Abstract
The reactions of ethanol over Rh/CeO 2 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/CeO 2 [J. Catal. 186 (1999) 279] and Pt/CeO 2 [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/CeO 2, Pd/CeO 2 and Pt/CeO 2, 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(1s)/Ce(3d) ratio of the CeO 2 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>Rh. FT-IR and TPD studies have shown that dehydrogenation of ethanol to acetaldehyde occurred over Pd/CeO 2, Pt/CeO 2 and Rh/CeO 2. Moreover, Rh/CeO 2 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 CH 4 over Rh/CeO 2 (450 K) when compared to that of Pd/CeO 2 (550 K) or Pt/CeO 2 (585 K).
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