Reactions of gaseous pollutants with solids. V. Infrared study of the sorption of NO on CaO

A Fourier transform spectrometer was used to record spectra of the surface layer formed on CaO by sorbed NO, and during the conversion and destruction of the layer by degassing and treatments with oxygen. NO was taken up at pressures in the low micro-Torr range, most of the surface layer being relatively firmly bound. Numerous infrared bands were observed, pointing to the existence of at least a dozen distinct surface species. Tentative band assignments suggest the formation of NO^-, NO₂^->, NO₃^-), NO⁺, and monodentate and bidentate nitrato complexes. At least six other species are unidentified, so that the mechanisms cannot be considered. The extreme complexity of the system and the numerous surface species found with CaO lead to the speculation that on other adsorbents, on which quite few NO_x species have been found, there may also exist numerous NO_x species.