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A quasi-homogeneous solution of gold nanoparticles prepared by the Turkevich method was used as an unconventional catalyst in the oxidation of glycerol (GLY) in the liquid phase. The highest obtained conversion was 100 % after 3 h of reaction at 100 °C under an oxygen atmosphere (5 bar). The main products were glyceric, glycolic, formic, tartronic, and oxalic acid with selectivities of 28, 36, 25, 9, and 2 %, respectively. Traces of hydroxypyruvic and acetic acid were also detected (combined selectivities below 1 %). To elucidate the reaction mechanism and specify the role of gold nanoparticles in the oxidation process, a series of experiments under various reaction conditions were carried out. The effect of reaction temperature, oxygen pressure, gold concentration, and GLY/base molar ratio was investigated. All catalytic results were systematically compared to the corresponding noncatalytic base-induced transformations (blank tests). Such an approach allowed us to separate and clarify the respective driving parameters for the transformation of GLY (presence of a base and activity of the gold catalyst). The reaction mechanism comprised a series of oxidation and C-C cleavage reactions, whereas additional oxidation-reduction reactions (of the Cannizzaro type) could also occur in the presence of the base.

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A series of silver supported catalysts have been developed and proposed for mild oxidation of glycerol in the liquid phase. High selectivity to glycolic acid, stability in both continuous-flow and periodic mode of reaction, and good resistance to crude glycerol impurities have been achieved.

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Abstract:The present work deals with the kinetic analysis and modelling of glycerol (GLY) oxidation in the liquid phase over a supported gold catalyst. A Langmuir-Hinshelwood model was proposed, after considering the effect of the reaction temperature, the NaOH/GLY ratio and the initial concentrations of GLY and GLY-Product mixtures. The proposed model effectively predicted the experimental results, and both the global model and the individual parameters were statistically significant. The results revealed that the C-C cleavage to form glycolic and formic acids was the most important reaction without a catalyst. On the other hand, the supported Au catalyst promoted the GLY oxidation to glyceric acid and its further conversion to tartronic and oxalic acids. Regarding the adsorption terms, glyceric acid showed the highest constant value at 60 • C, whereas those of GLY and OH − were also significant. Indeed, this adsorption role of OH − seems to be the reason why the higher NaOH/GLY ratio did not lead to higher GLY conversion in the Au-catalysed reaction.