Effect of pore structure on catalytic properties of mesoporous silica supported rhodium catalysts for the hydrogenation of cinnamaldehyde

Rhodium particles for catalyzing the hydrogenation were effectively confined in the mesopores of MCM-41 and MSU-H silica by using supercritical CO₂ as impregnation solvent. It was found that the calcination was an important step to control the size of Rh particles, and its influence was strongly dependent on the pore size distribution of mesoporous silica support. The prepared catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption, and transmission electron microscopy (TEM). While irregularly big Rh particles were often found on MCM-41 with smaller pore size (2.7 nm) during calcination at 873 K, homogeneous and small Rh particles were maintained inside MSU-H with relatively larger pore size (8.4nm). The hydrogenation of cinnamaldehyde using the prepared catalysts was carried out in supercritical CO₂. Rh/MSU-H which was calcined at 673K provided the highest catalytic activity among the studied conditions. The results indicated that the catalyst on the support with larger pore size and smaller size of Rh particles might be desirable to attain higher catalytic activity.