Synthese und Realstruktur-Eigenschaftsbeziehungen von katalytisch aktiven Nanoteilchen auf der Basis von Übergangsmetallsulfiden
Final Report Abstract
Pretreatment of the support SBA-15 plays a crucial role for simultaneous deposition of sulfidic Mo and W sources. The catalytic materials are characterized by low stacking and short MoS2 slabs. NiMoS catalysts are more active than NiWS catalysts in the HDS of DBT. For NiMoWS catalysts an unusual selectivity for the DDS pathway was observed. Using a new precursor a nanocomposite could be synthesized via thermal decomposition at T = 250 °C with greatly expanded interlayer separation of the MoS2 slabs as evidenced by HRTEM and XRD. The composite exhibits a much higher photocatalytic activity in the light driven hydrogen generation than bulk MoS2. After heating the precursor at T = 350 °C leads to a significant reduction of the interlayer separation. But this material was the most active photocatalyst. The decomposition of ATM in a hydrazine atmosphere leads to formation of an amorphous material with a Mo:S ratio of 1:2 (PX) containing additionally N and H. The material shows an unusual thermal stability and crystallization to form single MoS2 slabs occurs at T ≥ 350 °C (in situ HRTEM). The crystallization process can be controlled by applying different temperatures or dwelling times or even using different methods like the electron beam of a TEM. The photocatalytic activity in light driven hydrogen generation is highest for the amorphous material indicating that most likely Mo centers with N and S as neighbors are the catalytic active species. The unsupported Co-promoted MoS2-based catalysts for HDS were thoroughly characterized with XRD and HRTEM measurements. The catalytic properties, specifically the selectivity, which depends on the activation atmosphere, could be linked to sample properties like the dispersion of Co, the slab lengths, stacking heights and defects. The cobalt sulfide species in the samples prepared in H2/N2 have vanished after the HDS tests, indicating a better Co dispersion over the MoS2 edges. These samples showed a clear preference for the DDS pathway. For catalysts synthesized in N2 Co dispersion was also improved after the HDS reaction, but these samples showed less preference for DDS due to some remaining Co sulfide species. The promotion of MoS2 with Co or Ni applying a new synthesis strategy leads to an increased photocatalytic activity for light driven hydrogen generation. The most active catalysts were obtained for M/(M+Mo) = 0.25 (M = Co, Ni). Increasing the amount of the promotor reduces the activity.
Publications
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Dalton Trans. 23, 1287-1292, 2013
J. Djamil, S. A. Segler, A. Dabrowski, W. Bensch, A. Lotnyk, U. Schürmann, L. Kienle, S. Hansen, T. Beweries
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Appl. Catal. A-Gen., 497, 72-84, 2015
F. Niefind, W. Bensch, M. Deng, L. Kienle, J. Cruz-Reyes, J. M. D. Granados
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Chem. Eur. J., 21, 8918-8925, 2015
J. Djamil, S. A. W. Segler, W. Bensch, U. Schürmann, M. Deng, S. Hansen, T. Breweries, L. von Wullen, S. Rosenfeldt, S. Forster, H. Reinsch
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RSC Adv., 5, 67742-67751, 2015
F. Niefind, J. Djamil, W. Bensch, B. R. Srinivasan, I. Sinev, W. Grunert, M. Deng, L. Kienle, A. Lotnyk, M. B. Mesch, J. Senker, L. Dura, T. Beweries
