Synthesis of diethyl oxalate by transesterification of dimethyl oxalate with ethanol over ZnO catalyst
ZnO samples,synthesized with different morphologies and characterized by XRD,N2 low temperature physical adsorption,XPS,SEM and CO2-TPD,were employed as catalysts for the synthesis of diethyl oxalate(DEO)from transesterification between dimethyl oxalate(DMO)and ethanol(EtOH).The structure-activity relationship between ZnO morphology and its catalytic performance was analyzed,while the influence of reaction conditions on DMO conversion and DEO selectivity were investigated.Moreover,the catalyst deactivation after repeated use and the reaction kinetics were explored.The results showed that the catalytic activity of ZnO samples was closely related to their morphologies,with the flower-like ZnO(ZnO-f)exhibiting the best performance.The DMO conversion rate and DEO selectivity over ZnO-f catalysis reached 99.8%and 75.8%,respectively,under the optimal reaction conditions of DMO 1.18 g,n(EtOH)∶n(DMO)=12∶1,ZnO-f dosage 2.0%of the mass of DMO,reaction temperature 80℃,and reaction time of 120 min.The DEO selectivity decreased to 25.7%after four cycles of ZnO catalyst,respectively.The deactivation of the catalyst was attributed to the formation of Zn(OH)2 phase leading to a sharp decrease in the total number of basic sites and the loss of oxygen vacancies.The transesterification of DMO with ethanol over ZnO-f catalyst displayed an activation energy of 35.6 kJ/mol,and the abundant medium basic sites over ZnO-f contributed to its excellent catalytic activity in the transesterification reaction of DMO with ethanol,while the presence of strong basic sites would inhibit the progress of the reaction.
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