Abstract
Up to a sulfidation temperature of 473 K, the behaviour of Co/C catalysts with extremely low cobalt-loadings (ppm range) agrees with the trend observed before in the Mössbauer emission spectroscopy (MES) spectra of Co/C catalysts with much higher cobalt-loadings (0.04–4.3 wt.-%). Interestingly, sulfidation at 573 K results in a rather well-defined very highly dispersed (most likely monatomically) ‘Co-sulfide’ species which shows a doublet with the extremely large value Q.S. = 4.11 m/ms. In this species the cobalt atoms may be four-fold (square-planar) or five-fold (square-pyramid) coordinated by sulfur. Sulfidation at 673 K results in the disappearance of this highly dispersed “Co-sulfide” species and the newly formed species are again similar to the one previously found for Co/C catalysts with higher cobalt-loadings. It is worth noting that this finally formed ‘Co-sulfide’ species does not exhibit the “Co-Mo-S” MES spectrum (Q.S. between 1.0 and 1.3 m/ms) whereas its intrinsic thiophene hydrodesulfurization (HDS) activity equals that of cobalt in the “Co-Mo-S” phase. These observations clearly lead to the conclusion that there is no general relation between the thiophene HDS activity (measured at atmospheric pressure) and the amount of cobalt exhibiting a “Co-Mo-S” MES spectrum.
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call