Catalytic oxidation of 1,2-diols to α-hydroxy-carboxylates with stabilized gold nanocolloids combined with a membrane-based catalyst separation

Abstract

Gold (Au) nanosols stabilized with poly(vinylalcohol) can be used as homogeneous oxidation catalysts, both in water and in a variety of alcoholic solvents. Under 0.5 MPa O 2 pressure, 1,2-diols with varying chain length, such as 1,2-propanediol or 1,2-octanediol, are oxidized to the corresponding a-hydroxy-carboxylates with total chemoselectivity. The activity of the sol is of the same order as previously reported for stabilized nanoparticles deposited on carbon supports. The stabilized sols retain their activity over extended periods. The Au metal colloids can efficiently be recycled by means of a nanofiltration, either from an aqueous reaction medium, or from an organic solvent. The most suitable membranes for the Au sol recuperation are cellulose acetate membranes for the aqueous filtration, and poly(dimethyl)siloxane membranes for the solvent resistant filtration. Recycling tests after nanofiltration show that catalytic activity is largely preserved in consecutive runs.

Selective Oxidation Catalysis: Opportunities and Challenges

“…Another approach is to use a membrane to continuously remove the product, or to control the contact between the different reactants [137][138][139][140]. More recently, membrane reactors have also been used as an in situ nano-filtration system for the retention of catalytic nano-particles [141,142]. As such, the membrane reactor is used to recycle the catalyst, rather than to influence the product concentration.…”

Gold nanoclusters as colloidal catalysts for oxidation of long chain aliphatic 1,2-diols in alcohol solvents

“…The TOF values in these alcohol solvents (≤ 300 h -1 ) are appreciably lower than e.g. for 1,2-propanediol oxidation in water, where values up to 850 h -1 have been observed (15). A possible explanation is based on the mechanistic proposal that the aldehyde intermediate of the 1,2-diol oxidation is hydrated to a geminal diol before it is dehydrogenated to an acid.…”

“…of 1,2-propanediol in water (15). The physical properties of the aqueous sol were studied using absorption spectroscopy and electron microscopy, to obtain information about the gold dispersion and particulate dimensions.…”

“…The application of membrane filtrations is a relatively new approach to the recycling of dissolved catalysts (14), and in a preliminary report, we recently demonstrated that this method can be applied to the recuperation of catalytic Au nanocolloids, e.g. from aqueous reaction solutions (15).…”

Gold Nanoparticles Stabilized by Task-Specific Oligomeric Ionic Liquid for Styrene Epoxidation Without Using VOCs as Solvent

“…Owing to easy agglomeration of nanoparticle, these gold nanoparticles are generally stabilized by solid supports in catalytic reactions, especially in liquid-phase epoxidation/ oxidation. Although the supported solid catalysts show good activity in some liquid-phase reactions [5][6][7][8][9][10][14][15][16][17], the potential inaccessibility of the substrate to the catalytic active sites in the reaction system involving solid catalyst has stimulated researchers to use liquid stabilizer as an alternative solution [21][22][23][24]. On the other hand, liquidphase epoxidation/oxidation catalyzed by solid gold nanoparticle catalysts usually employ volatile organic compounds (VOCs) as solvents, such as benzene [14][15][16], methylcyclohexane [17], and 1,2,3,5-tetramethylbenzene [18].…”