Today, industrial plants that produce glycerol are closing down and others are opening that use glycerol as a raw material, owing to the large surplus of glycerol formed as a by-product during the production of biodiesel. Research efforts to find new applications of glycerol as a low-cost feedstock for functional derivatives have led to the introduction of a number of selective processes for converting glycerol into commercially valued products. This Minireview describes a selection of such achievements and shows how glycerol will be a central raw material in future chemical industries.

The metal-support interaction in catalysis is of relevance both for academic studies and for industrial applications, and theoretical concepts have contributed to understanding the basic principles behind this interaction. [1] In most cases, however, the metal-support interaction is only described in terms of catalytic behavior and its nature often remains debatable. In recent years interest in gold catalysts for various applications in organic and inorganic chemistry [2] has increased and, our and other research groups have investigated the liquid-phase oxidation of polyol, [3][4][5][6][7] aminoalcohols, [8] and glucose [9] to carboxylates, and the gas-phase oxidation of alcohols to the corresponding carbonyl derivatives [10] using metal particles supported on different materials. In liquid-phase applications, carbon was found to be the support of choice, and in the case of ethane-1,2-diol oxidation, by comparing different commercial carbons, a tentative hypothesis of metal-support interactions, connected to the density of phenolic groups at the carbon surface, was formulated.[11] However, the synergism between gold particles and carbon was not demonstrated and this point remained unresolved.Although gold colloids have widely been employed to prepare supported gold catalysts, no report of particles derived from colloidal dispersion being used as catalysts has appeared. We have now found that, under controlled conditions, water-dispersed gold sol exhibits a surprising activity when used as "naked particles", that is, in the absence of common protectors as polyvinylalcohol (PVA), polyvinylpyrrolidone (PVP), tetrahydroxymethylphosphonium chloride (THPC). As a model reaction, we have investigated the aerobic oxidation of glucose to gluconate which occurs under mild conditions.As shown in the conversion-time plot (Figure 1), naked gold particles having a mean diameter of 3.6 nm behave as an active catalyst allowing 21 % glucose conversion in the first 200 s.These particles are produced as a colloidal sol by reducing HAuCl 4 in the presence of a large excess of glucose acting either as reagent or protector. From the initial rate, a specific molar activity of 18 043 mol gluconate [mol Au] À1 h À1 (calculated with respect to the total gold) can be derived. Under similar conditions, Cu, Ag, Pd, and Pt colloidal particles of similar dimension (3-5 nm) were scarcely active. During the catalytic test, gold coagulated into larger particles owing to the formation of sodium gluconate that, as is common with other electrolytes, promoted sol coagulation leaving a colorless, inactive solution after about 400 s. The growth of gold crystallites during the reaction has been followed by X-ray diffraction (XRD) analysis at various time intervals, after sol immobilization on carbon (Figure 2).Gold particles are also poisoned by sulfur compounds, such as sulfides and sulfites, and inhibited by protecting molecules, such as polyvinyl alcohol. Although the short life of the gold sol does not allow its use as a practical catalyst, its acti...

Careful analytical determinations show that the gold-catalysed aerobic oxidation of glucose occurs through a two-electrons mechanism leading to gluconate and hydrogen peroxide. This latter decomposes before reaching the critical concentration for competing with O 2 in glucose oxidation. A mechanism of glucose oxidation on gold nanoparticles is presented.

As a result of the booming biodiesel and oleochemicals manufacturing taking place worldwide since more than a decade, 2 million tonnes of glycerol consistently reach the market every year, even though after a decade of growth the total glycerol supply is expected to slightly decrease in 2014. Today the supply of glycerol is entirely independent of its demand, as there is as much glycerol as the amount of vegetable oils and animal fats are hydrolyzed to make oleochemicals, or transesterified to produce biodiesel. This unique situation has led to consistently low glycerol prices, which initiated both the market penetration of glycerol in countries where it was not used due to traditional high price, as well as new uses of glycerol as raw material for the production of value added chemicals. This article sheds light on the market of this uniquely versatile chemical whose number of applications is unique amid all existing chemicals.

This critical review aims to update the recent development in the selective oxidation of organic compounds by gold catalysis, highlighting the progress in the last three years. Following the impressive developments in the last decades, several protocols for catalytic oxidation are today available, which are based on the extraordinary properties of gold in terms of catalytic activity, selectivity, reusability and resistance to poisons. Beside many other applications, gold can be recommended for green processes dedicated to fine chemicals, pharmaceuticals and the food industry owing to its recognized bio-compatibility. The collected literature is focused on experiments concerning the oxidation of different chemical groups and could be of interest, in the wide area of organic chemistry, for improving previous processes or for exploring new catalytic pathways (174 references).

This critical review covers the recent development of the catalytic properties of gold in the selective oxidation of organic compounds, highlighting the exciting contribution to the art of catalysis. The unique, outstanding properties of nanometre-scale particles of gold, a biocompatible non-toxic metal, have allowed the development of a new generation of stable and selective catalysts for the conversion of many organic feedstocks to valuable chemicals. A critical discussion of the results of different research groups is presented along with attempts to correlate the catalytic properties with catalyst morphology in non-equivalent series of experiments. Particular emphasis has been given to the international efforts towards optimised synthesis of products of industrial appeal such as propylene oxide, vinyl acetate monomer, cyclohexanol/cyclohexanone, gluconic acid and glyceric acid (168 references).

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