Transformations of Supported Heteropoly Compounds in Oxidative Conversion of Alkanes
- PDF / 606,116 Bytes
- 13 Pages / 595.22 x 842 pts (A4) Page_size
- 49 Downloads / 149 Views
Transformations of Supported Heteropoly Compounds in Oxidative Conversion of Alkanes Svetlana A. Tungatarova D.V.Sokolsky Institute of Organic Catalysis and Electrochemistry, Almaty, Kazakhstan Email: [email protected] ABSTRACT. Dynamics of structural transformation of supported heteropoly compound was investigated by IR-spectroscopy, XRD, TPR, and TPO methods. The 15-30 wt.% H3PMo12O40 and H3PV2Mo10O40, supported on SiO2 catalysts were investigated in process under various conditions by interaction with O2 (air) in the presence of water vapor, H2, alkane in TPR regime, O2 in TPO regime (298-1273K) and H2O (298, 923K). The rank of reversible structural conversion of supported heteropoly compounds was established under influence of temperature and medium. These new findings of reversible structural cycle explains the stability of the 12th series Mo heteropoly compounds supported on Si-containing carrier at high temperatures (8731073K) which is close to the actual operation temperatures of the partial oxidation reactions and oxidative dehydrogenation of alkanes. KEYWORDS: heteropoly acid, carrier, structure, medium, temperature. INTRODUCTION The combination of acid and red-ox properties which can be changed over a wide range by a variation of the structure and content of heteropoly compounds (HPC) on certain carrier, with the nature of the carrier is typical for 12 series Mo- and WHPC with Keggin structure [1-5]. Massive heteropoly compounds, heteropoly acids (HPA) and salts, have been widely applied in catalysis. They are catalysts of important low-temperature homogeneous, heterogeneous, petrochemical and some commercial processes. These compounds are frequently used as the model catalytic systems by successfully combining both acid and red-ox properties allowing fixing the composition and structure of catalytically active centers [4-14]. Compact HPA [9, 15-18] and supported catalysts on the base of 12 series HPC [19-31] were investigated in oxidative conversion of С1-С4 alkanes into oxygen-containing compounds (methanol, formaldehyde), olefins, and hydrogen. It was installed their high activity and stability at a temperature range Т = 473-1073K under atmospheric pressure in the reaction mixtures containing alkane, oxidizing agent, inert gas and water vapor. The reasons of high activity and thermal stability of supported HPA in the red-ox gasand vapor-phase processes at high-temperature were still not clear till now. At the same time, it is known, that compact 12 series Mo HPA have a series of structural transformations in air, argon, water vapor, hydrocarbon + О2 mixture. They may transfer into oxides of component elements at a temperature range between 673 and 873 K [1, 2, 26, 28, 32-38]. When W-HPA instead of Mo-HPA [1-3, 5, 14, 19, 39] were supported on carriers (aluminosilicate, SiO2, TiO2 or А12О3), finely divided crystallites and structures could be formed due to HPA-carrier interaction [19-25, 27, 39]. It was reported that introduction the proton's substituents (preferable elements of 1A and 2A groups) in
Data Loading...
