Sonja Eijsbouts

On the flexibility of the active phase in hydrotreating catalysts

Abstract This review deals with the structure of the active phase in sulfidic Co Mo and Ni Mo hydrotreating catalysts. Various models describing the catalyst and its interaction with the reaction environment are discussed in the light of the evolution of the active phase during the catalyst life cycle. Special attention is paid to the contribution of Mossbauer Emission Spectroscopy (MES), Extended X-ray Absorption Fine Structure (EXAFS), High Resolution Transmission Electron Microscopy (HR-TEM) and Molecular Modeling to the unraveling of the active phase structure. It is concluded that MoS 2 sintering and Co 9 S 8 (Ni 3 S 2 , NiS) segregation during the catalyst life cycle force the shift of the actual reaction mechanism from that involving a single site or an ensemble of sites to that of a close cooperation between segregated components. The adsorption of reactants can take place in many diferent ways, through the heteroatom or through the ring, on the Mo sites as well as on the Co (Ni) sites. The exact state of each active site depends on the reaction environment. If the catalyst is S deficient, the classical adsorption mechanism involving the S vacancy is dominant. With a fully sulfided catalyst surface the adsorption takes place through S S bonds. The catalyst is a dynamic evolving system adapting itself to its ever changing reaction environment. Each catalyst component fulfills multiple functions in determining the catalyst structure as well as its interaction with the reactant molecules.

MoS2 structures in high-activity hydrotreating catalysts. I: Semi-quantitative method for evaluation of transmission electron microscopy results. Correlations between hydrodesulfurization and hydrodenitrogenation activities and MoS2 dispersion

Abstract The dispersion and homogeneity of two series of sulfidic Al2O3 supported Co-Mo and Ni-Mo catalysts were investigated by transmission electron microscopy (TEM). Dispersion data were obtained by a novel semi-quantitative method for the evaluation of TEM micrographs. A detailed discussion of this method is given. It appears that the hydrodesulfurization and hydrodenitrogenation activities of the catalyst samples are proportional to the MoS2 dispersion. High-activity commercial catalysts are found to have very high MoS2 dispersions.

MoS2 structures in high activity hydrotreating catalysts. II: Evolution of the active phase during the catalyst life cycle. Deactivation model

Abstract Transmission electron microscopy (TEM) has been applied to study the changes of the dispersion and homogeneity of a sulfidic Ni-Mo/Al 2 O 3 catalyst during its life cycle. By using a semi-quantitative evaluation method for the TEM data, a correlation is found between the hydrodenitrogenation (HDN) activity and the MoS 2 dispersion. The deactivation appears to be related to the loss of MoS 2 dispersion. Regeneration of spent catalyst not only removes coke but also restores the MoS 2 dispersion. A model describing the evolution of the active phase during the catalyst life is proposed.

89 “Nebula”: A hydroprocessing catalyst with breakthrough activity

Abstract In this paper a new catalyst technology called NEBULA is presented. It has been developed by ExxonMobil, Akzo Nobel and Nippon Ketjen. NEBULA is based on a novel copound and it is several times more active than the hydroprocessing catalysts used in todays industrial units. The new catalyst has a much higher activity for desulfurization, dentrogenation and hydrogenation than the conventional CoMo and NiMo on alumina catalysts. The NEBULA catalyst currently in use in several commercial installations represents the biggest step forward in hydroprocessing over the last years. In this paper we will focus on the development of the NEBULA technology and on the applications for which it is appropriate.

Life cycle of hydroprocessing catalysts and total catalyst management

Abstract Ni/Co−Mo/W hydroprocessing catalysts are commercially used in different refinery applications over a wide range of conditions. Depending on the application, different deactivation mechanisms are of importance (coke formation, active phase sintering, metals deposition, poisoning). Except for extremely contaminated catalysts from residue or heavy vacuum gas oil applications, most catalysts are regenerated and reused. During their life cycle, they undergo several transformations from the oxidic into the sulfidic state and vice versa. Their life cycle is, therefore, very complex and involves many different steps and aspects. Not only it is extremely complicated from the fundamental point of view: There are also numerous technical, environmental as well as purely organizational issues involved. The leading catalyst manufacturers together with specialized firms offer the refineries total catalyst management during the entire catalyst life cycle, starting with the purchase of the fresh catalt and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance.

Deactivation of Mo/Al2O3 and NiMo/Al2O3 catalysts during hydrodesulfurization of thiophene

Abstract A Mo/Al 2 O 3 and a NiMo/Al 2 O 3 catalyst were subjected to the gas-phase hydrodesulfurization (HDS) of thiophene. The mechanism of catalyst deactivation was investigated. Sintering or modification of the active phase and blocking of the active sites or the pore structure by coke deposition were considered as possible causes. The freshly sulfided and the spent catalysts were characterized by quasi in situ TEM, IR spectroscopy on adsorbed CO, total carbon analysis, N 2 chemisorption and Hg porosimetry. For the NiMo/Al 2 O 3 catalyst the main cause for deactivation is loss of sulfur during the reaction. This process is fully reversible by H 2 S/H 2 treatment. In contrast coke deposition on the active sites is a major cause for deactivation of the Mo/Al 2 O 3 catalyst.

Improved NI-MO HDN catalysts through increased dispersion and intrinsic activity of the active phase

Abstract A series of Ketjenfine® Ni-Mo hydrodenitrogenation (HDN) catalysts has been analyzed by transmission electron microscopy (TEM). The differences in the dispersion and morphology of the catalysts have been evaluated. The TEM data have been used to calculate the number of the accessible active sites and to estimate which type of active sites is present. It has been shown that the HDN activity differences can be explained by the differences in the population of the active sites as well as by the different type of sites present in the catalysts. The newly developed grades, KF 846 and KF 848 have a significantly improved HDN performance over the existing grades.

67 Activity and deactivation of HDS catalysts: Studying the active phase using CO as a probe molecule

Publisher Summary This chapter investigates the initial deactivation of several hydrodesulfurization (HDS) catalysts using infrared spectroscopy using CO as a probe molecule (IR-CO). The chapter discusses the IR spectra of CO adsorbed on a freshly sulfided Mo/A12O3 catalyst at increasing CO pressure. Three prominent bands can be distinguished—the one at 2153 cm-1, which adsorbs CO weakly, is attributed to the hydroxyl groups on the alumina surface. Two other bands with a high CO adsorption strength, at 2105 and 2064 cm-1, are attributed to coordinatively unsaturated Mo2+ sites located at the edges and comers of the MoS2 slabs, respectively. The chapter reveals the IR spectra of 10 mbar CO adsorbed on the conventional NiMo/Al2O3 catalyst after being exposed to thiophene for different reaction times. Again, the interaction of CO with the support is evidenced by a band at 2153 cm-1. The thiophene treated catalysts show a broad band at 2080 cm-1, which is attributed to promote active sites responsible for the enhanced HDS activity.