Investigation of Structural Phase Conversions of an Iron-Containing Catalyst by Mossbauer Spectroscopy (Part 1)
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Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
INVESTIGATION OF STRUCTURAL PHASE CONVERSIONS OF AN IRON-CONTAINING CATALYST BY MOSSBAUER SPECTROSCOPY (PART 1) A. R. Khaidarova, A. V. Pyataev, I. I. Mukhamatdinov,* R. D. Zaripova, and A. V. Vakhin
UDC 543.42:541.128
The active form of an iron-containing catalyst including mixed Fe(II, III) oxides for refining Ashal′cha heavy oil was investigated using Mossbauer spectroscopy to establish the formation mechanism. The iron-oxide phase is involved during the formation process in the cleavage of carbon-heteroatom bonds in asphaltene and resin fractions of heavy oil and decreases their molecular masses. The disperse iron oxides are enriched in a sulfur-containing phase. The conversion degree of the compounds increases as the duration of the experiment increases, which indicates that the disperse iron compounds participate multiple times in the cleavage of chemical bonds. Results of Mossbauer spectroscopy indicate that maghemite is reduced to magnetite when the iron oxides react with water vapor during the catalytic aquathermolysis of crude oil at 250oC. Keywords: catalyst, iron oxide, aquathermolysis, heavy crude oil, Mossbauer spectroscopy. Introduction. Nonconventional hydrocarbon reserves, industrial development of which requires new technologies, are currently given special attention. Such reserves include shale oil and gas, heavy oils, and natural bitumens. Stable recovery of hydrocarbons will in the near term be directed mainly at such reserves [1–4]. Recovery of these feedstocks is accompanied by several problems associated with high contents of high-molecular-mass hydrocarbons and heteroatomic compounds in them and the lack of light fractions, which makes them poorly mobile under strata conditions. Research directed at improving recovery technologies, including aquathermolysis methods, is ongoing [5–10]. Work is being conducted on the synthesis of catalysts for use within strata and studies of their effectiveness for increasing recovery of heavy oil combined with steam pumping. Addition of a nanosized catalyst or oil-soluble precursors that can decompose in situ and form an active catalyst gives the best results. The active form consists mainly of oxides or sulfides of the corresponding metal. Nanosized catalysts, in contrast to traditional ones, do not have diffusion limitations and are stable in the active form [11–14]. Magnetite-like Fe3O4 phases have been studied [15]. Iron or nickel sulfates and carboxylates decompose during thermal treatment and convert into FeO·Fe2O3 oxide (magnetite) and the complex iron–nickel oxide NiFe2O4 [16–18]. The carboxylates form a superparamagnetic finely disperse iron and nickel oxide phase [19]. Toxic Fe3(CO)12 stabilized by oleic acid formed nanosized magnetite particles. Annealing of the products at 300, 700, and 900oC under an inert atmosphere gave a pure iron phase according to Mossbauer spectra [20]. The structures of magnetite particles with shells
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