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

Several different activated carbons were oxidized with H O , (NH ) S O and HNO in order to introduce different 22 4 2 2 8 3 oxygen surface complexes. The changes in the surface chemistry of the activated carbons after their oxidizing treatments were studied by different techniques such as temperature-programme desorption, X-ray photoelectron spectroscopy, titration with HCl and NaOH and measurements of the pH at the point of zero charge. The activity to produce dimethyl ether (DME) 1 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 (NH ) S O had the strongest acid groups and were the most 42 2 8 active in the dehydration reaction of methanol to DME. The high activity of these samples was only due to a small fraction of carboxyl acid groups, i.e., those that were decomposed at the lower temperatures, at the start of the CO desorption 2 profiles. © 2001 Elsevier Science Ltd. All rights reserved.