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

CeO2-La2O3 mixed oxides, formerly prepared via a sol-gel procedure and char acterised 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 deh ydration has been tested at atmospheric pressure in a fixed-bed flow micror eactor. The acid and base features of the catalysts markedly depend on the relative amounts of the two component oxides. For pure ceria, cerium and ox ygen ions are the source for acidity and basicity, respectively. Some contr ibution of OH groups to the acid-base character is probable for the mixed o xides. Most of the acid sites of each catalyst are weak, whereas most of it s base sites are strong. The concentration of the base sites tends to preva il over that of the acid sites as the lanthanum content increases. 4-Methyl pent-1-ene is by far the most abundant product of 4-methylpentan-2-ol conve rsion for all the catalysts, which are quite stable, even after repeated op eration cycles. Subtle differences in the relative extents of dehydration a nd dehydrogenation activity seem to be due to a shift in the reaction mecha nism, originated by changes in the relative amounts of acid and base sites.