5-Hydroxymethylfurfural and Furfural Base-Free Oxidation over AuPd Embedded Bimetallic Nanoparticles

One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

Al Rawas H, Heyte S, Paul S, Itabaiana Jr I, Pietrowski M, Zieliński M, Ghazzal MN, Dumeignil F, Wojcieszak R. Supported Gold Catalysts for Base-Free Furfural Oxidation: The State of the Art and Machine-Learning-Enabled Optimization

Supported gold nanoparticles have proven to be highly effective catalysts for the base-free oxidation of furfural, a compound derived from biomass. Their small size enables a high surface-area-to-volume ratio, providing abundant active sites for the reaction to take place. These gold nanoparticles serve as catalysts by providing surfaces for furfural molecules to adsorb onto and facilitating electron transfer between the substrate and the oxidizing agent. The role of the support in this reaction has been widely studied, and gold-support interactions have been found to be beneficial. However, the exact mechanism of furfural oxidation under base-free conditions remains an active area of research and is not yet fully understood. In this review, we delve into the essential factors that influence the selectivity of furfural oxidation. We present an optimization process that highlights the significant role of machine learning in identifying the best catalyst for this reaction. The principal objective of this study is to provide a comprehensive review of research conducted over the past five years concerning the catalytic oxidation of furfural under base-free conditions. By conducting tree decision making on experimental data from recent articles, a total of 93 gold-based catalysts are compared. The relative variable importance chart analysis reveals that the support preparation method and the pH of the solution are the most crucial factors determining the yield of furoic acid in this oxidation process.

Selective Oxidation of Furfural at Room Temperature on a TiO2-Supported Ag Catalyst

The catalytic performance of the Ag/TiO2 catalyst was evaluated in the oxidation of furfural (FF) to furoic acid (FA) in an alkaline aqueous solution under 15 bar of air in a batch reactor. The catalytic activity, yield, and stability of the catalyst were compared as a function of different reaction parameters including temperature (25–110 °C), nature of the atmosphere, base equivalent (nbase/nFF = 0.25–3), and nature of the inorganic bases used (NaOH, NaHCO3, and Na2CO3). Under optimum conditions, the yield of FA (96%) was achieved at room temperature, with an excellent carbon balance (>98%). The recyclability of the catalyst was also studied and the catalytic activity of the Ag/TiO2 catalyst slightly declined due to an increase in particle size as confirmed by TEM studies.

Strengthening the Connection between Science, Society and Environment to Develop Future French and European Bioeconomies: Cutting-Edge Research of VAALBIO Team at UCCS

The development of the future French and European bioeconomies will involve developing new green chemical processes in which catalytic transformations are key. The VAALBIO team (valorization of alkanes and biomass) of the UCCS laboratory (Unité de Catalyse et Chimie du Solide) are working on various catalytic processes, either developing new catalysts and/or designing the whole catalytic processes. Our research is focused on both the fundamental and applied aspects of the processes. Through this review paper, we demonstrate the main topics developed by our team focusing mostly on oxygen- and hydrogen-related processes as well as on green hydrogen production and hybrid catalysis. The social impacts of the bioeconomy are also discussed applying the concept of the institutional compass.

Au-Pd separation enhances bimetallic catalysis of alcohol oxidation

In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. This is exemplified by the oxidative dehydrogenation of alcohols, an important class of reactions with modern commercial applications^1-3. Supported gold nanoparticles are highly active for the dehydrogenation of the alcohol to an aldehyde⁴ but are less effective for oxygen reduction^5,6. By contrast, supported palladium nanoparticles offer high efficacy for oxygen reduction^5,6. This imbalance can be overcome by alloying gold with palladium, which gives enhanced activity to both reactions^7,8,9; however, the electrochemical potential of the alloy is a compromise between that of the two metals, meaning that although the oxygen reduction can be improved in the alloy, the dehydrogenation activity is often limited. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladium catalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect-a cooperative redox enhancement-offers an approach to the design of multicomponent heterogeneous catalysts.

Influence of Pd and Pt Promotion in Gold Based Bimetallic Catalysts on Selectivity Modulation in Furfural Base-Free Oxidation

Furfural (FF) has a high potential to become a major renewable platform molecule to produce biofuels and bio-based chemicals. The catalytic performances of AuxPty and AuxPdy bimetallic nanoparticulate systems supported on TiO2 were studied in a base-free aerobic oxidation of furfural to furoic acid (FA) and maleic acid (MA) in water. The characterization of the catalysts was performed using standard techniques. The optimum reaction conditions were also investigated, including the reaction time, the reaction temperature, the metal ratio, and the metal loading. The present work shows a synergistic effect existing between Au, Pd, and Pt in the alloy, where the performances of the catalysts were strongly dependent on the metal ratio. The highest selectivity (100%) to FA was obtained using Au3-Pd1 catalysts, with 88% using 0.5% Au3Pt1 with about 30% of FF conversion at 80 °C. Using Au-Pd-based catalysts, the maximum yield of MA (14%) and 5% of 2(5H)-furanone (FAO) were obtained by using a 2%Au1-Pd1/TiO2 catalyst at 110 °C.

Catalytic Transformation of Renewables (Olefin, Bio-Sourced, et al.)

The objective of this Special Issue is to provide new diverse contributions that can demonstrate recent applications in biomass transformation using heterogeneous catalysts [...]

Selective oxidation of bio-based platform molecules and their conversion products over metal nanoparticle catalysts: a review

The conversion of bio-renewable raw materials into valuable products (biofuels, bifunctional carbonyls/carboxyls) that serve as the basis for biopolymers, has become one of the most important areas in the development of novel hybrid catalysts.

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

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 C5 (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.