The Reactions of Ethanol over Au/CeO2

Abstract

The reaction of ethanol has been investigated on the surface of Au/CeO 2 by temperature programmed desorption (TPD), infra red (IR) absorption and in steady state catalytic conditions. The objective of this study is to compare Au/CeO2 to the other previously studied CeO 2 [J. Catal. 186 (1999) 279], Pd/CeO2 [J. Catal. 186 (1999) 279], Pt/CeO2 [J. Catal. 191 (2000) 30] and Rh/CeO 2 [Catal. Today 63 (2000) 327] for the same reaction. At 300K, the surface is covered with both ethoxide species and weakly bonded ethanol. Most of these species desorb giving back ethanol (about 50%; TPD) by 400-450K with some formation of acetaldehyde (7.5%; TPD). A small part of the remaining ethoxides gives bridging CO (ν: 1916cm-1). Most of CO is oxidized to CO2 (CO2/CO≈25, TPD) translating the powerful nature of Au for the oxidation process. In the absence of Au, the same ratio drops to 0.7 [J. Catal. 186 (1999) 279]. By 600K, the surface is covered with carbonates species (ν: 1524cm-1). These carbonates are mainly decomposed to CO2; IR and TPD. Steady state reactions in presence of oxygen showed the formation of mainly three hydrocarbon-products with a distribution depending on the reaction temperature. At 573K, acetaldehyde was the main reaction products. Methane desorbed in two distinct reaction-temperatures (673 and 973K) while acetone was the largest reaction product at ca. 773K. Among the non-hydrocarbon products (CO2, CO and H2), CO2 was the largest at low temperatures (up to 700K with a peak at ca. 573K (52% molar yield)). Increasing the reaction temperature up to 1073K resulted in increasing amounts of H2 and CO ca. 10 and 30% molar yield, respectively. Insight into the reaction mechanism is given with the potential role of direct oxidation, water gas shift and reforming of methane discussed. © 2003 Elsevier B.V. All rights reserved.