Elżbieta Skrzyńska

Selective catalytic oxidation of glycerol: perspectives for high value chemicals

Due to its three hydroxyl groups, glycerol is a potential starting material for various high value fine chemicals such as dihydroxyacetone, tartronic acid and mesoxalic acid. The corresponding oxidation reactions are catalysed by various metals such as palladium, platinum, bismuth or gold. Nevertheless, the selectivity not only depends on the type of the active phase, but is also influenced by numerous parameters such as the metal particles size, the pore size of the support and the pH of the reaction medium. This review not only describes the recent developments in the field of research for new catalysts but also spotlights the role of the reaction conditions as well as the possible transport limitations in this tri-phasic system. Furthermore, an economical analysis of some processes is given, which shows that this is realistic to envision sustainable production of, e.g., dihydroxyacetone.

Quasi-Homogeneous Oxidation of Glycerol by Unsupported Gold Nanoparticles in the Liquid Phase

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.

Performance of Ag/Al2O3 catalysts in the liquid phase oxidation of glycerol – effect of preparation method and reaction conditions

This paper presents a systematic study of alumina supported silver catalysts, a novel catalytic system proposed for the liquid phase aerobic partial oxidation of glycerol to glycolic acid, the smallest α-hydroxyacid with numerous industrial applications (raw material in the chemical industry, ingredient in textiles, food, cosmetics, plastics, adhesives, pharmaceuticals, etc.). We evaluated the effect of the preparation method, the silver loading and the type of alumina support on the properties and the activity of the solids. We showed that numerous parameters can affect the catalytic performances, the most important of which were the following: the type of solvent used during preparation, the basicity and phase composition of the support, as well as the amount of base used during glycerol oxidation. The most active catalysts were at the same time the most selective ones to glycolic acid, which clearly differentiates the silver catalysts from other noble metals conventionally used in glycerol oxidation, such as Au, Pd and Pt, characterized by a high selectivity to glyceric acid. The best results in terms of conversion and selectivity to glycolic acid were obtained over the catalyst prepared by the chemical reduction method in a basic methanol solution, using formaldehyde as a reductant. After 3 h of reaction at 60 °C under 5 bar of oxygen pressure over such a catalyst loaded with 3.6 wt% Ag, an 85% glycerol conversion together with a 57.1% selectivity to glycolic acid were achieved. Moreover, the catalysts showed good stability in the continuous mode and very good resistance to the impurities present in a crude glycerol fraction.