TPD, XPS and ESR Studies of the Surface Processes Involved in the Oxidation ofn-Pentane on a (VO)2P2O7 System

Abstract

Surface-sensitive techniques such as XPS, temperature-programmed desorption–mass spectrometry (TPD–MS) and electron spin resonance (ESR) have been used to study the effect of O2 treatment on the interaction ofn-pentane with the surface of an ‘equilibrated’ (VO)2P2O7 catalyst. The study was carried out by means of TPD studies after the catalyst had been in contact withn-pentane at 613 K in the presence and in the absence of O2 and by comparing the results, depending on whether the sample was subjected or not to O2 pretreatment at 613 K previously, ton-pentane adsorption. The valence state of vanadium and the changes in the short-range order around vanadium at the surface after former pretreatments were studied by XPS and ESR techniques, respectively. It was concluded that no oxygen radicals can be created on this catalyst, thus excluding the possibility that these kinds of radicals are involved in the oxidation process. On the other hand, despite the fact that the valence state of vanadium at the surface is an important variable, surface topology around vanadium centres at the surface of the ‘equilibrated’ (VO)2P2O7 sample clearly influences the interaction ofn-pentane with the surface. The short-range order around the vanadium sites does not seem to have much effect on the first steps of interaction ofn-pentane on the catalyst, but instead alters the further oxidation processes acting on the molecules resulting from the first steps.© 1997 by John Wiley & Sons, Ltd.