Identification And Modulation On The Active Sites Of Cu/H-MOR Catalysts For The Carbonylation Of Dimethyl Ether

As an important chemical raw material and ideal alternative energy source of traditional fuels, ethanol has an expansive development potential and promising application foreground. Based on the energy structure of China, a novel syngas-to-ethanol route, including carbonylation of dimethyl ether(DME) to methyl acetate(MA) and hydrogenation of MA, is developed and has attracted much attention. It has been shown that H-MOR emerges enzyme-like specific selectivity for DME carbonylation reaction because of the spatial confinement effect of 8-member ring channels. Modification of H-MOR catalyst by Cu dopant leads to an obvious enhancement on the catalytic performance. This work focuses on identification of the copper active species in Cu/H-MOR and elucidation of their evolution during the preparation and reaction. Besides, it offers methods to modify Cu/H-MOR catalysts with more and better-dispered Cu~0 species in order to improve catalytic activity.Ion-exchange with copper ammonia solution and solid state ion-exchange with CuCl methods were applied to synthesize Cu/H-MOR samples with different Cu loading, labeled as Cu/H-M(x) and SSIE Cu/H-M(x) respectively. Compared with H-MOR, the reduced Cu/H-M(x) catalysts exhibited an enhanced DME conversion, while the DME conversion on SSIE Cu/H-M(x) samples descreased sharply with the increasing of Cu loading. To confirm the evolution of Cu species during prepareation, reduction and reaction process, the concentration and distribution of acid sites as well as the location and valence state of Cu species were characterized for as-prepared, reduced and spent Cu/H-M(x) samples. The quantitative relationship between Cu species and Br?nsted acid were established, and it is confirmed that there is a synergistic effect between Cu~0 and Br?nsted acid sites to improve the catalytic activity. Moreover, both the deterioration of pore structure for MOR and the aggregation of Cu~0 species would result in a negative impact on catalytic performance.In order to improve the availability of Cu and further enhance the catalytic acitivity, the modulation of reduction temperature and preparation methods was applied to obtain high dispersion of Cu~0 for Cu/H-MOR samples with low Cu loading. It was found that appropriate reduction temperature and ammonia evaporation process were beneficial to increase the amount of highly dispersed Cu~0. The DME conversion for Cu/H-MOR prepared by ammonia evaporation method was 30% higher than that prepared by ion-exchange with copper ammonia solution methods.