Surface reaction rate of hydrogenation of adsorbed carbon monoxide as examined by an emissionless infrared diffuse reflectance spectrometer

Abstract

The behaviors of adsorbed CO species during the methanation of CO on supported metal catalysts were examined by using an EDR (emissionless infrared diffuse reflectance spectrometer). Major adsorbed species observed under steady-state CO-H/sub 2/ reaction were adsorbed CO and surface formate, and appreciable absorption could not be observed in C-H and O-H regions. The rate constants of disappearance of adsorbed species on 0.5% Pd/Al/sub 2/O/sub 3/ under the reaction conditions were also measured from the transient responses of IR spectra. The intensities of the bands due to surface formate did not change with time, showing that the surface formate is not an intermediate. The rate constants of disappearance of adsorbed CO (linear CO and bridge CO) were essentially identical with each other and were in good agreement with the rate constant of CH/sub 4/ formation measured by PSRA (pulse surface reaction rate analysis). These data indicate that the rate-determining step in the methanation of CO is the C-O bond dissociation of adsorbed species and the hydrogenation of the adsorbed carbon species proceeds rapidly. 8 figures, 1 table.