Study On The Supported HMS Catalysts For The Synthesis Of Diethyl Carbonate By Oxidative Carbonylation Of Ethanol

Diethyl carbonate (DEC) is a versatile compound that represents an attractive eco-friendly alternative to both ethyl halides and phosgene for ethylation and carbonylation processes, respectively. In recent years, diethyl carbonate is found to substitute for methyl tert-butyl ether (MTBE), which is used as an oxygen-containing fuel additive. In this paper, supported PdCl₂-CuCl₂ catalysts for the vapor phase synthesis of DEC by the oxidative carbonylation of ethanol in the gas phase were studied.Diethyl carbonate (DEC) has been produced by the oxidative carbonylation of ethanol in the gas phase over a heterogeneous PdCl₂-CuCl₂ catalyst supported on mesoporous HMS silica. The effects of the various quaternary ammonium salt (QAS) promoters and the promoter loading level were investigated. The catalytic performance of the PdCl₂-CuCl₂/HMS catalyst was greatly improved by the addition of promoter tetraethyl ammonium bromide (TEAB). Under the PdCl₂- CuCl₂-TEAB/HMS catalyst system, space time yield (STY) of DEC is 210.9 g /(L·h) , and conversion of EtOH is 13.6%. The functions of promoters were investigated on the basis of catalyst characterization and activity by means of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low-temperature electron spin resonance (ESR) spectroscopy, and infrared resonance (IR) spectroscopy. It can be concluded that the essential role of TEAB promoter is to improve the order degree of mesoporous structure, which is interrelated with the concentration of surface Si species.PdCl₂/Cu-HMS has been investigated, which demonstrated excellent selectivity to DEC by oxidative carbonylation of ethanol in the gas-phase reaction. The effects of various quaternary ammonium salt (QAS) promoters and promoter loading amounts were investigated. The catalytic performances of the PdCl₂/Cu-HMS catalyst were significantly improved by the addition of a promoter tetraethyl ammonium bromide (TEAB). From XRD, XPS, ICP and IR characterization and analysis, it can be concluded that copper species incorporated into HMS frame and was highly dispersed in the frame of silica. An optimized Si/Cu ratio exists for catalytic activity, which is about 50/1. The catalytic performances of PdCl₂/Cu-HMS with the different Si/Cu ratio of the Cu-HMS support are related with both Cu content in the Cu-HMS and the order degree of mesoporous structure for Cu-HMS. The catalytic reaction mechanism was illuminated by the interaction between Pd²⁺ loaded on the surface and Cu²⁺ in Cu-HMS frame.