Search

Abstract: Catalytic synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate was carried out over HZSM-5 with Si/Al ratios from 50 to 250. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH3-TPD) and pyridine IR techniques. As revealed by the results of NH3-TPD and pyridine IR spectra, a significant decrease in acidic strength and the number of acidic sites is observed with increasing Si/Al ratio from 50 to 250. The benzene conversion and ethylbenzene selectivity increases obviously with increasing Si/Al ratio from 50 to 200. With a further increase in Si/Al ratios, a slight decrease in the conversion of benzene and selectivity for ethylbenzene is detected, indicating that a proper acidic strength was required in this reaction. In addition, the effects of temperature and feed ratio on the catalytic activity and product distributions are also investigated in this study. [Copyright &y& Elsevier]

Abstract: Acidity adjustment of MCM-22 was carried out by hydrothermal treatment of parent MCM-22 with flowing pure steam at high temperature. XRD, SEM and N2 adsorption/desorption results indicated that the crystallinity and pore properties of MCM-22 were affected slightly by hydrothermal treatment at different temperatures. NH3-TPD and FT-IR with pyridine adsorption showed only a slight decrease in Brønsted acid sites, compared with parent MCM-22, with hydrothermal treatment temperature in the range 773–873K. The strength of Brønsted acid sites was reduced severely at hydrothermal treatment temperatures of 973 and 1073K. The Lewis acid sites were only slightly affected by hydrothermal treatment. A substantial improvement in ethylbenzene selectivity along with a slight decrease in benzene conversion was achieved in catalytic synthesis of ethylbenzene by alkylation of benzene with diethyl carbonate over MCM-22 hydrothermally treated at 873K. A sharp decrease in benzene conversion was detected over MCM-22 hydrothermally treated at 973K. The results indicate that alkylation of benzene with diethyl carbonate occurred mainly on Brønsted acid sites, and the effect of Lewis acid sites on the alkylation process is negligible. Reduction of Brønsted acid sites of the catalyst can suppress side reactions and improve selectivity for ethylbenzene. It was found that a particular acid strength of catalyst was required to maintain high benzene conversion and ethylbenzene selectivity. [Copyright &y& Elsevier]