Carbonylation Of Dimethyl Ether To Methyl Acetate Over Zn-modified Mordenite Zeolites

A novel route to produce ethanol,which contsists of carbonylation of dimethyl ether?DME?to methyl acetate?MA?and the hydrogenation of MA to ethanol,has attracted worldwide attention.The key to the process is to develop a DME carbonylation catalyst with high activity and high stability.In this paper,the zinc modified mordenite catalysts?H-Zn-MOR?were directly synthesized by hydrothermal method.We investigated the effect of the content of Zn²⁺on the carbonylation performance of the H-Zn-MOR catalysts.We found that with the increase of Zn²⁺content,the catalytic performance of the catalysts for carbonylation of DME increases and then decreases,showing a"volcano type"trend.The Zn-0.005 catalyst shows the best catalytic performance for carbonylation of DME among all the catalysts.TEM,EXAFS and XPS results indicate that isolated Zn²⁺ions exist at the ion-exchange sites of MOR.H₂O-TPD,NH₃-TPD and ²⁷Al-MAS NMR results show that the introduction of Zn affects the content and the distribution of the acid sites on the catalysts.The introduction of Zn selectively reduces the acid sites in the 12 membered ring of MOR and reduces the rate of carbon deposition during carbonylation of DME.We investigated the effect of the complexing agents on the catalytic performance of the H-Zn-MOR catalysts for carbonylation of DME.When the complexing agents were added,the amount of Zn²⁺in MOR was increased.The initial activity for carbonylation of DME over the catalysts is in the order of Zn-NH₃>Zn-CA>Zn-0.005.However,the order of the stability of the catalysts is the opposite:Zn-NH₃<Zn-CA<Zn-0.005.The NH₃-TPD results show that the introduction of the complexing agent changes the acid strength of the catalyst and the distribution of the acid sites.We think this is the cause of the change in the activity and the stability of the catalysts.The Zn²⁺modified HMOR catalyst was prepared by ion exchange method.Compared with the HMOR catalyst,the initial activity of Zn-IE catalyst for carbonylation of DME was reduced,but the stability of the catalyst was improved.