Effects of structural defects and acid–basic properties on the activity and selectivity of isopropanol decomposition on nanocrystallite sol–gel alumina catalyst

Abstract

The surface acid–basic properties of sol–gel alumina catalysts were studied by Fourier transform infrared (FTIR) spectroscopy of pyridine adsorption and temperature-programmed desorption of CO 2 and NH 3. The number of acid and basic sites on the samples varied with the calcination temperatures of the samples. The populations of the three different aluminum ions—tetrahedral, pentacoordinated and octahedral, which were identified by the 27 Al MAS NMR, were strongly affected by the sample calcination temperature and the crystalline composition. In the reaction temperature range between 100 and 250°C, isopropanol decomposition on sol–gel alumina catalysts was carried out. It was found that isopropanol decomposition on alumina catalyst was a structural-defect sensitive reaction. The dehydrogenation selectivity to acetone depended on the surface basic sites and the concentration of aluminum vacancies in the crystalline structure of γ-Al 2O 3. Bimolecular reaction to isopropylether was largely governed by the pentacoordinated aluminum ions which were related to the coordinately unsaturated aluminum ions. A mechanism for the formation of isopropylether was proposed: oxygen vacancies were suggested to involve the adsorption step of isopropanol, an intermediate species, (CH 3) 2HC +, reacted with (CH 3) 2HCO − yielding isopropylether molecule.