Cobalt catalysts behavior

The present study revealed effects of various rutile/anatase ratios in titania on the reduction behaviors of titania-supported cobalt catalysts. It was found that the presence of rutile phase in titania could facilitate the reduction process of the orbalt catalyst. As a matter of fact, the number of reduced cobalt metal surface atoms, which is related to the overall activity during CO hydrogenation increased. 

Effect of a Novel Nitric Oxide Calcination on the Catalytic Behavior of Silica-Supported Cobalt Catalysts during Fischer-Tropsch Synthesis, and Impact on Performance Parameters... 

The above behavior of narrow-pore supported cobalt catalysts toward co-fed water can also be explained in terms of relative size of cobalt clusters, pore network of support, expected location of cobalt clusters within the pore network, and relative differences in the residence time of water vapor within and outside the... 

These adducts are more active than the iron ones in the conversion of syngas. At 250°C, a higher yield of methane is observed (Table U) and carbon dioxide is produced in smaller amounts. Inspection of Table 5 summarizing the influence of the H2/CO ratio on products selectivity also indicates a higher production of saturated hydrocarbons. This behavior is typical for cobalt catalysts in F-T synthesis (j2,25). The chain-length distribution is similar to that observed for catalysts derived... 

More insights are given in a publication by Varghese et al. in 2010 [23]. An alt-PPG sample prepared with a homogeneous cobalt catalyst shows that Lewis acids and water may generate hydroxide or carbonate chain ends with subsequent fast unzipping at temperatures as low as 150°G [23]. This behavior was observed for a product with catalyst residues and with thermally unstable linkages in the main... 

The general behavior of rhodium catalysts with respect to stability thus appears to be similar to that seen for cobalt catalysts an inverse relationship between carbon monoxide partial pressure and reaction temperature is apparent. Stability decreases rapidly with increasing temperature, and raising the pressure tends to improve catalyst stability. It is not certain whether the adverse effects of increasing the H2/CO ratio are merely the result of a decreased CO partial pressure, or whether increased hydrogen partial pressure induces catalyst instability. 

Variations in reaction conditions, particularly with respect to acid and iodide concentrations, have profound effects on the positions of these equilibria, and these have, for the most part, added significant complexity to the behavior of the systems. It has also been determined that the catalytic activity of the cobalt catalyst system is increased with the introduction of H2 (44) or halides (vide infra), though these increases in rate are quite often at the expense of selectivity. The presence of added H2 serves as an alternate route to the formation of the hydride species ... 

A value of c equal to 0.3, previously used to describe FT selectivity data on Ru catalysts (4), was also chosen here to describe the behavior of cobalt catalysts. This equation for hydrocarbon diffusion in melts reflects the strong influence of molecular size in reptation and entanglement models of transport in such systems (IJ6). Our model also requires the input of intrinsic values for jSn (given by the asymptotic j8r), jSo, j8r, and j8s, measured independently. After such parameters are specified, the model yields a non-Flory carbon number distribution of increasingly paraffinic hydrocarbons that agrees well with our experimental observations (Fig. 16). 

Both cobalt and nickel catalysts could be modified to give either Type A or Type B behavior depending on the temperature used to reduce the catalyst. 2 Cobalt catalysts reduced at lower temperatures (250-300°C) gave primarily... 

On the other hand, it is known that catalyst support exerts a great influence on the catalytic properties of the metallic particles deposited on it during the carbon dioxide reforming of methane. So for a given metal, catalytic activities can be changed [5], product selectivities modified [6] and carbon deposition resistivity altered [7]. Also the addition of certain promoters can improve the catalytic behavior of a given supported metal catalyst. In particular we have shown the benefit of the MgO addition to cobalt catalyst [ 8, 9]. 

Nickel precipitation catalysts. Fischer and Meyer (11) carried out exhaustive research work trying to develop active Ni catalysts for the synthesis of higher hydrocarbons. In spite of the failure of all previous attempts, Fischer and Meyer found two types of nickel catalysts with a behavior similar to that of the best cobalt catalysts. 

