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

Abstract

We have recently developed a 'solvent-deficient' method of synthesizing high surface area γ-Al 2 O 3 nanoparticles that show promise for catalyst support applications. Here, we investigate doping the alumina with La 3+ to stabilize the gamma phase to higher temperatures. The One-pot method for synthesizing La-doped γ-Al 2 O 3 nanoparticles developed here has several advantages over conventional methods including requiring only 3 hours 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 gamma phase by 100°C. In order to begin understanding the mechanism of stabilization, the location of the La 3+ atoms in our doped γ-Al 2 O 3 nanoparticles is investigated via X-ray PDF and EXAFS analyses which indicate that the La dopant adsorbs as single, isolated atoms on the γ-Al 2 O 3 surface. As calcination temperature increases, the immediate oxygen coordination shell of the La becomes increasingly like La 2 O 3 though an extended La 2 O 3 lattice is not formed due to the sparse (3 wt%) concentration of La atoms. During the γ-to-α transition, the La environment changes drastically to become more like LaAlO 3 than La 2 O 3 , suggesting that the La is enveloped by the alumina lattice during the alpha phase transition though an extended LaAlO 3 lattice is not formed.

Structural Effects of Lanthanide Dopants on Alumina

“…Furthermore, scenarios (ii) and (iii) were ruled out due to the amount of dopant used in this study, as ~0.03271% (by weight) of the total molecular weight of Ln 0.002 Al 1.998 O 3 was not enough for the formation of separate phases or layers of LnAlO 3 /Ln 2 O 3 . This was also confirmed through spectroscopy studies in this report8. In addition, assuming a homogeneous lattice with sparse Ln cations well dispersed in the matrix, the distortion that occurred from one cation would not interfere with other dopants.…”

“…The existence of several crystalline polymorphs and vacant octahedral sites enables alumina to be adopted for a variety of doping studies and technological applications345. Lanthanide (Ln 3+ ) ion-doped Al 2 O 3 is particularly appealing, since the local environment of the doped ions is known to critically influence the optical and mechanical properties of Al 2 O 3 due to the large size mismatch between Ln dopants and aluminum678. For example, the presence of dopants (ytterbium, gadolinium or lanthanum) strengthens the grain boundaries of alumina, largely affecting the mechanical properties91011.…”

Recent Advances in Bifunctional Catalysts for the Fischer–Tropsch Process: One-Stage Production of Liquid Hydrocarbons from Syngas

“…Rahmati el al. 174 found that the presence of Si on alumina-supported Co−Ru catalysts allowed the catalyst to be calcined at higher temperatures (1100 °C) 176 while retaining its γ-alumina phase and avoiding the transition to α-alumina (which occurs naturally at 900 °C). 177 The α-alumina phase is undesirable for FT applications because of its lower surface area and pore volume compared with γ-alumina.…”

Synthesis and electrochemical characterization of La0.75Sr0.25Mn0.5Cr0.5−xAlxO3, for IT‐ and HT‐SOFCs

“…Al 2 O 3 is a highly attractive material from thermal and chemical stability perspective . It able to increase the total BEs while doped with La 3+ precursors . The XPS spectra of Al 2 p of La 0.75 Sr 0.25 Mn 0.5 Cr 1− x Al x O 3− δ are shown in Figure and were plotted for as‐prepared and pre‐reduced samples.…”