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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 study, 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, VOx). 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 VOx 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 VOx species. It was shown that the shape of TiO2 support does not pose evident effect on either the structure of surface VOx species or the catalytic performance of surfacemore » VOx species in isobutane ODH reaction. Finally, 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.« less

The addition of 0.10 wt% Li to Rh/TiO2 more than doubled the CO conversion for CO hydrogenation while increasing ethanol selectivity. The addition of Li also increases formation of C2 oxygenates at the expense of C1 species, methanol and methane. This is attributed to enhanced dispersion of Rh by Li that appears to reduce dissociation of CO, which previous studies have shown requires large ensembles of Rh atoms on the surface. Li promotion appears to increase the associatively adsorbed CO, allowing for increased H2 chemisorption on the surface compared to the dissociative adsorption of the same number of CO atoms. This increases selectivity to ethanol compared to the unpromoted catalysts. CO-TPD shows more reactive adsorbed CO species on the Li-promoted catalyst. FTIR results suggest that Li promotion alters CO bonding at bridged or interfacial sites and its effect is more structural than electronic.