La-Dopant Location in La-Doped γ-Al2O3 Nanoparticles Synthesized Using a Novel One-Pot Process

摘要

We have recently developed a "solvent-deficient" method of synthesizing high surface area γ-Al2O3 nanoparticles that show promise for catalyst support applications. Here, we investigate doping the alumina with La~(3+) to stabilize the y phase to higher temperatures. The one-pot method for synthesizing La-doped γ-Al2O3 nanoparticles developed here has several advantages over conventional methods including requiring only 3 h instead of 3 days and wasting no lanthanum. TEM, X-ray PDF, and BET analyses as a function of calcination temperature show that the La stabilizes the y phase by 100 °C. In order to begin understanding the mechanism of stabilization, the location of the La~(3+) atoms in our doped γ-Al2O3 nanoparticles is investigated via X-ray PDF and EXAFS analyses which indicate that the La dopant adsorbs as single, isolated atoms on the γ-Al2O3 surface. As calcination temperature increases, the immediate oxygen coordination shell of the La becomes increasingly like La2O3 though an extended La2O3 lattice is not formed due to the sparse (3 wt %) concentration of La atoms. During the y-to-a transition, the La environment changes drastically to become more like LaAlO3 than La2O3, suggesting that the La is enveloped by the alumina lattice during the a phase transition though an extended LaAlO3 lattice is not formed.