Structural Dynamics of Dispersed Titania During Dehydration and Oxidative Dehydrogenation Studied by In Situ UV Raman Spectroscopy

Abstract

The structural dynamics of dispersed titania, i.e., silica supported titania, is investigated during dehydration and oxidative dehydrogenation (ODH) of ethanol using optical spectroscopy. UV Raman spectroscopy enabling resonance enhancements proves to be a valuable tool to identify Ti–OH, Ti–O–Si, and Ti–O–Ti groups. Upon dehydration, a transformation of Ti–OH into Ti–O–Si and Ti–O–Ti groups is observed. Two types of Ti–OH vibrations (isolated, geminal) are identified at around 700 and 800 cm− 1 in agreement with theoretical models. Dispersed titania is catalytically active in ethanol ODH with a performance comparable to dispersed vanadia. In situ UV Raman spectra reveal a consumption of Ti–O–Ti, Ti–O–Si, and Ti–OH groups during ethanol adsorption to the titania surface. The presented results are consistent with an ODH reaction mechanism involving a structural transformation of oligomerized or closely neighbored monomeric TiOX structures. The relevance of the proposed mechanism is discussed in the context of other supported transition metal oxide catalysts. Graphical Abstract: [Figure not available: see fulltext.]