Dimethyl ether carbonylation to methyl acetate over highly crystalline zeolite seed-derived ferrierite

摘要

Gas-phase carbonylation of dimethyl ether (DME) to methyl acetate (MA) was investigated on ferrierite (FER) zeolite having different Si/Al molar ratios of 10.4-12.5 as well as high crystallinity synthesized by using various zeolite seed materials such as MOR, ZSM-5 and USY. The enhanced crystallinity of the FER prepared by simply using FER seeds (denoted as FER@FER) having newly formed mesopore structures was responsible for an increased amount of active BrOnsted acid sites, which resulted in a higher MA productivity of 2.94 mmol g(cat) h(-1) with MA selectivity of above 99%. The highly crystalline FER@FER revealed the suppressed deposition of aromatic coke precursors due to the presence of fewer defect sites. Compared to other zeolite seed-derived FER zeolites, the lesser amount of defect sites (extra-framework Lewis acid Al species, EFAL) on the FER@FER was successfully controlled through a recrystallization process. The active BrOnsted acid sites for the DME carbonylation reaction mainly originated from the preferential formation of stable tetrahedral Al sites (especially the T2 sites of the Al-O-Si-O-Al framework of FER) on the 8- and 10-membered ring channels of the FER@FER. On those stable T2 sites having proper acid strength, the adsorbed methyl intermediates formed by the dissociation of DME can be transformed to acetyl adsorbates by a relatively faster CO insertion rate on the vicinal BrOnsted acid sites, which results in a high catalytic stability and activity of the highly crystalline FER@FER.