Reaction‐Based Quantification of Surface Brønsted Acid Site Densities in Large‐Pore Zeolites and Their Consequences for Bulky Molecule Transformations

ABSTRACT This study extracts densities of surface Brønsted acid sites (SBAS) in large‐pore zeolites via reactions of bulky micropore‐excluded molecules. Self‐etherification of 1‐pyrenemethanol, a polycyclic primary alcohol not accessible to protons within medium‐ or large‐pore zeolites, was measured on a suite of zeolites. A linear correlation was established between extracted zero‐order rate constants and independently measured SBAS densities in a series of MFI zeolites and was extended to large‐pore frameworks. Parity among MFI, MOR, BEA, and FAU zeolites in SBAS‐catalyzed Hofmann elimination reactions indicated accurate SBAS quantification and was consistent with Brønsted acid strength that is independent of pore topology and location (i.e., internal, external, T‐site) in the absence of pore confinement effects. SBAS densities in the large‐pore frameworks were used to inform reaction mechanisms under severe internal diffusion limitation, as in polyolefin upcycling. Polyethylene (PE) catalytic cracking rates were found to be commensurate with increasing SBAS densities, although ingress of SBAS‐cleaved species still contributed significantly to rates. Extensively, SBAS densities—and the universal methodology employed to quantify them, herein—can be widely used to inform a broad range of catalytic systems involving diffusion‐limited or ‐prohibited molecules.