CeO2–La2O3 catalytic system. Part II. Acid–base properties and catalytic activity for 4-methylpentan-2-ol dehydration

Abstract

CeO₂–La₂O₃ mixed oxides, formerly prepared ia a sol–gel procedure and characterised by several techniques, have been further investigated as to their acid–base properties and catalytic activity. Surface acidity and basicity have been assessed by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. Catalytic activity for 4-methylpentan-2-ol dehydration has been tested at atmospheric pressure in a fixed-bed flow microreactor. The acid and base features of the catalysts markedly depend on the relative amounts of the two component oxides. For pure ceria, cerium and oxygen ions are the source for acidity and basicity, respectively. Some contribution of OH groups to the acid–base character is probable for the mixed oxides. Most of the acid sites of each catalyst are weak, whereas most of its base sites are strong. The concentration of the base sites tends to prevail over that of the acid sites as the lanthanum content increases. 4-Methylpent-1-ene is by far the most abundant product of 4-methylpentan-2-ol conversion for all the catalysts, which are quite stable, even after repeated operation cycles. Subtle differences in the relative extents of dehydration and dehydrogenation activity seem to be due to a shift in the reaction mechanism, originated by changes in the relative amounts of acid and base sites.