Room temperature synthesis of diphenylmethane over MCM-41 supported AlCl3 and other Lewis acids Original Research Article

The catalytic properties of MCM-41 activated with AlCl3, ZnCl2 and other Lewis acids, such as FeCl3, NiCl2 and CuCl2 were investigated for room temperature Friedel–Crafts benzylation in the liquid phase. The catalysts were studied under batch-wise as well as continuous operation conditions. AlCl3/MCM-41 showed higher activity than ZnCl2/MCM-41, while FeCl3/MCM-41, CuCl2/MCM-41 and NiCl2/MCM-41 were inactive under identical conditions. ZnCl2 offered some advantages due to reduced hydrolytic sensitivity and better selectivity. The optimized ZnCl2 loading of ZnCl2/MCM-41 was 4 mmol g−1. For AlCl3/MCM-41, the pore size of MCM-41 did not affect the activity nor the selectivity in the benzylation of benzene. Very low selectivity was observed in the benzylation of substituted aromatics using AlCl3/MCM-41 as catalyst due to a tendency for migration or transfer of the substituent group. With its inherently lower activity, ZnCl2/MCM-41 did not catalyze this reaction. In a continuous trickle bed reactor, sustained activity of the AlCl3/MCM-41 catalyst could be demonstrated. Hence, MCM-41 supported with AlCl3 or ZnCl2 may be promising candidates to replace AlCl3 in the industrial manufacture of diphenylmethanes.