(731e) Controlled Deposition of Metal Oxide Layers By Non-Hydrolytic Sol-Gel for Tailored Acid Sites Generation and Beyond
The method is based on non-hydrolytic sol-gel chemistry using mixtures of metal alkoxides and metal halides. For instance, addition of a 1/3 mol/mol mixture of Ti(iPrO)4 and TiCl4 to a toluene suspension of Cu2O spheres led to the formation of a thin conformal TiO2 overcoat. Thickness can be adjusted by the number of deposited layers with a growth rate of 0.5 nm/cycle. Furthermore, this method allows deposition of TiO2 layers inside the pores of SBA-15 while maintaining 2D hexagonal structure and high porosity. The mixed oxide created at the interface generates medium strength Lewis acid sites which catalyze 1-phenylethanol dehydration to styrene. High Lewis acid sites density with medium acid strength was obtained with 6 TiO2 layers which lead to the highest yields of styrene and the highest catalyst stability. In contrast, a zeolitic catalyst often used for this reaction (HZSM-5) deactivates due to polystyrene formation on strong Lewis acid sites. The technique has also been employed to overcoat supported metal particle yielding metal-acid bifunctional catalysts, where overcoat porosity can be adjusted by ageing in basic media. Finally, an analogous method was developed for deposition of alumina, yielding strong acid sites.
The easy implementation and tunable porosity of the present technique contrasts with the heavy instrumentation and limited structural control associated with gas phase methods such as atomic layer deposition or chemical vapor deposition on powder substrates. We anticipate that the method reported can be used for the rational design of catalytic materials used in a wide range of applications.