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

Héroguel, Florent, Silvioli, Luca, Du, Yuan-Peng, Luterbacher, Jeremy S.
Journal of catalysis 2018 v.358 pp. 50-61
Lewis acids, catalysts, gels, guaiacol, nanoparticles, sol-gel processing, surface area, titanium dioxide
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.