Features of the phase composition, acidity, and isomerization activity of Pt/WO 3 /ZrO 2 catalysts
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Russian Chemical Bulletin, International Edition, Vol. 69, No. 9, pp. 1714—1718, September, 2020
Features of the phase composition, acidity, and isomerization activity of Pt/WO3/ZrO2 catalysts* M. D. Smolikov, V. A. Shkurenok, O. V. Dzhikiya, D. I. Kir´yanov, E. V. Zatolokina, and A. S. Belyi Center of New Chemical Technologies BIC**, Boreskov Institute of Catalysis, 54 ul. Neftezavodskaya, 644040 Omsk, Russian Federation. Fax: +7 (381 2) 67 3334. E-mail: [email protected] Textural characteristics, phase composition, and acidic properties of Pt/WO3/ZrO2 catalysts for C7-alkanes isomerization were studied. It was shown that the most active and selective catalysts are samples with WO3 content of 15—25 wt.% with a fraction of the active tetragonal phase of ZrO2 of 73—94 wt.%. It was found that an increase in the number of Bronsted acid sites contributes to an increase in the activity of tungstated zirconia catalysts in the isomerization of n-heptane. Key words: isomerization, n-heptane, tungstated zirconia, platinum.
Modification of zirconia with tungstate anions makes it possible to obtain catalysts with an optimal acid function for the reactions of heptanes isomerization. 1—4 Isomerization catalysts are bifunctional systems. Accordingly, for the synthesis of an active catalyst, the acid component (WO3/ZrO2) is supplemented with a metal performing a hydrogenating function, platinum as a rule. The study of tungstated zirconia catalysts were covered by several publications in which their physicochemical and catalytic properties,1—11 along with the structure of acid sites on the surface of WO3/ZrO212—15 were considered. However, there is no clear understanding of how the chemical composition of tungstated zirconia catalysts can be related to phase composition, acidic and catalytic properties in the isomerization of С7-alkanes. In this work, we studied the effect of the content of tungsten oxide in Pt/WO3/ZrO2 catalysts on their textural characteristics, phase composition, acidity, as well as their catalytic activity in n-heptane isomerization. Experimental Synthesis of Pt/WO3/ZrO2 catalysts. Zirconium hydroxide was precipitated by adding Zr(SO)4•xH2O solution to an aqueous ammonia solution at a constant рН = 9.5±0.5 and vigorous stirring. The resulting precipitate was stored for 1 h in the mother solution, then was filtered, washed with distilled water * Based on the materials of the XXI Mendeleev Congress on General and Applied Chemistry (September 9—13, 2019, St. Petersburg, Russia). ** Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences.
until the filtrate is free of SO42– ions, and dried at 100 °C for 5 h. The WO3/ZrO2 catalyst was obtained by anionic modification of zirconium hydroxide with a solution of ammonium metatungstate (NH4)6H2W12O40 (Aldrich, >85 wt.% of WO3) followed by forming, drying at 120 °C for 3 h, and calcination at 800 °C for 2 h. The content of WO3 in the catalysts was 10—35 wt.%. Pt/WO3/ZrO2 catalysts were prepared by impregnating WO3/ZrO2 with an H2PtCl6 solution followe
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