Thermal stability of surface nitrogen–oxygen complexes and phase transitions in ZrO₂

The IR spectra of surface compounds observed in the course of the temperature-programmed desorption (TPD) of NO_x and the TPD spectra are compared. The high-temperature peaks of desorption are related to the decomposition of surface nitrites and nitrates. The low-temperature peaks of NO_x desorption with maximums below 140°C are caused by the decomposition of surface nitrosyls. On the heating of surface nitrosyls, the following two reaction paths are possible: desorption at low temperatures and conversion into nitrates. The shape of the TPD spectra of NO depends on the phase composition of test samples. The transition of a tetragonal phase into a monoclinic one occurred upon the surface dehydroxylation of polycrystalline particles with the formation of particles with a tetragonal nucleus and a monoclinic crust. This transition is reversible. The cooling of a sample in a moist atmosphere leads to the transition of the monoclinic crust to the tetragonal phase.