SURFACE-TREATED ACTIVATED CARBONS AS CATALYSTS FOR THE DEHYDRATION AND DEHYDROGENATION REACTIONS OF ETHANOL

Two activated carbons were prepared from olive stones with different d egrees of activation and oxidized with a (NH4)(2)S2O8 solution for var iable periods of time to introduce different amounts of oxygen surface complexes. Samples so prepared were characterized to know their surfa ce area, porosity, and surface chemistry and then were used as catalys ts in the conversion reactions of ethanol. The dehydration reactions t o obtain ethene and ether only occurred on the oxidized samples, where carboxyl groups placed on the external surface of the particles were responsible for these reactions. The dehydrogenation reaction to yield acetaldehyde took place on either acid or basic surface sites placed not only on the external surface, but also on some part of the interna l surface. During the reaction some surface active sites for dehydroge nation were lost because some hydrogen remained bound to them. The pre sence of air in the reactant mixture cleaned some of these sites, incr easing the dehydrogenation activity and decreasing the dehydration act ivity. Also studied was the effect on their activity of the pretreatme nts of the catalysts in He or H-2 flow at different temperatures up to 1273 K.