Silicon-Wafer Based Planar Models for Hydrotreating Catalysts
E. J. M. Hensen, L. Coulier, A. Borgna, J. A. R. van Veen and J. W. Niemantsverdriet
Schuit Institute of Catalysis, Eindhoven University of Technology,
P.O. Box 513, 5600 MB Eindhoven (The Netherlands), E-mail: e.j.m.hensen@tue.nl
Abstract
In the present study the use of planar silicon-based models for hydro-treating catalysts is discussed. The specific flat nature makes these models amenable to high resolution surface-sensitive techniques such as XPS. The additional possibility to measure the activity of such model catalysts in thiophene hydrodesulfurization provides a powerful tool to determine structure-activity relations. Here, we study the effect of chelating agents (NTA and EDTA) on the sulfidation order of NiMo catalysts. The XPS results clearly show that the use of these chelating agents retards the sulfidation of Ni with respect to Mo. Especially, EDTA is effective by postponing Ni sulfidation after Mo is completely sulphided. The latter catalyst also displays the highest activity which is attributed to the highest amount of `Ni-Mo-S'-type phases. In essence, the results underpin the notion that such `Ni-Mo-S' phase can be formed effectively when Ni sulfidation proceeds after MoS2 has been formed. When Ni sulfides at too low temperature, inactive bulky Ni3S2 clusters are formed.
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