Metal-activated carbon catalysts

Pd showed significantly promotional effect than Pt and Ru for Co/Si02 catalyst in hydroformylation of 1-hexene [4], Cobalt free lwt% Ru, Pt and Pd supported on active carbon were prepared and tested in hydroformylation reaction. As shown in Table 1, these kinds of catalysts showed very low activity for 1-hexene hydroformylation. For the Ru catalyst, the 1-hexene eonversion was 81.3%, but the 1-hexene was only converted to isomerization produets. For the Pt and Pd catalysts, both the 1-hexene conversion and oxygenates selectivity were very low. Results show in Table 1 indicate that the noble metal/active carbon catalysts themselves had no catalytic activity of 1-hexene hydroformylation to form oxygenates. 

K. Aika et al. [1] studied alkali metal/transition metal/active carbon catalysts in ammonia synthesis. Authors postulated that carbon support enables electron transport from alkali metal... 

Nitrogen adsorption experiments showed a typical t)q5e I isotherm for activated carbon catalysts. For iron impregnated catalysts the specific surface area decreased fix>m 1088 m /g (0.5 wt% Fe ) to 1020 m /g (5.0 wt% Fe). No agglomerization of metal tin or tin oxide was observed from the SEM image of 5Fe-0.5Sn/AC catalyst (Fig. 1). In Fig. 2 iron oxides on the catalyst surface can be seen from the X-Ray diffractions. The peaks of tin or tin oxide cannot be investigated because the quantity of loaded tin is very small and the dispersion of tin particle is high on the support surface. 

The objective of most research in the area of pyrolyzed metal/N/C materials has centered around understanding the nature of the active site for the ORR. Similar to heat-treated macrocycles, there has been a parallel controversy over the nature of the active sites and the role of Fe or Co in these metal-nitrogen-carbon catalysts. Based on the activity attainable from a wide-range of precursors, it seems safe to assume that above a certain temperature, the active site formed is the same regardless of the metal-nitrogen-carbon starting material (macrocycle or otherwise). Initially, some researchers believed that the metal clusters protected by a layer of carbon (which prevented leaching of the metal in the acidic electrolyte) were the source of catalytic... 

Rh > Ir > Ni > Pd > Co > Ru > Fe A plot of the relation between the catalytic activity and the affinity of the metals for halide ion resulted in a volcano shape. The rate determining step of the reaction was discussed on the basis of this affinity and the reaction order with respect to methyl iodide. Methanol was first carbonylated to methyl acetate directly or via dimethyl ether, then carbonylated again to acetic anhydride and finally quickly hydrolyzed to acetic acid. Overall kinetics were explored to simulate variable product profiles based on the reaction network mentioned above. Carbon monoxide was adsorbed weakly and associatively on nickel-activated-carbon catalysts. Carbon monoxide was adsorbed on nickel-y-alumina or nickel-silica gel catalysts more strongly and, in part, dissociatively,... 

It has been discovered that the performances of platinum and palladium catalysts may be improved by promotion with heavy metal salts. However, there is little information available about the role and chemical state of the promoter 8,9). We have recently found that a geometric blocking of active sites on a palladium-on-activated carbon catalyst, by lead or bismuth, suppresses the by-product formation in the oxidation of l-methoxy-2-propanol to methoxy-acetone 10). 

Another part of our investigation deals with the effect of heat treatment on the leaching behavior of palladium on activated carbon catalysts. Heat treatment is a known technique to increase the performance of catalysts. (3) Therefore, standard carbon supported palladium catalysts were exposed to different temperatures ranging from 100 to 400 °C under nitrogen. The catalysts were characterized by metal leaching, hydrogenation activity and CO-chemisorption. 

The effect of reaction conditions (temperature, pressure, H2 flow, C02 and/or propane flow, LHSV) and catalyst design on reaction rates and selectivites were determined. Comparative studies were performed either continuously with precious-metal fixed-bed catalysts in a trickle-bed reactor, or batchwise in stirred-tank reactors with supported nickel or precious metal on activated carbon catalysts. Reaction products were analyzed by capillary gas chromatography with regard to product composition, by titration to determine iodine and acid value, and by elemental analysis. 

The comparison of the methane decomposition reaction in the presence of metal and carbon catalysts reveals some similarities and differences, as shown in Figure 3. The initial hydrogen concentrations in the effluent gas of methane decomposition over Fe and AC-1 catalysts at 850°C are very close and approach the equilibrium value. This indicates that the catalytic activities of fresh AC-1 and Fe catalysts are almost equal at high temperatures. At lower temperatures, however, carbon catalysts are less active than metal catalysts. 

