Facet Effect of Single-Crystalline Pd Nanocrystals for Aerobic Oxidation of 5-Hydroxymethyl-2-furfural

Mechanistic Studies into the Selective Production of 2,5-furandicarboxylic Acid from 2,5-bis(hydroxymethyl)furan Using Au-Pd Bimetallic Catalyst Supported on Nitrated Carbon Material

Aerobic oxidation of bio-sourced 2,5-bis(hydroxymethyl)furan (BHMF) to 2, 5-furandicarboxylic acid (FDCA), a renewable and green alternative to petroleum-derived terephthalic acid (TPA), is of great significance in green chemicals production. Herein, hierarchical porous bowl-like nitrogen-rich (nitrated) carbon-supported bimetallic Au-Pd nanocatalysts (AumPdn/ N-BNxC) with different nitrogen content and bimetal nanoparticle sizes were developed and employed for the highly efficient aerobic oxidation of BHMF to FDCA in sodium carbonate aqueous solution. The reaction pathway for catalytic oxidation of BHMF went through the steps of BHMF→HMF→HMFCA→FFCA→FDCA. Kinetics studies showed that the activation energies of BHMF, HMF, HMFCA, and FFCA were 58.1 kJ·moL−1, 39.1 kJ·moL−1, 129.2 kJ·moL−1, and 56.3 kJ·moL−1, respectively, indicating that the oxidation of intermediate HMFCA to FFCA was the rate-determining step. ESR tests proved that the active species was a superoxide radical. Owing to the synergy between the nitrogen-rich carbon support and bimetallic Au-Pd nanoparticles, the Au1Pd1/N-BN2C nanocatalysts exhibited BHMF conversion of 100% and FDCA yield of 95.8% under optimal reaction conditions. Furthermore, the nanocatalysts showed good stability and reusability. This work provides a versatile strategy for the design of heterogeneous catalysts for the highly efficient production of FDCA from BHMF.

Base-Free Aerobic Oxidation of Furfuralcohols and Furfurals to Furancarboxylic Acids over Nitrogen-Doped Carbon-Supported AuPd Bowl-Like Catalyst

Upgrading furfuralcohols and furfurals to furancarboxylic acids is of great significance for high value-added downstream chemicals synthesis and biomass conversion. Developing an efficient catalyst is the key to acquiring a completely sustainable process. Herein, nitrogen-doped carbon-supported bimetallic AuPd bowl-like catalysts were synthesized. The surface wettability of nitrogen-doped carbon was well adjusted by the nitrification process. Benefiting from the alloying effect of bimetallic AuPd catalyst and the formation of hydroxyl radical initiated by H₂ O dissociation on the hydrophilic surface of nitrated nitrogen-doped carbon, base-free aerobic oxidation of 5-hydroxymethylfurfural (HMF) could produce the highest 2,5-furandicarboxylic acid (FDCA) yield of 93.9 %. In-situ infrared spectroscopy uncovered adsorption configuration of HMF, and the nitrated carbon surface was favorable for HMF and intermediates to enter the active sites, greatly promoting the catalytic oxidation process. Employing other furfuralcohols (furfuryl alcohol, furan-2,5-diyldimethanol, 2,5-bishydroxymethylfuran) as well as furfural and 5-methylfurfural as starting materials, 35.6-95.4 % yield of furancarboxylic acids (FDCA, 2-furoic acid, 5-methyl-2-furoic acid) were also obtained. Moreover, the developed catalysts could maintain excellent stability and activity after four successive runs. This deep insight into the role of bimetallic synergy and surface wettability provides a basis for the rational design of the highly efficient catalysts for the oxidation of furfuralcohols and furfurals and related reactions.

Research Progress of Highly Efficient Noble Metal Catalysts for the Oxidation of 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) is considered to be one of the most pivotal multifunctional biomass platform chemicals. This Review discusses recent advances in catalytic oxidation of HMF towards high-value products. The reaction mechanism of different noble metals and the path of HMF oxidation to high-value products have been deeply investigated in the noble metal catalytic system. The reaction mechanisms of different noble metals and HMF conversion paths were compared in detail. Moreover, the factors affecting the performance of different noble metal catalysts were summarized. Finally, effective strategies were put forward to improve the catalytic performance of noble metal catalysts. The purpose is to provide a valuable reference for the academic research on the preparation of oxidation products from biomass-based HMF and the industrial application of noble metal catalysts.

Metal vs. Metal-Free Catalysts for Oxidation of 5-Hydroxymethylfurfural and Levoglucosenone to Biosourced Chemicals

Lignocellulosic feedstocks, such as forestry biomass and agricultural crop residues, can be utilized to generate biofuels and biochemicals. Converting these organic waste materials into biochemicals is widely regarded as a remedial approach to develop a sustainable, clean, and green energy source. Nevertheless, are these methods sustainable and clean? Prior studies have shown that most such conversions use metals - including heavy metals or noble metals - as catalysts. In addition to the fact that many metals (e. g., aluminum, cobalt, titanium, platinum) have been listed as critical minerals, these methods suffer from high cost, deactivation, and leakage problems and the release of toxic wastes. This Review summarizes catalytic methods using metal and metal-free catalysts for the oxidation of the platform molecules 5-hydroxymethylfurfural and levoglucosenone and demonstrates the potential and effectiveness of metal-free catalysts.

