[Study on performance of Ni3 V2O8 catalyst and analysis of X-ray photoelectron spectroscopy].

ABSTRACT

Ni3V2O8 catalyst was prepared by oxalate co-precipitation method with microwave heating in this paper. In order to study the relationship between the catalytic performance and the surface species, the catalyst was characterized by XRD, BET, H2-TPR, XPS, TEM and conductivity measurement. The surface property of Ni3V2O8 was studied by XPS and the catalytic performance of the oxidative dehydrogenation of propane to propylene was also investigated. The results of XRD showedthat pure Ni3V2O8 with nice structure was obtained. TEM experiments results demonstrated that the prepared Ni3V2O8 catalyst at 700 degrees C calcination showed uniform particle with the mean particle size of 30 nm. The surface area of the catalyst was 8.623 m2 x g(-1). The diagram of the relationship between electrical conductivity and oxygen partial pressure of Ni3V2O8 showed dsigma/dPO2, >0, implying that Ni3V2O8 catalyst was a p-type semiconductor. H2-TPR results showed that only one unsymmetrical reduction peak appeared at 663.5 degreesC within 300-900 degrees C region over Ni3V2O8 catalyst and no obvious shoulder peak was observed. It could also be found that the ratio of non complete reduction oxygen species was about 33.59% (O(-) 27.55%, O2(2-) 6.04%) from the O(1s) XPS result and more V4+ species existed on the Ni3V2O8 catalyst surface. The TPR and XPS results illustrated that the transformation of the lattice oxygen to non-complete reduction oxygen in NiV2O8 catalyst might promote the oxidation-reduction reaction between different valence vanadium and promoted the oxygen vacancy formation. This then led to abundant non-complete reduction oxygen O(-) and V4+ species formation on the surface of Ni3V2O8 catalyst. The active result of oxidative dehydrogenation of propane to propylene showed that the 60.02% propylene selectivity could be reached at 18.60% propane conversion. Compared with the reported results over the coexistent NiO and Ni3V2O8 system from the literature, pure Ni3V2O8 catalyst system in this present paper showed higher propylene selectivity than the coexistent NiO and Ni3V2O8 system under the same propane conversion condition, suggesting that the performance of propane to propene is correlated to the oxidation-reduction of V4+ / V5+ couple and non complete reduction oxygen species (O(-) or O2(2-)). This result further illustrated that NiV2O8 was active phase for oxidative dehydrogenation of propane to propylene. Combining the active and characterization results, it was found that catalytic activity was correlated to the surface non-complete reduction O(-) and V4+ species, which was beneficial to improving the propylene selectivity.