ACTIVE SITES AND MECHANISMS OF DEHYDRATION OF METHANOL AND METHYLATION OF METHYLANILINE ON ALUMINA AND ON SILICA-ALUMINA

The active sites of alumina and silica-alumina catalysts for the dehydration of methanol, as well as the mechanisms of this reaction, were studied in a flow system at 228 °C by poisoning the catalyst during the run with nitrogen bases. On alumina, methanol dissociates upon adsorption on the Lewis acid sites, and the random combination of surface groups gives the dimethyl ether. Poisons also adsorb and dissociate reversibly, and their poisoning action is caused by their strong adsorption on the acid sites, in competition with methanol. On silica-alumina protonic sites are involved and the nitrogen bases are irreversible poisons, because they form stable quaternary ions with the proton. In the methylation of methylaniline, under the same working conditions as those of the methanol dehydration, the same active sites are involved and the mechanisms are also similar. For methylation, relatively weaker acid sites are necessary, and they are not poisoned by nitrogen bases. © 1969.