The reactions of ethanol over Au/CeO2

The reaction of ethanol has been investigated on the surface of Au/CeO2 by temperature programmed desorption (TPD), infrared (IR) absorption and in steady state catalytic conditions. The objective of this study is to compare Au/CeO2 to the other previously studied CeO2 [J. Catal. 186 (1999) 279], Pd/CeO2 [J. Catal. 186 (1999) 279], Pt/CeO2 [J. Catal. 191 (2000) 30] and Rh/CeO2 [Catal. Today 63 (2000) 327] for the same reaction. At 300 K, the surface is covered with both ethoxide species and weakly bonded ethanol. Most of these species desorb giving back ethanol (about 50%; TPD) by 400-450 K with some formation of acetaldehyde (7.5%; TPD). A small part of the remaining ethoxides gives bridging CO (v: 1916 cm(-1)). Most of CO is oxidized to CO2 (CO2/CO approximate to 25, TPD) translating the powerful nature of An for the oxidation process. In the absence of Au, the same ratio drops to 0.7 [J. Catal. 186 (1999) 279]. By 600 K, the surface is covered with carbonates species (v: 1524 cm(-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 573 K, acetaldehyde was the main reaction products. Methane desorbed in two distinct reaction-temperatures (673 and 973 K) while acetone was the largest reaction product at ca. 773 K. Among the non-hydrocarbon products (CO2, CO and H-2), CO2 was the largest at low temperatures (up to 700 K with a peak at ca. 573 K (52% molar yield)). Increasing the reaction temperature up to 1073 K resulted in increasing amounts of H-2 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. (C) 2003 Elsevier B.V. All rights reserved.