Fuel, Vol.110, 259-267, 2013
Atomic ratio effect on catalytic performance of FeW-based carbides and nitrides on thiophene hydrodesulfurization
Synthesis of bulk and alumina-supported, Fe-promoted W carbides and nitrides were carried out by using oxidic precursors with atomic ratios (Fe/(Fe + W)) varying from 0 to 1. These materials were prepared by temperature-programmed reaction up to 700 degrees C of the precursors under flow of 20 vol.% CH4/H-2, for carbides, and of NH3 for nitrides. Crystalline structure of catalysts was established by X-ray diffraction (XRD), while textural properties were determined by N-2 physisorption. Catalytic tests of thiophene hydrodesulfurization (HDS) were carried out in a fixed bed reactor at 400 degrees C and atmospheric pressure and monitored by FID-GC. The catalysts were activated in situ under a CS2/H-2 mixture at 300 degrees C/2 h prior to HDS. In addition, both fresh and exhausted catalysts were analyzed by elemental chemical analysis (ECA) of C, N and S. XRD results showed a main bimetallic phase Fe2WO6 for supported oxidic precursors, while bulk catalysts revealed a mixture of Fe2WO6 and FeWO4. On the other hand, for supported carbides, XRD revealed the presence of the cubic Fe3W3C mixed phase, and bulk carbides showed the presence of Fe6W6C. For supported nitrides, XRD data revealed the presence of the hexagonal FeWN2 mixed phase for bimetallic catalysts and W2.2N2 and Fe3N for each monometallic catalyst. In contrast, for bulk monometallic W nitride it was found that W2N was the monometallic crystalline phase obtained. Texture analysis showed that specific surface area of catalyst decreased with respect to alumina, when Fe and W were incorporated and this effect increased with increasing Fe content. Catalytic tests revealed that the catalyst based on W carbide had the highest activity, followed by the carbide catalyst with atomic ratio 0.1, which turned out to be more active than W-based nitride catalyst and the nitride catalyst with atomic ratio 0.1. Finally, after HDS, catalyst showed an increase in S content due to the displacement of C or N atoms by S atom during presulfurization and HDS reaction, which was corroborated with the decrease in C and N content of exhausted catalysts in comparison with the initial contents. (C) 2012 Elsevier Ltd. All rights reserved.