Dehydration of methanol to dimethyl ether catalyzed by oxidized activated carbons with varying surface acidic character

Several different activated carbons were oxidized with H2O2, (NH4)(2)S2O8 a nd HNO3 in order to introduce different oxygen surface complexes. The chang es in the surface chemistry of the activated carbons after their oxidizing treatments were studied by different techniques such as temperature-program me desorption, X-ray photoelectron spectroscopy, titration with HCl and NaO H and measurements of the pH at the point of zero charge. The activity to p roduce dimethyl ether (DME) was related to the concentration of H+ ions at the point of zero charge of the samples, from which the turnover frequency of the reaction was obtained. Activated carbons oxidized with (NH4)(2)S2O8 had the strongest acid groups and were the most active in the dehydration r eaction of methanol to DME. The high activity of there samples was only due to a small fraction of carboxyl acid groups, i.e., those that were decompo sed at the lower temperatures, at the start of the CO2 desorption profiles. (C) 2001 Elsevier Science Ltd. All rights reserved.