Improving the Thermodynamic Stability of Aluminate Spinel Nanoparticles with Rare Earths

Journal Article · Wed Jun 29 00:00:00 EDT 2016 · Chemistry of Materials

DOI:https://doi.org/10.1021/acs.chemmater.6b02577· OSTI ID:1369180

Hasan, M. M. ^[1]; Dey, Sanchita ^[1]; Nafsin, Nazia ^[1]; Mardinly, John ^[2]; Dholabhai, Pratik ^[3]; Uberuaga, Blas P.  ^[3]; Castro, Ricardo H. R. ^[1]

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1. Univ. of California, Davis, CA (United States). Dept. of Materials Science and Engineering, and Nanomaterials in the Environment, Agriculture, and Technology- Organized Research Unit (NEAT ORU)
2. Arizona State Univ., Tempe, AZ (United States). John Cowley Center for High Resolution Electron Microscopy, LeRoy Eyring Center for Solid State Science (HREM, LE-CSSS)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Surface energy is a key parameter to understand and predict the stability of catalysts. In this work, the surface energy of MgAl₂O₄, an important base material for catalyst support, was reduced by using dopants prone to form surface excess (surface segregation): Y³⁺, Gd³⁺, and La³⁺. The energy reduction was predicted by atomistic simulations of spinel surfaces and experimentally demonstrated by using microcalorimetry. The surface energy of undoped MgAl₂O₄ was directly measured as 1.65 ± 0.04 J/m² and was reduced by adding 2 mol % of the dopants to 1.55 ± 0.04 J/m² for Y-doping, 1.45 ± 0.05 J/m² for Gd-doping, and 1.26 ± 0.06 J/m² for La-doping. Atomistic simulations are qualitatively consistent with the experiments, reinforcing the link between the role of dopants in stabilizing the surface and the energy of segregation. Surface segregation was experimentally assessed using electron energy loss spectroscopy mapping in a scanning transmission electron microscopy image. Finally, the reduced energy resulted in coarsening inhibition for the doped samples and, hence, systematically smaller particle sizes (larger surface areas), meaning increased stability for catalytic applications. Moreover, both experiment and modeling reveal preferential dopant segregation to specific surfaces, which leads to the preponderance of {111} surface planes and suggests a strategy to enhance the area of desired surfaces in nanoparticles for better catalyst support activity.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC). Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1369180
• Report Number(s): LA-UR-16-22939; 1520-5002 (Electronic)
• Journal Information: Chemistry of Materials, Vol. 28, Issue 14; ISSN 0897-4756
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY