Scheme 32.

The lanthanide-containing oxide-oxide system represents a two-phase structure, where the optically active phase is crystalline and the matrix is amorphous. The processing of these composites can offer materials with properties that are glasslike in most respects, except for the spectroscopy, where they are crystal-like.

Westin et al. have used ErAl3(OPr')12 in a sol-gel process to obtain Er-doped Al-Si-Ti oxide glasses (Fig. 74) [614]. The optical characterization of the material shows that using a SSP as the doping source endows a high homogeneity with respect to the cation dispersion, and the films were free from Er-rich clusters, which is the case in conventionally prepared Ln-doped material. The high dispersity of Er ions in the matrix is reflected in the high emission in the infrared region.

Narula et al. have used lanthanum and cerium alkoxy-aluminates (MAl3(OPr')12; M = La, Ce) in a sol-gel process to obtain high-surface-area alumina incorporating lanthanum and cerium for automotive catalyst substrate applications [256, 297]. The NMR experiments performed to follow the hydrolysis reactions show that lanthanides remain bonded to aluminum in the early stages of hydrolysis. They have impregnated the wash coat of automotive catalysts with alkoxide-derived sols and compared it with the commercial wash coat for the oxidation of hydrocarbons and CO and the reduction of NOx. As shown in Figure 75, a higher channel volume was achieved in the sol-gel-processed wash coat.

0 0

Post a comment