Influence of Support Basic Sites in Green Oxidation of Biobased Substrates Using Au-Promoted Catalysts

Abstract

We report herein HMF (5-hydroxymethylfurfural) and furfural oxidation to 2,5-furandicarboxylic (FDCA) and furoic acids, respectively, in water, under base-free conditions and using supported gold nanoparticles. Prepared catalysts showed high catalytic activity under environmentally friendly conditions. Especially, the use of base-free conditions enables getting rid of the most usually needed neutralization step generating salts that must be further handled/eliminated. We showed that the conversion and the selectivity to desired products depend on the basicity of the support. To this respect, the Au/MgO catalyst was the most active sample (100% and 90% yields to furoic acid and 2,5furandicarboxylic acid, respectively), although a partial leaching of Mg was observed (89 ppm). Novel Au/MgF 2 -MgO catalysts were also very active (97% yield of furoic acid) with a final pH of 7.5. High yields of acid were also obtained (78%) with an acid final pH of 3.8, actually enabling the isolation of products under their acid form directly from the reaction medium without a neutralization step.

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

“…1000 25 22 A more in-depth study was made with Au catalysts that were supported on basic oxides under these conditions ( Figure 5). The Sr-based catalyst was also synthesized and tested, as a decrease in activity had already been detected when going down in the alkaline earth group (Au/MgO > Au/CaO > Au/BaO) for furfural oxidation [32]. The results show the same trend as previously observed, thus confirming the Au/MgO catalyst as the most active in this transformation.…”

“…Au-based catalysts were prepared by the pre-formed nanoparticle immobilization method (sol immobilization method) because of its reproducibility. AuPVA NPs of about 3 nm, as determined by TEM [32], were first prepared and then supported on different metal oxides. As expected, the Au nanoparticles size was preserved after immobilization on different metal oxides, e.g.…”

“…This forms atomic oxygen with strong basic properties that could easily activate CH 3 OH and increase the reaction rates [31]. The application of gold catalysis in oxidations and oxidative esterification has grown a lot, but the issue of the use of base remains unsolved [32].…”

Aerobic oxidation of 1,6-hexanediol to adipic acid over Au-based catalysts: the role of basic supports

“…The supported Au catalysts were prepared by using the solimmobilization method. 48,49 2 wt% polyvinyl alcohol solution (PVA, Sigma-Aldrich, MW 55 000 g mol −1 ) was dropped to the HAuCl 4 (99.9%, Sigma-Aldrich) water solution (0.5 mM) under magnetic stirring [PVA/Au (w/w) = 1.2]. To reduce the gold particles, a solution of NaBH 4 (98%, Sigma-Aldrich, 0.1 M, NaBH 4 /Au (mol/mol) = 5] was added to the PVA/Au solution.…”

Liquid Phase Furfural Oxidation under Uncontrolled pH in Batch and Flow Conditions: The Role of In Situ Formed Base

“…Apart from furfural oxidation, many works in the literature describe the use of basic solid supports, such as MgO, CaO and hydrotalcites, to perform catalytic reactions in aqueous medium but not taking in consideration the connection between catalyst activity and instability related to soluble base formation [13][14][15]. Considering the use of MgO, the authors already observed the support leaching phenomena on furfural oxidation [16] and further studied the use of more stable oxides such as MnO2 [17]. In the present work, a heterogeneously-catalyzed process to produce furoic acid by selective oxidation of furfural using different hydrotalcites-supported gold nanoparticles is proposed as an alternative to the Cannizzaro reaction.…”