The reactions of ethanol over M/CeO2 catalysts: Evidence of carbon-carbon bond dissociation at low temperatures over Rh/CeO2

The reactions of ethanol over Rh/CeO2 have been investigated using the techniques of temperature programmed desorption (TPD) and FT-IR spectroscopy, in addition to steady state catalytic tests. A comparison with previous studies of ethanol adsorption over Pd/CeO2 [J. Catal. 186 (1999) 279] and Pt/CeO2 [J. Catal. 191 (2000) 30] catalysts is presented. The apparent activation energy for the reaction was 49, 40, and 43 kJ mol(-1) for Rh/CeO2, Pd/CeO2 and Pt/CeO2. respectively, while the turnover number (TON) at 400 K was 5.9, 8.6 and 2.6, respectively. Surface compositions of catalysts were characterised by XPS. A decrease of the atomic O(ls)/Ce(3d) ratio of the CeO2 support indicates its partial reduction upon addition of the noble metal. The extent of reduction per metal atom was in the following order: Pt > Pd > Ph. FT-IR and TPD studies have shown that dehydrogenation of ethanol to acetaldehyde occurred over Pd/CeO2, Pt/CeO2 and Rh/CeO2. Moreover, Rh/CeO2 readily dissociated the C-C bond of ethanol at room temperature to form adsorbed CO (IR bands at 1904-2091 cm(-1)). This was corroborated by the low desorption temperature of CH4 over Rh/CeO2 (450 K) when compared to that of Pd/CeO2 (550 K) or Pt/CeO2 (585 K). (C) 2000 Elsevier Science B.V. All rights reserved.