Preparation And Application Of A₂B₂O₇ Rare Earth Complex Oxides

The nanocrystal La₂Ti₂O₇ phase can be formed at an evidently lower temperature of 700℃ by metallorganic decomposition method (MOD). The resulting powders exhibit small and uniform grains. The probable reason is that acetylacetone can associate with La³+ to form La-acetylacetone chelate complexes, small precursor particles can be formed at a homogeneous and low La³+ concentration by control release from the complexes; these small, uniform and more active precursor particles probably make it possible to form nanocrystal at significantly lower preparation temperature.It was found that La₂Ti₂O₇ has photocatalytic activity in this paper. Thus, Nd_xLa₂-xTi₂O₇ (x=0, 1, 2) were prepared by MOD. Their photocatalytic activities were examined by degradation of methyl orange solution. And the possibility mechanism of their photocatalysis was investigated. As a result, La₂Ti₂O₇, La₂Ti₂O₇ and NdLaTi₂O₇ with prevokite structure were successfully prepared, which activities perform extremely good at 800℃. By comparison, the photocatalytic activity of La₂Ti₂O₇ (78%) catalyst was higher than NdLaTi₂O₇ (62%) and Nd₂Ti₂O₇ (56%), which strongly depend to their electronic structure.A novel and highly active solid superacid of sulfated La₂Zr₂O₇ was prepared by aqueous impregnation method. The structure, morphology, heat stability and acidic properties of catalyst were examined by XRD, SEM, FT-IR and TG-DTA. The results show that the morphology and crystal size of sulfated La₂Zr₂O₇ were altered. It was found that the photocativity of La₂Zr₂O₇ was quite low while the sulfated La₂Zr₂O₇ exhibited excellent reaction activity for photocatalytic degradation of 2-nitrophenol. This may be related that the recombination of holes and electrons induced by irradiation was avoided by sulfate ion was anchored on the surface of La₂Zr₂O₇.The acid strength of the sulfated La₂Zr₂O₇ estimated by pyridine-absorption IR was higher than that of sulfated titania, a well-known solid superacid. The sulfated La₂Zr₂O₇ displays photoactivity much higher than that of sulfated TiO₂ for 2-nitrophenol degradation in the same condition. Meanwhile, it is found that the excellent photocatalytic activity for acid red 3B degradation was occurred. Acid red 3B was completely degraded for 35 min.To explore the catalytical capability of SO42"/ La2Ti2O7, series of esterification reactions were carried out. It can be effectively catalyzed esterification reaction to achieve a product yield of greater than 97.8% (ethyl acetate), 96.8% (n-butyl propionate) and 88.8% (n-butyl benzoate), respectively. At the same time, the catalytic activities of SO42"/ La2Ti2O7 in above three reactions were better than traditional solid superacid, SO4 7TiC>2 and SO4 7ZrC>2, which is noted that SO42"/ La2Ti2O? is a good catalyst.