The differences in the temperature dependence and the shape of the kinetic curves for metal- and AC-catalyzed reactions point to the apparent dissimilarities in the mechanism of methane decomposition in the presence of metal and carbon catalysts. The nature of active sites responsible for the efficient decomposition of methane over the fresh surface of carbon catalysts is yet to be understood. 

Y. Uemichi, Y. Makino, and T. Kanaznka, Degradation of polyethylene to aromatic hydrocarbons over metal-snpported activated carbon catalysts, J. Anal. Appl. Pyrolysis 14, 331 (1989). 

On the other hand, activated carbon may be considered as a catalyst in the cracking of waste plastics. This is because it is a neutral catalyst with a high surface area and, therefore, it might be more resistant to impurities and coke formation. It has been reported that Pt-, Fe- and Mo-supported activated carbon catalysts were effective for the pyrolysis ofPEandPP [11,14,15]. Use of metal-supported activated carbon catalysts has enhanced the formation of aromatics via dehydrocychzation of straight- or branched-chain radicalic intermediates. 

First NO is formed and then it is oxidized in the atmosphere to NOj. Since in combustion, the origin of nitrogen is not only from N-rich fuel but also from air supphed for oxidation, in the elimination of NO, postcombustion methods are important. So far the most effective technique has been selective catalytic reduction of NO . on various catalysts. When the activated carbons are used as removal media, the elimination process includes also adsorption combined either with oxidation or reduction. Oxidation usually leads to the formation of nitric acid whereas Nj is the product of NO, reduction. As in the cases of other pollutants addressed in this review, for NO, removal either unmodified or impregnated (caustics, catalytic metals) activated carbons have been used [101-114]. 

Liquid phase carbonylation of methanol to acetic acid with a rhodium complex catalyst is a well known process (ref. 1). The authors have found that group 8 metals supported on carbonaceous materials exhibit excellent activity for the vapor phase carbonylation of methanol in the presence of iodide promoter(ref. 5). Especially, a nickel on active carbon catalyst gave acetic acid and methyl acetate with the selectivity of 95% or higher at 100% methanol conversion under 10 atm and 250 °C. In the present study it has been found that a small amount of hydrogen which is always contained in the commercially available CO and requires much cost for being removed completely, accelerates greatly the carbonylation reaction. 

Figure 15.4 Transmission electron micrograph of palladium on activated carbon catalyst (a) the metal crystallites are located on the edge of the carbon support (b) uniform distribution of the crystallites. In both cases the crystallites are 2 to 3 nm in size.

Catalysts were prepared by impregnation of Pt inside the pore structure of carbon fibers. Care was taken to eliminate the active metal from the external surface of the support. A very high dispersion of Pt was measured. Four reactions were carried out in a fixed-bed reactor competitive hydrogenation of cyclohexene and 1-hexene, cyclization of 1-hexene, n-heptane conversion and dehydrogenation of cyclohexanol. Three types of carbon fibers with a different pore size and Pt-adsorption capacity along with a Pt on activated carbon commercial catalyst were tested. The data indicate a significant effect of the pore size dimension on the selectivity in each system. The ability to tailor the pore structure to achieve results drastically different from those obtained with established supports is demonstrated with heptane conversion. Pt on open pore carbon fibers show higher activity with the same selectivity as compared with Pt on activated carbon catalysts. 

Besides oxide supported Sn-Ru catalysts, carbon supported catalysts also find application in hydrogenation reactions. Sn Mossbauer spectroscopy was used to investigate the tin component of ruthenium and tin supported on activated carbon catalysts containing 2 wt. % ruthenium and having Sn/(Sn-f Ru) ratios between zero and 0.4. Four major components in the Sn Mossbauer spectra were attributed to both Sn(II) and Sn(IV) oxides and to Ru-SnOx species formed on the surface of ruthenium metal particles. In addition to this " Sn spectra reveal the presence of minor amounts of Ru3Sn7 alloy phase. ... 

The Function of Added Noble Metal to Co/Active Carbon Catalysts for Oxygenate Fuels Synthesis via Hydroformylation at Low Pressure... 

Band d (vco = 1800-1806 cm" ) corresponds to three-fold bridged CO on metallic rhodium particles. The intensity of band d increases systematically, its increase suggests a slow reduction of Rh(III) and Rh(I) to Rh(0). The metallic Rh may play an important role in increasing the mobility of CO on the catalyst surface and in the activation of reagents during the carbonylation reaction as observed at the hydrocarboxylation of ethylene in the presence of hydrogen (favors the appearance of metallic Rh) on RhCls/active carbon and on H[Rh(CO)2l2]/active carbon catalyst. ... 

Reaction conditions see footnote a in Table 9. Catalyst 2.5 wt% metal/activated carbon. 

---