Cobalt catalysts experiment

Supported Cobalt Catalysts. Experiments were conducted with [Co(PC)]/Si02 at 340°C to determine the important variables for the catalysis of a typical [M(PC)]. Table IV gives the results for runs which were conducted for varying periods of time. It is seen that even at 100 hr. the conversion only reached 36%. The equilibrium conversion at 342°C can be estimated to be 97%. (9) Thus, the reaction is quite far from equilibrium even at long times. This may be taken as evidence for product inhibition of the catalysis. This might be expected since tetrahydroquinoline is a stronger Lewis base than quinoline. Thus, the product could bind to the metal center and prevent activation of the substrate and/or hydrogen. One important conclusion is that the reaction is not over in 24 hours and it can be assumed that the difference in conversions noted in Table I with different [M(PC)] are due to differences in inherent activity of the [M(PC)]. 

Hydrogen chemisorption Static H2 chemisorption at 100°C on the reduced cobalt catalysts was used to determine the number of reduced surface cobalt metal atoms. This is related to the overall activity of the catalysts during CO hydrogenation. Gas volumetric chemisorption at 100°C was performed using the method described by Reuel and Bartholomew [6]. The experiment was performed in a Micromeritics ASAP 2010 using ASAP 2010C V3.00 software. 

Although the FTS is considered a carbon in-sensitive reaction,30 deactivation of the cobalt active phase by carbon deposition during FTS has been widely postulated.31-38 This mechanism, however, is hard to prove during realistic synthesis conditions due to the presence of heavy hydrocarbon wax product and the potential spillover and buildup of inert carbon on the catalyst support. Also, studies on supported cobalt catalysts have been conducted that suggest deactivation by pore plugging of narrow catalyst pores by the heavy (> 40) wax product.39,40 Very often, regeneration treatments that remove these carbonaceous phases from the catalyst result in reactivation of the catalyst.32 Many of the companies with experience in cobalt-based FTS research report that these catalysts are negatively influenced by carbon (Table 4.1). 

Bertole et al.u reported experiments on an unsupported Re-promoted cobalt catalyst. The experiments were done in a SSITKA setup, at 210 °C and pressures in the range 3-16.5 bar, using a 4 mm i.d. fixed bed reactor. The partial pressures of H2, CO and H20 in the feed were varied, and the deactivation, effect on activity, selectivity and intrinsic activity (SSITKA) were studied. The direct observation of the kinetic effect of the water on the activity was difficult due to deactivation. However, the authors discuss kinetic effects of water after correcting for deactivation. The results are summarized in Table 1, the table showing the ratio between the results obtained with added water in the feed divided by the same result in a dry experiment. The column headings refer to the actual experiments compared. It is evident that adding water leads to an increase in the overall rate constant kco. The authors also report the intrinsic pseudo first order rate-coefficient kc, where the overall rate of CO conversion rco = kc 6C and 0C is the coverage of active... 

The hydroformylation of alkenes was accidentally discovered by Roelen while he was studying the Fischer-Tropsch reaction (syn-gas conversion to liquid fuels) with a heterogeneous cobalt catalyst in the late thirties. In a mechanistic experiment Roelen studied whether alkenes were intermediates in the "Aufbau" process of syn-gas (from coal, Germany 1938) to fuel. He found that alkenes were converted to aldehydes or alcohols containing one more carbon atom. It took more than a decade before the reaction was taken further, but now it was the conversion of petrochemical hydrocarbons into oxygenates that was desired. It was discovered that the reaction was not catalysed by the supported cobalt but in fact by HCo(CO)4 which was formed in the liquid state. 

The concept of a (bound) formaldehyde intermediate in CO hydrogenation is supported by the work of Feder and Rathke (36) and Fahey (43). Experiments under H2/CO pressure at 182-220°C showed that paraformaldehyde and trioxane (which depolymerize to formaldehyde at reaction temperatures) are converted by the cobalt catalyst to the same products as those formed from H2/CO alone. The rate of product formation is faster than in comparable H2/CO-only experiments, and product distributions are different, apparently because secondary reactions are now less competitive. However, Rathke and Feder note that the formate/alcohol ratio is similar to that found in H2/CO-only reactions (36). Roth and Orchin have reported that monomeric formaldehyde reacts with HCo(CO)4 under 1 atm of CO at 0°C to form glycolaldehyde, an ethylene glycol precursor (75). The postulated steps in this process are shown in (19)—(21), in which complexes not observed but... 

Knowledge of patents claiming cobalt catalysts for the conversion of H2/CO mixtures to ethylene glycol (31-33) appears to have led to initial investigation of rhodium catalysts for this reaction at Union Carbide (27, 85-87). Early experiments by Pruett and Walker at pressures of about 3000 atm indicated that the activity of rhodium was notably greater than that found for cobalt. Several other potential catalyst precursors, including compounds of Sn, Ru, Pd, Pt, Cu, Cr, Mn, Ir, and Pb, were screened for activity under pressures of about 1500 atm and found not to produce detectable... 

