Gadolinium scandate (GdScO) has been synthesized at 300 °C through the decomposition of a mixed cation hydroxide hydrogel in a humid environment. Increasing the reaction temperature produced larger particles that better adopted the Wulff shape. A lack of water vapor during the synthesis caused the solid network of the hydrogel to collapse upon heating so an amorphous xerogel was produced. Water vapor in the system imbibed the hydrogel and allowed for greater diffusion of the atomic species to allow for crystallization into the perovskite phase at temperatures lower than typical sol-gel processes. Temperatures less than 300 °C, or an excess of water vapor, promoted the formation of Gd(OH) and ScOOH in addition to or in lieu of GdScO.
A general approach to the formation of well-faceted nanoparticles is discussed and successfully applied to the production of several rare-earth scandates. Two steps were used, with higher temperatures first to nucleate the perovskite phase, followed by lower temperatures to smooth the particle surfaces. Exploiting these two different regimes led to smaller nanoparticles with more faceting. This general approach may be tailored to other material systems as a step towards producing shape-controlled nanoparticles for a desired application.
Some catalytic oxide supports are
more equal than others, with
numerous variable properties ranging from crystal symmetry to surface
chemistry and electronic structure. As a consequence, it is often
very difficult to determine which of these act as the driver of performance
changes observed in catalysis. In this work, we hold many of these
variable properties constant with structurally similar LnScO3 (Ln = La, Sm, and Nd) nanoparticle supports with cuboidal shapes
and a common Sc-rich surface termination. Using CO oxidation over
supported Au nanoparticles as a probe reaction, we observe higher
activation energy and a slower rate using NdScO3 as the
support material. This change is found to correlate to the strength
of CO2 binding to the support surface, identified by temperature-programmed
desorption measurements. The change is due to differences in the 4f
electrons of the lanthanide cations, the cations’ Lewis acidity,
and the inductive effect they impose.
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