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EnglishVanadyl pyrophosphate catalysts having different P/V ratio were studied. In-situ surface characterization were carried out by means of Raman Spectroscopy, to reproduce the phase changes in function of the catalyst composition. It was found that surface composition changes as a function of gas-phase composition (N2 or air), steam partial pressure and catalyst P/V ratio [2,3]. For catalysts having a slight excess of P, the surface oxidation of VPP to δ-VOPO4 occurs at lower temperature (380°C). On the contrary, for sample prepared with stoichiometric P/V ratio, αI-VOPO4 forms. The excess of P favours the formation of δ-VOPO4 and improves its stability with the reaction mixture. The catalytic behaviours of these catalysts in n-butane oxidation to maleic anhydride differ greatly at temperatures ranging between 340 and 400°C. Specifically, a catalyst having P/V close to 1.0 is very active but poorly selective to maleic anhydride, whereas a catalyst having a slight excess of P, is moderately active but selective. The two catalysts, instead, gave similar performance at temperature lower than 340°C and higher than 400°C. This means that the formation of αI-VOPO4 is responsible for the lower selectivity to MA, while the excess of P favours the formation of δ-VOPO4 and improves its stability under reaction mixture, ensuring high selectivity to MA.
| Titolo: | The surface dynamics of vanadium oxide-based catalysts: the generation of the active species in V/P/O and V/O-TiO2 |
| Autore/i: | CAVANI, FABRIZIO; LUCIANI, SILVIA |
| Autore/i Unibo: | |
| Anno: | 2010 |
| Titolo del libro: | Atti del Convegno |
| Pagina iniziale: | 11 |
| Pagina finale: | 11 |
| Abstract: | Vanadyl pyrophosphate catalysts having different P/V ratio were studied. In-situ surface characterization were carried out by means of Raman Spectroscopy, to reproduce the phase changes in function of the catalyst composition. It was found that surface composition changes as a function of gas-phase composition (N2 or air), steam partial pressure and catalyst P/V ratio [2,3]. For catalysts having a slight excess of P, the surface oxidation of VPP to δ-VOPO4 occurs at lower temperature (380°C). On the contrary, for sample prepared with stoichiometric P/V ratio, αI-VOPO4 forms. The excess of P favours the formation of δ-VOPO4 and improves its stability with the reaction mixture. The catalytic behaviours of these catalysts in n-butane oxidation to maleic anhydride differ greatly at temperatures ranging between 340 and 400°C. Specifically, a catalyst having P/V close to 1.0 is very active but poorly selective to maleic anhydride, whereas a catalyst having a slight excess of P, is moderately active but selective. The two catalysts, instead, gave similar performance at temperature lower than 340°C and higher than 400°C. This means that the formation of αI-VOPO4 is responsible for the lower selectivity to MA, while the excess of P favours the formation of δ-VOPO4 and improves its stability under reaction mixture, ensuring high selectivity to MA. |
| Data prodotto definitivo in UGOV: | 25-feb-2011 |
| Appare nelle tipologie: | 4.02 Riassunto (Abstract) |
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