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.
The choice of temperature and gas conditions used in
a water pressure-controlled
reactor is guided by density functional theory (DFT) to synthesize
nearly phase-pure lanthanide scandate nanoparticles (LnScO3, Ln = La, Nd, Sm, Gd). In this synthetic method, low water-vapor
partial pressures, well below water’s gas liquidus, inhibit
particle growth, while an excess of water vapor results in undesired
rare-earth hydroxide and oxyhydroxide secondary phases. The optimal
humidity for high-purity LnScO3 particle synthesis is shown
to vary with the lanthanide; DFT is used to calculate the thermodynamics
of secondary phase formation for each lanthanide tested such that
the role of water vapor may be quantified and used to maintain phase
purity (greater than 96 mol %) across the series. The combination
of thermodynamic calculation and experimental confirmation with this
pressure-controlled reactor provides an opportunity to explore analogous
syntheses of other inorganic perovskite nanoparticles.
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