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

Abstract

Furfural (FF) is a strategic product for the development of highly valued chemicals from biomass. The oxidation product of FF, furoic acid (FA), is an important precursor for the synthesis of green esters, such as methyl furoate. Taking into account issues with the direct furfural oxidation, furfural derivatives, such as alkyl furoates, can be easily prepared via oxidative esterification.Here, Au nanoparticles that were immobilized on alkaline-earth metal oxide supports were studied for the oxidative esterification of furfural while using alcohol as both reactant and solvent. The formation of esters is favored by the presence of basic sites on catalyst surface, resulting in high selectivity, preventing the formation of the acetal as a by-product. The Au/MgO sample provided up to 95% methyl furoate (MF) yield, a fast reaction rate, and high performance for furfural:Au molar ratios between 50 and 300. Furthermore, this catalyst was stable during reuse, since both the selectivity and the activity were maintained after four cycles. Oxidative esterification products were achieved in the presence of other alcohols, leading to the formation of esters of up to C 5 (isopentyl furoate) with high selectivity (>99%). Linear and branched esters were formed, but the long-chain linear alcohols resulted in higher yields, such as n-butyl furoate in 94% yield.Catalysts 2020, 10, 430 2 of 14 considered to be one of the most important platform compounds in biorefineries of the future [8][9][10]. Several products that are obtained via HMF oxidation are of great interest for the polymer industry because their derivatives can be used as C6 monomers to replace petrochemical monomers [1-10]. 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]. The direct use of FDCA in the industry is difficult due to its low solubility in most commonly used solvents. The furan-2,5-dimethylcarboxylate ester (FDMC) is actually more suitable for the subsequent polymerization reaction, thanks to its better solubility. For this reason, the development of catalytic systems that are capable of producing FDMC directly from the HMF has received much attention today. One alternative is the production of FDCA can be obtained from furoic acid (furfural oxidation product) via the Henkel reaction [13]. However, the use of Au catalysts can also be a viable alternative. FDCA can be obtained from furoic acid (furfural oxidation product) via the Henkel reaction [13]. Recently, Au catalysts have been successfully applied for the oxidative esterification of alcohols [14-17] and they have also been explored for the esterification of furfural and HMF [18][19][20][21][22][23][24][25][26][27][28]. The first example of HMF esterification to produce dimethyl-2-furoate (FDMC) required the use of a base (NaOMe) [29]. Although other catalytic systems have then been reported, there are few examples of successful Au catalytic systems for t...

Study of the oxidative esterification of furfural catalyzed by Au25(glutathione)18 nanocluster deposited on zirconia

“…Here we observed the presence of furfural dimethyl acetal besides methyl-2-fuorate (Scheme 3). Some literature studies propose that this dimethyl acetal is not an intermediate towards methyl-2-furoate, in contrast to the methyl hemiacetal (Scheme 3), but is formed as a side product stable under reaction conditions [3,27]. However in our case performing the reaction over a longer time allows a consumption of this compound after 5 h with concomitant formation of target methyl-2-furoate (while furfural conversion remained stable).…”

“…no base formation is due to the absence of basic sites in the reaction medium [27], preventing selective ester formation. Another report claims that the formation of this dimethyl acetal can be due to the Lewis acid sites of zirconia [13].…”

Versatility of Supported Gold Nanoparticles on Hydrotalcites used for Oxidation and Reduction Reactions

“…The development and understanding of efficient technologies for the production of platform molecules (small molecules derivable from biomass used as building blocks for chemical industry) and valuable chemicals from renewable biomass have attracted immense attention from researchers [1][2][3][4]. Until now, the direct partial reduction of carboxylic acid to the corresponding aldehyde using heterogeneous catalysts has been rarely discussed in the literature [5].…”

Systematic Incorporation of Gold Nanoparticles onto Mesoporous Titanium Oxide Particles for Green Catalysts

“…Nontoxic metal-based materials have been extensively fabricated to develop reactive catalysts that can be operational in environmentally friendly conditions for various chemical transformation reactions [1][2][3][4][5]. One attractive candidate is a colloidal form of nanoscale metal particles that can be prepared in green solution media (e.g., water and EtOH) and still show catalytic reactivity and recyclability [2,[6][7][8]. Among many metal nanoparticles, gold nanoparticles (AuNPs) have shown ideal characteristics due to their biocompatible nature and well-established preparation strategies for diverse structures [2,[9][10][11][12][13].…”