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 MAPS spectrometer to analyse pyridine chemisorption over ZSM-5 that has experienced specific sample treatments. The MAPS measurements will concentrate on hydroxyl modes (stretch and deformation) associated with Brønsted acidity and the pyridinium N-H stretch modes generated by reaction with pyridine. A linked application for TOSCA time will concentrate on characterising the presence and diminution of pyridinium ion modes as a function of the reaction coordinate.