The dissertation is devoted to the study of influence of additives (Bi, La, Mo, Te, Fe, W, Zr, Ті, Ag, Ni metal ions) on the physical-chemical properties of VPO catalysts of the n-pentane oxidation. It was established that mainly a modification of the VPO catalysts by additives does not lead to the change of a phase composition – the semihydrate vanadyl phosphate (VОНPO4·0,5Н2О) rests the basic phase, with the exception lanthanum and molybdenum ions introduction. The introduction of the lanthanum accompanied by VOPO4 phase formation and molybdenum ions lead to the formation of molybdenum phosphate phase.
It was shown that the additives introduction in VPO composition changes a temperature of the catalyst active component - vanadyl pyrophosphate phase ((VО)2P2O7) crystallization and the temperature of its oxidation to the vanadyl phosphate (VОPO4). It was established the Ti, Bi, Fe ions decrease the values of the first temperature and increase the second temperature that have positive effect connected with the reduce the activation temperature of VPO catalyst and to raise the range of its stability work without loss of a selectivity. The introduction of the W, Te, Mo (Mo/V=0,10) ions in basic composition increases both temperatures that necessary to take in account for the effective conducting of the activation stage. Other additives decrease both temperatures. This fact must be taken into account at determination of critical temperature of the catalyst exploitation.
It was established that additives introduced in the basic VPO composition can be distributed by two ways: 1) highly dispersive and evenly (Fe, Te, Ni, Ag), 2) with formation of X-ray amorphous phase of the additive phosphate (Ti, Bi, La, W, Zr). It was shown that the additives introduction has any effect on an oxidation state of phosphorus but the oxidation state of vanadium changed. It was the increase of the P/V ratio on a surface of catalysts was observed after the introduction of additives and this fact has positive effect on life time of the catalyst.
It was established that the introduction of additives, its nature and content affect on acidic properties of the catalyst surface, namely the namber of acid centers and ratio of Brönsted and Lewis centres.
The study of mechanism of n-pentne transformation by different methods permits to propose the principle new scheme of the n-pentane oxidation. According this scheme the activity of the catalyst, connected with proton abstraction from hydrocarbon, determines by effective negative charge on surface oxygen which can be relative to BE O 1s-electrons. It was shown that a main route of the PhA formation is the Diels-Alder reaction between MA and an unsaturated hydrocarbon C4. So, the ratio of MA and PhA in products of n-pentane oxidation is determined by the containt of Brönsted and Lewis centres. The increase of the Lewis acidic centres on the surface of catalyst allows to an increase the PhA selectivity. These established relations permit to predict the ways of VPO catalyst modification by additives introduction and regulate the catalytic activity and selectivity to one of anhydride formation.
It was proposed the layered loading of two different catalysts with different acidic properties in catalytic reactor which permits to an increase the PhA selectivity on 6-10 %.
