IR study of acid sites on WO 3-ZrO 2

Abstract

The mechanism of the generation of protonic acid sites from molecular hydrogen on WO 3-ZrO 2 was studied by IR spectroscopy. The spectral changes in the WO stretching and the OH stretching regions were observed in response to the exposure to hydrogen and the removal of hydrogen. By heating in the presence of hydrogen, the WO stretching bands at 1021 and 1014 cm −1 eroded and a broad band around 980 cm −1 was developed. The peaks at 1021, 1014 and 980 cm −1 restored to their original intensities on heating in a vacuum. A broad OH stretching band around 3600 cm −1 was intensified by heating in the presence of hydrogen and restored to its original intensity by removal of the hydrogen from a gas phase. Pyridine adsorption caused essentially the same changes in the WO stretching region as hydrogen adsorption. Based on the spectral changes, the changes in the structure of acid sites caused by hydrogen adsorption are proposed.