CONTRIBUTION OF HRTEM TO THE CHARACTERIZATION OF SILICA-INCORPORATED COPPER-OXIDE CATALYSTS PREPARED BY THE SOL-GEL TECHNIQUE

The aim of the present work is a structural characterization study of silica-incorporated copper-oxide (CuO-SiO2) catalysts using HRTEM. The catalysts were prepared by the sol-gel synthetic route. Two calcined catalysts (at 400 degrees C and 800 degrees C, respectively) were anal yzed before and after the ''NOx + H-2'' catalytic reaction. It was fou nd that in the 400 degrees C calcined catalyst, the copper is present as CuO crystallites in a structureless form, while in the 800 degrees C calcined catalyst, it was assumed that the copper is atomically disp ersed into the silica matrix since no traces of crystalline copper wer e observed. Under a reducing atmosphere, i.e., after reaction, the for mer showed large crystallites of CuO, while in the latter a segregatio n of colloidal crystallites, a mixture of Cu2O and metallic Cu, was ob served. It is worth noting that in the case of the 400 degrees C ''aft er-reaction'' catalyst, a change in color was observed after a few min utes of air exposure. This result suggested that the reduced copper-ox ide phase obtained after reduction was unstable. (C) 1998 Wiley-Liss, Inc.