Active carbons as catalysts for liquid phase reactions

This paper gives three examples of applications of activated carbons, including synthetic carbons obtained from polymers, in selective liquid phase organic reactions. It is shown that ruthenium supported on activated carbon cloths (ACC) obtained by carbonisation of woven rayon fabric are very selective in the hydrogenation of glucose to sorbitol. This is attributed to an easy mass transfer from the micropores to the liquid phase which favours the fast desorption of sorbitol avoiding epimerisation to mannitol. Synthetic carbons obtained by carbonisation of cross-linked phenolic resins are active in the oxidation with air of cyclic ketones (cyclohexanone, cyclododecanone, 3,3,5-trimethylcyclohexanone) to the corresponding dicarboxylic acids. The activity and selectivity depend upon treatments favouring the presence of surface functional groups, particularly quinone/carbonyl groups. This paper also shows that activated carbons obtained from natural sources can be modified by thermal treatments favouring the presence of basic sites which improve the rate of the oxidative decarboxylation of N-phosphonomethyl iminodiacetic acid to glyphosate. The nitrogen-containing basic functions generated by high temperatures thermal treatment of the activated carbon in NH3 are particularly active.