The Study Of Cu Based Catalyst For Hydrogenation Of Dimethyl Oxalate To Produce Ethanol

Ethanol（EtOH）is an important green and environmentally friendly chemical raw material and is widely used as preservatives,solvents,disinfectants,etc.In recent years,methyl tert-butyl ether has proven to be a potential environmental pollutant.Thus,ethanol is used as an additive to enhance gasoline octane level.With the implementation of our country’s policies for ethanol gasoline,the market demand of fuel ethanol will be enormous.In China,the storage of coal is relatively abundant than oil and natural gas.Thus,the conversion of coal to EtOH may be a route to relax the pressure in the near future.The synthesis of ethanol by one-step hydrogenation of dimethyl oxalate（DMO）represents a highly efficient way.A high active and stable hydrogenation catalyst play an important role in this route.Traditionally,the Cu-based catalyst is widely applied in the hydrogenation of DMO to ethylene glycol（EG）.However,a poor thermal stability and low selectivity of the target product ethanol was observed when the traditional Cu catalyst was used in hydrogenation of DMO to ethanol.These restrict their further commercial application.Therefore,catalyst design is crucial to the selective hydrogenation of DMO to ethanol.Compared with traditional copper-based catalysts,the bifunctional character of this Re-Cu catalysts,the oxophilic Re sites favour C-O bond hydrogenolysis,particularly from methyl glycolate to methyl acetate,and the copper sites promote the hydrogenation of the C-O bond.N₂ adsorption revealed that ammonia evaporation method endows catalyst with sufficient surficial area.XRD and TEM revealed good thermal stability of Re-Cu catalysts.XPS and CO-FTIR revealed intense interaction between Re and Cu.Under the optimal reaction conditions:T=230℃,WLHSV（DMO）=0.36 h^-1,P=1.5 MPa,H₂/DMO=280,the conversion rate of DMO is 100%,the selectivity of ethanol is 91.6%.And excellent stability performance was further demonstrated in an 800 h time-onstream test without any apparent catalyst deactivation.In addition,the both of Re₅Cu₅/SiO₂ and Re₅Cu₂₀/SiO₂ catalyst exhibited excellent performance,indicating that Re-Cu/SiO₂ can achieve good activity at a low copper content.Furtherly,a series of Re-Cu catalysts were prepared by a co-impregnation method with TiO₂,SiO₂,ZrO₂,Al₂O₃,and active carbon（AC）as support.The Re₂Cu₅/ZrO₂ catalyst exhibited the best catalytic performance due to the strong metal-support interaction when ZrO₂is used as a carrier.N₂ adsorption revealed that supports play enormous impact on surficial area of catalysts.XRD and TEM revealed that thermal stability of Re-Cu catalysts can be adjusted by supports.XPS and CO-FTIR revealed that electronic effect of Re-Cu catalysts can be adjusted by supports.Under the optimal condition:T=250℃,P=5.5 MPa,H₂/DMO=350,WLHSV（DMO）=0.29 h^-1,a DMO conversion 100%,and the ethanol selectivity 93% was obtained.