It has been shown that yttria-stabilized zirconia is
an effective
catalyst for ethanol to n-butanol Guerbet coupling.
The variation of the calcination temperature allows an improvement
in the catalytic characteristics of this material via stabilization
of the tetragonal phase of zirconia, having higher basicity than the
monoclinic one. The treatment of yttria-stabilized zirconia at an
optimal calcination temperature of 500 °C induces the increase
in surface basicity required for the aldol condensation step, along
with a decrease in surface acidity, which is responsible for the side
reaction such as ethylene formation. The catalyst obtained significantly
exceeds in selectivity and n-butanol yield than individual
zirconia and other oxide systems which have been studied in this reaction.
The structure development of nanocrystalline yttria-stabilized
zirconia (ZrO2–3.4 mol % Y2O3) synthesized by coprecipitation of hydroxides followed by microwave
drying and calcination in the temperature range from 300 to 1000 °C
was investigated. A complex series of methods was used for the structure
characterization: X-ray diffraction (XRD) analysis, radial distribution
function of electronic density (RDF), small-angle X-ray scattering
(SAXS), and high-resolution transmission electron microscopy (HRTEM).
The wide range of the used techniques allowed us to reveal the structure
formation at all hierarchic levels of organization: atomic level,
where features of the local atomic arrangement were discovered; crystallite
level; and the level of secondary particles (aggregates), where grain
boundaries are formed and nanostructuring takes place. The nanostructure
features, the grain boundaries containing a lot of defects, were found
to improve the catalytic performance of zirconia in CO oxidation.
The results demonstrated that significant changes of zirconia properties
can be expected when the material is transformed into the nanostructural
state.
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