H2 and CO2 coadsorption effects in CO adsorption over nanosized Au/γ-Al2O3 catalysts

The present study is focused on the kinetic investigation of the effects of H-2 and CO2 on the rates related to the elementary steps of CO sorption over Au/gamma-Al2O3. The kinetic study was carried out in a wide temperature range (50-300 degrees C) by the novel methodology of reversed flow gas chromatography (RF-GC). The findings of preliminary coadsorption studies of CO with H-2, O-2 and O-2 + H-2 indicate that a reductive pre-treatment of the Au catalyst with a mixture of CO in excess of H-2 can be more beneficial concerning CO oxidation activity at low temperatures, compared to the usual reduction in a diluted hydrogen atmosphere, most probably due to the easier activation of oxygen molecules. At high temperatures the rate of reversed water gas shift reaction becomes significant resulting in H-2 and CO2 consumption. The kinetic findings indicate that hydrogen strongly influences the adsorption of CO over Au/gamma-Al2O3, by enhancing CO adsorption at lower temperatures and weakening the strength CO binding. On the other hand, CO2 adsorption competes that of CO under hydrogen-rich conditions. However, the strength of CO2 bonding is higher compared to that of CO and it further increases at higher temperatures, in agreement with the observed deactivation of the selective CO oxidation in the presence of CO2. (C) 2008 Elsevier B.V. All rights reserved.