Design Of (Zn,Zr) Catalytic Materials And Their Application In The Preparation Of Dimethyl Carbonate By Transesterification Method

The synthesis of DMC by the transesterification reaction of PC and methanol has both economic and environmental advantages and is a very promising route for the preparation of DMC.Meanwhile,the by-product propylene glycol produced by this route one-for-one is also a widely used,high-value chemical.Most of the catalysts used in industry for catalytic transesterification reactions are homogeneous catalysts,such as sodium methanol,etc.Although their catalytic activity is excellent,separation is difficult and recovery is not easy.Therefore,it becomes more and more important to find efficient multiphase catalysts that can be easily separated from the products to replace the homogeneous catalysts for the transesterification reaction.Breaking traditional material design thinking and using suitable materials to reasonably construct the catalytic activity of heterogeneous catalytic materials is the key to achieving efficient catalysis.Zn-based heterogeneous catalytic materials are widely welcomed in the field of catalytic research due to their ease of preparation,nontoxicity,affordability,and high catalytic activity.In this paper,a series of Zn-based and zirconium-bonded materials have been reasonably constructed and successfully prepared for the transesterification of PC and methanol to synthesize DMC,effectively improving the yield and selectivity of DMC in the transesterification reaction.A series of characterization methods have been used to analyze and explore the physical and chemical properties,morphology,structure,and relationship between catalytic performance and catalytic performance of catalytic materials.The main research contents are summarized as follows:(1)A series of catalytic materials of microspheres were successfully prepared by hydrothermal and thermal decomposition methods.The layered structure exposed more active sites in the pore channels,and the calcination temperature had an effect on the integrity of the layered structure.Before zirconium doping,ZnO(300)microspheres had the largest pore capacity and the most uniform layered microsphere morphology.The catalytic performance of ZnO(300)microspheres was the best,with a selectivity of 89.3%and a yield of 52.4%DMC(reaction temperature:180 ℃,reaction time:4 h),but its stability was poor.To solve the problem of poor stability of the catalytic material,ZnO(300)microspheres were treated with Zr doping.The appropriate amount of zirconium doping resulted in strong Zn-Zr interactions.The performance test results of the catalyst proved the rationality of our material design.After zirconium doping,the 5%Zr doping greatly improved the stability of the catalytic material.Its selectivity decreased only 3.3%after three cycles,while the ZnO(300)microspheres showed a 15.7%decrease in selectivity after one cycle.This superior stability after ion doping not only makes the microsphere catalytic materials feasible for application in the field of transesterification reactions,but also provides new insights in doping modification.(2)In order to simplify the preparation method and improve the catalytic activity,we successfully prepared MOF series catalysts at room temperature and applied them to the reaction of PC and methanol transesterification reaction for the synthesis of DMC to test their performance.We found that the calcination temperature has a great influence on the morphology and specific surface area of the MOF series catalytic materials,and the specific surface area size is closely related to their catalytic performance.A series of characterization techniques reveal that if the calcination temperature is too low,the specific surface area of the catalytic material is too small and the surface active sites are not effectively activated;if the calcination temperature is too high,the skeleton of the catalytic material collapses and the specific surface area becomes so small that the catalytic active sites are lost.The catalytic performance test results showed that the best catalyst performance was achieved when the calcination temperature was 300℃,t e selectivity of DMC was 90.5%and the yield of DMC was 55.8%(reaction temperature:160 ℃,reaction time:4 h).The catalytic performance of the catalysts was improved to different degrees by different levels of zirconium doping,with the best catalytic performance achieved at 10%zirconium doping,with a DMC selectivity of 91.5%and a DMC yield of more than 56.6%(reaction temperature:160℃,reaction time:4 h).This performance,which is better than that of other metal-organic skeleton materials,will open up new avenues and ideas for the application of MOF in the synthesis of DMC by ester exchange reaction.(3)To further simplify the preparation method and improve the catalytic activity,we introduced ZnO/ZrO2 solid solution,prepared by the co-precipitation method,as a catalyst.The ZnO/ZrO2 solid solution created defective structures of coordinative unsaturation in the form of oxygen vacancies(Ov)by substituting Zn atoms for Zr atoms in ZrO2 crystals.Characterizations showed that electrons were transferred to the surrounding Zn atoms upon the formation of these Ov,leading to a local enrichment of electrons and the formation of basic active centers.The number of oxygen defects and the alkalinity were effectively regulated by changing the ratio of the two metal atoms in the solid solution.Experiments demonstrated that the catalyst had the best DMC selectivity(92.2%)and the highest DMC yield(57.2%)at a 1:1 ratio of Zn to Zr,at 160℃ and 4 h.This superior performance not only establishes the feasibility of solid solution catalysts in synthesizing DMC but also provides a new perspective on the essential understanding of the active centers of such catalysts.