Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture |
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Authors: | L I Kuznetsova N I Kuznetsova S V Koshcheev V A Rogov V I Zaikovskii B N Novgorodov L G Detusheva V A Likholobov D I Kochubey |
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Institution: | (1) Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russia;(2) Institute of Hydrocarbon Processing, Siberian Branch, Russian Academy of Sciences, Omsk, 644040, Russia |
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Abstract: | The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H2PtCl6 or H2PtCl4 and H3PMo12O40 were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt 1?n 0 Pt n II ClmOxHy) (H3+p PMo 12?p VI Mo p V O40) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: Pt n II PMo12O40] (I s) (n = 0.3?0.8) and Pt n 0 PMo 12 red O40] (II s) (n ≈ 1). Under exposure to air, the solutions of I s were stable (pH ~2), whereas Ptmet was released from II s. After the drying of I s, the solid association species (Pt n II ClmOxHy). (H3PMo12O40), where n = 0.3?0.8, m = 0.2?1, and x = 3?0, (I solid) were obtained. The I solid/SiO2 supported samples were prepared by impregnating SiO2 with a solution of I s and drying at 100°C. Platinum metal particles of size ~20 Å and a mixed-valence association species of platinum with the HPA were observed after the reduction of I solid/SiO2 with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O2-H2-N2 mixture. |
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