Recent Developments in Gold Nanomaterial Catalysts for Oxidation Reaction through Green and Sustainable Routes - Advanced Materials for Agriculture, Food and Environmental Safety - page 230

Methanol was oxidized on Au(110) via the activation of the O-H bond
by adsorbed atomic oxygen to form methoxy at 200 K temperature. h is
methoxy group further reacted to from methanol, hydrogen, and methyl
formate at 250 K and CO 2 at 350 K temperature [165]. h e expected prod-
uct formaldehyde was not observed, which may be due to the fundamen-
tal dif erence in the bonding of methoxy to the gold surface, rendering it
more susceptible to attack by the aldehyde [166]. Methoxy decomposed to
adsorbed formaldehyde on gold at a lower temperature (250 K), so that its
reaction with adsorbed methoxy to form methyl formate was more likely
due to a longer surface lifetime during heating. Formate also existed as a
stable intermediate on Au(110) through secondary oxidation of formalde-
hyde [165]. h e decomposition temperature of the formate on Au(110) was
350K, lower than that observed on Ag(110) (400 K) and Cu(110) (475 K)
[167]. h e formation of methyl formate via coupling of formaldehyde with
methanol was attributed to the fact that the decomposition temperature of
methoxy via β-H elimination is lower than the desorption temperature of
the aldehyde formed [168]. In methanol oxidation reaction some groups
detected H 2 O, CO and CO 2 as the decomposed product of the methoxy
group [169, 170], whereas some other research groups claimed that methyl
formate, formaldehyde and formic acid are formed as a decomposed prod-
uct of the methoxy group [171]. h e discrepancies in their result may be
due to the following factors: (i) the method for preparing oxidized Au(111)
surface was dif erent, possibly leading to dif erences in the bonding envi-
ronment of the oxygen; (ii) methanol was exposed to the surface at a
higher temperature (160 K), close to the temperature where water leaves
the surface; (iii) the extent of the esterii cation reaction appears to be low,
so the methyl formate may have gone undetected if the mass spectrometer
detector is far away from the sample.
Ethanol oxidation is an important reaction from an industrial perspec-
tive. Ethanol was selectively oxidized on Au(111) surface with the forma-
tion of acetaldehyde and water as a main product [172]. No other partial
oxidation products (i.e., methane, ethane, ethylene, ethanol, acetic acid,
ethylene oxide and methyl formate) or C1-containing species (i.e., CO,
CO 2 , formaldehyde, and formic acid) were detected during the reaction
[172]. A trace amount of ethyl acetate was detected during the reaction.
When the surface of gold was covered by higher oxygen coverage, CO 2 was
also formed in ethanol oxidation reaction. At lower oxygen coverage ethyl
acetate is the main product for ethanol oxidation reaction. Liu et al. showed
that in ethanol oxidation reaction acetaldehyde was the main product; also
that ethyl acetate (230 K) and acetic acid (450 and 545 K) were formed on