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A series of B 2 O 3 /HZSM-5 catalysts were prepared by impregnation of HZSM-5 zeolites with triethyl borate, trimethyl borate and boric acid. The selective synthesis of para -diethylbenzene by alkylation of ethylbenzene with diethyl carbonate was carried out over the B 2 O 3 /HZSM-5 catalysts. The physicochemical properties of the catalysts were characterized by X-ray diffraction, N 2 adsorption–desorption, Fourier-transform infrared spectroscopy with pyridine adsorption and NH 3 temperature programmed desorption. The characterization results indicated that the 15% B 2 O 3 /HZSM-5 catalyst prepared by using triethyl borate as the precursor exhibited an outstanding shape-selectivity along with a high catalytic activity in alkylation of ethylbenzene with diethyl carbonate. This might be ascribed to the large molecular size of triethyl borate, which would lead to the formation of B 2 O 3 on the external surface of HZSM-5 zeolite and preserve the acid sites in the micropores of HZSM-5 zeolite. By contrast, the B 2 O 3 /HZSM-5 catalysts prepared by using trimethyl borate or boric acid led to the severe reduction in catalytic activity, which was attributed to the decrease in the amount of the total acid sites caused by the blockage of the partial pores of HZSM-5 zeolite. [ABSTRACT FROM AUTHOR]

Abstract: Shape-selective catalysts of MgO/MCM-22 were prepared by a novel two-step impregnation method and evaluated in the catalytic synthesis of p-xylene by alkylation of toluene with dimethyl carbonate. The two-step impregnation process combines the advantages of general impregnation and complexation impregnation for the preparation of metallic-oxide modified zeolite shape-selective catalysts. The coverage of the acidic sites on the external surface of the zeolite and the adjustment of the pore size of the zeolite can be achieved by two-step impregnation. Consequently, significant improvement in selectivity for p-xylene over the MgO/MCM-22 catalyst was realized. [Copyright &y& Elsevier]

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]