Cobalt Promoted

The di(hydroxyaLkyl) peroxide (2) from cyclohexanone is a soHd which is produced commercially. The di(hydroxyaLkyl) peroxide (2) from 2,4-pentanedione (11, n = 1 X = OH) is a water-soluble soHd which is also produced commercially (see Table 5). Both these peroxides are used for curing cobalt-promoted unsaturated polyester resins. Because these peroxides are susceptible to promoted decomposition with cobalt, they must exist in solution as equihbrium mixtures with hydroperoxide stmctures (122,149). 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

Catalyst choice is strongly influenced by the nature of the feedstock to be hydrotreated. Thus, whereas nickel-promoted and cobalt—nickel-promoted molybdenum catalysts can be used for desulfurization of certain feedstocks and operating conditions, a cobalt-promoted molybdenum catalyst is generally preferred in this appHcation. For denitrogenation and aromatics saturation, nickel-promoted molybdenum catalysts usually are the better choice. When both desulfurization and denitrogenation of a feedstock are required, the choice of catalyst usually is made so that the more difficult operation is achieved satisfactorily. 

Fischer Tropsch synthesis is catalyzed by a variety of transition metals such as iron, nickel, and cobalt. Iron is the preferred catalyst due to its higher activity and lower cost. Nickel produces large amounts of methane, while cobalt has a lower reaction rate and lower selectivity than iron. By comparing cobalt and iron catalysts, it was found that cobalt promotes more middle-distillate products. In FTS, cobalt produces... 

The molybdenum on alumina catalyst was also tested for activity with and without arsenic. Although this catlyst has a much lower intrinsic activity for HDS, the results in Figure 4 show that 3.6% arsenic almost completely deactivates the catalyst. The small amount of activity remaining is that expected for AI2O3 alone. Thus arsenic also deactivates catalysts without cobalt promoters. 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

Cobalt-promoter alloy formation. Metal alloying or bimetallic alloy formation may also influence the activity and selectivity of Co F-T catalysts. 

Figure 4 The different modes of action of electronic promotors in Co-based Fischer-Tropsch catalysis (A) promoter metal oxide decoration of the cobalt surface (B) the SMSI effect and (C) cobalt-promoter alloy formation...

Summarizing, there are still many scientific challenges and major opportunities for the catalysis community in the field of cobalt-based Fischer-Tropsch synthesis to design improved or totally new catalyst systems. However, such improvements require a profound knowledge of the promoted catalyst material. In this respect, detailed physicochemical insights in the cobalt-support, cobalt-promoter and support-support interfacial chemistry are of paramount importance. Advanced synthesis methods and characterization tools giving structural and electronic information of both the cobalt and the support element under reaction conditions should be developed to achieve this goal. 

Fischer-Tropsch synthesis Iron and cobalt promoted with KjO and... 

D.S. Atomic-Scale Structure of the Cobalt-Promoted Catalyst... 

Fig. 25. (a) Ball model of the proposed CoMoS structure. The CoMoS cluster is shown in top view, exposing the unpromoted molybdenum edge and a cobalt-promoted sulfur edge (molybdenum dark sulfur bright cobalt dark with white spot). Also shown on the basal plane is a single cobalt inclusion. 

The optimal activity for a cobalt-molybdenum-alumina catalyst is obtained by calcination at the higher temperatures. This means that the cobalt ions, present as a cobalt aluminate phase according to the reflectance spectra and the magnetic susceptibility measurements, still have a pronounced promoting action after this calcination. The assumption of cobalt present in the surface layer of the alumina lattice explains both the high activity due to the cobalt promotion as well as the presence of the second Lewis band. This configuration is shown schematically in Figure lib. 

The most stable position for the cobalt promoter atoms was calculated to be at the edge, substituting as it were for the molybdenum atoms (38). The promoter decreased the equilibrium sulfur coverage of the edge from 50 to 0-17% for Co/Mo(edge) = 1, and it weakened the sulfur-metal bond... 

Figure 4 Representation of the three components of a typical HDS catalyst (alumina, M0S2, and cobalt promoter) and the spatial relation between them.

Further evidence for the catalytic importance of amorphous material comes from experiments carried out with cobalt-doped catalysts. Hutchings et al. (217) found that doping of the catalysts with cobalt improved their performance. Moreover, Sajip et al. (148) found that the cobalt-promoted catalysts are far more disordered than the undoped catalysts. In the doped catalysts, the promoter is dispersed in the amorphous phase, and cobalt is not found in the vanadyl pyrophosphate crystals. It is thought that one of the properties of the cobalt promoter is to stabilize the disordered phase and V -containing phases in the final catalysts, which leads to improved performance. This suggestion implies that the disordered material is the catalytically active vanadium phosphate phase. 

The promotional effects of cobalt (148,150,165,167,169,173,179,182,191-203) and iron (66,148,166,167,171,176,179-181,193-195,201,204-207) have been widely investigated recently. Abdelouahab et al. (193) considered the effects of these promoters on the structure of catalysts prepared with organic solvents. Both cobalt and iron promoters were found to increase the selectivity to MA the butane conversion was found to decrease with cobalt promoters and increase with iron promoters. 

As in the investigation with zirconium promoters carried out by Zeyss et al. (174), cobalt and iron were found to promote the formation of VOPO4 phases during the conversion of the precursor to the active catalyst. The difference in activity between the iron- and cobalt-promoted catalysts is considered to be a consequence of the different redox potentials of the promoters. As the ratio decreases, the butane conver-... 

This phenomenon has also been observed for catalysts prepared using an aqueous route (182). Both the iron and cobalt promoters led to an increase in selectivity. The iron-promoted catalyst was characterized by an increase in activity, but the cobalt-promoted catalyst was characterized by a decrease in activity. The decrease in activity of the cobalt-doped catalyst was attributed to the formation of VOPO4 in the final catalyst. The VOPO4 is formed by the oxidation of V0HP04 1 H20 during the introduction of the promoters in the incipient wetness technique. A similar effect was reported for catalysts doped with indium and tetraethy-lorthosilicate (TEOS) (181). The improved performance was observed only with both promoters in the catalyst. It was proposed that the... 

Cobalt-Promoted Formation of Five-Membered Rings— The Pauson-Khand Reaction... 

Cobalt-promoted molybdenum sulfides supported on alumina are widely used in petroleum refining for sulfur removal [1]. However, there is now increasing necessity to further improve their performance (activity, selectivity, and stability), due to more and more stringent legislation on sulfur contents in transportation fuels [2]. It is thus primordial to understand the detailed structure and catalytic behavior of these catalysts. In this respect, controlled preparation of catalysts with desired composition and structure has great importance in permitting fundamental study of structure-performance correlation. 

As the edge sites of sulfide slabs are generally known as active sites in hydrotreating reactions [1], it seemed thus possible to us that reactions take place preferentially between sulfide edge sites and organometallic complexes, if placed in contact each other. Selective modification of edge sites could then be made by different metals like cobalt or tin. In this study, we applied SOMC to the modification of the conventional hydrotreating catalysts alumina-supported molybdenum sulfides with or without cobalt promoter. The Co and Sn... 

---