Papers by Author: Gloria Del Angel

Abstract: Perovskite-type compounds such as alkali tantalates, ATaO3 (A = Li, Na and K), prepared by the sol-gel method are reported as heterogeneous basic catalysts for the acetone aldol condensation. It has been proposed that the activity order and the selectivity patterns (LiTaO3 > > KTaO3 > NaTaO3) depend on the octahedral arrangements of the TaO6 tantalates.

Abstract: Au/TiO2 and Au/TiO2-CeO2 catalysts were prepared by the sol-gel method and carbon monoxide, hydrogen chemisorption and TEM spectroscopy have been exploited to determine the size of gold particles. The gold nanoparticles (8.1 to 2.1 nm) were deposited by using the deposition-precipitation method. The XRD characterization shows the presence of anatase as the TiO2 crystalline phase; while by XPS spectroscopy, the presence of Au°, Au2O3, Ce3+ and Ce4+ species co-existing in the Au/TiO2-CeO2 catalysts is shown. The characterizations by TPD-CO as well as by TPD-H2 (temperature programmed desorption) showed that on catalysts containing cerium, the gold particle size can be determined with great accuracy by using these chemisorption methods. The gold particle size calculated from either the CO or H2 thermodesorption values is in good agreement with that obtained by High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy (STEM) analyses. It was proposed that the TPD-CO and/or TPD-H2 techniques could be helpful for the characterization of the gold particles by TEM; especially when the high contrast in the pictures of the supports containing CeO2 prevents the particle size from being determined.