Supported Vanadium Oxide Catalysts: Quantitative Spectroscopy, Preferential Adsorption of V^4+/5+, and Al₂O₃ Coating of Zeolite Y

Abstract

A series of supported vanadium oxide catalysts were prepared by the incipient wetness method as a function of the support composition (Al 2 O 3 , SiO 2 , and USY), the metal oxide loading (0-1 wt %), and the impregnation salt (vanadyl sulfate and ammonium vanadate). These catalysts have been studied by combined DRS-ESR spectroscopies in order to quantify the amount of V 4+ and V 5+ and to unravel their coordination geometries. These spectroscopic fingerprints have been used to study the preferential adsorption of V 4+/5+ ions on SiO 2 , Al 2 O 3 , and USY. Both V 4+ and V 5+ were preferentially adsorbed on Al 2 O 3 and showed a much smaller preference for USY and SiO 2 . The observed preference orders are discussed in relation with the properties of the support. In addition, a novel method is proposed to coat the external surface of USY with a thin film of Al 2 O 3 . The method is based on the deposition of USY with the so-called Keggin ion, [Al 13 O 4

Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

“…This implies insight in the adsorption properties of supported vanadium oxides. In a recent study, the preferential adsorption of V 4+/5+ ions on SiO 2 , Al 2 O 3 and USY has been studied with combined DRS-ESR spectroscopies in quite detail [210]. By taking the spectroscopic fingerprints of V 4+/5+ on these supports as reference spectra it was possible to monitor the preferential adsorption of V 4+/5+ onto physical mixtures of these oxides.…”

“…It was shown that both V 4+ and V 5+ ions were preferentially adsorbed on Al 2 O 3 and showed a much smaller preference for USY and SiO 2 . Based on this observation, a novel method was developed to coat the external surface of USY with a thin film of Al 2 O 3 [210,211]. This method is based on the deposition of USY with the so-called Keggin ion, [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ , which is too big to enter the USY channels or pores.…”

AlOx Coating of Ultrastable Zeolite Y: A Possible Method for Vanadium Passivation of FCC Catalysts

“…Vanadium Passivation. In a previous paper 6 we have studied the preferential adsorption and mobility of vanadium species on different oxidic supports. We found that both V 4+ and V 5+ ions show the following preference order: Al 2 O 3 > SiO 2 g USY.…”

“…The efficiency of the proposed method, based on the deposition of USY with the so-called Keggin ion, [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ , was only indirectly proven via electron spin resonance of the vanadium impregnated materials. 6 A more detailed characterization of the Al species deposited on the external surface of the zeolite is obviously necessary.…”

The coordinatively saturated vanadium MIL-47 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene

“…By introducing catalytically active metal-connecting points or functional groups into the highly porous MOF structure, MOFs exhibit clear advantages in heterogeneous catalysis. Moreover, unlike traditional immobilized catalysts 9,10,11 , the active catalytic sites in MOFs are well protected by the coordination bonds which prevents leaching to a higher extent. Although the research in this field is relatively new, MOFs have been studied as catalysts in hydrogenation and oxidation reactions 12,13,14,15,16,17,18 enantioselective reactions 19,20,21 , photocatalysis 22 , carbonyl cyanosilylation 23,24,25 , hydrodesulfurization 26 and esterification 27 .…”