Accessibility of Acid Sites and Catalytic Performance of FCC Catalysts on Different Matrices Studied by Super-Resolution Fluorescence Microscopy

Abstract

The accessibility of acid sites in fluid catalytic cracking (FCC) catalysts is a decisive factor influencing their catalytic performance. This study selected three FCC catalysts with different matrices (CAT-1: pure kaolinite; CAT-2: 90 wt% kaolinite +10 wt% APM-7; CAT-3: 90 wt% kaolinite +10 wt% APM-9). By combining super-resolution single-molecule fluorescence microscopy (N-STORM), confocal microscopy, and multiple characterization techniques (SEM, N₂ physisorption, NH₃-TPD, Py-FTIR), we systematically investigated the influence mechanism of matrix structure on acid site accessibility and catalytic performance. For the first time, nanoscale visualization of acid sites on FCC catalyst surfaces was achieved through fluorescence oligomerization of thiophene probe molecules at Brønsted acid sites. The results demonstrate that CAT-2, owing to the incorporation of APM-7, exhibits optimal pore connectivity (mesopore volume: 0.179 cm³/g) and Brønsted acid density (0.199 mmol/g). This significantly enhances acid site accessibility, leading to a more than 2-fold improvement in thiophene conversion efficiency compared to CAT-1. This study not only provides a novel strategy for the rational design of FCC catalysts, but also demonstrates the unique advantages of super-resolution fluorescence microscopy in investigating active sites of heterogeneous catalysts, offering critical theoretical support for industrial catalyst optimization.