Catalytic reactions of methylcyclohexane (MCH), on partially reduced tungsten oxide(s)

Abstract

In situ XPS–UPS characterization of bulk WO 3 defines the reduction conditions to obtain different W 2 O 5 and WO 2 phases. UPS enabled us to clearly define the presence of WO 2 . The presence of both, Brönsted and metal functions in WO 2 (H x ) ac explains the catalytic behaviour of the sample towards the isomerization–dehydrogenation of methylcyclohexane. Figure: UPS of WO 3 following reduction by H 2 : (a) as received and (b) 773 K for 2 h. In situ XPS–UPS characterization of the reduction processes of bulk WO 3 following the exposure of the sample to hydrogen at different temperatures up to 773 K enabled us to define the reduction conditions at which each of the different W 2 O 5 and WO 2 phases could be obtained. The reduction process takes place in the upper 10–15 atomic layers, most probably in a sandwich like atomic layer superposition structure of different tungsten oxide(s) at each set of reduction conditions. In order to define the nature of the chemical composition of the outermost surface layer; responsible for the chemical activity, the combination of XPS–UPS techniques proved to be valuable. The depth detection limit and relatively high collision cross section in the low binding energy valence electrons of UPS enabled us to clearly define the presence of WO 2 , with the bifunctional WO 2 (H x ) ac structure on its surface at reduction temperatures above 673 K. The presence of both, Brönsted and metal functions on the same surface of WO 2 (H x ) ac explains the catalytic behaviour of the sample towards the isomerization–dehydrogenation of methylcyclohexane.