Selective Hydrogenolysis of 5-Hydroxymethylfurfural to 2-Hexanol over Au/ZrO2 Catalysts

2-Hexanol (2-HOL) is a versatile biomass-derived platform molecule for synthesis of liquid transportation fuels, lubricants, or detergents. Herein, a one-step preparation of 2-HOL using 5-hydroxymethylfurfural (HMF) as a substrate was reported for the first time. Several Au-based catalysts supported on different metal oxides were prepared to explore the relationship between carrier and catalytic activity. The results showed that the highest 2-HOL yield of 65.8 % was obtained at complete HMF conversion over the 5 %Au/ZrO₂ catalyst. The 5 %Au/ZrO₂ catalyst exhibited excellent durability after five consecutive recycling runs, while confirming its remarkable ring-opening hydrogenolysis on other biomass-derived furanics, furfural, with a total yield of 1-pentanol and 2-pentanol of 67.4 %. The distinguished ring-opening hydrogenolysis performance of the Au/ZrO₂ catalyst originated from a synergistic effect between the interfacial Au-O-Zr oxygen vacancies-induced Lewis acidic sites (activating C-OH/C=O bonds) and metallic Au (activating H₂ ). This work provides a possibility for producing 2-HOL from HMF with high yield, expanding the sustainable application of lignocellulosic biomass.

Mechanistic insights into CoOx–Ag/CeO2 catalysts for the aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

CoOx–Ag/CeO2 catalysts achieve satisfactory FDCA yield from HMF, and a fundamental understanding about the reaction mechanism is provided.

Sulfidation of nickel foam with enhanced electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Electrochemical oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is an intriguing way of biomass conversion. Herein, a sulfidation of nickel foam (Ni₂S₃/NF) was attempted via a hydrothermal method, achieving high selectivity and efficiency for HMF oxidation. The optimized Ni₂S₃/NF electrode exhibits a nearly 100% conversion of HMF, 98% yield of FDCA, and 94% high faradaic efficiency. This material is stable and retains activity after 6 consecutive measurements. This work provides a facile route to design and prepare electrocatalysts for biomass upgrading.

Coordinately unsaturated O2c–Ti5c–O2c sites promote the reactivity of Pt/TiO2 catalysts in the solvent-free oxidation of n-octanol

Coordination unsaturated O_2c–Ti_5c–O_2c of TiO₂ (001) facets promote the formation of low-coordinate Pt metal clusters, which enhances catalytic performance in aerobic 1-octanol oxidation.

Nitrogen modulated NiMoO4 with enhanced activity for the electrochemical oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

NiMoO4 catalyst modified with nitrogen can significantly improve the electrocatalytic oxidation performance of HMF to FDCA.

Optimized Nb-Based Zeolites as Catalysts for the Synthesis of Succinic Acid and FDCA

Nb(0.05 moles%)-zeolites prepared via a post synthesis methodology (BEA, Y, ZSM-5), or a direct sol-gel method (Silicalite-1) were investigated in the hydroxymethylfurfural (HMF) oxidation by both molecular oxygen, in aqueous phase, and organic peroxides, in acetonitrile. The catalysts prepared through the post synthesis methodology (i.e., Nb-Y5, Nb-ZSM25, Nb-Y30, Nb-BEA12, and Nb-BEA18) displayed a mono-modal mesoporosity and contain residual framework Al-acid sites, extra framework isolated Nb(V)O-H and Nb₂O₅ pore-encapsulated clusters, while Nb-Sil-1, prepared through a direct synthesis procedure, displayed a bimodal micro-mesoporosity and contains only -Nb=O species. These modified zeolites behave as efficient catalysts in both HMF/glucose wet oxidation to succinic acid (SA) and HMF oxidation with organic peroxides to the 2,5-furandicarboxylic acid (FDCA). The catalytic behavior of these catalysts, in terms of conversion and especially the selectivity, mainly depended on the base/acid sites ratio. Thus, the HMF/glucose wet oxidation occurred with a total conversion and a selectivity to SA of 37.7% (from HMF) or 69.1% (from glucose) on the Nb-Y5 catalyst, i.e., the one with the lowest base/acid sites ratio. On the contrary, the catalysts with the highest base/acid sites ratio, i.e., Nb-ZSM25 and Nb-Sil-1, afforded a high catalytic efficiency in HMF oxidation with organic peroxides, in which FDCA was produced with selectivities of 61.3-63.8% for an HMF conversion of 96.7-99.0%.

