based catalysts were measured under fuel reformer conditions for fuel cell applications (7% CO, 8.5% CO2, 22% H2O, 37% H-2, and 25% Ar) at 1 atm total pressure and temperature in the range of 200degreesC. The rate per unit of Cu surface area at the stated concentrations was 0.8 x 10(-6) mol m(-2) s(-1) at 200degreesC. The overall reaction rate as a function of the forward rate (r(f)) is r = r(f)(1 - beta), where r(f) = k(f)[CO](0.8)[H2O](0.8)[CO2](-0.7)[H-2](-0.8), k(f) is the forward rate constant, beta = ([CO2][H-2])/(K[CO][H2O]) is the approach to equilibrium, and K is the equilibrium constant for the water-gas shift reaction. This expression indicates a strong inhibition on the forward rate by H2 and C02. When ceria was added to the catalyst, it decreased the Cu surface area and did not increase the rate per unit of Cu surface area, suggesting that ceria is not a promoter. The addition of ZnO did not increase the rate per unit of Cu surface area either. Thus, Cu is the active site for catalysis. It was proposed that the kinetics can be explained based on the "Redox" mechanism with CO* + O* reversible arrow CO2* + * as the rate-determining step. (C) 2003 Elsevier Science (USA). All rights reserved.