Variation in Structural Characteristics of a Hydrotreatment Catalyst with Deactivation/Regeneration Cycles

Abstract

The effect of reaction/regeneration cycles on some structural characteristics of a NiMo/Al2O3 hydrotreatment catalyst has been studied. The first regeneration produces increases in pore volume, porosity, and specific area. Above 5% coke deposit, various changes in such properties appear. Mo and Ni relative XPS intensities depend on the reaction/regeneration cycles Ni exposure decreases with them, whereas Mo exposure follows the opposite trend. The effect of coke on metal dispersion seems to be almost negligible. Coke concentration proved to be the variable which really influenced coke composition (H/C), independently of the history of the catalyst. The equation relating both variables is H/C = 0.4378 + 1.342 exp[(−C c/S e)/0.059] where C c is the percentage coke concentration and S e the specific surface area.

X-ray absorption near edge structure and X-ray photo electron spectroscopy analyses of NiMo/Al2O3 catalysts containing boron and phosphorus

“…The higher the percentage of sulfur in the form of the oxidation state of −2, the higher the extent of sulfidation and hence catalyst activity. The peak at the binding energy (BE) of 162.5 ± 0.2 eV indicates the formation of Ni Mo S phase or NiS [39] due to OSS of −2, which is close to the value reported in the literature [35,38,39,50,53,55]. Another peak at a higher BE (169.3) was also observed.…”

“…Table 6 also shows that significant amount of oxidic Ni is still present on the catalyst surface after 30 days of run time. Brito et al [35] also reported significantly higher concentrations of oxidic Ni on the coked catalyst surface.…”

“…Ozkan et al [39] and Eijsbouts et al [40] also observed a significant improvement of A Mo3d /A Al2p ratio after sulfidation. Brito et al [35] observed an increase in Mo/Al ratio after deactivation of the catalyst. It was observed that the dispersion of Mo increased significantly with TOS due to the incorporation of boron in NiMo/Al 2 O 3 catalyst (see Table 4).…”

“…The deactivation is a complex process that may involve several different routes with different intermediates and mechanisms [34]. It is believed that coke deposition is the consequence of a polymerization/hydrogenation reaction which generates coke structures capable of physically impeding the access of reagents to active centers and progressively blocking the porous structure of the catalyst [35]. Therefore, it is necessary to study the carbon deposition at different stages of reactions to correlate which stages are responsible for maximum carbon deposition on the catalyst and hence catalyst deactivation.…”

“…This shows two different oxidation states for Mo ions (Mo 4+ and Mo 6+ ) and the corresponding binding energy (BE). The peak at 229.4 ± 0.2 eV is due to the presence of Mo 4+ ions in the type of MoS 2 or MoO 2 [35,[44][45][46][47][48]. The peak at 234.1 ± 0.2 eV is due to the presence of MoO 3 or Al 2 (MoO 4 ) 3 [47][48][49].…”