Infrared photoacoustic spectroscopy of adsorption on powders

A photoacoustic cell for adsorption spectroscopy on powders is described. The cell permits spectra to be obtained, with a flowing gas and temperatures up to 400°C. Experiments were performed examining methanol adsorption on silica and Na-Y zeolites. On the silica, methoxy groups quantitatively displaced surface hydroxyl groups at elevated temperatures. On the Na zeolite, methanol seemed to associate with cation centers. The photoacoustic spectra were able to clearly display the entire spectrum from 4000-400 cm^-1, and the methoxy C-O stretching band was clearly visible superimposed on the Si-O bands. Adsorption studies of CO on Pt/Al₂O₃ and Pt-black showed that photoacoustic spectra could be obtained for supported metal catalysts, but not for massive metal catalysts. Criteria are presented that relate the applicability of PAS to the physical properties of the powder.