Aluminate cobalt aluminates

Cobalt alloys, cast Cobalt aluminate Cobalt aluminate [1333-Cobalt alumimdes... 

The oxidation of cobalt metal to inactive cobalt oxide by product water has long been postulated to be a major cause of deactivation of supported cobalt FTS catalysts.6 10 Recent work has shown that the oxidation of cobalt metal to the inactive cobalt oxide phase can be prevented by the correct tailoring of the ratio Ph2cJPh2 and the cobalt crystallite size.11 Using a combination of model systems, industrial catalyst, and thermodynamic calculations, it was concluded that Co crystallites > 6 nm will not undergo any oxidation during realistic FTS, i.e., Pi[,()/I)i,2 = 1-1.5.11-14 Deactivation may also result from the formation of inactive cobalt support compounds (e.g., aluminate). Cobalt aluminate formation, which likely proceeds via the reaction of CoO with the support, is thermodynamically favorable but kinetically restricted under typical FTS conditions.6... 

Geometrical arguments are used only for the reduced metal to obtain an estimate of cluster size. This is equivalent to the assumption that the unreduced cobalt is interacting with the support or is present as a cobalt aluminate species. Despite the inherent assumptions of the method, the resulting cluster size much more closely approximates the true cluster size in comparison with reported data that erroneously assume that the cobalt is 100% reduced (i.e., excludes the reoxidation step). 

Li et al.22 investigated the effect of water for a platinum-promoted Co/y-Al203 catalyst during Fischer-Tropsch synthesis in a CSTR-type reactor. The catalyst lost activity in the presence of water, and it was found that small quantities of water (3-25 vol%) led to mild and reversible deactivation, whereas large amounts of water (>28 vol%) deactivated the catalyst more severely and permanently. The deactivation was attributed to the formation of cobalt oxide or cobalt aluminate. 

Goodwin and coworkers have studied the formation of cobalt aluminates.25,26 Jongsomjit et al. studied cobalt aluminate formation by TPR and RAMAN spectroscopy.26 The catalysts investigated were 25% Co/y-Al203 and Ru-promoted (0.5%)-25% Co/y-Al203. The Raman spectra of the samples after various pretreatments are shown in Fig. 3. 

A. Sirijaruphan, A. Horvath, J. G. Goodwin, Jr and R. Oukaci, Cobalt aluminate formation in alumina-supported cobalt catalysts effects of cobalt reduction state and water vapor, Catal. Lett., 2003, 91, 89-94. 

Cobalt alloys, 7 219-226. See also Cobalt high temperature alloys for orthopedic devices, 3 728 selenium and metallurgy of, 22 98 Cobalt alloy T-800, 7 223 properties, 7 223t CobaltCII) aluminate, uses, 7 241t Cobalt aluminate blue spinel, formula and DCMA number, 7 348t Cobalt Aluminate Blue, pigment for plastics, 7 370t... 

Zinc Chrome Cobalt Aluminate Blue pigment for plastics, 7 370t Zinc chromite... 

Stabilizing the Support Oxide. Promoter elements can be added to the support oxide resulting in a decreased Co compound formation with the support oxide. This is illustrated in Figure 3A. More specifically, strategies should be followed to avoid the formation of either cobalt titanate, cobalt silicate or cobalt aluminate as a result of Co solid-state diffusion under reducing or regeneration conditions in the subsurface of these support oxides. Some transition metals, for example Zr or La, could act in such a way. 

The majority of phosphors for cathode-ray tubes are coated with an oxide, silicate, or phosphate before use to improve their processing properties and stability to bum-in. Pigmenting of Y202S Eu3+ with finely divided Fe203 and of ZnS Ag+ with ultramarine or cobalt aluminate is also known. The pigment, which has the same body-color as the emission color of the phosphor, absorbs incident ambient light, effecting an increase in contrast [5.430]. 

