The synthesis and characterization of building block-based titanosilicates and their activity toward alcohol dehydration/dehydrogenation reactions

Catalysis, in general, plays an integral part to many aspects of everyday life. Next-generation heterogeneous catalysts need well defined site structures to correlate with activity in order to maximize selectivity and activity. The building block methodology is a widely-applicable route to synthesizing single-site catalysts that are atomically dispersed. The building block methodology has been used to synthesize a series of titanosilicates with different site structures that mimic the potential sites in current titanosilicates. These catalysts have been characterized via EXAFS and gravimetric analysis. The EXAFS suggest single-site nature for the embedded (TiO₄) and surface (ClTiO₃) titanosilicate and suggest composite structure for the two intermediate titanosilicates ClTiO₃ and Cl₂TiO₂. An embedded tripodal titanosilicate ([superscript i]PrO)TiO₃ was synthesized as well to mimic the tripodal sites without the presence of chloride ligands. Alcohol dehydration/dehydrogenation reactions have been used to characterize the acidity and basicity of heterogeneous catalysts. Isopropanol and ethanol were used to characterize the embedded TiO₄ and embedded tripodal ([superscript i]PrO)TiO₃ building block titanosilicates as well as the embedded building block vanadium(V)-silicate and vanadium(IV)-silicate. The catalysts were highly selective toward isopropanol dehydration with the post-calcination catalysts exhibiting higher conversion at lower temperatures than the pre-calcination catalysts. The titanosilicates exhibited no selectivity toward ethanol decomposition reactions while the vanadium-silicates were more selective toward ethylene production. The differences in reactivity and selectivity illustrate the differences in the type of site and metal used.