Infrared Study of Ozone Adsorption on CaO

Ozone adsorption on CaO pretreated at different temperatures was studied by FTIR spectroscopy at 77−300 K. Besides physisorption effects, a weak complex was observed formed by ozone molecules with the OH surface groups, which have pronounced basic properties, as shown by a downward shift of the ν OH band by about 21 cm -1 and by slight changes in ozone vibrational frequencies. Chemisorption of O 3 occurred on CaO activated at 973 K as evidenced by the appearance of a band at 812 cm -1 accompanied by two weaker peaks at 1859 and 625 cm -1 attributed to the ν 3, ν 1 + ν 3, and ν 2 vibrational modes, respectively, of the surface ozonide O 3 - ions. Experiments with 18 O substitution supported this assignment. Effect of CO preadsorption showed ozone chemisorption to occur on the same coordinate-unsaturated O 2- surface sites that accounted for the formation of the “carbonite” CO 2 2- ion from CO adsorbed on highly activated CaO.