Carbon as a catalyst in oxidation reactions and hydrogen halide elimination reactions

✍ Scribed by H.Peter Boehm; Gunther Mair; Thomas Stoehr; Ana R. De Rincón; Bela Tereczki

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 354 KB
• Volume: 63
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(84)90188-1

✦ Synopsis

Carbon catalyses many reactions, mainly oxidation reactions with oxygen and with halogens, e.g. S0,+1/20,-+S03, or CO+CI,-+COCI,.

It is known, however, that different carbons behave quite differently in the reduction of oxygen on fuel cell cathodes. Thereforethecatalytic activity of carbons has been studied in other reactions. A convenient test reaction is the oxidation of dilute aqueous sulphurous acid. It became apparent that all catalytically active carbons contain small quantities of nitrogen, and inactive carbons such as wood charcoal or carbon blackscan be rendered highly active by treatment with NH, or HCN at elevated temperatures. Photoelectron spectra indicate that the catalytic activity increases parallel to the incorporation of a nitrogen species which is pyridine-like, i.e. incorporated in the aromatic layers. Treatment with NH, at 900°C leads also to massive gasification of the carbons, increasing their surface area. Other reactions studied included the oxidation of aqueous oxalic acid and of methanol to formaldehyde.

A quite different type of reaction is the elimination of hydrogen chloride from lchloroalkanes, e.g. 1 -chlorobutane.

Again, activity changes in parallel to nitrogen content. Reaction products are olefins, dimers of the alkyl groups, and a polymer on the catalyst surface. The formation of alkyl dimers, e.g. n-octane in the case of n-butylchloride, suggests that radicals are involved in the reaction.