Acidity-enhanced Al-MCM-41 synthesized by phase transformation of MWW-type zeolites for the liquid-phase alkylation of lignin-derived phenolic compounds

Abstract

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 ²⁹Si and ²⁷Al MAS NMR, NH₃-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.