Assessing Inter and Intra-particle Heterogeneity in Alumina-poor H-ZSM-5 Zeolites

We reveal the presence of significant variations in Brønsted catalytic activity within and between individual H-ZSM-5 zeolite crystals. Fluorescence microscopy in combination with a fluorogenic probe was used to resolve the catalytic activity at the nanoscale. The observed variations in catalytic activity could be directly linked to structural parameters and crystal morphology observed in scanning electron microscopy and by specifically staining crystal defects. The obtained results are directly compared with ensemble averaged information from techniques such as pyridine IR spectroscopy and nitrogen physisorption, typically used to characterize acid zeolites. The inter- and intra-particle heterogeneities resolved by the employed fluorescence approach remain unaddressed by bulk characterization. Our experimental results relate the heterogeneous catalytic activity to variation in both the Si/Al ratio and mesoporosity induced during the zeolite synthesis.