Дослідження кислотних властивостей складної манган-нікельфосфатної каталітичної системи

Abstract

Individual manganese and nickel phosphates and 7 complex acid catalytic systems based of type хMn2P2O7·уNi3(PO4)2.were synthesized with different content of both phosphates. Modern methods of physical and chemical analysis: X-ray (RFA), differential-thermal (DTA), IR-spectroscopic investigated the influence of synthesis conditions on the composition and structure of the obtained catalysts, the nature and nature of the formation of active surface centers and other physico-chemical parameters of the samples. The acidic properties of the surface of the obtained individual phosphates of manganese and nickel and complex manganese-nickel phosphate catalytic systems and the distribution of active centers on it are investigated. The modifying role of Ni2+ nickel ions in the structure of manganese phosphate catalyst has been confirmed. The presence of a synergistic effect of both of these phosphates on the acidity in the structure of the synthesized complex catalytic systems has been established. It is proved that, as predicted, due to the increase of Ni3(PO4)2 content in the Mn2P2O7 structure, there is a sharp increase in surface acidity, the maximum value of which is reached on the K-6 sample. The total acidity of all complex manganese-nickel phosphate catalysts is higher than that of the individual phosphates Mn2P2O7 and Ni3(PO4)2. The acidity of the surface of the phosphate catalysts is determined by the annealing temperature and the chemical content of them. This suggests that in the process of dehydration of metal ions, which form phosphate, free orbitals appear. These vacant orbitals and their associated electron vapor affinity are the cause of the surface acidity of phosphate catalysts. Since the acidity of the surface has a decisive influence on the selectivity of the contacts, it should be expected that among the synthesized complex phosphate solids there will be highly selective catalysts for the oxidation of n-alkanes into valuable products. The results again confirmed that in mixed complex oxides, which are composed of several cations with different charges, the acidic properties are enhanced compared to the single oxides separately taken. The amount of acidity is determined by the donor-acceptor properties of the cations that are part of the complex oxide. Therefore, the amount of surface acidity is an important and necessary characteristic of complex oxide catalysts for the partial oxidation of paraffin hydrocarbons. It is confirmed that the peculiarities of the obtained complex catalytic systems of type хMn2P2O7·уNi3(PO4)2., as predicted, are the presence of all the necessary parameters: high thermal and chemical stability, developed specific surface area, optimal acidity, active centers on the surface, which enables them in catalytic processes as effective catalysts for the partial oxidation of hydrocarbons into valuable products. Keywords: catalysis, catalyst; heterogeneous oxidation; partial oxidation of n-alkanes; C1-C4 – hydrocarbons; ethane; ethylene; phosphates.