Reaction pathway of benzonitrile formation during toluene ammoxidation on vanadium phosphate catalysts |
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Authors: | A. Martin H. Berndt B. Lücke M. Meisel |
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Affiliation: | (1) Institut für Angewandte Chemie Berlin-Adlershof e. V., Rudower Chaussee 5, D-12489 Berlin, Germany;(2) Institut für Anorganische und Allgemeine Chemie, Humboldt Universität zu Berlin, Hessische Strasse 1-2, D-10115 Berlin, Germany |
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Abstract: | The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH4+ ions located on BrØnsted sites, coordinatively bound NH3 on Lewis sites and NH2– groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH4+ ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed. |
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Keywords: | ammoxidation vanadium phosphate catalysts catalyst/feed interaction reaction mechanism FTIR spectroscopy TAP technique isotope experiments TPD TPRS |
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