CoMo sulfides

Enhanced surface segregation. The variation in catalytic activity with Co/Mo ratio is proposed to be due to a surface enhancement of Co species in a mixed CoMo-sulfide phase, the Co being considered a promoter (127). This model does not specify the promotion mechanism nor does it take account of any role of the support. 

TMS catalyst, used in refineries, are mixed sulfides of cobalt-molybdenum (CoMo) or nickel-molybdenum (NiMo) with a promoter atomic ratio Co(Ni)/[Co(Ni) -I- Mo(W)] between 0.2 and 0.4 (2), supported on high surface area materials such as alumina to increase dispersion of the active component of the catalyst. Although CoMo sulfide is the favorite catalyst for HDS reactions, the use of NiMo sulfide is preferred in HDN reactions and hydrogenation processes, to treat feedstock with a high concentration of unsaturated compounds. 

Centeno A, Laurent E, Delmon B. 1995. Influence of the support of CoMo sulfide catalysts and of the addition of potassium and platinum on the catalytic performances for the hydrodeoxygenation of carbonyl, carboxyl, ant guaiacol-type molecules. J Catalysis 154 288-298. 

G. Li, W. Li, M. Zhang, K. Tao, 2004, Morphology and hydrodesulfurization activity of CoMo sulfide supported on amorphous Zt02 nanoparticles combined with AI2O3, Appl.Catal. A, 273, 233-238. 

Figure 9.5. Schematic picture of a sulfided CoMoS catalyst, along with a top view of the M0S2 structure, which is built up from trigonal prisms. Cobalt may be present in three states ...

Figure 6 shows spectra of NO adsorbed on a similar series of catalysts having the same concentrations of metals on Filtrol 90 alumina which, as discussed, sulfides the catalyst during subsequent reduction. The effect of sulfide, as on Mo/alumlna catalysts (8,10) and as later seen on CoMo catalysts after more-usual sulfiding, was mainly a marked reduction In the Intensities of the NO bands. These were roughly a fourth as Intense as those on unsulflded catalysts on... 

Figure 9 shows CO adsorbed on CoMo catalysts made on two alumina supports. Most of the CO was weakly-held, being largely removed by evacuation for 5 min. at 50 C. Depending on the extent of sulfiding during reduction, various bands were obtained. In the absence of sulfide, as previously seen on Mo/alumlna catalysts (, only Mo (4+ ) or Co (2+) Ions appear to be exposed after reduction, giving... 

Figure 7. Spectra of NO adsorbed on Co on sulfided CoMo/alumlna obtained by subtraction of NO/Mo bands from the spectra of Figure 6.

This work is a contribution to the understanding of the effect of spillover hydrogen in a type of catalyst of considerable industrial importance, namely that composed of transition metal sulfides and amorphous acidic solids. This is typically the case of sulfided CoMo supported on silica-alumina used for mild hydrocracking. 

The IR spectra in Fig.7 indicate the preferential adsorption of NO on the Co sites. It may be conjectured that the Mo sulfide species are physically covered by the Co sulfide species or that Co-Mo mixed sulfide species are formed and the chemical natures of the Co and Mo sulfides are mutually modified. The Mo K-edge EXAFS spectra were measured to examine the formation of mixed sulfide species between Co and Mo sulfides. The Fourier transforms are presented in Fig.8 for MoSx/NaY and CoSx-MoSx/NaY. The structural parameters derived from EXAFS analysis are summarized in Table 1. The structure and dispersion of the Mo sulfides in MoSx/NaY are discussed above. With the Co-Mo binary sulfide catalyst, the Mo-Co bondings are clearly observed at 0.283 nm in addition to the Mo-S and Mo-Mo bondings. The Mo-Co distance is close to that reported by Bouwens et al. [7] for a CoMoS phase supported on activated carbon. Detailed analysis of the EXAFS results for CoSx-MoSx/NaY will be presented elsewhere. It is concluded that the Co-Mo mixed sulfides possessing Co-S-Mo chemical bondings are formed in CoSx-MoSx/NaY. 

Olive, J.-L. Biyoko, S. Moulinas, C., and Geneste, P., Hydroprocessing of Indole and o-Ethylaniline over Sulfided CoMo, NiMo, and NiW Catalysts. Appl. Catal, 1985. 19 pp. 165-174. 

Interestingly, retardation of either nickel or cobalt sulfidation to temperatures where MoS2 has already been formed can also be achieved by applying chelating agents, such nitrilotriacetic acid, which bind cobalt or nickel and release these elements at higher temperatures. In this way one can prepare the CoMoS phase on... 

The active components of this so-called CoMoS catalyst, cobalt and molybdenum, are only active as sulfides. This implies that sulfur should always be present in the gas to keep the metals in the sulfided state. The operating temperature... 

