Preparation And Performance Of Palladium Catalyst For Dimethyl Oxalate By Coupling MN And Co

In this paper,a novel supported palladium catalyst was prepared usingα-Al₂O₃as support by doping a large amount of copper auxilars.A series of catalysts were synthesized to prepare dimethyl oxalate（DMO）by coupling of methyl nitrite（MN）with carbon monoxide.The catalyst formulation and preparation process were optimized,and the effects of different temperature,raw material ratio and space velocity on MN conversion and DMO selectivity were investigated.Based on the optimized catalyst,the intrinsic kinetics of the target reaction was studied.Pd/α-Al₂O₃catalysts with and without copper additives were prepared by impregnation method and gas reduction method.The results show that the addition of copper additive can improve the activity and stability of the catalyst,and the life of the catalyst can be increased from 14h to more than24h.XPS analysis shows that Pd exists in the form of Pd²⁺and Pd⁰,while Cu exists in the form of Cu⁺.The effects of palladium loading rate,copper/palladium molar ratio,metal impregnation sequence and reduction temperature on the catalytic performance of the catalysts were investigated by single factor experiment.The results show that the conversion rate of MN and selectivity of DMO remain unchanged with the increase of palladium loading rate.With the increase of Cu/Pd molar ratio,the conversion rate of MN and selectivity of DMO first increased and then decreased.Compared with the step impregnation method,the catalyst prepared by co-impregnation method has better performance.The performance of the catalyst increased first and then decreased with the increase of reduction temperature.The optimum preparation conditions were determined as follows:theoretical palladium loading rate of 0.4%,copper-palladium molar ratio of 40:1,reduction temperature of 300℃and co-impregnation loading method.Using the catalyst prepared under the optimal conditions as the model catalyst,the effects of raw material ratio（CO:MN=0.5-2.0:1）,temperature（110～160℃）and space velocity(500～10000 ml·g^-1·h^-1)on the preparation of DMO from CO coupled MN were investigated by single factor experiment.The results showed that the conversion rate of MN and DMO selectivity increased first and then remained unchanged with the increase of CO in raw materials.With the increase of temperature,the transformation of MN increases first and then remains unchanged,while the selectivity of DMO increases first and then decreases.With the increase of airspeed,the transformation of MN first remains unchanged and then decreases,while the selectivity of DMO increases first and then remains unchanged.At 130℃,the ratio of CO:MN=1.5:1 and the airspeed 4000 ml·g^-1·h^-1,the conversion of MN and the selectivity of DMO reached the highest value,both exceeding 98%.Based on the optimized model catalyst,under atmospheric pressure,110～160℃and 20000 ml·g^-1·h^-1airspeed conditions,the intrinsic kinetics experiment of CO coupling MN reaction was carried out.The fourth-order Rungekutta method was used to analyze and optimize the experimental data,and the coupling reaction intrinsic kinetics model was established as shown below:...