Carbon as Catalyst

JOSE LUIS FIGUEIREDO and MANUEL EERNANDO R. PEREIRA 

In addition to its use as a catalyst support (see Chapter 4), carbon can find applications as a catalyst on its own. Activated carbon catalysts have long been used in the production of phosgene [1,2] and sulfur hahdes [3], The corresponding technologies seem to be well established, although the mechanistic details are not known in detail [4], The only recent pubhcation on this subject concerns the reduction of the by-product carbon tetrachloride using Sibunit (a carbon material developed at the Boreskov Institute of Catalysis) instead of the coconut shell-based activated carbon catalyst [5], 

The performance of a catalyst depends on the availability of suitable active sites, capable of chemisorbing the reactants and forming surface intermediates of adequate strength. Oxygen and nitrogen functional groups, which can be incorporated into the carbon materials by a variety of methods, play an important role in this context. The pertinent literature is discussed in this chapter, with particular emphasis on cases in which the active sites have been properly identified and useful activity correlations established. 

Carbon Materials for Catalysis, Edited by Philippe Serp and Josd Luts Figueiredo Copyright 2009 John Wiley Sons, Inc. 

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Diacetone-L-sorbose (DAS) is oxidized at elevated temperatures in dilute sodium hydroxide in the presence of a catalyst (nickel chloride for bleach or palladium on carbon for air) or by electrolytic methods. After completion of the reaction, the mixture is worked up by acidification to 2,3 4,6-bis-0-isoptopyhdene-2-oxo-L-gulonic acid (2,3 4,6-diacetone-2-keto-L-gulonic acid) (DAG), which is isolated through filtration, washing, and drying. With sodium hypochlorite/nickel chloride, the reported DAG yields ate >90% (65). The oxidation with air has been reported, and a practical process was developed with palladium—carbon or platinum—carbon as catalyst (66,67). The electrolytic oxidation with nickel salts as the catalyst has also... 

The preparation of iron impregnated activated carbon as catalysts and the catalytic performance of these catalysts were studied in benzene hydroxylation with hydrogen peroxide as oxidant. 5.0Fe/AC catalyst containing 5.0 wt% iron on activated carbon yielded about 16% phenol. The addition of Sn on 5.0Fe/AC catalyst led to the enhancement of selectivity towards phenol. 

Polyurethanes have also been used for many years. They can be applied from a solvent such as perchloroethylene, but such solvents are increasingly under environmental scrutiny. An aqueous polyurethane formulation is normally applied by padding, followed by baking at 150 °C using sodium carbonate as catalyst. 

Figure 6 presents the polarization curves of one and the same electrode with active carbon as catalyst when operating with air and with pure oxygen. 

The dispersion and solid-state ion exchange of ZnCl2 on to the surface of NaY zeolite by use of microwave irradiation [17] and modification of the surface of active carbon as catalyst support by means of microwave induced treatment have also been reported [18]. The ion-exchange reactions of both cationic (montmorillonites) and anionic clays (layered double hydroxides) were greatly accelerated under conditions of microwave heating compared with other techniques currently available [19.]... 

The immobilization of Pd(acac)2 as hydrogenation catalyst in the ionic liquids [BMIM][BF4] and [BMIM][PF6] was reported by Dupont et al. in 2000 [70]. These authors compared the biphasic hydrogenation of butadiene with the homogeneous system with all reactants being dissolved in CH2C12, with the reaction in neat butadiene and with a heterogeneous system using Pd on carbon as catalyst. 

Carbenicillin Carbenicillin, [25 -(2a,5a,6j3)]-3,3-dimethyl-7-oxo-6-(2-carboxy-2-phenylacetamido)-4-thia-l-azabicyclo[3.2.0]-heptan-2-carboxylic acid (32.1.1.32), is synthesized by direct acylation of 6-APA in the presence of sodium bicarbonate by phenylmalonic acid monobenzyl ester chloride, which forms the benzyl ester of carbenicillin (32.1.1.31), the hydrogenolysis of which using palladium on carbon or calcium carbonate as catalyst gives the desired product (32.1.1.32) [51-58]. 

PiCHO + H2NC6H4N(CH3)2 This is the favored procedure for preparing the aldehyde (Refs 11 24). Reaction (A) is done at room temp in pyridine, using iodine as catalyst (Ref 11), or in alcohol-acetone mixt with anhyd Na carbonate as catalyst (Ref 24) earlier procedures (see refs cited in Vol 2, B35-R) are reported to be unsatisfactory (Ref 11). Reaction (B) proceeds in strong aq hydrochloric acid overall yields are 39—52%. Reaction (A) proceeds in 80% yield in aq medium in the presence of light (Ref 90), with less by-product formation than noted in the other methods... 

Lucking F, Koser H, Jank M, Ritter A. Iron powder, graphite and activated carbon as catalysts for the oxidation of 4-chlorophenol with hydrogen peroxide in aqueous solution. Water Res 1998 32 2607-2614. 

