Identifying the Active Silver Species in Carbonylation of Dimethyl Ether over Ag−HMOR

As one of the key steps in ethanol production from syngas, dimethyl ether (DME) carbonylation to methyl acetate (MA) catalyzed by zeolite has drawn much attention. H-mordenite (HMOR) modified with metal has been continuously developed for improving catalytic performance. Here, we investigated the role of Ag species through three series of Ag-HMOR catalysts prepared through altering Ag loading, varying reduction temperature and additional ion exchange. TEM, XPS, CO FTIR and UV-Vis spectroscopy were employed to identify the nature and the amount of Ag species in xAg-HM with different Ag loading. Taken together with catalytic performance evaluation, 5Ag-HM with the moderate size of Ag-0 species (Ag-n(delta+) and Ag-m clusters) was proved to have greatest promotion effect on DME carbonylation. This was also evidenced by further improved MA formation rate over catalysts via elevating reduction temperature or via additional NH4Cl ion exchange, which contained more Ag-0 and fewer Ag+ species respectively. These provide insight into metal-modified HMOR, inspiring design and fabrication of zeolite catalysts with multi-active sites.