Zeolites are microporous materials that are used as heterogeneous acid catalysts in reactions. It is important to study reactive intermediates in zeolites in order to understand the catalytic reactions in these important materials. Avoided Level Crossing muon Spin Resonance will be used to characterize pyridine radicals in zeolites with the variation of Si/Al ratio and with temperature. The silica to aluminium ratio (Si/Al) of ZSM-5 should determine the number of available Brønsted acid sites that may interact with pyridine molecules. This experiment tries to answer an open question regarding how sensitive is MuSR spectroscopy to the chemistry of the acid sites in the most widely employed acid catalysts. Understanding acidity in zeolites is still an open discussion among the zeolite community and we believe our approach will shed light on the structure of acidity.