The quality of the kieselguhr (diatomaceous earth) is of importance for the behavior of the cobalt catalyst. Kieselguhr of different origin resulted in catalysts of different activity. Ruhrchemie therefore investigated the reasons for the different behavior and issued standards for kieselguhr. The preliminary thermal treatment should be carried out... 

Figure 13 presents an example for changes in the behavior of a cobalt catalyst used for synthesis of hydrocarbons from carbon monoxide and hydrogen, and analytical investigations of a cobalt catalyst at different distances from the gas inlet (94). 

Cobalt and nickel catalysts convert the oxygen of the carbon monoxide preferentially to water, iron catalysts to carbon dioxide. The different behavior of the iron can not be explained by conversion of primarily produced water with carbon monoxide. The water gas shift reaction can be carried out in the presence of cobalt catalysts as well as in the presence of iron catalysts. The amount of carbon dioxide increases with increasing synthesis temperatures, and also in the presence of cobalt catalysts. 

In 1930, Smith, Hawk, and Golden (16) discovered that ethylene, when added to the synthesis gas, enters into the oil-producing reaction on a Co-Cu-MnO catalyst but not on an Fe-Cu catalyst. In the latter case, most of the ethylene appears as ethane in the products. It was pointed out also that water was the main oxygenated product from the cobalt catalyst, whereas carbon dioxide was the chief corresponding product on the iron catalyst. The behavior of ethylene when added to 83mthesi8 gas and passed over a cobalt catalyst was verified by Craxford (17) in 1939. 

Main different behaviors of iron and cobalt catalysts are the following ... 

Cobalt and iridium complexes can also function as hydroformylation catalysts, but of course the cobalt catalysts are much better known.t The reduced activity of Co and Ir compared to Rh has been attributed to the greater stability of their 18-electron complexes to ligand dissociatioii. The Co and Ir systems do provide some interesting comparisons with Rh, both in the behavior of the catalytic systems and in the identification of catalytic intermediates. 

The study of the crosshnking of dimethacrylate-based VERs using scanning/isothermal DSC and DMTA describes the correlation between the reaction kinetics, as well as the relaxational behavior, cure temperature and peroxide and cobalt catalyst concentration [195]. An increase in the methylethylketone peroxide concentration increased the polymerization rate and reduced the gel time. The use of cobalt octoate as the promoter also reduced the gel time but retarded the reaction rate, except at very low concentrations. This could be explained by the dual role of the cobalt species as a catalyst of the formation of radicals from MEKP (Scheme 30) ... 

Nevertheless, it is generally accepted that the oxidation behavior of cobalt catalysts is related to the FTS reaction conditions, especially, to water and cobalt crystallite size. Gong et studied the water for-... 

The present research showed a dependence of various ratios of rutile anatase in titania as a catalyst support for Co/Ti02 on characteristics, especially the reduction behaviors of this catalyst. The study revealed that the presence of 19% rutile phase in titania for CoATi02 (C0/RI9) exhibited the highest number of reduced Co metal surface atoms which is related the number of active sites present. It appeared that the increase in the number of active sites was due to two reasons i) the presence of ratile phase in titania can fadlitrate the reduction process of cobalt oxide species into reduced cobalt metal, and ii) the presence of rutile phase resulted in a larger number of reduced cobalt metal surface atoms. No phase transformation of the supports further occurred during calcination of catalyst samples. However, if the ratios of rutile anatase were over 19%, the number of active sites dramatically decreased. 

The catalyst remained stable for a long diile (over 50 h) under reaction conditions at the above ten erature. In order to try to tmderstand this interesting behavior, let us first focus our attention on the behavior of monometallic cobalt and platinum mordenite samples. 

The [Co(CN)5]3 complex is an effective catalyst for some reactions, particularly the isomerization of alkenes. Newer and more efficient catalysts have been developed for some of the processes, but the catalytic behavior of the pentacyanocobalt(II) ion is also significant from a historical perspective. In reactions such as that shown in Eq. (22.10), two Co2+ ions increase one unit in oxidation state, instead of the more common situation in which one metal ion increases by two units in oxidation state. The cobalt complex also reacts with CIT3I, Cl2, and H202, which are indicated as X-Y in the equation... 

---