Conversion of 4-methylpentan-2-ol over alkali–metal ion-exchanged X and Y zeolites: a microcalorimetric and catalytic investigation

Abstract

The acid-base properties of alkali–metal ion-exchanged X and Y zeolites were investigated by ammonia and sulfur dioxide adsorption microcalorimetry, in parallel with a catalytic reaction, viz. 4-methylpentan-2-ol conversion. Li and Na zeolites present much higher heats of NH₃ adsorption and greater coverage at the same pressure than the other zeolites. The acidic strength of X differs by only a few kilojoules per mole from the corresponding Y zeolites. The amounts of SO₂ adsorbed are very similar for all the Y zeolites except for LiY, on which the amount is smaller. X zeolites adsorb higher amounts than Y zeolites. Most of the samples have centres possessing significant basicity (Q>150 kJ mol⁻¹). The main product from 4-methylpentan-2-ol, for both X and Y catalysts, was 4-methylpent-2-ene; on Y zeolites, which exhibited the higher catalytic activity, a larger amount of other types of isomer was generally formed. In the case of Cs-exchanged X, excess cesium oxide was also added by impregnation with Cs acetate. Microcalorimetric measurements indicated that the extra framework cesium oxide provided even stronger basic adsorption sites; the catalytic runs showed that a significant amount of 4-methylpentan-2-one was produced only on CsX containing excess Cs oxide.