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Due to its highly functionalized nature, glycerol is also used as a feedstock for the synthesis of useful oxygenates. Several oxygenated compounds such as mesooxalic acid, glyceric acid, dihydroxyacetone, oxalic acid, tartronic acid, hydroxyethanoic acid, etc., can be produced from the complex reaction pathway through oxidation of glycerol. These compounds, especially mesooxalic acid and tartronic acid, are important chelating agents, which have the potential for the production of valuable polymers and chemicals. Dihydroxyacetone can be used as a building block in organic synthesis and as a basic repeating unit of new degradable polymers [12, 13]. To date, these chemicals have inadequate utilization because they are either synthesized using expensive and environmentally harmful oxidation processes (e.g. K₂Cr₂O₇, HNO₃, H₂CrO₄) or less productive fermentation process The possible reaction pathways to oxygenated derivatives of glycerol is shown in Scheme 4.5.

The heterogeneous catalytic oxidation process can be used for the oxidation of a unique structure of glycerol using low-cost oxidizing agents such as oxygen, air, and H₂O₂ instead of environmentally harmful oxidants, e.g., K₂Cr₂O₇, HNO₃, H₂CrO₄, etc. The synthesis of a highly selective catalyst is the main challenge in this oxidation reaction. This catalyst must be selective towards either the oxidation of the primary alcohol group, to produce glyceric acid, or the oxidation of the secondary alcohol group, to synthesized hydroxypyruvic acid and dihydroxyacetone. Several studies have been reported for chemoselective glycerol oxidation over supported noble metal nanoparticles such as Pt, Pd, and Au. In general, the selective oxidation of glycerol takes place in the aqueous medium. Table 4.3 summarizes the performance of different catalysts.

The Au particles supported on multiwalled carbon nanotubes enhance the chemoselectivity for glycerol oxidation towards the formation of dihydroxyacetone. The catalyst shows 60% selectivity along with the high activity. The results were compared by using activated carbon under similar metal loading and particle size. The activated carbon encourages the synthesis of glyceric acid. The study suggests that the type of supports play significant role in chemoselectivity [47]. Selective oxidation of crude glycerol into lactic acid and glyceric acid has been carried by different groups using carbon as a support for Pt, Pd, Cu–Pt and Au–Pd etc. [48–50].

Scheme 4.5 Plausible reaction plan for the production of oxygenated derivatives from glycerol [9].