Aqueous-phase ketonization of acetic acid over Ru/TiO2/carbon catalysts

Abstract

The ketonization of acetic acid over Ru/TiO2 and Ru/TiO2/C catalysts has been accomplished in the liquid phase at temperatures significantly lower than those typically needed for this reaction. The catalysts were prepared by impregnating the activated carbon support with titanium(IV) isopropoxide, followed by slow hydrolysis and calcination in the absence of air. The resulting TiO2/C powder 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°C. By contrast, when the TiO2/C sample was pre-calcined in air before the addition of Ru, the resulting catalyst showed significantly lower activity, even when it was pre-reduced in situ, and was essentially inactive without pre-reduction. It is believed that surface Ti3+ species can be readily formed and favor the ketonization reaction in the presence of liquid water. A combination of techniques including TEM, BET, TPR, XRD, XPS, and EPR was used to characterize the reducibility of the catalysts as well as the formation of and stability of Ti3+ sites. It is proposed that the presence of Ru on TiO2 facilitates the formation of these reduced sites. Furthermore, the hydrophobicity of the carbon support is believed to slow down the typical inhibiting effect of water for reactions catalyzed by reduced Ti3+ sites.