Active solid acid catalysts prepared by sulfonation of carbonization-controlled mesoporous carbon materials

A novel sulfonic acid group-functionalized mesoporous carbon was prepared through vapour-phase transfer sulfonation of CMK-3 type mesoporous carbon with the controllable carbonization degree. The method of vapour-phase sulfonation, that is, through contacting the sample powders with the vapor from fuming sulfuric acid in a closed autoclave, proved to be more effective than both the direct dipping of the carbon in concentrated or fuming H₂SO₄ and the treatment with pure SO₃ gas. The influence of carbonization temperature on the sulfonation was investigated, suggesting an optimum temperature of 823 K. The SO₃H group-functionalized mesoporous carbon, CMK-3-SO₃H, was characterized by means of XRD, SEM, TEM, N₂ adsorption-desorption, ¹³C NMR, FTIR and elemental analysis, which indicated that it had uniform mesopores together with an extremely high surface area, and also contained an amount of acid sites as high as 1.3 mmol g^-1. CMK-3-SO₃H catalyzed efficiently the liquid-phase Beckmann rearrangement of cyclohexanone oxime and condensation reactions involving bulky aromatic aldehydes.