Selective staining of zeolite acidity: Recent progress and future perspectives on fluorescence microscopy

This perspective article highlights recent methodical approaches for probing acid sites in zeolites using selective chemical staining methods. Research and method development on model systems (large zeolite crystals) is presented in close relation to the investigation of industrially relevant catalyst particles for Fluid Catalytic Cracking (FCC) and zeolite-based extrudates. The article begins with an (1) introduction on characteristics of zeolites and industrial catalyst particles, followed by a methodical overview on (2) probing acidity in zeolites, including temperature programmed desorption (TPD), solid state nuclear magnetic resonance (NMR) spectroscopy, and infrared (IR) spectroscopy. Instrumental details on (3) fluorescence microscopy are provided to prepare for the focus on (4) selective staining by probe molecules and oligomerisation reactions to highlight or distinguish materials (i.e. zeolite vs. binder or matrix components) and visualise acid sites within zeolites. Confocal fluorescence yields, in contrast to the other discussed techniques, a high spatiotemporal resolution giving way to exciting prospects such as probing single (fluorescent) reaction products. (5) Concluding remarks and future perspectives envision how Brønsted and Lewis acid sites can be investigated selectively. Sections: (1) Introduction (2) Probing acidity – methodical overview (3) Confocal fluorescence microscopy – instrumentation (4) Selective staining (5) Concluding Remarks and Future Perspectives