L. Coulier et al., On the formation of cobalt-molybdenum sulfides in silica-supported hydrotreating model catalysts, TOP CATAL, 13(1-2), 2000, pp. 99-108
Model catalysts, consisting of a conducting substrate with a thin SiO2 laye
r on top of which the active catalytic phase is deposited by spincoating im
pregnation, were applied to study the formation of the active CoMoS phase i
n 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. C
omplexing Co to nitrilotriacetic acid complexes retarded the Co sulfidation
, resulting in the most active catalyst. Due to the retardation of Co in th
ese 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 acti
ve phase and a lower activity in thiophene HDS.