Molybdenum oxide - alumina systems have been studied in detail (4-8). Several authors have pointed out that a molybdate surface layer is formed, due to an interaction between molybdenum oxide and the alumina support (9-11). Richardson (12) studied the structural form of cobalt in several oxidic cobalt-molybdenum-alumina catalysts. The presence of an active cobalt-molybdate complex was concluded from magnetic susceptibility measurements. Moreover cobalt aluminate and cobalt oxide were found. Only the active cobalt molybdate complex would contribute to the activity and be characterized by octahedrally coordinated cobalt. Lipsch and Schuit (10) studied a commercial oxidic hydrodesulfurization catalyst, containing 12 wt% M0O3 and 4 wt% CoO. They concluded that a cobalt aluminate phase was present and could not find indications for an active cobalt molybdate complex. Recent magnetic susceptibility studies of the same type of catalyst (13) confirmed the conclusion of Lipsch and Schuit. 

Visible Reflection Spectra. The final calcination temperature of MoCo-124 samples has been varied in order to study its influence on the coordination of the cobalt ions. The reflection spectra are shown in Figure 1. The spectra of MoCo-124, calcined at 400 and 500°C show a broad absorption band, covering the whole spectral region, with a weak superposition of the characteristic triplet of cobalt aluminate. This indicates that the cobalt ions are for the greater part still on the catalyst surface and not in the alumina lattice. The spectra of the MoCo-124 samples, calcined at 650-700 °C show a strong increase in intensity of the triplet band, while the broad absorption band has disappeared. This indicates the formation of a cobalt aluminate phase. 

Spectra of adsorbed pyridine have been recorded for the MoCo-124 catalysts, for which the final calcination temperature after the cobalt impregnation has been varied. It turns out that the 400 and 500°C calcined samples and the 650 and 700°C calcined samples show very similar spectra. Therefore we show only the spectra of the 400°C (low calcined) and the 650°C (high calcined) samples. Figure 4 shows spectra after desorption at 150 and 250°C. Few Brdnsted acid sites are observed in the low calcined MoCo-124 samples. The reflection spectra (Figure 1) indicate for these low calcined samples the presence of cobalt on the catalyst surface, because no cobalt aluminate phase could be detected. The high calcined samples do show the presence of Brdnsted acid sites the presence of a cobalt aluminate phase is concluded from the reflection spectra (Figure 1) for these samples. 

Boehmite Based. Catalysts. Hedvall (24) has discussed the formation of cobalt aluminate from CoO and AI2O3. He has shown that a relatively fast solid state reaction takes place when the alumina undergoes a phase change, viz. y-Al203 ->rt-A Og. This phenomenon is known as the Hedvall effect. 

For the high temperature calcined cobalt-molybdenum-alumina catalysts, the presence of a cobalt aluminate phase has been concluded from the reflection spectra. The BrtSnsted acid sites reappear in the spectrum of absorbed pyridine, indicating that the... 

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. 

Some bulk cobalt aluminate formation is expected to take place for the boehmite based catalyst, owing to a Hedvall effect (24).The spectrum of adsorbed pyridine on CoMo-124 B shows indeed a weaker 1612 cm l band, comparable with the intensity of this band for the MoCo-123 catalyst. This indicates that about 25 % of the cobalt ions has disappeared in the bulk of the alumina. (Figure lid). 

Beale AM, Sankar G. Understanding the crystallization of nanosized cobalt aluminate spinel from ion-exchanged zeolites using combined in situ QEXAFS/XRD. Chemistry of Materials. 2005 18(2) 263-272. 

Regulated Colorants That Are FDA Approved. It often seems a contradiction that many of the colorants that are suitable for use in food contact applications must also appear on an MSDS as a reportable or hazardous material. Examples include zinc oxide and zinc sulfide, both zinc compounds chromium oxide green (pigment green 17), a chromium compound carbon black and cobalt aluminate blue (pigment blue 28), which is not only reportable because of its cobalt content but is also a suspected carcinogen. 

Thenard A process for making white lead pigment (basic lead carbonate) by boiling litharge (lead monoxide) with lead acetate solution and passing carbon dioxide gas into the suspension. L.J. Thenard (1777 to 1857) was an eminent French chemist, more famous for his invention of Thenard s blue (cobalt aluminate). 

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