EPR Study of the Oxygen Adsorbed on CoCr₂O₄ in Controlled-atmosphere Catalytic Oxidation of Tetralin

The catalytic activity and selectivity to tetralone of CoCr₂O₄ catalyst in oxidation of tetralin are higher than that of CoO and Cr₂O₃.By election paramagentic resonance(EPR),the oxygen adsorbed or desorbed on three catalysts,and the action contacted with tetralin in cotrolled-atmosphere have been investigated respectively.The results of EPR confirm that a signal with 3-g values (2.000~2.085) comes from the species of surface adsorbing oxygen,and that they can be assigned to super-oxide species O₂^- which is chemisorbed on the samples.It is stable under the conditions of room or 157K temperature and vacuum of 1.33×10^-2Pa.The O₂^- on CoCr₂O₄ could not be detected under the conditions of 673K and vacuum of 1.33×10^-2Pa,neither could O₂^- on Cr₂O₃ under all conditions.It was found that the signal intensity of the O₂^- reduced when CoCr₂O₄ was contacted with tetralin under conditions of 323K and without oxygen gas.At the same time,the signal (C=0) was given by IR.The results show that the species O₂^- might be the active species oxygen,and that the cobalt is active position of chemisorbed oxygen.The concentration of O₂^- is increased and its complex state is changed by addition of chromium.