Probing cationic and ‘true’ Lewis acid sites in zeolite Y with NO and CO. An adsorption and EPR study

Adsorption isotherms of CO and NO in HY and ZnY zeolites at −25 and 25°C as well as EPR spectra of NO at −196°C with and without coadsorbed CO were measured. From a quantitative analysis of the adsorption isotherms, the concentration of Lewis acid sites in HY and cation sites in ZnY were determined. The spin concentrations evaluated from the calibrated intensities of the EPR signals originating from NO, were found to be about 10–20% of the NO concentrations from the adsorption experiments. Coadsorbed CO in ZnY drastically reduces the EPR signal intensity permitting the identification of the adsorption sites of EPR active NO.