The benzylation of xylenes using heterogeneous catalysts from rice husk ash silica modified with gallium, indium and iron

Rice husk ash (RHA) was used to synthesize RHA-Ga, RHA-In and RHA-Fe catalysts by direct incorporation of the respective ions into rice husk ash silica at room temperature. The prepared catalysts were used to catalyze the benzylation of p-xylene (p-Xyl) with benzyl chloride (BC). The catalysts had a BET specific surface area of ca. 272-347 m(2) g(-1). The catalytic activity increased with a decrease in the p-Xyl/BC molar ratio. However, the selectivity towards the mono-benzylated product decreased. RHA-Fe showed the highest catalytic activity whereas RHA-In and RHA-Ga gave higher selectivity to 2,5-dimethyldiphenylmethane (2,5-DMDPM). The catalytic activity followed the order: RHA-Fe > RHA-In > RHA-Ga. The activity of RHA catalyst towards Xyl isomers was found to follow the order: o-Xyl > m-Xyl > p-Xyl whereas the selectivity for DMDPM products decreased in the order: in-Xyl >p-Xyl > o-Xyl. (C) 2008 Elsevier B.V. All rights reserved.