Adsorption-Free Growth of Ultra-Thin Molybdenum Membranes with a Low-Symmetry Rectangular Lattice Structure

Although low-symmetry lattice structure of 2D transition metals is highly anticipated for both fundamental research and potentially distinctive application, it still has not been experimentally realized, which greatly hinders the exploration of the unique properties. Here, ultra-thin body-centered-cubic (bcc) phase molybdenum (Mo) membranes are successfully synthesized with a low-symmetry rectangular (110) crystal face via an adsorption-free reaction. Through experimental and density functional theory studies, no foreign atoms being adsorbed is shown to be a key factor for the successful preparation of the bcc phase 2D transition metal with (110) faces. The realization of 2D Mo(110) with a low-symmetric rectangular lattice structure extends the scope of 2D structures and is also beneficial for the exploration and development of low-symmetry rectangular lattice-structured materials with unique properties.

The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

For the production of chemicals from biomass, new selective processes are required. The selective oxidation of 5-(Hydroxymethyl)furfural (HMF), a promising platform molecule in fine chemistry, to 2,5-furandicarboxylic acid (FDCA) is considered a promising approach and requires the oxidation of two functional groups. In this study, Au/ZrO2 catalysts with different mean particle sizes were prepared by a chemical reduction method using tetrakis(hydroxymethyl)phosphonium chloride (THPC) and tested in HMF oxidation. The catalyst with the smallest mean particle size (2.1 nm) and the narrowest particle size distribution was highly active in the oxidation of the aldehyde moiety of HMF, but less active in alcohol oxidation. On the other hand, increased activity in FDCA synthesis up to 92% yield was observed over catalysts with a larger mean particle size (2.7 nm), which had a large fraction of small and some larger particles. A decreasing FDCA yield over the catalyst with the largest mean particle size (2.9 nm) indicates that the oxidation of both functional groups require different particle sizes and hint at the presence of an optimal particle size for both oxidation steps. The activity of Au particles seems to be influenced by surface steps and H bonding strength, the latter particularly in aldehyde oxidation. Therefore, the presence of both small and some larger Au particles seem to give catalysts with the highest catalytic activity.

Untangling the active sites in the exposed crystal facet of zirconium oxide for selective hydrogenation of bioaldehydes

A quantitative yield of furfuryl alcohol from furfural in isopropanol was achieved with ZrO₂ having monoclinic phase with a maximum exposed (−111) facet, whereas ZrO₂ possessing predominantly tetragonal phase yielded only 8.0% of furfuryl alcohol.

Advances in porous and nanoscale catalysts for viable biomass conversion

Solid catalysts with unique porosity and nanoscale properties play a promising role for efficient valorization of biomass into sustainable advanced fuels and chemicals.

Selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Au/CeO2 catalysts: the morphology effect of CeO2

A morphological effect of Au/CeO₂ catalysts in 5-hydroxymethylfurfural (HMF) oxidation.

M3+O(–Mn4+)2 clusters in doped MnOx catalysts as promoted active sites for the aerobic oxidation of 5-hydroxymethylfurfural

M³⁺O(–Mn⁴⁺)₂ clusters in doped MnO_x catalysts are principal active sites that make oxygen ‘easy come, easy go’.

Efficient conversion of 5-hydroxymethylfurfural to high-value chemicals by chemo- and bio-catalysis

5-hydroxymethylfurfural (HMF) is a very important versatile platform compound derived from renewable biomass.

Competitive C-C and C-H bond scission in the ethanol oxidation reaction on Cu(100) and the effect of an alkaline environment

Direct ethanol fuel cell technology is impeded by inefficient, yet expensive anode catalysts. As such, research on effective and cheap anode catalysts towards complete ethanol oxidation reaction (EOR) is greatly needed. Herein, we report the investigations of the competitive C-C and C-H bond scissions in the EOR involving CH₃CO, CH₂CO, and CHCO species on Cu(100) using density functional theory and transition state theory calculations. The easiest C-C bond cleavage was found in CH₂CO while the most difficult C-H bond cleavage was also found in CH₂CO, both with an activation energy of 1.02 eV. The feasible C-C bond scission may take place in CH₂CO with a rate constant ratio of the C-C to the C-H bond scission at 100 °C of 0.32. Furthermore, in an alkaline environment, the C-H bond scission activation barrier is considerably lowered but the C-C bond cleavage activation barrier is slightly increased for both CH₃CO and CH₂CO species. The reaction of CH₃CO species on Cu(100) under alkaline conditions produces mainly acetic acid with a barrier of 0.49 eV and a rate constant of 4.93 × 10⁵ s^-1 at 100 °C.

Direct catalytic effect of nitrogen functional groups exposed on graphenic materials when acting cooperatively with Ru nanoparticles

Various carbon materials (including doped graphenic materials) have been used as supports of Ru nanoparticles to determine their catalytic effects in the base-free aqueous-phase oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.