(264d) Aqueous-Phase Ketonization of Acetic Acid Over Ru/TiO2/Carbon Catalysts

Ketonization of acetic acid has been accomplished in the liquid phase on Ru/TiO₂ and Ru/TiO₂/C catalysts, at temperatures significantly lower than those typically needed for this reaction.  The catalysts were prepared by first impregnating the activated carbon support with titanium (IV) isopropoxide, followed by slow hydrolysis and calcination in the absence of air. The resulting TiO₂/C sample was further impregnated with Ru (III) chloride, dried, and calcined in air.  After an in-situ pre-reduction in H₂, the resulting Ru/TiO₂/C exhibited high activity and selectivity to acetone in both, organic and aqueous phases at 180^oC.  By contrast, when the TiO₂/C sample was precalcined in air before the addition of Ru, the resulting catalyst showed significantly lower activity when it was pre-reduced in-situ, and was essentially inactive without the pre-reduction.  While it is usually expected that in water the oxygen vacancies are filled, it is shown here that under the conditions investigated, they remain active for long time. A combination of techniques including XRD, XPS, and TPR were used to characterize the reducibility of the catalysts and the formation of oxygen vacancies.  It is proposed that the presence of Ru on TiO₂ facilitates the formation of Ti³⁺ sites, which are responsible for the observed activity.  Furthermore, the hydrophobicity of the carbon support is believed to decelerate the typical inhibiting effect of water for reactions catalyzed by oxygen vacancies.