Recent Developments in Gold Nanomaterial Catalysts for Oxidation Reaction through Green and Sustainable Routes - Advanced Materials for Agriculture, Food and Environmental Safety - page 226

catalysts is to prevent leaching of the active species. h e reactants, and par-
ticularly the carboxylic acid-type byproducts, are frequently excellent che-
lating agents and accelerate dissolution and deactivation of the catalysts.
h e hydroxyl group is the primary functional group in aliphatic alcohols
and has greater gas-phase Brönsted acidity than water. h e reactions of
alcohols on oxygen-covered gold nanoparticles catalysts are initiated by
the activation of O-H bonds by adsorbed atomic oxygen to form adsorbed
alkoxy and water [134]. h e dif erences in the product distributions of over
supported gold nanoparticles catalysts depend on the structure of the alkyl
groups present in the alcohol as well as the atomic oxygen coverage over
the catalysts.
Recently, gold nanoparticles have been widely applied for alcohol oxi-
dation reaction by maintaining a mild condition in liquid phase. h e
catalytic activities of gold nanoparticles strongly depend on the size
of gold nanoparticles, nature of support material (for supported gold
nanoparticles), oxidation state of gold nanoparticles, etc. h e applica-
tion of gold nanoparticles on oxidation reaction is not yet broad, but
extensive research is going on in this i eld. Gold has an advantage com-
pared to other precious metals like Ag, Pt, and Pd because leaching of
gold nanoparticles is lower compared to other metals. In order to obtain
highly active gold catalysts, a chemical grat ing and reduction process was
developed in which amino, thiol or diamino groups were grat ed onto the
surfaces support material and then Au was introduced via a neutraliza-
tion reaction, followed by a reduction procedure [135-137]. Rossi and
Prati [138-150] have shown that supported gold nanoparticles can be
very ef ective catalysts for the oxidation of alcohols, including diols. Gold
is highly active and selective in glycerol oxidation reaction [151-153].
Carbon-supported gold nanoparticles are ef ective for a range of sub-
strates in gas-phase and liquid-phase oxidation reaction. h ese studies
using Au/carbon catalysts were extended by Carrettin et al. [26, 154, 155]
to show that Au supported on graphite can oxidize glycerol to glycerate
with 100% selectivity using dioxygen as the oxidant under relatively mild
conditions with yields approaching 60%. It was observed that the selec-
tivity to glyceric acid and the glycerol conversion were dependent upon
the glycerol/NaOH ratio. In general, with high concentrations of NaOH,
exceptionally high selectivities to glyceric acid can be observed. However,
decreasing the concentration of glycerol and increasing the mass of the
catalyst and the concentration of oxygen lead to the formation of tartronic
acid via consecutive oxidation of glyceric acid. Interestingly, this product
is stable with these catalysts. It is apparent that, with careful control of
the reaction conditions, 100% selectivity to glyceric acid can be obtained