As part of an on-going programme of work to better understand critical factors in the methanol-to-hydrocarbon process over ZSM-5 zeolite catalysts, it is becoming increasingly important to more precisely describe the nature and form of the active site distribution. This proposal seeks to use the TOSCA spectrometer to analyse pyridine chemisorption over ZSM-5 that has experienced specific sample treatments. The TOSCA measurements will concentrate on characterising the presence and diminution of pyridinium ion modes as a function of the reaction coordinate. A linked application for MAPS time will concentrate on characterising the hydroxyl modes (stretch and deformation) that convey the Brønsted acidity exhibited by this catalyst.