title: Contribution of HRTEM to the characterization of silica-incorporated copper-oxide catalysts prepared by the sol-gel technique.
abstract: 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 analyzed before and after the "NOx + H2" catalytic reaction. It was found 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 automatically dispersed into the silica matrix since no traces of crystalline copper were observed. Under a reducing atmosphere, i.e., after reaction, the former showed large crystallites of CuO, while in the latter a segregation of colloidal crystallites, a mixture of Cu2O and metallic Cu, was observed. It is worth noting that in the case of the 400 degrees C "after-reaction" catalyst, a change in color was observed after a few minutes of air exposure. This result suggested that the reduced copper-oxide phase obtained after reduction was unstable.
authors.affiliation: Instituto de Física-UNAM, México D.F., México. mohamed@fenix.ifisicacu.unam.mx
authors.forename: M
authors.initials: M
authors.lastname: Benaïssa
authors.forename: G
authors.initials: G
authors.lastname: Diaz
mesh_terms: D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D005782:Gels; D008854:Microscopy, Electron / Q000379:methods*; D012822:Silicon Dioxide / Q000032:analysis*
chemical_list: D005782:Gels; D012822:Silicon Dioxide; D003300:Copper; C030973:cupric oxide