Diyuk O. Physico-chemical properties of bulk and supported VPO-catalysts for the oxidation of n-butane and ethane

The dissertation is devoted to the study of the influence of the conditions traditional and alternative (barothermal and mechanochemical) methods of bulk and supported VPO-catalysts synthesis on the formation of VPO-phases and their physicochemical properties. The catalytic properties of VPO catalysts in oxidative dehydrogenation of ethane to ethylene and selective oxidation of n-butane to MA (maleic anhydride) with both standard hydrocarbon (1.5-1.7 vol. % n-butane) and rich hydrocarbon concentrations (3.4 – 10 vol. % n-butane) were studied. It was shown that the modification of the conditions of traditional synthesis of bulk VPO-samples by Bi and Zr additives introduction leads to VOHPO4 • 0,5H2O (VPO) formation with different basal and lateral plane ratios. The samples with predominant orientation on basal (001) plane have a high rate of n-butane oxidation, while the samples with predominant orientation in the lateral (220) plane demonstrate better performance in ethane oxidation. The activity of the samples in both reactions determines by the effective negative charge on the oxygen atoms of the catalysts. The optimal conditions of the barothermal synthesis (BTS) of bulk VPO-samples were established and the possibility of the morphology of VPO changes from “rose-like” shape to “jute” shape with a high content of basal plane was shown. The prepared samples demonstrate of high oxidation rate of n-butane in hydrocarbon-rich mixtures. It is established that the using of the reducing agents and their nature significantly influence on formation of the VPO-phase at BTS, but the previous mechanochemical treatment of V2O5 permits to exclude the reducing agent from the synthesis process. It was shown that the mechanochemically treated V2O5 uses in the synthesis and next mechanochemical treatment of the synthesized VPO-samples leads to the formation of samples with predominant orientation on lateral plane, which were effective in the selective oxidation of ethane (Ukraine patent). The possibility of the VPO phase formation on supports surface (pyrogenic silica, TiO2, SiC and aerosilogel were used as support) was shown. Previous barothermal modification of the aerosilogel surface by organic compounds improves the performance of the supported VPO-catalyst in the oxidation processes of the studied hydrocarbons. The conditions of mechanochemical treatment of the mixture of hemihydrate vanadyl hydrogen phosphate and TiO2 were optimized, which permits to obtain supported VPO/TiO2 catalysts with "jutes" morphology and high content of basal plane. These catalysts were effective in oxidation of n-butane to maleic anhydride at high concentrations of n-butane in air (3.4, 5.0 and 10.0 vol. %) (Ukraine patent). The use of these catalysts permits to improve the process of n-butane oxidation with an increase of the MA productivity by recycle technology or cascade scheme application.