Solid acidic Al-MCM-41 materials are characterized by a high specific surface area and well-ordered hexagonally shaped mesopores. However, their relatively weak acidity compared to microporous zeolites significantly limits their practical applications in industrial catalytic reactions, particularly in upgrading biomass-derived organic feedstock that involves reactions with bulky molecules. Herein, we report a novel synthesis route for preparing acidity-enhanced Al-MCM-41 through the phase transformation of MWW-type zeolite precursors. The phase transformation approach markedly facilitates the incorporation of aluminum species into the MCM-41 framework, leading to strong Brønsted acidity of the resultant Al-MCM-41-T samples, as evidenced by comprehensive characterizations including 29 Si and 27 Al MAS NMR, NH 3 -TPD, and Py-IR. Owing to the enhanced acidity and its large pore structures, the as-prepared Al-MCM-41-T-15 sample (with Si/Al = 15) exhibited superior activity and selectivity toward C-alkylated products in both liquid-phase phenol-cyclohexanol and 4-cyclohexylphenol (4-CHP)-cyclohexene alkylation reactions compared the commercial Al-MCM-41-C with a similar Si/Al ratio. These findings afford an effective approach for preparing acidity-enhanced mesoporous solid acids, which hold significant potential for catalyzing lignin-derived bio-oils.
Ben Liang,Meng-Nan Liu,Ning An,Fang Ren,Qun-Xing Luo,Huiyong Chen,Jun Hu,Xiaoxun Ma,Qing-Qing Hao
The environmentally benign and long-lived zeolite catalyst is highly desired for Friedel-Crafts (FC) alkylation of benzene with long-chain olefins. Herein, MWW zeolites with different layer arrangements and surface structures are employed as model catalysts to investigate the effects of microscale structure on the catalytic behaviors for the alkylation of benzene with 1-dodecene. It is revealed that two kinds of acid sites located on the external surface and within surface 12-membered ring (12MR) pockets of MWW zeolites are effective for this reaction. Unexpectedly, the turnover frequency (TOF) of the effective acid sites over single-layer MWW (SL-MWW) is significantly lower than that of MCM-22. Kinetic study indicates that apparent activation energy ( E a ) is decreased in the order of MCM-36 > MCM-22 > SL-MWW. Combined with DFT calculation, the lowest TOF and E a over SL-MWW can be reasonably attributed to the higher proportion of acid sites in the 12MR pockets and its higher diffusional limitation for products. Moreover, the highest E a of MCM-36 and adsorption energy verified the decreased diffusion limitation of 12MR pockets due to the structure defect resulting from the desilication. Finally, the highly efficient and stable MCM-36 catalyst was achieved in the optimal reaction conditions, which is a potential catalyst for industrial application in the field of FC alkylation reactions.
Zeolite nanosheets are a burgeoning class of two-dimensional (2D) nanomaterials due to their fascinating properties and diverse applications. However, the effective and controllable preparation of advanced 2D zeolite materials with hierarchical structure and enhanced properties still needs to be investigated. Here, we report highly dispersed oligolayer MWW nanosheets (ca. 2–4 layers) with c-axis-penetrated mesopores, prepared by H2O2-induced micro-explosion coupled with ethanolamine pre-treatment from the multilayered precursor MCM-22P. The vertically aligned mesopores are well merged with intrinsic microporosity within MWW oligolayers with structural integrity. Meanwhile, the removal of OSDA and surface-grafted ethanolamine can be simultaneously achieved apart from the construction of the hierarchical structure. The porosity can be easily regulated by adjusting the H2O2 content, while the framework structure, composition, and intrinsic acidity are retained. Furthermore, benefiting from the greatly improved accessibility of intralayer 10-MR sinusoidal channels, the c-axis-penetrated mesoporous MWW zeolite nanosheet shows enhanced adsorption/diffusion properties and catalytic performances for bulky substrate conversion. This work provides a synergetic post-treatment method for the more rational and controllable design and application of novel layered hierarchical zeolite catalysts, and the efficient and versatile approach reported here shows great potential for industrial applications.
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