The water-gas-shift reaction at short contact times

We have examined the water-gas-shift reaction over noble metals and metals with ceria for catalyst contact times between 0.008 and 0.05 s for temperatures from 300 to 1000 degreesC. With reactants of CO, H-2, and H2O at a 1/2/4 composition, the reaction approached equilibrium at these contact times for temperatures as low as 380degreesC, which corresponds to a 5011 H-2/CO ratio. All results follow the equilibrium conversion versus temperature curve at high temperatures and then the rate decreases rapidly as temperature decreases. All metals show considerable promotion upon ceria addition, with Pt/ceria showing the most promise in terms of promotion, stability, and lack of methanation activity. A simple kinetic model that assumes first-order reversible reaction in all species fits all data at all temperatures from equilibrium to low conversions. The rate is nearly independent of surface area over a wide variation of parameters, and rates indicate that mass-transfer limitations are not dominant. (C) 2004 Elsevier Inc. All rights reserved.