The chemistry of catalysts based on vanadium-phosphorous oxides: Note II The role of the method of preparation |
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| Affiliation: | 1. Institute di Metallurgia Viale Risorgimento 4, 40100 Bologna ,Italy;2. Institute di Tecnologie Chimiche Specialeb, Viale Risorgimento 4, 40100 Bologna ,Italy;1. Department of Chemistry, University of Oregon, 1253 University of Oregon, Eugene, OR 97403, United States;2. Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, OR 97331, United States;3. Department of Natural Sciences, Oregon Institute of Technology, Klamath Falls, OR 97601, United States;1. Dept. of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada, B3H3J5;2. 3M Co., 3M Center, St. Paul, MN, 55144-1000, USA;3. Dept. of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, B3H4R2;1. Chemistry Department, Faculty of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia;2. Department of General Studies, Riyadh Corporation of Technology, Technical and Vocational Training Corporation, PO Box 42826, Riyadh 11551, Saudi Arabia;3. Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée, France |
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| Abstract: | Vanadium-phosphorous mixed oxides, specific catalysts for C4. oxidation to maleic anhydride, were prepared using two methods as follows; i) method A, by reduction of V2O5 with HCl after addition of H3PO4 and ii) method B, by addition of NH4VO3 to a solution containing H3PO4 and oxalic acid as reducing agents. It was observed that, with both procedures, H3PO4 in excess to that for a ratio of P/V = 1.1 serves to stabilize the tetravalent form of vanadium in calcination at high temperatures. The nature of the compounds formed was different for the two methods. For P/V less than 1.1, βVOPO4 was formed with method A and amorphous αVOPO4 was formed with method B. For P/V greater than 1.1, method A gave the β-phase, described in the literature as the active phase, while method B gave other crystalline and amorphous compounds. It is suggested that the β-phase formed as a polyphosphate of V(IV) containing excess phosphorous. The differences observed with the two preparation procedures are related to the different precursors which formed after the drying stage at 125°C. Method A gave (VO)2P2O7,2H2O and method B VO(NH4)P04,4H2O. |
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