Influence of the calcination temperature on the nano-structural properties, surface basicity, and catalytic behavior of alumina-supported lanthana samples

The influence of the calcination temperature on the lanthana distribution, surface basicity, and catalytic properties of a La 2O 3/Al 2O 3 sample, with lanthana loading close to the theoretical monolayer, is discussed. The resulting materials represent an advantageous alternative to pure lanthana as highly basic catalysts. We investigate a series of three La 2O 3/Al 2O 3 samples, with a lanthana loading close to the theoretical monolayer, obtained by calcination at 773 K, 973 K, or 1173 K from a common precursor. The samples were characterized by N 2 adsorption at 77 K, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), a variety of nano-analytical and nano-structural electron microscopy techniques, temperature programmed desorption (TPD-CO 2), and volumetric CO 2 adsorption techniques. By combining the information obtained from all these studies, a detailed description of their texture, nano-structure, lanthana distribution, and chemical properties could be gained. Three different forms of supported lanthana have been identified, and their relative weight evaluated quantitatively. As revealed by CO 2 adsorption, these forms show strong, weak, or not measurable surface basicity, respectively. Upon increasing the calcination temperature, a progressive inter-conversion of the co-existing lanthana forms with inherent loss of surface basicity is observed. The effect, though moderate, is particularly noticeable on the sample calcined at 1173 K. The amount of CO 2 irreversibly chemisorbed on the different samples, including the alumina support, correlates well with their catalytic activity for the Meerwein–Ponndorf–Verley reaction of cyclohexanone with 2-propanol. This behavior is discussed with reference to that expected for pure lanthana. We conclude that our supported lanthana samples represent an advantageous alternative to pure La 2O 3 as highly basic catalytic materials.