Combustion, 27 189, 190 reaction, sites for, 33 161-166 reaction scheme, 27 190, 196 Commercial isomerization, 6 197 CoMo catalysts, 40 181 See also Cobalt (nickel)-molybdenum-sulfide catalysts Compact-diffuse layer model, 30 224 Compensation behavior, 26 247-315 active surface, 26 253, 254 Arrhenius parameters, see Arrhenius parameters... 

The coals used were PSOC 1098 Illinois 6 and Beulah-Zap North Dakota lignite from the Argonne coal bank. The analytical data of these coals are shown in Table I. The ratio of catalyst to coal was approximately 0.6 mmoles of metal per gram of coal. The organometallic catalysts were molybdenum(II) acetate dimer, Mo2(OAc)4, obtained from Strem, molybdenum(II) allyl dimer Mo2(OAc)4, was prepared by die method of Cotton and Pipal (25). The NiMo supported catalyst was prepared by addition of bis(l,5-cyclooctadiene) Ni(0) (Strem) to sulfided Mo on alumina (. Cp2Mo2( l-SH)2(p.-S)2, referred to as MoS2(OM), was prepared by modification of method of Dubois et al. (26), and Cp2Mo2Co2( i3-S)2(li4-S)(CO)4, CoMo(OM) was prepared by the method of Curtis et al. (27). Pentacarbonyl iron was obtained from Aldrich,... 

The use of nitrides, along with sulfides and carbides, as catalysts for hydroprocessing has recently been extensively reviewed by Furimsky and will not be discussed in detail here. Subsequently, Al-Megren et have published a comparison of the activities of bulk CoMo carbide, oxide, nitride and sulfide catalysts for pyridine hydrodenitrogenation. Of these, the sulfide catalysts were reported to possess more stable activity, with the carbide being next, followed... 

It can also be observed from the schematic of the interactions shown in Fig. 10 that interaction zones that provide the possibility for sharing sulfur atoms by the two different phases exist. The structure of these interaction zones are crucial to understanding the interaction of sulfides with supports and promoter phases. The basal plane interaction with a second phase can be expected to be weak, but charge transfer might be expected if metal atoms are exposed on the second phase. Such an interaction would be similar to an intercalation interaction. The edge interaction will be much stronger, and here a transition zone with a possible epitaxial relationship between MoS2 and the second phase is expected. It is in this zone that we can expect to find the surface phases as described above (for example, the CoMoS phase). But in the cases described here, the surface phase becomes a line phase at the boundary between the two bulk phases. It is our belief that the detailed study of these phases represents a key area for future research in TMS catalysis. 

These tetrahedral distorted cobalt atoms can be observed by NMR as a pure phase on carbon supports in the absence of molybdenum and are thus stable these probably correspond to the Co sites observed by Topspe s group using Mossbauer spectroscopy because Craje et al. (93) found a similar Mossbauer doublet for both cobalt in CoMo catalysts and pure cobalt sulfide on carbon support. They are also active for HDS and confirm the findings of Prins and co-workers (94) and Ledoux (96). These different structures are in full agreement with the XANES experiments performed by Prins and co-workers (95) and Ledoux (96). These structures also led Ledoux et al. to an incorrect interpretation of the synergy effect (64). On poorly dispersed catalysts supported on silica or in bulk form, their presence and activity are large enough to explain the increase in activity when cobalt is added to molybdenum, but on well-dispersed catalysts i.e., on alumina or carbon support this interpretation is shown to be incorrect if the activity is carefully measured. 

Rate constants (x 10 min. g.cat ) for hydrogenation of 4-chloronitrobenzene (k. ) and hydrogenolysi s of 4-chloroaniline (kg) over sulfided CoMo HR 306 and NiMo HR 348 catalysts at temperatures ranging from 50°C to 250°C and 20 bar of hydrogen pressure... 

Recently we have proposed an HDS catalytic treatment based on sodium-doped CoMo catalysts [Ref. 1-3]. Previous studies concerned essentially alumina-supported catalysts. As carbon was shown to be a good support for sulfided CoMo catalysts [Ref.4], we decided to investigate the performance of carbon-supported catalysts in terpene HDS. 

Impregnation of cobalt and molybdenum (without sodium) increases largely the isomerizing activity of the catalyst the /3-pinene is then completely converted. The catalysts prepared with sodium molybdate and sodium hydroxide (Co-Mo-Na and Na-Co-Mo-Na) have lower isomerizing activities while their HDS activities are significantly increased. As in the case of alumina supported catalysts the sulfided CoMo phase protected by a double layer of alkaline ions on the carbon support gives the best results in HDS of /3-pinene. The behaviour of this catalyst was examined in desulfurization of the turpentine oil (40% a-pinene, 25% /3-pinene, 25% A -carene and 10% camphene + dipentene + myrcene, 1500 ppm S). The results are recorded in Table 6. 

---