L. Coulier

On the formation of cobalt-molybdenum sulfides in silica-supported hydrotreating model catalysts

Model catalysts, consisting of a conducting substrate with a thin SiO2 layer on top of which the active catalytic phase is deposited by spincoating impregnation, were applied to study the formation of the active CoMoS phase in HDS catalysts. The catalysts thus prepared showed representative activity in the hydrodesulfurization of thiophene, confirming that these models of HDS catalysts are realistic. Combination of the sulfidation behaviour of Co and Mo studied by XPS and activity measurements shows that the key in the formation of the CoMoS phase is the retardation of the sulfidation of Co. Complexing Co to nitrilotriacetic acid complexes retarded the Co sulfidation, resulting in the most active catalyst. Due to the retardation of Co in these catalysts, the sulfidation of Mo precedes that of Co, thereby creating the ideal conditions for CoMoS formation. In the CoMo catalyst without NTA the sulfidation of Co is also retarded due to a Co–Mo interaction. However, the sulfidation of Mo still lags behind that of Co, resulting in less active phase and a lower activity in thiophene HDS.

TiO2-Supported Mo Model Catalysts: Ti as Promoter for Thiophene HDS?

The combination of thiophene hydrodesulfurization (HDS) activity measurements and X-ray photoelectron spectroscopy on flat model systems of sulfided HDS Mo catalysts showed that sulfided Ti-species can act as a promoter in the same way as Co and Ni, although less effectively. This explains the higher thiophene HDS activity and hydrogenation selectivity of Mo/TiO2 compared with Mo/Al2O3, while for Ni-promoted Mo catalysts the difference between the two supports is negligible.

Surface science models for CoMo hydrodesulfurization catalysts: Influence of the support on hydrodesulfurization activity

Flat model systems of supported oxidic CoMo hydrodesulfurization (HDS) catalysts, consisting of a conducting substrate with a thin SiO2 or Al2O3 layer on top of which the active catalytic phase is deposited by spin coating, were used to study the influence of the support and the use of chelating agents on the formation of the active CoMoS phase. On Co/Al2O3 catalysts Co can only be partially sulfided due to the strong interaction with Al2O3. In the mixed phase CoMo/Al2O3 system, the presence of Mo facilitates the sulfidation of Co. Due to the interaction of Mo with the support the Co–Al2O3 interaction is blocked. In these catalysts the sulfidation of Co and Mo proceed at the same rate. In the case of CoMo/SiO2 catalysts the weak interaction with the SiO2 support results in the complete sulfidation of Co at low temperatures, while Mo sulfides at a slower rate. Thiophene HDS activity measurements showed that due to the stronger interaction, Al2O3 is a better support for CoMoS formation. By complexing CoMo o...

Preparation of highly active NiW hydrotreating modelcatalysts with1,2-cyclohexanediamine-N,N,N′N′-tetraacetic acid (CyDTA) as a chelating agent

Changing the order in which oxidic W and Ni convert to sulfides by adding 1,2-cyclohexanediamine-N,N,N′,N ′-tetraacetic acid (CyDTA) as a chelating agent for nickel in the preparation of NiWS–SiO2 catalysts is the key ingredient in obtaining a high activity for thiophene hydrodesulfurization.