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Abstract: The MgO/MCM-22 catalysts were prepared by complexation–impregnation method and their shape-selective performances in the synthesis of para-dialkylbenzenes by alkylation of alkylbenzenes were investigated. Characterization results indicate that the dispersion of the Mg2+ complex is limited to the external surface of the zeolites during complexation–impregnation process, and this results in the nearly complete coverage of the external Brønsted acid sites. Consequently, the shape-selective catalysts prepared by complexation–impregnation method have improved shape-selectivity and maintain the high catalytic activity. Compared with the conventional method for preparation of shape-selective catalysts, the strategy developed here is simple and efficient. [Copyright &y& Elsevier]

Abstract: A novel, shape-selective H-MCM-22/MCM-41 composite catalyst is synthesized for the first time by overgrowing MCM-41 over the external surface of H-MCM-22. Results of FT-IR characterization with 2,4-dimethylquinoline adsorption indicate that the Brønsted acidic sites of H-MCM-22 located on the external surface can virtually be completely covered by the generated layer of MCM-41. When applied to the synthesis of p-xylene by the alkylation of toluene with dimethyl carbonate, the H-MCM-22/MCM-41 composite exhibits significant enhancement in p-xylene selectivity, which can be ascribed to the decrease in the number of external Brønsted acid sites of the composite. [ABSTRACT FROM AUTHOR]