Zeolites are porous solid acids heavily used in chemical and petrochemical industries to convert fossil as well as renewable feedstock into transportation fuels, bulk chemicals and intermediates for the pharmaceutical industries. Understanding the full complexity of zeolite catalysts and reaction mechanisms will lead to the development of new and more efficient zeolite catalysts and chemical processes. The use of analytical tool, especially under in-situ or more relevant working conditions, gives rise to great advances in the working principles of catalysts. In fact, Last decade has witnesses the blooming of in-situ and operando spectroscopy to understand catalysts. This presentation will focus on our recent developments on the investigation of zeolitic materials under relevant reaction conditions. I will put emphasis on the importance of understanding catalyst at the single particle level. Two main catalytic systems will be discussed, ranging from the well-established fluid catalytic cracking technology to the promising methanol-to-olefins process.