Surface Characterization and Properties of Ordered Arrays of CeO₂ Nanoparticles Embedded in Thin Layers of SiO₂

Abstract

We demonstrated the surface composite character down to the nanometer scale of SiO(2)-CeO(2) composite high surface area materials, prepared using 5 nm colloidal CeO(2) nanoparticle building blocks. These materials are made of a homogeneous distribution of CeO(2) nanoparticles in thin layers of SiO(2), arranged in a hexagonal symmetry as shown by small-angle X-ray scattering and transmission electron microscopy. Since the preparation route of these composite materials was selected in order to produce SiO(2) wall thickness in the range of the CeO(2) nanoparticle diameter, these materials display surface nanorugosity as shown by inverse chromatography. Accessibility through the porous volume to the functional CeO(2) nanoparticle surfaces was evidenced through an organic acid chemisorption technique allowing quantitative determination of CeO(2) surface ratio. This surface composite nanostructure down to the nanometer scale does not affect the fundamental properties of the functional CeO(2) nanodomains, such as their oxygen storage capacity, but modifies the acid-base properties of the CeO(2) surface nanodomains as evidenced by Fourier transform IR technique. These arrays of accessible CeO(2) nanoparticles displaying high surface area and high thermal stability, along with the possibility of tuning their acid base properties, will exhibit potentialities for catalysis, sensors, etc.

A quantitative morphological analysis of nanostructured ceria–silica composite catalysts

“…With the analysis developed in this paper, we have attained the following results listed in Table 2. The quasi‐periodic pores network characterized by our analysis is in agreement with the suggestion of a structure with well‐defined hexagonal symmetry obtained by small‐angle X‐ray scattering (Chane‐Ching et al ., 2005). We estimate the pores diameter within a range of about 3.5–4.5 nm, which is close to the result obtained by N 2 adsorption (7.5 nm) (Chane‐Ching et al ., 2005).…”

“…The quasi‐periodic pores network characterized by our analysis is in agreement with the suggestion of a structure with well‐defined hexagonal symmetry obtained by small‐angle X‐ray scattering (Chane‐Ching et al ., 2005). We estimate the pores diameter within a range of about 3.5–4.5 nm, which is close to the result obtained by N 2 adsorption (7.5 nm) (Chane‐Ching et al ., 2005). We also estimate that the mean size of the fields of ceria is about 4.4–5.3 nm, which is identical to the result obtained by high‐angle X‐ray diffraction (5 nm) (Chane‐Ching et al ., 2005).…”

“…The catalytic functionality of these materials is ensured by the insertion of 5‐nm‐wide ceria nanoparticles in the copolymer network during the mineralization process. The copolymer network is then calcined, giving rise to a hexagonal network of porous channels, in which a certain volume fraction of ceria emerges (Shinkai et al ., 2003; Chane‐Ching et al ., 2005). The manufacture process and hence the properties of these catalysts can be significantly improved from morphological information on the ceria nanoparticles and their distribution (Nooney et al ., 2002): compactness, sphericity and localization either in the pores and or in the silica walls.…”

Synthesis of CeO2@SiO2 core–shell nanoparticles by water-in-oil microemulsion. Preparation of functional thin film

“…If a large number of reports can be found on the synthesis of CeO 2 nanoparticles, there are only a few dealing with surface modification. Recently, the nanostructured SiO 2 -CeO 2 system has become very popular for chemoselective catalysis thanks to the fact that the mineral binder SiO 2 is able to generate high specific surface area and thermal stability in nanoparticles arrays [22][23][24][25][26][27]. In the case of coating oxide particles with silica, various routes have been investigated: aggregation of small colloids [28], condensation of silica oligomers produced by solubilization of silica particles in highly basic medium [29], hydrolysis of functionalized or not silicon alkoxides [22][23][24][25][26][27][30][31][32][33], microemulsion route [34][35][36][37].…”

Cério: propriedades catalíticas, aplicações tecnológicas e ambientais

“…Além dessa função reguladora de oxigênio, a presença de CeO 2 também evita que os catalisadores CTV percam a eficiência em altas temperaturas, pois ela inibe/ desloca as transições de fase de outros materiais como, por ex., do suporte de alumina 16,19,22 . A adição de íons lantânio, zircônia, BaO e SiO 2 à estrutura do CeO 2 pode contribuir para aumentar a quantidade de defeitos na rede cristalina e proporcionar ao CeO 2 maior capacidade para armazenar oxigênio 22,[27][28][29][30][31][32][33]35,38,[42][43][44][45] , melhorando o desempenho dos catalisadores CTV. Atualmente, o uso de CeO 2 neste tipo de catalisador é uma das principais aplicações tecnológicas deste elemento e tem consumido a maior parte do cério produzido mundialmente 4,6 .…”