Carbonylation of dimethyl ether over MOR and Cu/H-MOR catalysts: Comparative investigation of deactivation behavior

MOR zeolite exhibits high initial activity and selectivity to the target product in the carbonylation of dimethyl ether to methyl acetate, but suffers a rapid deactivation due to the carbonaceous deposits on Bronsted acid sites. The nature and evolution of the carbonaceous deposits have been fully characterized using TGA, C-13 NMR spectroscopy, FTIR, UV-vis and N-2 physisorption. The results reveal that the carbonaceous species are mainly alkylated aromatic species and the micropore volume of the spent catalysts decreases with increasing the coke content. Meanwhile, the amount of Bronsted acid sites in the 12 membered ring (B12-MR) declines during the reaction with no significant change of Bronsted acid sites in the 8 membered ring (B8-MR). As the B8-MR is generally accepted as active sites for this reaction, the deactivation can be linked to the coke deposition in the 12 membered ring channels of zeolite and block of the main channels. Furthermore, a kinetic model for coke formation is proposed to compare the deactivation behaviors of H-MOR with Cu/H-MOR. In terms of activation energies for the formation of carbonaceous species, the presence of Cu accelerates the formation of non-condensed single aromatics species, but inhibit them to be more condensed.