Highly selective synthesis of para-diethylbenzene by alkylation of ethylbenzene with diethyl carbonate over boron oxide modified HZSM-5

• Triethyl borate was used as the precursor of B2O3 to prepare B2O3/HZSM-5 catalysts.
• High para-selectivity is obtained in ethylbenzene alkylation with diethyl carbonate.
• The large molecular size of triethyl borate contributes to the shape-selectivity.

A series of B2O3/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 B2O3/HZSM-5 catalysts. The physicochemical properties of the catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, Fourier-transform infrared spectroscopy with pyridine adsorption and NH3 temperature programmed desorption. The characterization results indicated that the 15% B2O3/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 B2O3 on the external surface of HZSM-5 zeolite and preserve the acid sites in the micropores of HZSM-5 zeolite. By contrast, the B2O3/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.

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