Ir and XPS Study of NO and CO Interaction with Palladium Catalysts Supported on Aluminosilicates

Adsorption of CO and NO individually and as a mixture of both on palladium catalysts has been investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The effect of sodium ions has been considered by comparing Pd/SiO2 catalyst, sodium-doped Pd/ SiO2, and Pd on natural and synthetic silicoaluminates containing sodium in their bulk structure but differing in the surface area of the support. The presence of sodium induces a different adsorption behavior depending on its location, either at the surface of the catalysts or inside the support structure. As a consequence, different species are formed from the reaction between NO and CO at room temperature and at high temperature. Modification of the metal surface of the various catalysts is observed upon the gas treatments. Palladium is oxidized to a certain extent depending on the type of the catalyst support. Moreover different chemical states of the adsorbed nitrogen species are found.