Acylation of anisole with acetic anhydride over Hβ/MCM-41 composite molecular sieves

Hβ/MCM-41 composite molecular sieves with different Si/Al ratios were synthesized by using β zeolites as the silicaalumina source of mesoporous phases. The catalytic performance of the as-synthesized composite molecular sieves in the acylation of anisole with acetic anhydride was evaluated and compared with that of mesoporous MCM-41 and microporous Hβ zeolites. The composite molecular sieve exhibits much higher stability than MCM-41 and Hβ. UVVis spectra and elementary analysis of the spent catalysts suggested that with the composite Hβ/MCM-41 as catalyst, the amounts of coke deposited during the reaction and C/H mol ratio of the deposited coke was much lower than that with Hβ as catalyst. The composite Hβ/MCM-41 is provided with both the strong acidity of microporous Hβ and the large pore of mesoporous MCM-41; the large pores in Hβ/MCM-41 facilitated the evacuation of heavier products from active sites of the molecular sieve and therefore preserve its catalytic activity provided by the strong acidity.