Prepration And Application Of Copper-based Catalysts For Ethylene Glycol Synthesis Via Dimethyl Oxalate Gas-phase Hydrogenation Procedure

Ethylene glycol(EG),an important and versatile organic compound as well as intermediate,is widely used.The two-step route of EG synthesis,combining the coupling of syngas with nitrate esters to gain dimethyl oxalate(DMO)with the following hydrogenation of DMO to EG,can not only avoid the pollution problems caused by the conventional approaches,but also make full use of the abundant coal resources of our country which is consistent with our energy structure and is considered as a green process both in economy and technology.Cu/SiO2 is the most commonly used catalyst for ester hydrogenation.However,it has disadvantages like being sensitive to temperature and of poor thermal stability.Herein,the thermal stability and catalytic performance are improved by adding promoter Zn to the impregnation-synthesized Cu/SiO2 catalyst or making full use of the preparation parameters of the deposition-precipitation method.The main content and results are as follows.A series of catalysts with different copper loadings were prepared by incipient wettness impregnation method.By comparing the characterizations like BET,XRD,TPR,etc.,with the activity test results,it's found that the opimal loading is 20 wt%.Then Zn was added as a promoter for improving the dispersion and the reducibility of the active metal where copper loading was the optimal value.Through the characterization and corresponding activity test,a dope of 0.5 wt%Zn was found to function best,giving a conversion of 98.41%and an EG selectivity of 71.92%,exceeding largely those of the Cu20I catalyst under the same reaction conditions.Two series of catalysts,namely 0703 and 0715,were prepared using precipitation-deposition/ion-exchange method.Characterization results elucidated that the physical stucture,surface copper species as well as the reducibility of the two series were completely different,leading to the totally different catalytic performance in DMO hydrogenation directly.After studying the effect of ammonia amount used on the Cu0/Cu+ ratio of 0703 series catalysts,it was found that this ratio descented with the increasing amount of ammonia and that the selectivity of EG was related to the ratio within the experiment range.Using 2.5 ml of concentrate ammonia(n(NH3)/n(Cu2+)=0.9)for precipitation,a suitable Cu0/Cu+ratio could be obtained after reduction,gaining a conversion of 99.81%as well as an EG selectivity of 93.12%.After studing the changes of the surface particles of 0715 series catalysts under different reduction temperatures,it's found that the catalysts were of high thermal stability,and when comparing the selectivity of EG with the surface Xcu0,a similar change of the two was found within the experiment range.The catalyst reduced at 573 K had the highest surface Xcu0 and when applying to DMO hydrogenation a conversion of 99.65%and an EG selectivity of 93.86%were obtained.