Study On The Synthesis Of Dimethyl Carbonate Over Cu/AC Catalysts Prepared By Microwave Carbothermic Reduction Method

Dimethyl carbonate(DMC) is a non-toxic reagent, which was regarded as a new building block in the chemical industry. Because of its special structure, DMC is a replacement for toxic and dangerous reagents in methylation and methoxycarbonylation reactions. The applications of dimethylcarbonate cover several fields, such as medicine, pesticide, paint, batteries and so on. In all routs for the synthesis of DMC, the Vapor phase oxidative carbonylation method has attracted impressive attention because of its advantages of environment and economy. Since traditional chlorine catalysts often cause catalyst deactivation and equipment corrosion, chlorine-free copper catalysts are required.Microwave, as a rapid and uniform heating method, promotes to decrease the size of nanoparticles and enhance the interaction between active species and support. Introduce microwave irradiation to carbothermic reduction, not only decrease reaction time, but also improve efficiency.In this paper the microwave carbothermic reduction method is applied to prepare Cu/AC catalyst. As the reducing agent, AC support reduce copper oxide in situ. The main conclusions are listed as follows.(1) The effect of microwave heating rate on catalyst is caused mainly by decrease of grain size. The heating rate is enhanced and the grain size is decreased. The best heating rate is48℃/min.(2) The heating behavior of Cu/AC in microwave is carried out in three stages. The first stage, from room temperature to about100℃, shows the evolution of the hydration water and gases. The second stage, from100℃to about250℃, shows the decomposition of Cu2(OH)3NO3, the gasification of AC, the reduction of CuO by CO and the carbothermic reduction of Cu2O. The third stage, from250℃to350℃, shows the carbothermic reduction of Cu2O.(3) The content of Cu0is increasing with the rise of irradiation temperature. The smaller grain size leads to a higher active specific surface area, which promotes the weak adsorption of CO.(4) The addition of Li promotes to enhance the catalytic performance of Cu/AC. The best Li content is0.15wt%. The STYDMC reaches540.6mg/g-h, SDMC is81.4%and CCH3OH is4.5%.(5) The addition of moderate content of lithium into the Cu/AC catalyst enhances the auto-reduction of copper species to Cu0, leading to more well-dispersed Cu nanoparticles with more uniform grain size on the surface of active carbon. The Cu0specie is the main active centers for the synthesis of DMC. The addition of lithium enhances CO weak adsorption centers, which favors the insertion reaction between CO molecules and Cu-OCH3intermediates.(6) The addition of moderate content of lithium is benefit to enlarge the pore volume and aperture of catalysts. Compared with the specific surface area and structure of AC, the effect of Li promoter on the pore structure of catalysts is weak sufficiently. It can be negligible.