Preparation And Performance Study Of Pd-Cu/α-Al₂O₃ Catalyst In CO Coupling To Dimethyl Oxalate Reaction

In this paper,we focus on the preparation of dimethyl oxalate by CO coupling with methyl nitrite(MN)reaction system,the preparation and performance evaluation of nano-palladium-based catalysts are also carried out.The effects of the types and amounts of metal promotors,types and amounts of surfactants,types and amounts of organic complexes agent,aging time,synthesis temperature and ultrasonic time on physicochemical properties and catalytic properties of the catalysts are systematically investigated.The results show that the addition of Cu of the four metal promotors has the superior catalyst performance improvement effect of Pd/α-Al2O3 catalysts.TEM analysis shows that the catalyst prepared by n(Cu)/n(Pd)=1.5,Pd and Cu can be uniformly dispersed on the surface of the support α-Al2O3.The average particle size of the nanoparticles is 8～10 nm;XPS analysis shows that the precursor Na2PdCl4 is successfully reduced to Pd0,and CuCl2 is present in the form of Cu2O after reduction.HRTEM analysis shows that the surface of Pd-Cu/α-Al2O3 prepared by n(Cu)/n(Pd)=1.5 is exposed to Pd(111)crystal plane,which is beneficial to the CO coupling with methyl nitrite(MN)reaction.The catalyst performance results show that PVP as surfactant and anhydrous citric acid as organic complexing agent is more suitable for the preparation of Pd-Cu/α-Al2O3 catalyst,when the catalyst prepared by m(PVP)/m(Pd)=80 and n(C6H8O7)/n(Pd)=30,the average particle diameter of the prepared catalyst is 4 to 6 nm,and the dispersion degree of the active metal Pd has remarkably improved.The relative suitable control indexes of synthesis temperature,aging time and ultrasonic time are 30℃,8 h and 10 min respectively.Under this condition,the Pd actual loading increased from 0.32%to 0.42%,the result has been confirmed through the ICP analysis,and the average particle size of Pd nanoparticles has decreased to 4.0 nm.The catalyst performance evaluation result shows that the DMO selection and MN conversion of the catalyst prepared under this condition in CO coupling to dimethyl oxalate reaction are 94%respectively.Based on the above optimized synthesis conditions,Pd-Cu/α-Al2O3 catalyst(3～5 nm Pd grain,loading 0.5%),the industrial factor process conditions of CO coupling to dimethyl oxalate reaction are studied,we investigate the effect of reaction temperature,the ratio of CO:MN and space velocity in CO-MN coupling reaction.The results show that the relative optimum process conditions:reaction temperature is 130℃,reaction gas ratio is CO:MN=1.25:1 and space velocity is 4000 ml·h-1·g-1.In this industrial condition,the MN conversion and DMO selection were 95%and 95.4%respectively,the product yield of DMO is 90%。...