Study of Te and V as counter-cations in Keggin type phosphomolybdic polyoxometalate catalysts for isobutane oxidation

Abstract Keggin-type phosphomolybdic acid and cesium salts with protons partially substituted by tellurium and by both tellurium and vanadium have been prepared, characterized using several techniques and tested as catalysts in the partial oxidation of isobutane into methacrylic acid (MAA). The results showed that tellurium when introduced as counter-cation was present as Te 4+ capping the Keggin anion and was randomly distributed in the acid or in the cesium salt. This cation induced a positive effect on the selectivity to MAA and methacrolein (MA) without significant effect on the activity except in the acid at low loading where it also increased the activity. The co-substitution of protons by vanadyl cations had a slight effect on the selectivity but increased the activity especially at low level of substitution, which led to a very efficient catalyst. Selectivity to MAA and MA and isobutane conversion rate of 65 and 17% respectively were reached at 350 °C and were both very constant with time on stream. The catalytic results obtained in both stationary and transient conditions allowed to propose a reaction mechanism very close to one already proposed with four intermediates amongst which one is common to both MAA and MA. These results were used to understand the catalytic effect of tellurium and vanadium.

[1]  L. Marosi,et al.  Catalytic performance of Csx(NH4)yHzPMo12O40 and related heteropolyacids in the methacrolein to methacrylic acid conversion: in situ structural study of the formation and stability of the catalytically active species , 2003 .

[2]  Yves Schuurman,et al.  TAP-2: An interrogative kinetics approach , 1997 .

[3]  Koichi Nagai,et al.  Kinetics of isobutane selective oxidation over Mo-V-P-As-Cs-Cu-O heteropoly acid catalyst , 2001 .

[4]  J. Spence,et al.  Intermediate-range structure of tellurite glasses from near-edge absorption spectra , 2004 .

[5]  M. Misono,et al.  Catalysis by heteropoly compounds Part 39 The structure and redox behaviour of vanadium species in molybdovanadophosphoric acid catalysts during partial oxidation of isobutane , 1998 .

[6]  L. Jalowiecki-Duhamel,et al.  Oxidation of isobutane on a heteropolycompound hydrogen reservoir , 1996 .

[7]  U. Ozkan,et al.  Study of Cesium or Cesium–Transition Metal-Substituted Keggin-Type Phosphomolybdic Acid As Isobutane Oxidation Catalysts: II. Redox and Catalytic Properties , 1999 .

[8]  C. Hill,et al.  A Bivanadyl Capped, Highly Reduced Keggin Polyanion, [PMoV6MoVI6O40(VIVO)2]5- , 1996 .

[9]  F. Cavani,et al.  Main aspects of the selective oxidation of isobutane to methacrylic acid catalyzed by Keggin-type polyoxometalates , 2001 .

[10]  Y. Montardi,et al.  Synthesis, optical properties and electronic structures of polyoxometalates K3P(Mo1-xWx)12O40 (0≤x≤1) , 2004 .

[11]  L. Marosi,et al.  X-ray powder diffraction analysis of the heteropoly-molybdate (MoO2)0.5PMo14O42 , 2003, Powder Diffraction.

[12]  U. Ozkan,et al.  Study of cesium or cesium-transition metal-substituted Keggin-type phosphomolybdic acid as isobutane oxidation catalysts. I. Structural characterization , 1999 .

[13]  V. Kozhukharov,et al.  The structure of glasses in the TeO2-P2O5 system , 1980 .

[14]  S. Paul,et al.  Kinetic Investigation of Isobutane Selective Oxidation over a Heteropolyanion Catalyst , 1997 .

[15]  N. Mizuno,et al.  Oxidation of Isobutane Catalyzed by Partially Salified Cesium Molybdovanadophosphoric Acids , 1998 .

[16]  G. Centi,et al.  Selective Oxidation by Heterogeneous Catalysis , 2001 .

[17]  R. Grasselli.  Genesis of site isolation and phase cooperation in selective oxidation catalysis , 2001 .

[18]  J. Rehr,et al.  High-order multiple-scattering calculations of x-ray-absorption fine structure. , 1992, Physical review letters.

[19]  J. Baran,et al.  Structure and IR spectra of the solid complex of bis (betaine)—telluric acid , 1992 .

[20]  G. Scholz,et al.  Structural evolution of H4PVMo11O40·xH2O during calcination and isobutane oxidation : New insights into vanadium sites by a comprehensive in situ approach , 2007 .

[21]  T. Ui,et al.  Enhancing the Productivity of Isobutane Selective Oxidation Over a Mo–V–P–As–Cs–Cu–O Heteropoly Acid Catalyst , 2003 .

[22]  J. Moisan,et al.  A New Method to Prepare Transition Metal Salts of Bulk and Supported Heteropolyacids. Application to the Catalysis of the Oxidative Dehydrogenation of Isobutyric Acid , 2002 .

[23]  D. H. Maylotte,et al.  A Study of the K-edge Absorption Spectra of Selected Vanadium Compounds. , 1984 .

[24]  R. Schlögl,et al.  Thermally and Chemically Induced Structural Transformations of Keggin-Type Heteropoly Acid Catalysts , 2001 .

[25]  A. Ankudinov,et al.  REAL-SPACE MULTIPLE-SCATTERING CALCULATION AND INTERPRETATION OF X-RAY-ABSORPTION NEAR-EDGE STRUCTURE , 1998 .

[26]  J. Millet,et al.  Bulk oxidation state of the different cationic elements in the MoVTe(Sb)NbO catalysts for oxidation or ammoxidation of propane , 2005 .