Environmental Engineering Reference
In-Depth Information
8.4 Glucose Oxidation
Selective oxidation of natural resources is a task of key importance for pro-
ducing oxygenates to be employed as building blocks in chemical processes
that range from kilogram-scale applications in pharmaceuticals to thou-
sands of tone-scales in chemicals. Oxidation of glucose to gluconic acid
with heterogeneous catalyst is a typical example of these green chemistry
principles (Scheme 8.2). Gluconic acid, used as an intermediate in the food
and pharmaceutical industry and is a biodegradable chelating agent, is pro-
duced by biochemical oxidation of glucose as the only industrial route [94].
h e worldwide availability of carbohydrates has for a long time attracted
interest in their oxidative transformation. According to the expected trend,
catalytic aldose oxidation occurs at the aldehydic group, leading to car-
boxylic acid or carboxylate. In this area, ef orts have been mainly devoted
to the improvement of the catalyst ei ciency and process operation. h e
great interest in the valorization of renewable biological resources has led
to extensive investigation on the catalytic oxidation of glucose and other
carbohydrates since 2002. Free gluconic acid is presently manufactured
starting from calcium gluconate and sulfuric acid, thus producing a large
amount of CaSO 4 as a byproduct. h is is due to the fact that at low pH val-
ues the enzymatic catalysis is inhibited. Applying catalytic methods, it has
been found that Pd, Pt, and Au catalysts are scarcely active (TOFs 2, 60 and
50 h -1 , respectively) in the presence of free gluconic acid [95].
h ere have been several reports on supported palladium or platinum
catalysts which have intensively investigated the aerobic oxidation of glu-
cose. However, the major drawbacks to these catalysts are that they have
low catalyst durability and relatively low selectivity [96]. Figure 8.18 shows
the conversion-time plot; naked gold particles having a mean diameter of
3.6 nm behave as an active catalyst allowing 21% glucose conversion in
the i rst 200 s. Under similar conditions, Cu, Ag, Pd, and Pt colloidal par-
ticles of similar dimension (3-5 nm) were scarcely active [97]. Huiming et
al. reported that unsupported nanoporous gold (NPG) catalysts exhibited
ef ective catalytic activity and high gluconic acid selectivity (~99%) [98].
OH
O
OH
OH
O 2 / H 2 O 2
Au/Support
pH > 8.5
Te m p 5 0 - 6 0 0 C
O
HO
HO
ONa
OH
HO
OH
OH
OH
Scheme 8.2 Catalytic oxidation of glucose to gluconic acid.
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