Oxidative dehydrogenation of isobutane over vanadia catalysts supported by titania nanoshapes

Support plays a complex role in catalysis by supported metal oxides and the exact support effect still remains elusive. One of the approaches to gain fundamental insights into the support effect is to utilize model support systems. In this paper, we employed for the first time titania nanoshapes as the model supports and investigated how the variation of surface structure of the support (titania, TiO₂) impacts the catalysis of supported oxide (vanadia, VO_x). TiO₂ truncated rhombi, spheres and rods were synthesized via hydrothermal method and characterized with XRD and TEM. These TiO₂ nanoshapes represent different mixtures of surface facets including [1 0 1], [0 1 0] and [0 0 1] and were used to support vanadia. The structure of supported VO_x species was characterized in detail with in situ Raman spectroscopy as a function of loading on the three TiO₂ nanoshapes. Oxidative dehydrogenation (ODH) of isobutane to isobutene was used as a model reaction to test how the support shape influences the activity, selectivity and activation energy of the surface VO_x species. It was shown that the shape of TiO₂ support does not pose evident effect on either the structure of surface VO_x species or the catalytic performance of surface VO_x species in isobutane ODH reaction. This insignificant support shape effect was ascribed to the small difference in the surface oxygen vacancy formation energy among the different TiO₂ surfaces and the multi-faceting nature of the TiO₂ nanoshapes.