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

The surface acid-basic properties of sol-gel alumina catalysts were studied by Fourier transform infrared (FTIR) spectroscopy of pyridine adsorption a nd temperature-programmed desorption of CO2 and NH3. 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 Al-27 MAS NM R, were strongly affected by the sample calcination temperature and the cry stalline composition. In the reaction temperature range between 100 and 250 degrees C, isopropanol decomposition on sol-gel alumina catalysts was carr ied out. It was found that isopropanol decomposition on alumina catalyst wa s a structural-defect sensitive reaction. The dehydrogenation selectivity t o acetone depended on the surface basic sites and the concentration of alum inum vacancies in the crystalline structure of gamma-Al2O3. Bimolecular rea ction to isopropylether was largely governed by the pentacoordinated alumin um ions which were related to the coordinately unsaturated aluminum ions. A mechanism for the formation of isopropylether was proposed: oxygen vacanci es were suggested to involve the adsorption step of isopropanol, an interme diate species, (CH3)(2)HC+, reacted with (CH3)(2)HCO- yielding isopropyleth er molecule. (C) 1999 Elsevier Science B.V. All rights reserved.