XPS SURFACE CHARACTERIZATION OF A CU SIO2 CATALYST OXIDIZED BY NO OR O2/

The oxidation of a Cu/SiO2 catalyst with NO or O2 at temperatures vary ing from 313 to 513 K has been investigated using XPS. Upon admission of NO or O2 to a previously reduced catalyst, a rapid transformation o f Cu(0) to Cu(I) is observed. This first stage is followed by slow oxi dation of Cu(I) to Cu(II). After exposure to NO the presence of a surf ace nitride at the catalyst surface is evident. Exposure at low temper atures also leads to the formation of nitrito and nitrato like surface species. These species decompose at 523 K. Desorption of the surface nitride is observed after heating the catalyst at 723 K. The XPS measu rements performed on the supported catalyst are in good agreement with experimental data obtained on single crystals.