PROCESSES OF HETEROPHASE CHEMICAL TRANSFORMATION OF TiO2 UNDER THE IMPACT OF CHAIN GAS-PHASE OXIDATION AND CHLORINATION REACTIONS OF HYDROCARBONS AND HYDROGEN WITH OBTAINING TARGET COMPOUNDS AND MATERIALS

Abstract

yan, A.V. Zaprosyan, M.M. Abrahamyan, A.T. Drnoyan

Based on the heterophase chemical conversion of titanium dioxide (TiO₂) under the effect of gas-phase chain reactions (CRE method), a fundamentally new method for obtaining target catalysts, as well as for the synthesis of compounds and materials with special properties, has been proposed and developed. The work is a continuation of diverse research in the new field of radical-chain heterophase chemical CRE-processes devoted to the study of the modification and reduction of TiO₂ under the effect of various gas-phase chain reactions, as well as the production of highly selective catalysts. On the basis of experimental data, new regularities are revealed and the prospects of practical possibilities for the development of technologies for obtaining target catalysts and materials with desired characteristics for the implementation of industrially important processes are determined. The undoubted advantage of the conjugated CRE-process over the traditional heterophase methods for processing and reduction of titanium oxides has been established.

It is shown that under the effect of chain gas-phase reactions of oxidation and chlorination of hydrocarbons (RH) and hydrogen (H₂), powdered TiO₂ of different crystal structure (syngony) and chemical purity undergoes effective and intensive modification and activation. It has been found that when ''technical'' titanium dioxide with an iron impurity is exposed to the chain reaction chlorination of RH, intensive modification and conversion is observed, and the sample is simultaneously completely purified from impurities that sublimate and are removed in the gas flow in the form of valuable products. In the case of CRE-processing of finely dispersed TiO₂ grade “Extra Pure” (a mixture of anatase and rutile) under the effect of an active gas mixture of hydrocarbons and oxygen (O₂), as well as a mixture of H₂+O₂ (CRE mode), a significant decrease in the oxygen content in the

modified sample against the stoichiometric with the formation of TiO_2-x and a noticeable change in the crystal structure is revealed. The modified samples, depending on the conditions of the CRE-effect, exhibit pronounced paramagnetism. A change in the important physicochemical properties of the samples were studied when they were used as target catalysts using the low-temperature oxidation reaction RH as an example. The study of the catalytic activity of the original and modified by the CRE-method samples in the oxidation of isobutane showed a significant advantage of the CRE-synthesized catalyst. In the presence of modified samples, the catalytic process proceeds with a decrease in the yield of non-target reaction products: CO (by 6 times), CO₂ (by 3 times) and secondary hydrocarbons (by 10 times), as a result, the selectivity of the process for target products (aldehydes and alcohols) increases.