Preparation And Performance Study Of Supported Palladium-based Catalysts For The Reaction Of CO And MN Coupling To Dimethyl Oxalate

The forceful demand for polyesters drives the development of China’s ethylene glycol industry,coal to ethylene glycol(CTEG)technology has been promoted in China because the traditional ethylene glycol process is too dependent on petroleum resources,but how to use coal resources cleanly and efficiently is still a topic worthy of in-depth study.In this paper,we take dimethyl oxalate by coupling reaction of CO and methyl nitrite as the object,the preparation and performance of supported catalyst with palladium as major active component were studied.CuPd@Pd/α-Al2O3 and Cu-Pd/α-Al2O3 catalysts were prepared by the liquid-phase reduction method.The effect of the presence of Cu on the surface of the catalyst on the structure and performance of the nanoparticles was investigated by a combination of experimental evaluation and characterization analysis(XPS,EDS,HRTEM,etc.).The results show that when CuPD alloy is the main inner layer and Pd metal is the main outer layer of nanoparticles on the catalyst surface,the methyl nitrite conversion rate can reach 88.6%,and the selectivity of dimethyl oxalate is 95.2%.If Cu does not nucleate with Pd and only dispersed on the surface of the catalyst,a catalyst with Cu-Pd/α-Al2O3 structure will be formed,the conversion rate of methyl nitrite and the selectivity of dimethyl oxalate can only reach 83%and 89%,respectively.Compared with NaCl and NaI,the CuPd@Pd/α-Al2O3 catalyst prepared with NaBr as an additive has better coupling catalytic performance.When the amount of polyvinylpyrrolidone,synthesis time,Pd loading,and ultrasonic time are respectively:m(PVP)/m(Pd)=1.5,1.5 h,0.8wt%,10 min,it is more suitable to prepare the catalyst,the conversion rate of methyl nitrite is increased by about 4%compared with catalyst before optimization.The characterization result of the catalyst prepared under the optimized conditions is still CuPd@Pd/α-Al2O3 structured catalyst.Using XPS to determine the valence state of Pd,calculate the CuPd bimetal accounts for 32.6%and the shell metal Pd accounts for 55.6%.Based on the optimized CuPd@Pd/a-Al2O3 catalyst,the single factor experiment method was used to investigate the influence of temperature(100℃-150℃),feed gas ratio(CO/MN=0.5-2.5),space velocity(2000 ml·h-1·g-1-6000 ml·h-1·g-1)on the catalyst performance.The final relatively suitable process conditions for this catalyst are:140℃,CO/MN=1.75,and Space velocity is 4000 ml·h-1·g-1.Under these conditions,the conversion of methyl nitrite and the selectivity of dimethyl oxalate are 96%and 96.6%,respectively.