ZHANG Jialiang, XUE Bing, XU Jie, LIU Ping, LI Yongxin*

(Institute of Petrochemical Technology, Changzhou University, Changzhou 213164, China)

Abstract: MgO modified MCM-22 was prepared by complexation impregnation method in the present of malic acid as the complexing agent. Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate (DMC) was carried out in a continuous flow fixed-bed rector over MgO-modified MCM-22 zeolite. Physico-chemical properties of the catalysts were characterized by means of XRD, NH₃-TPD, pyridine-IR and BET. It was found that under the optimal conditions, i.e. reaction temperature of 380℃, n (toluene): n (DMC) of 4 and WHSV of 1 h^-1, the conversion of toluene and the selectivity to p-xylene were 29.0 % and 48.2 %, respectively. The results of characterization show that the complex compounds derived from the malic acid-coordinative Mg²⁺ loaded only on the external surface of MCM-22 and did not enter the pores. As a result, the cover of the external acidic sites and the protection of the inner acidic sites of zeolite can be achieved simultaneously. Consequently, catalysts prepared by complexation impregnation method exhibits high para-selectivity along with high activity in alkylation of toluene with DMC.

Key words: complexation impregnation; shape-selectivity; MCM-22; p-xylene

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Journal of Molecular Catalysis, Vol. 25, Issue 6, 2011, 514-519