Hydrodesulfurization, catalyst model

Figure 4.23. Infrared spectra of NO probe molecules on sulfided Mo, Co, and Co-Mo hydrodesulfurization catalysts. The peak assignments are supported by the IR spectra of organometallic model compounds. These spectra allow for a quantitative titration of Co and Mo sites in the Co-Mo catalyst.

Coulier, L. Kishan, G. van Veen, J. A. R., and Niemantsverdriet, J. W., Surface science models for CoMo hydrodesulfurization catalysts Influence of the support on hydrodesulfurization activity. Journal of Vacuum Science Technology A Vacuum, Surfaces, and Films, 2001. 19(4) pp. 1510-1515. 

Perez De la Rosa, M., Trader, S. Berhault, G., et al., Structural studies of catalytically stabilized model and industrial-supported hydrodesulfurization catalysts. J. Catal., 2004. 225 pp. 288-299. 

We illustrate the use of RBS with a study on the sulfidation of molybdenum hydrodesulfurization catalysts supported on a thin layer of Si02 on silicon [21], As explained in connection with the SIMS experiments on this model system (Fig. 4.8), the catalyst is sulfided by treating the oxidic Mo03/Si02 precursor in a mixture of H2S and H2. RBS is used to determine the concentrations of Mo and S. 

LEIS has been applied to study the surface composition of Co-Mo and Ni-Mo hydrodesulfurization catalysts [46-48], Fe-based Fischer-Tropsch [49] and ammonia synthesis catalysts [50], and model systems such as Pt evaporated on Ti02 [51]. The review of Horrell and Cocke [52] describes several applications. 

What is the structure of this Co-Mo-S phase A model system, prepared by impregnating a MoS2 crystal with a dilute solution of cobalt ions, such that the model contains ppms of cobalt only, appears to have the same Mossbauer spectrum as the Co-Mo-S phase. It has the same isomer shift (characteristic of the oxidation state), recoilfree fraction (characteristic of lattice vibrations) and almost the same quadrupole splitting (characteristic of symmetry) at all temperatures between 4 and 600 K [71]. Thus, the cobalt species in the ppm Co/MoS2 system provides a convenient model for the active site in a Co-Mo hydrodesulfurization catalyst. 

Mo(CO)6 and Co(CO)3NO NaY zeolite Adsorption from vapor phase and H2S treatment Intrazeolite Co2Mo2S i clusters, model hydrodesulfuration catalyst [25]... 

Dihydro-277-l-benzothiopyran-4-ol has been used as a model sulfur-containing compound in a study of molecular metal sulfide cluster substrate binding to oil-refinery hydrodesulfurization catalysts <2002IC1336> and also as a model compound in an evaluation of the removal of heterocyclic S-containing compounds from oil precursors by supercritical water <1995MI1485>. 

Those deactivation models accounting for both coke and metal sulfides are rather simple. Coke and metals foul residue hydrodesulfurization catalysts simultaneously via different processes, and decrease both intrinsic reaction rate and effective diffusivity. They never uniformly distribute in the commercial reactors. We have examined the activity and diffusivity of the aged and regenerated catalysts which were used at the different conditions as well as during the different periods. This paper describes the effects of vacuum residue conversion, reactor position, and time on-stream on the catalyst deactivation. Two mechanisms of the catalyst deactivation, depending on residue conversion level and reactor position, are also proposed. 

Beckler, R. K. and M. G. White, Polynuclear Metal Complexes as Model Mixed Oxide Catalysts Selective Chemisorption of NH3 and NO , J. Catal, 109, pp. 25-36 (1988) Beckler, R. K. and M. G. White, Polynuclear Metal Complexes as Model Mixed Oxide Catalysts Isomerization Activity , J. Catal, 110, pp. 364-374 (1988). Coulier, L., V. G. Kishan, J. A. R. van Veen, and J W. Niemantsverdriet, Surface science models for CoMo Hydrodesulfurization Catalysts the Influence of the support on hydrodesulfurization acidity , J. Vac Scl Technol A. 19, Issue 4, 1 July/August 2001, pp 1510-5. 

Feed properties and operation conditions determine catalyst life in the residue hydrodesulfurization. In a high conversion operation of vacuum residue, catalyst deactivation due to coke is as important as the one due to metals. Though many researchers have worked on understanding and modelling deactivation of residue hydrodesulfurization catalysts, there has still been a controversy in a coke deactivation mechanism [2, 3]. Very few publications are available discussing an effect of a bed temperature profile on catalyst deactivation in large scale adiabatic commercial reactors. Most of the studies on deactivation of residue hydrodesulfiirization catalysts have been done with small-scale isothermal reactors [2,3,4,5]. The activity tests of the used catalysts were conducted to study the catalyst deactivation in the commercial reactors. This paper also describes an effect of a bed temperature profile on coke deactivation, which was tested in the commercial reactors. 

P. Mills, S. Korlaim, M.E. Bussell, M.A. Reynolds, M.V. Ovchinnikov, R.J. Angelici, C. Stinner, T. Weber R. Prins (2001). J. Phys. Chem. A, 105, 4418-4429. Vibrational study of organometallic complexes with thiophene ligands Models for adsorbed thiophene on hydrodesulfurization catalysts. 

In this chemistry, it is natural to focus on models for the catalytic reactions that are most important economically or which are most poorly understood because of difficulties of direct study. One which best fits these criteria is the catalytic hydrotreatment of petroleum feedstocks, which is used to remove sulfur and other heteroatoms, which interfere with subsequent catalytic reactions such as petroleum reforming, from the hydrocarbons. Molybdemun sulfide is the most common metal sulfide used in this catalysis, and hydrogen activation and C-S bond hydrogenolysis are known to be key reactions occurring at the catalyst surface but details are difficult to obtain. Study of model binuclear and cluster complexes has elucidated mechanisms of several of the key reactions and Section 2.6 describes important recent advances in this field, with the focus being on models for hydrodesulfurization catalysts. 

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