Study On Metal Carbide Catalysts For The Hydrogenation Of Dimethyl Oxalate To Ethanol

Ethanol?EtOH?,as a promising fuel alternative,gains much attention from industry researchers.Due to the“deficient oil,rich gas”energy structure in China,the route of ethanol synthesis from syngas via dimethyl oxalate?DMO?hydrogenation has the advantages of mild reaction condition,little by-production and environment protection,which could decrease the over-dependence on oil resources.Therefore,this technology exhibits a prospective future in industrial application.Transition metal carbides?TMC?are produced by incorporating C atoms into the interstitial sites of traintion metal atoms.It is now well established that TMCs often show catalytic properties similar to Pt-group metals in hydrogenation,dehydrogenation and hydrogenolysis reactions.Furthermore,TMCs exhibit some advantages than Pt-group metal catalysts due to their features of extreme hardness,high melting temperatures,corrosion resistance and low price.Now,TMCs have been widely used for industrial production.We screen a series of TMCs for the hydrogenation of DMO to EtOH.The presence of acid sites in W,Zr and Ti-based catalysts resulted in the formation of methanol,followed by the sequential dehydration of methanol to dimethyl ether.However,Fe-based catalyst showed excellent activity and selectivity of EtOH.To further insight into the performance and structure-activity relationship of Fe-based catalyst in hydrogenation of DMO to EtOH,the effect of the carbonization temperature,reaction temperature and reactor WHSV was systematically studied.Fe₅C₂ spcices was proved to be the main active sites for the hydrogenation.Higher carbonization temperature contributed to the formation of Fe₅C₂ spcices.Over the traditional Cu-based catalyst,methyl glycolate?MG?is first generated by DMO hydrogenation,ethylene glycol?EG?is subsequently obtained via the MG hydrogenation and finally EtOH is achieved by deep hydrogenation of EG.However,the reaction route on the Fe-based catalyst is much different with that on copper-based catalyst.Upon Fe-based catalyst,the C-O bonds of intermediate MG is preferentially hydrogenated with the formation of methyl acetate?MA?,which is further hydrogenated to EtOH.A higher EtOH selectivity of 89.6%can be obtained with DMO conversion of 100%at the optimal reaction conditions(533 K and WHSV=0.2 h^-1).When the WHSV was increased to 0.8 h^-1,the conversion of DMO was kept at 100%with the selectivity of EtOH as high as 75%.The excellent performance of Fe-based catalyst in the preferential hydrogenation of DMO to ethanol opens a new route for the industrial production of ethanol.Based on above findings,Ag-Fe₅C₂ catalyst was further fabricated and tested in the hydrogenation of DMO to EtOH.It was found that the strong interaction between Ag and Fe-based catalyst promoted the formation of more Fe₅C₂ species.15Ag-Fe₅C₂presented higher ethanol selectivity of 91.6%at DMO converstion of 100%under the reaction conditions:T=533 K,P=2.5 MPa,WHSV=0.2 h^-11 and H₂/DMO=180.