Elucidating the Acidic and Textural Properties of ZMQ-1, a 28-membered Ring Mesoporous Aluminosilicate Zeolite

ZMQ-1 is a recently discovered aluminosilicate zeolite featuring atomically ordered mesopores (28 × 10-membered rings), providing a unique, intrinsically bimodal micro/mesoporous framework. This study systematically investigates how residual inorganic phosphate species, derived from the biphosphonium organic structure-directing agent, influence the textural and acidic properties of the material. Using argon physisorption, solid-state NMR, in situ FTIR, and DFT calculations, we demonstrate that vacuum calcination or targeted postsynthetic washing (NH₄Cl, CsNO₃) removes ∼90% of residual phosphorus species, which otherwise severely diminishes Brønsted acid sites density and accessibility. Crucially, the determination of accurate molar extinction coefficients for pyridine and 2,6-di-tert-butylpyridine revealed that residual phosphorus markedly hinders probe molecule accessibility and diminishes acid strength. DFT modeling identifies preferred Al substitution sites that orient Brønsted protons toward the 28-MR mesoporous channels. The catalytic potential of this architecture was interrogated via the sterically demanding alkylation of 2,4-di-tert-butylphenol with tert-butyl alcohol. Phosphorus-free ZMQ-1 achieves a 15.5% yield of the bulky target, 2,4,6-tri-tert-butylphenol─a 31-fold increase over hierarchical USY (0.5%) and vastly outperforming amorphous-walled Al-MCM-41. These findings establish ZMQ-1 as a landmark catalyst bridging the gap between zeolitic acidity and mesoporous accessibility and further push the catalytic operating boundaries of nanoporous solid acid catalysts.