Topology-acidity-catalytic activity interplay in hierarchical nanolayered aluminosilicate zeolites for Friedel-Crafts alkylation

Abstract

Nanolayered zeolites are at the forefront of research as efficient catalysts for reactions involving bulky molecules. To date, various zeolites have been synthesized in nanolayered form via direct hydrothermal crystallization using Gemini-type surfactants, and their enhanced catalytic performance has been demonstrated in acid-catalyzed transformations of bulky substrates. However, the influence of zeolite topology on the strength and coordination environment of surface acid sites and its effect on catalytic behavior remains insufficiently understood. This study explores topology-acidity-activity relationships using a series of nanolayered aluminosilicate zeolites with FER, MFI, MOR, and BEA topologies in the alkylation of mesitylene with benzyl alcohol as a surface-acid-site-sensitive model reaction. In situ FTIR-monitored thermodesorption of substituted pyridines showed comparable surface Brønsted acid strength across the zeolites, while ²⁷Al MAS NMR spectroscopy revealed a topology-dependent increase in fraction of distorted tetrahedral Al sites: MFI (21 %) < FER (30 %) < MOR (57 %) < BEA (64 %). Catalytic activity increased with surface-accessible Brønsted acid site concentration (mmol/g) or density (mmol/m²) in nanolayered MFI, FER, and MOR, with FER showing the highest yield (37 %) and selectivity (84 %). This trend was disrupted in BEA, which, despite the reasonably high surface Brønsted acid site concentration, showed lower activity. The findings of this study highlight the impact of topology-dependent structural features on catalytic performance of nanolayered zeolites.