Contributions of post-synthesized mesopore structures of ferrierite zeolite for gas-phase dimethyl ether carbonylation activity

Improved catalytic performance in gas-phase dimethyl ether carbonylation over facile NH4F etched ferrierite

Gas-phase dimethyl ether (DME) carbonylation to methyl acetate (MA) initiates a promising route for producing ethanol from syngas. Ferrierite (FER, ZSM-35) has received considerable attention as it displays excellent stability in the carbonylation reaction and its modification strategy is to improve its catalytic activity on the premise of maintaining its stability as much as possible. However, conventional post-treatment methods such as dealumination and desilication usually selectively remove framework Al or Si atoms, ultimately altering the intrinsic composition, crystallinity, and acidity of zeolites inevitably. In this study, we successfully prepared a series of hierarchical ZSM-35 materials through post-treatment with NH4F etching, which dissolved framework Al and Si at similar rates and preferentially attacked the defective sites. Interestingly, the produced pore systems effectively penetrated the [100] plane, offering elevated access to both the 8-membered ring (8-MR) and 10-membered ring (10-MR) channels. The physicochemical and acid properties of the pristine and NH4F etched ZSM-35 samples were comprehensively characterized using various techniques, including XRD, XRF, FESEM, HRTEM, Nitrogen adsorption-desorption, NH3-TPD, Py-IR, 27Al MAS NMR, and 29Si MAS NMR. Under moderate treatment conditions, the intrinsic microporous structure, acid properties, and crystallinity of zeolite were retained, leading to superior catalytic activity and stability with respect to the pristine sample. Nonetheless, severe NH4F etching disrupted the crystalline framework and created additional defective sites, bringing about faster deposition of coke precursors on the interior Brønsted acid sites (BAS) and decreased catalytic performance. This technique provides a novel and efficient method to slightly enhance the micropore and mesopore volume of industrially pertinent zeolites through a straightforward post-treatment, thus elevating the catalytic performance of these zeolites.

Recent Advances in the Seed-Directed Synthesis of Zeolites without Addition of Organic Templates

Zeolites have been widely employed in fields of petroleum refining, fine chemicals and environmental protection, but their syntheses are always performed in the presence of organic templates, which have many drawbacks such as high cost and polluted wastes. In recent years, the seed-directed synthesis of zeolites has been paid much attention due to its low-cost and environmentally friendly features. In this review, the seed-directed synthesis of Al-rich zeolites with homonuclear and heteronuclear features, the seed-directed synthesis of Si-rich zeolites assisted with ethanol and the utility of seed-directed synthesis have been summarized. This review could help zeolite researchers understand the recent progress of seed-directed synthesis.