Dehydrochlorination of 1,2-dichloroethane over Ba-modified Al2O3 catalysts

摘要

Bimodal mesoporous alumina (Al2O3) was prepared using polyethyleneglycol (PEG 20 000) and cetyl trimethyl ammonium bromide as a template. The incorporation of Ba with various loadings was carried out by incipient wetness. Characterization was performed by XRD, N-2 sorption isotherms, and pyridine FTIR. Ba can be highly dispersed on Al2O3 covering the strong acid sites of Al2O3. In the catalytic dehydrochlorination of 1,2-dichloroethane (1,2-DCE), the Ba/Al2O3 catalysts present a high activity, of which Al2O3 is most active with 95% conversion at 325 degrees C, related to the more Lewis acidic Al3+ sites in a tetrahedral environment. 1,2-DCE adsorbs dissociatively on Lewis acid-base pair sites, forming chlorinated ethoxy species, which are supposed to be intermediate species for vinyl chloride (VC) production. At a temperature higher than 400 degrees C, the dehydrochlorination of VC occurs on the strong acid sites of Al2O3. Ba can promote greatly the selectivity for VC through a decrease in the strong acid sites. A high stable activity for dehydrochlorination and high selectivity for VC can be obtained over Ba/Al2O3 in the presence of oxygen.