Catalytic behavior of NaV6O15 bronze for partial oxidation of hydrogen sulfide

[EN] Na-containing V2O5 materials have been prepared hydrothermally from gels with Na/V ratios of 0.02-0.26, and calcined at 500 degrees C. The calcined samples have been characterized and tested as catalysts in the partial oxidation of H2S to elemental sulfur. At low Na-contents, V2O5 and NaV6O15 bronze are formed, with the NaV6O15/V2O5 ratio increasing with the Na-content. Pure NaV6O15 bronze is mainly formed from gels containing a Na/V ratio of 0.18. However, NaV6O15 and Na1.164V3O8 are formed from gels with Na/V ratio higher than 0.35. NaV6O15 based catalyst shows high conversion for the oxidation of H2S with a high selectivity into elemental sulfur. These catalysts are more active and stable than pure or Na-doped V2O5 catalysts. V4O9 is observed after reaction in both pure Na-doped V2O5 catalysts but also in NaV6O15/V2O5 mixed catalysts. However, no changes in the NaV6O15 crystalline structure are observed in the Na-promoted catalysts. Accordingly, NaV6O15 crystalline phase is stable for several hours of catalysisat a difference with V2O5. The active sites in V-containing vanadium catalysts are probably V5+-O-V4+ pairs as previously proposed for V4O9 crystalline phase. The best catalytic performances were achieved on V2O5-NaV6O15 mixtures which are transformed into V4O9-NaV6O15 mixtures during the catalytic tests. These catalytic results could be due to the intrinsic physical properties of both phases but also because of the optimal dispersion obtained in the synthesis procedure. (C) 2014 Elsevier B.V. All rights reserved.
The authors would like to thank the DGICYT in Spain (Projects CTQ2012-37925-C03-01, CTQ2012-37925-C03-03 and MAT2010-19837-C06-05) for financial support.