Morphological and structural features of Co/TiO₂ catalysts prepared by different methods and their performance in the liquid phase hydrogenation of α, β unsaturated aldehydes

Abstract

The effect of the preparation method of Co/TiO₂ catalysts on the performance in the liquid phase hydrogenation of cinnamaldehyde and crotonaldehyde has been studied. The Co/TiO₂ catalysts were prepared by impregnation on titania (TiO₂, P-25), sol-gel, and precipitation procedures. Different reduction-oxidation-reduction cycles were carried out in order to detect possible changes in the nature of the phases and their reduction degrees. The catalysts were characterized by specific area measurements, TEM, ED, XPS and TPR/TPO studies. The catalysts prepared by the sol-gel and precipitation method exhibit higher resistance to sintering when they are treated under the same reduction-oxidation-reduction cycles, than the impregnated catalyst. Morphological changes observed by TEM were used to explain the catalytic behavior showed by the catalysts. The presence of Coº, CoO and Co3O4 phases in the reduced samples were detected by different methods. XPS results show the existence of small particles of CoO, which are interacting with the support, which are very difficult to reduce. TEM and electron diffraction structural studies show an effect of metalsupport interaction by the appearance of channels and pill-box form in the particles. The highest yield in both catalytic hydrogenation reactions were obtained with the Co/TiO₂ catalysts prepared by precipitation and sol gel methods. The selectivity was closed to 50 and 30 % for cinnamyl alcohol and crotyl alcohol, respectively.