Study of the Interaction between Simple Molecules and W−Sn-Based Oxide Catalysts. 1. The Case of WO3 Powders

Abstract

In this work, the interaction between WO3 powder and methanol, 1-butanol, and benzyl alcohol has been studied, at atmospheric pressure as well as under high-vacuum (HV) conditions, both in the presence and in absence of oxygen. The chemisorptions carried out at atmospheric pressure have been studied by means of diffuse reflectance IR spectroscopy while quadrupolar mass spectrometry and X-ray photoelectron spectroscopy have been used to follow the reactions under HV conditions. At atmospheric pressure, methanol oxidizes to formic acid and CO2 when chemisorbed in mixture with oxygen at temperature higher than 423 K. Formic acid chemisorption was investigated for comparison. Methanol chemisorption under HV conditions results in the alcohol oxidation to formaldehyde (when oxygen is present) with desorption maxima around 520 and 720 K. These results are compared with those obtained after the chemisorption of formaldehyde. At atmospheric pressure, 1-butanol chemisorption leads mainly to the formation of CO2 while the benzyl alcohol oxidizes to benzaldehyde when chemisorbed in mixture with Ar and to benzaldehyde and benzoate when chemisorbed in mixture with O2. Under HV conditions, butanol decomposes to carbon oxides and to hydrocarbons both with and without oxygen. Benzyl alcohol is very resistant to decomposition or oxidation. The catalyst has been characterized with DRIFT spectroscopy, XPS, and XRD, and particular attention has been paid to the behavior of the active site, such as OH groups with Brönsted acid character.