In recent years a simplifying attempt to overcome this complexity was to analyze carbon by TPD and to integrate the total CO and CO2 emission and to correlate the results with sample pretreatment and chemical reactivity [33]. The limited validity of such an approach is apparent. As is illustrated below, the chemically complex surfaces which are not described by such crude correlations are those with the highest catalytic activity. In applications of carbons as catalyst support it is immediately apparent that the details of the car-bon-to-metal interaction depend crucially on such details of surface chemistry. This explains the enormous number of carbon supports commercially used (several thousands). A systematic effort to understand these relationships on the basis of modern analytical capabilities is still missing. 

Suarez-Ojeda, M.E., Stuber, F., Fortuny, A., Fabregat, A., Carrera, J. and Font, J. (2005) Catalytic wet air oxidation of substituted phenols using activated carbon as catalyst. Appl. Catal. B Environ. 58,105-114... 

In the reductive alkylation of ammonia with cyclohexanone, Skita and Keil found that, although cyclohexylamine was obtained in 50% yield over a nickel catalyst, over colloidal platinum dicyclohexylamine was produced as the predominant product even in the presence of an excess molar equivalent of ammonia. Steele and Rylander compared the selectivity to primary amine, secondary amine, and alcohol in the reductive alkylation of ammonia with 2- and 4-methylcyclohexanones over 5% Pd-, 5% Rh-, and 5% Ru-on-carbon as catalysts.18 As seen from the results shown in Table 6.2, the formation of secondary amine is greatly depressed by the methyl group at the 2 position. Thus over Pd-C the secondary amine was formed predominantly with cyclohexanone and 4-methylcyclohexanone while the primary amine was produced in 96% selectivity with 2-methylcyclohexanone. Over Ru-C the alcohol was formed quantitatively with 4-methylcyclohexanone without the formation of any amines, whereas with 2-methylcyclohexanone the alcohol was formed only to an extent of 57%, accompanied by the formation of 4 and 39% of the secondary and primary amines, respectively. These results indicate that secondary amine formation is affected by the steric hindrance of the methyl group to a much greater extents than is the formation of the primary amine or the alcohol. The results with Ru-C and Rh-C also indicate... 

Quan., X., Zhang., Y., Chen., S., Zhao, Y, and Yang, F. 2007. Generation of hydroxyl radical in aqueous solution by microwave energy using activated carbon as catalyst and its potential in removal of persistent organic substances. Journal of Molecular Catalysis A Chemical, 263 216-22. 

The first step in the two-step synthesis of l,l-difluoro-1-phcnylethane (4) is the hydro-fluorination of phenylacetylene with hydrogen fluoride cither in diethyl ether at 0 C (18% yield) or at 150 C in the gas phase with 13-14% mercury(II) oxide on activated carbon as catalyst to give the vinyl monomer... 

Dupont P., Vedrine J. C., Paumard E., et al.. Heteropolyacids supported on activated carbon as catalysts for the esterification of acrylic acid by butanol. Appl. Catal. A-Gen 129 (1995) pp. 217-227. 

Peters and van Bekkum noted that the original method of Sakurai and Tanabe suffered from problems due to the competitive reduction of the A A -dimethylaniline. In their modified procedure, diisopro-pylethylamine is used as HCl acceptor/catalyst regulator, and 10% palladium on carbon as catalyst. As for the Sukarai-Tanabe procedure, the reaction is carried out at room temperature and atmospheric pressure in acetone or ethyl acetate. In the latter solvent, which is said to be marginally preferable, the reduction is complete within minutes for aliphatic acyl chlorides, although aromatic substrates may take several days. 

Oxazolinones are not so stable and 2-oxazolin-5-ones (166), for example, react with sodium borohy-dride to yield 2-hydroxyamides (167), and their alkylidene derivatives (168) are converted into the corresponding alkyloxazolinones (169) by hydrogenation over palladium on carbon as catalyst. These... 

Benzo-l,4-thiazines (236) undergo ring opening and ring contraction when hydrogenated over Raney nickel, or palladium on carbon, as catalyst. Here the initial step in the reaction is reductive frag-... 

In the preface to their landmark monograph. Mattson and Mark 61 wrote Carbon researchers have, for the most part, considered the surface chemistry of activated carbon to be in such a state of disarray that they want to avoid lengthy discussions of surface phenomena. More than two decades later, with vast improvements in our knowledge of the role of surface chemistry in carbon gasification [37,6181 and in the use of carbons as catalyst supports [22], it is argued here that this is no longer true. 

One major problem, which will emerge in the consideration of carbons as catalysts or as reacting species, is that of impurities in the carbon. These obviously depend on the nature and preparation of the carbon, with graphite being, under the correct conditions, a very pure form of carbon. The importance of impurities will obviously depend upon individual systems and they are best discussed later. It is important to note, however, that traces of impurities may have a very large effect on the behaviour of a given carbon. 

Wu, X.X., Schwartz, V., Overbury, S.H., and Armstrong, T.R. Desulfurization of gaseous fuels using activated carbons as catalysts for the selective oxidation of hydrogen sulfide. Energy Fuels, 2005, 19, 1774. 

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