Recent Developments in Gold Nanomaterial Catalysts for Oxidation Reaction through Green and Sustainable Routes - Advanced Materials for Agriculture, Food and Environmental Safety - page 198

• the stoichiometric process must be replaced by a catalytic
process; and
• durable heterogeneous catalyst of very high activity and
desired product selectivity must be designed.

Design of reaction-specii c catalyst is a key technology for these aspects.
It not only reduces the environmental burden but also increases the reac-
tant conversion and desired product selectivity, which is the main purpose
of sustainable chemistry. Dif erent types of industrially demanded chemi-
cals, e.g., ethylene oxide, propylene oxide, aldehyde, -caprolactam, phe-

nol, hydrogen peroxide, etc., are produced by oxidation reaction.
In 1857, Michael Faraday delivered the Bakerian Lecture to the Royal
Society of London, entitled “Experimental Relations of Gold (and Other
Metals) to Light” [3]. He reasoned that there was merit in observing the
action of light on metal particles which were small compared to the wave-
length of light; gold sprang to mind because “known phenomena appeared
to indicate that a mere variation in the size of its particles gave rise to a variety
of resultant colours” . h e physical and chemical properties of solid depend
on the type of motions that its electrons may execute, which depends on the
space available for their motion, i.e., their surface coni nement.
Bulk and nanoparticles of palladium and platinum show many simi-
larities in catalytic activity [4, 5]. However, gold nanoparticles show an
exceptional behavior as reported in literature. Prof. Haruta's [6] pioneer-
ing discovery of the catalytic activity of gold nanoparticles has opened up
new horizons in the chemistry of gold nanoparticles, which is supported
by many interesting literature reports [7]. Nowadays, gold nanoparticles
are widely used as a catalyst for dif erent types of oxidation reactions in gas
phase like propylene epoxidation, ehanol oxidation, and in liquid phase for
oxidation of glucose, hydrogenation, dehydrogenation, N-formylation, [8]
and many other types of chemical reactions [9-12].
Gold (Au) is the most noble metal of the periodic table; it has the high-
est electron ai nity, with several known compounds that show Au with
a negative oxidation number; its Pauling electronegativity has a value of
2.54, which is the largest among all metals [13]. Gold is resistant to any
kind of corrosion: Au 2 O 3 is the only oxide that has a positive formation
enthalpy (ΔH f °

ε

= + 19.3 kJ/mol) [14]. From dif erent literature reviews and
experimental observations, the origin of the catalytic activity of gold nan-
oparticles was considered to be dependent on:

• Quantum size ef ects;

• the presence of low-coordinated gold sites;