Controlled deposition of titanium oxide overcoats by non-hydrolytic sol gel for improved catalyst selectivity and stability

Advances in the synthetic control of surface nanostructures could improve the activity, selectivity and stability of heterogeneous catalysts. Here, we present a technique for the controlled deposition of TiO₂ overcoats based on non-hydrolytic sol-gel chemistry. Continuous injection of Ti(ⁱPrO)₄ and TiCl₄ mixtures led to the formation of conformal TiO₂ overcoats with a growth rate of 0.4 nm/injected monolayer on several materials including high surface area SBA-15. Deposition of TiO₂ on SBA-15 generated medium-strength Lewis acid sites, which catalyzed 1-phenylethanol dehydration at high selectivities and decreased deactivation rates compared to typically used HZSM-5. When supported metal nanoparticles were similarly overcoated, the intimate contact between the metal and acid sites at the support-overcoat interface significantly increased propylcyclohexane selectivity during the deoxygenation of lignin-derived propyl guaiacol (89% at 90% conversion compared to 30% for the uncoated catalyst). For both materials, the surface reactivity could be tuned with the overcoat thickness.