Advances in Base-Free Oxidation of Bio-Based Compounds on Supported Gold Catalysts

Abstract

Abstract:The oxidation of bio-based molecules in general, and of carbohydrates and furanics in particular, is a highly attractive process. The catalytic conversion of renewable compounds is of high importance. Acids and other chemical intermediates issued from oxidation processes have many applications related, especially, to food and detergents, as well as to pharmaceutics, cosmetics, and the chemical industry. Until now, the oxidation of sugars, furfural, or 5-hydroxymethylfurfural has been mainly conducted through biochemical processes or with strong inorganic oxidants. The use of these processes very often presents many disadvantages, especially regarding products separation and selectivity control. Generally, the oxidation is performed in batch conditions using an appropriate catalyst and a basic aqueous solution (pH 7-9), while bubbling oxygen or air through the slurry. However, there is a renewed interest in working in base-free conditions to avoid the production of salts. Actually, this gives direct access to different acids or diacids without laborious product purification steps. This review focuses on processes applying gold-based catalysts, and on the catalytic properties of these systems in the base-free oxidation of important compounds: C5-C6 sugars, furfural, and 5-hydroxymethylfurfural. A better understanding of the chemical and physical properties of the catalysts and of the operating conditions applied in the oxidation reactions is essential. For this reason, in this review we put emphasis on these most impacting factors.

Efficient Oxidative Esterification of Furfural Using Au Nanoparticles Supported on Group 2 Alkaline Earth Metal Oxides

“…Currently, special attention has been given to the oxidation of biomass-derived substrates due to their potential to replace petroleum products [1][2][3][4][5][6][7]. When considering the high extent of functionality and hydrophilic properties, biomass-derived substrates should be processed in liquid phase, typically in an aqueous phase [1][2][3][4]. Thus, the development of efficient liquid phase technologies is desired, as well as catalysts working under mild conditions [1][2][3][4].…”

“…When considering the high extent of functionality and hydrophilic properties, biomass-derived substrates should be processed in liquid phase, typically in an aqueous phase [1][2][3][4]. Thus, the development of efficient liquid phase technologies is desired, as well as catalysts working under mild conditions [1][2][3][4]. Several routes for the conversion of bio-based compounds into fuels and highly valued chemicals involve the production of furfural and 5-hydroxymethylfurfural (HMF) (Scheme 1) [8].…”

“…The high performance of Au/CeO 2 catalyst under base free conditions inspired the development of Au catalysts for oxidative furfural esterification in the absence of a base [8]. Titania, ceria, and zirconia were studied by different research groups; however, Signoretto et al revealed that the performance of catalysts in the absence of a base followed the order: Au/ZrO 2 > Au/CeO 2 >> Au/TiO 2 [30].Catalysts 2019, 9, x FOR PEER REVIEW 2 of 14 interest for the polymer industry because their derivatives can be used as C6 monomers to replace petrochemical monomers [1][2][3][4][5][6][7][8][9][10]. For example, 2,5-furandicarboxylic acid (FDCA) is a monomer in the production of polyethylene 2,5-furandicarboxylate (PEF), being a green alternative to polyethylene terephthalate (PET) [11][12][13].…”

“…Catalysts 2019, 9, x FOR PEER REVIEW 2 of 14 interest for the polymer industry because their derivatives can be used as C6 monomers to replace petrochemical monomers [1][2][3][4][5][6][7][8][9][10]. For example, 2,5-furandicarboxylic acid (FDCA) is a monomer in the production of polyethylene 2,5-furandicarboxylate (PEF), being a green alternative to polyethylene terephthalate (PET) [11][12][13].…”

Furfural Oxidation on Gold Supported on MnO2: Influence of the Support Structure on the Catalytic Performances

“…In recent decades, supported gold nanoparticles have been extensively studied because of their unusual catalytic properties [1][2][3][4]. It is well recognized that the size of gold nanoparticles determines both the activity and the selectivity of the final catalyst [4,5].…”