Water gas shift activity and kinetics of Pt/Re catalysts supported on ceria-zirconia oxides

Abstract

UTRC has developed a stable, high activity water gas shift (WGS) catalysts for the removal of carbon monoxide from hydrogen containing reformate, generated from natural gas. Hydrogen streams that contain lower concentrations of carbon monoxide poison can extend the life of proton exchange membrane (PEM) fuel cell stacks. This study presents WGS reactivity and kinetics experiments performed comparing platinum and platinum/rhenium (T.H. Vanderspurt, F. Wijzen, X. Tang, M.P. Leffler, R.R. Willigan, C.A. Newman, R. Radhakrishnan, F. Feng, B.L. Laube, Z. Dardas, S.M. Opalka, Y. She, US Patent Application 0235526 A1 (2003)) supported on high surface area (∼200m2/g), nano-crystalline (∼4nm) large average pore size (∼5nm) ceria-zirconia under various reaction conditions. These represent gas compositions and temperatures that the catalysts see in fuel processing systems. It was found that rhenium enhanced the WGS activity of ceria-zirconia supported platinum catalysts and that rhenium carbonyl Re2(CO)10 was an optimal source for introducing rhenium to the platinum/ceria-zirconia catalysts. The optimal platinum to rhenium ratio for these catalysts was approximately 2:1 (Pt/Re) where the platinum loading was about 2wt.%. A simple kinetic model adequately represents the rhenium promotion effect sufficient to size the WGS reactors for a system. This model suggests that the enhancement in reaction rates was a function of a larger positive order dependency for H2O concentration with lower inhibitory orders for CO2 and H2 concentrations for the platinum/rhenium catalyst compared to the platinum only catalyst.