In Situ DRIFTS Study Of Oxidative Carbonylation To Dimethyl Carbonate Over Cuβ Catalyst

Dimethyl carbonate （DMC） is a widely used green chemical. It can be used tosynthesize a variety of organic intermediates and pharmaceutical products, and it canalso be a gasoline additive to improve gasoline quality. Oxidative carbonylation toDMC follows the principles of green chemistry, and the byproduct is water, so it hasbright prospect for development. As a kind of chlorine free zeolite catalyst, Cuβcatalyst shows a good selectivity and it is an excellent catalyst for oxidationcarbonylation. In this paper, oxidative carbonylation to dimethyl carbonate over Cuβcatalyst was studied using in situ diffuse reflectance infrared Fourier transformspectroscopy（in situ DRIFTS）.The adsorption of reactants and products were investigated, including methanol（CH₃OH）, carbon monoxide （CO）, dimethyl carbonate （DMC） and so on. Resultsshowed that methoxy could be formed during CH₃OH adsorption due to the presenceof lattice oxygen. There was only one active site on Cuβ catalysts and MMC can begenerated by the decomposition of the DMC on Cuβ catalyst.The adsorption order of three reactants was changed. It indicated that O₂favoredthe generation of methoxy and formate species. It was competitive adsorptionrelationship between CH₃OH and CO, but CH₃OH adsorbed stronger than CO.Di-methoxy species was indirectly confirmed and DMC could be generated morewhen CO adsorbed after CH₃OH.The reaction mechanism for DMC synthesis on Cuβ catalyst was investigated.The resluts showed that there were two pathways of the mechanism: mono-methoxidepathway and di-methoxide pathway. Carbon monoxide can react withmono-methoxide species to form monomethyl carbonate（MMC） and MMC can reactwith methoxide to form DMC, and DMC can also be formed through carbonmonoxide inserting the di-methoxide species. The di-methoxide pathway was morelikely to carry out on Cuβ catalyst.