Fell also described the hydroformylation of fatty acids with heterogenized cobalt carbonyl and rhodium carbonyl catalysts [37]. The products of the reaction with polyunsaturated fatty acids were, depending on the catalyst metal, poly- or monoformyl products. The catalyst carrier was a silicate matrix with tertiary phosphine ligands and cobalt or rhodium carbonyl precursors on the surface. The cobalt catalyst was applied at 160-180°C and gave mostly monofunctionalized fatty acid chains. With linoleic acid mixtures, the corresponding rhodium catalyst gave mono- and diformyl derivatives. Therefore, the rhodium catalyst was more feasible for polyfunctionalized oleocompounds. The reaction was completed in a batch experiment over 10 h at 100 bar and 140°C rhodium leaching was lower than 1 ppm. 

The hypothesis of formation of oxygenated compounds as intermediate products was rejected by Eidus on the basis of experiments on the conversion over cobalt of methyl and ethyl alcohols and formic acid which were found to form carbon monoxide and hydrogen in an intermediate step of the hydrocarbon synthesis (76). Methylene radicals are thought to be formed on nickel and cobalt catalysts (76) by hydrogenation of the unstable group CHOH formed by interaction of adsorbed carbon monoxide and hydrogen, while on iron catalysts methylene radicals are probably formed by hydrogenation of the carbide (78,81). Carbon dioxide was found to interact with the alkaline promoters on the surface of iron catalysts as little as 1 % potassium carbonate was found to occupy 30 to 40% of the active surface area. The alkali also promotes carbide formation and the synthesis reaction on iron (78). 

Strong evidence for the homogeneous nature of the hydrogenation in the presence of a cobalt catalyst was provided by the experiments of Wender, Orchin, and Storch (10). The basis of these experiments was the postulation that either dicobalt octacarbonyl or cobalt hydrocarbonyl, both of which are soluble in most organic solvents, was the essential catalyst for the hydrogenation. 

In the first experiment, no carbon monoxide was present. The reduction proceeded smoothly the calculated pressure drop was secured and butanol was isolated as the reaction product. This experiment demonstrated the activity of the reduced metallic cobalt catalyst for the usual type of heterogeneous catalysis. 

Experiments by Bezemer et al. (10) demonstrated a strong decrease in activity of cobalt catalysts when the cobalt particles became smaller than 4 mn in diameter. The authors excluded support effects by using an inert support. They also concluded that the cobalt particles remained metallic. These results agree with earlier reports of a structure dependence of the Fischer-Tropsch reaction (11,12). 

In a recent study, R. Pettit et at. examined the validity of tire Fischer-Tropsch carbide mechanism, the Anderson-Emmett hydroxy carbene mechanism and the Pichlcr-Schulz mediaiiism [174. In a first experiment, the Schulz Flory distribution obtained by CO/H conversion over a cobalt catalyst in the absence and in the presence of CH N] was studied. It was found that addition of CHjN resulted in a signillcant increase of the propagation rate which is in favour of the assumption of methylene as a building block, as predicted by the carbide mechanism. Furthermore, the reaction was carried out using labeled CO (90% CO and 10% CO), H2. and CHjNj in variable ratios. The number of atoms in the propenc fraction was calculated according to the three... 

Deuteration experiments showed that the p-H atom in the product stems from borohydride whereas the a-H atom is introduced by proton transfer from ethanol. Formation of the a-(C-H) bond is nonstereoselective accordingly, the reduction of analogous substrates with an a- instead of a p-disubstituted double bond leads to racemic products (a mechanistic model rationalizing the stereoselectivity of (semicorrinato)cobalt catalysts is available ). 

Group 9. Eligh-pressure in situ NMR experiments were used to follow the reaction of CO with [Co(CO)3L]2, where L = tertiary phosphine.1140 Similar experiments (31P) were used to monitor reactions of phosphine ligands derived from (P)-(+)-limonene with cobalt catalyst systems (Co2(CO)8, HCo(CO)4.1141... 

As has already been described, the nickel-catalyzed-system is currently the most general protocol for the polymerization of isocyanides. An initial report [5] described that Ni(CO)4, Ni(CO)3(PPh3), Cp2Ni, and CpNi(CO)2 show high catalytic activity in the polymerization of cyclohexyl isocyanide in benzene, yielding poly(isocyanide) 2 as a white powder, although the nickel catalysts are a little less active than the corresponding cobalt catalysts (Scheme 7). In a typical experiment, the polymerization of cyclohexyl isocy-... 

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