Adsorption and Reaction of Acetaldehyde on Shape-Controlled
CeO<sub>2</sub> Nanocrystals: Elucidation of Structure–Function
Relationships
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Abstract
CeO<sub>2</sub> cubes with {100} facets, octahedra with {111} facets,
and wires with highly defective structures were utilized to probe
the structure-dependent reactivity of acetaldehyde. Using temperature-programmed
desorption (TPD), temperature-programmed surface reactions (TPSR),
and <i>in situ</i> infrared spectroscopy, it was determined
that acetaldehyde desorbs unreacted or undergoes reduction, coupling,
or C–C bond scission reactions, depending on the surface structure
of CeO<sub>2</sub>. Room-temperature FTIR indicates that acetaldehyde
binds primarily as η<sup>1</sup>-acetaldehyde on the octahedra,
in a variety of conformations on the cubes, including coupling products
and acetate and enolate species, and primarily as coupling products
on the wires. The percent consumption of acetaldehyde ranks in the
following order: wires > cubes > octahedra. All the nanoshapes
produce
the coupling product crotonaldehyde; however, the selectivity to produce
ethanol ranks in the following order: wires ≈ cubes ≫
octahedra. The selectivity and other differences can be attributed
to the variation in the basicity of the surfaces, defects densities,
coordination numbers of surface atoms, and the reducibility of the
nanoshapes