W-SBA based materials as efficient catalysts for the ODS of model and real feeds: Improvement of their lifetime through active phase encapsulation

Abstract

Incorporated W-SBA based catalysts were prepared by a direct synthesis method involving phosphotungstic acic (HPW) together with mixed structure directing agents, and by incipient wetness impregnation for comparison purpose. In the oxidative desulfurization (ODS) of dibenzothiophene (DBT, 500–1500 ppmS) and of a Straight Run Gas Oil (SRGO, 2000 ppmS) in batch reactor, the impregnated solids showed higher efficiency than the incorporated ones, which was attributed to a better accessibility of the active phase present at the surface of the support in the impregnated catalysts. However, in continuous evaluation using a fixed bed reactor, the incorporated catalyst showed a stable conversion in the ODS of SRGO 2000 ppmS for 9 days while within 24 h the impregnated solid was almost completely deactivated. Higher interaction of the active phase with the support in incorporated catalysts was evidenced by Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS) analysis, which can be at the origin of less leaching of tungsten species during reaction and thus explain their better resistance towards deactivation. The lower efficiency of incorporated catalysts compared to impregnated ones in ODS reaction carried out in a batch reactor is clearly compensated by their resistance towards leaching of the active phase in a continuous test. These results highlight the importance of evaluating not only the catalysts performance but also their lifetime in conditions more representative of industrial ones.