1. College of Chemistry & Environmental Science, Inner Mongolia Normal University, Huhhot 010022, China 2. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China 3. School of Science of Beijing Jiaotong University, Beijing 100044, China
Abstract：A series of Co—V—O (meta-CoV2O6, pyro-Co2V2O7, and ortho-Co3V2O8) catalysts were prepared by microwave oxalate co-precipitation method and characterized by (XRD), TEM, BET, FTIR, XPS, H2-TPR and conductivity measurement. The catalytic characters of the catalysts for propane oxidative dehydrogenation were investigated. The FTIR spectra of catalysts were obtained in the range of 400-1 100 cm-1 and their major bands were assigned. The peak separation fitting of O(1s) XPS spectra was carried out and the quantity of oxygen species was calculated. The results of XRD characterization showed that pure meta-CoV2O6, pyro-Co2V2O7, and ortho-Co3V2O8 with nice structure were obtained. The TEM images demonstrated that the catalysts showed uniform particle with the mean particle size of 20-30 nm. The diagram of the relationship between electrical conductivity and oxygen partial pressure of Co3V2O8 and Co2V2O7 showed dσ/dPO2＞0, which implied that these were p-type semiconductor, and CoV2O6 reverse showed dσ/dPO2＜0, which implied n-type semiconductor. 48.12%, 47.82% and 35.24% of C3H6 selectivities were obtained for p-type semiconductor Co3V2O8, Co2V2O7 and n-type CoV2O6 catalysts respectively at 10% C3H8 conversion, and the results showed that p-type semiconductor catalysts Co3V2O8 and Co2V2O7 showed higher activity than n-type catalyst CoV2O6. The results of FTIR, XPS, H2-TPR and conductivity measurement indicated that transferring between non-stoichiometric and lattice oxygen that easily happened in Co3V2O8 and Co2V2O7 catalysts might promote the oxidation-reduction reaction between different valence vanadium species, and promoted the oxygen vacancy formation. Furthermore, the forming of Co—O—V bridge bond that was easy to shift between Co and V increased the mobile oxygen species of O-2, O2-2 and O- and made the redox reaction among different valence V be realized. It is concluded that high catalytic properties of p-type semiconductor Co3V2O8 and Co2V2O7 can be attributed to the abundant oxygen species O- that existed in these catalysts.
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