The adsorption of CH3OH on Pt/CeO2-Al2O3, Pt/CeO2-SiO2, CeO2-Al2O3 and Pt/CeO2-SiO2 and its subsequent decomposition has been studied by IR spectroscopy. The presence of CeO2, in the supported Pt catalysts causes significant changes in the decomposition of absorbed CH3OH. The initially formed surface methoxy species are transformed at elevated temperatures to absorbed formate and carbonate species on oxide sites and CO adsorbed on Pt sites. (C) 1997 Elsevier Science B.V.

The adsorption of CH3OH on PtCeO2Al2O3, PtCeO2SiO2, CeO2Al2O3 and PtCeO2SiO2 and its subsequent decomposition has been studied by IR spectroscopy. The presence of CeO2 in the suppo Pt catalysts causes significant changes in the decomposition of absorbed CH3OH. The initially formed surface methoxy species are transformed at elevated temperatures to absorbed formate and carbonate species on oxide sites and CO adsorbed on Pt sites.

IR spectra have been measured following adsorption of butane and propene on reduced Pt/CeO2–Al2O3 catalysts containing 0–20% CeO2 and also on catalysts exposed to O2 at ambient temperature. Adsorption of butane on oxidised catalysts containing CeO2 produced surface formate and hydrogencarbonate species on Al2O3 after it was heated to 350 °C, although these species were not formed in the absence of CeO2. By contrast, adsorption of butane on reduced catalysts yielded either surface CO alone (1–5% CeO2) or CO and carbonate ( 10% CeO2), after heating to 350 °C. CO adsorption experiments provided evidence for Pt site deactivation after adsorption of butane. Adsorption of propene on reduced catalysts yielded adsorbed CO and either surface acrylate (Pt/Al2O3) or carbonate (Pt/CeO2–Al2O3) on heating to 350 °C. Subsequent exposure to O2 at ambient temperature, followed by heating to 450 °C, resulted in the desorption of all surface species. These observations are interpreted in terms of the electronic theory of catalysis and a strong Pt–CeO2 interaction.

The products of the thermal decomposition of butane at temperatures up to 600 degrees C were identified by Raman spectroscopy. Heating to 500 degrees C resulted in tbe formation of a number of hydrocarbon products, in accordance with established reaction mechanisms. Heating to 600 degrees C, however however, led to methane as the sole product. By contrast, heating in the presence of either Al2O3 or Pt-Al2O3 yielded a different product distribution, attributed to interaction with Lewis acid sites on the Al2O3 surface. The Raman results were compared with data obtained by GC analysis.

Raman spectra have been obtained from a series of Pt/Al2O3 catalysts containing from 0 to 20% CeO2, and a Pt/CeO2 catalyst, prepared by sol-gel processing. Spectra were recorded following calcination of the catalyst Precursors at various temperatures up to 600-degrees-C and compared with thermogravimetric data. The results clearly present evidence for a strong interaction between Pt and CeO2. The surface mixed oxide species persists in an oxidising environment up to 600-degrees-C and in a reducing environment up to 170-degrees-C.