Catalytic Hydroconversion of 5-HMF to Value-Added Chemicals: Insights into the Role of Catalyst Properties and Feedstock Purity

Catalytic conversion of chitin biomass into key platform chemicals

Chitin is the most abundant nitrogen-containing biomass on Earth and presents a compelling alternative to fossil fuels for chemical production. The catalytic conversion of chitin offers a viable approach for harnessing its inherent carbon and nitrogen contents, contributing to developing a green and sustainable society. This feature article reviews recent advances in shell waste biorefinery, with an emphasis on the contributions from our group. Efficient and sustainable chitin extraction methods are highlighted, along with the conversion of chitin biomass (N-acetyl-D-glucosamine (NAG), D-glucosamine, chitosan, and chitin) into key platform chemicals, mainly including furans, amino/amide sugars, organic acids and amino/amide acids. Catalytic strategies and production pathways are detailed, and current challenges and future research directions in chitin valorization are discussed.

Critical Factors Affecting the Selective Transformation of 5-Hydroxymethylfurfural to 3-Hydroxymethylcyclopentanone Over Ni Catalysts

The ring-rearrangement of 5-hydroxymethylfurfural (HMF) to 3-hydroxymethylcyclopentanone (HCPN) was investigated over Ni catalysts supported on different carbon supports and metallic oxides with different structure and acid-base properties. Their catalytic performance was tested in a batch stirred reactor in aqueous solution at 180 °C and 30 bar of H2. Under these conditions, the HMF hydrogenation proceeds through three possible competitive routes: (i) a non-water path leading to the total hydrogenation product, 2,5-di-hydroxymethyl-tetrahydrofuran (DHMTHF), and two parallel acid-catalyzed water-mediated routes responsible for (ii) ring-opening and (iii) ring-rearrangement reaction products. All catalyst systems primarily produced HCPN, but reaction rates and product distribution were influenced by several variables, some of them intensely analyzed in this work. The most proper conditions resulted to be the presence of the medium/strong Lewis's acidity of a Ni/ZrO2 catalyst (initial TOF=5.99 min-1 and 73 % HCPN selectivity) or the Brønsted acidity originated by an oxidized high surface area graphite, Ni/HSAG-ox (initial TOF=5.92 min-1 and 87 % HCPN selectivity). However, too high density of acidic sites on the catalyst support (Ni/Al2O3) and sulfur impurities from the HMF feedstock led to catalyst deactivation by coke deposition and Ni poisoning, respectively.

CO2-Assisted Controllable Synthesis of PdNi Nanoalloys for Highly Selective Hydrogenation of Biomass-Derived 5-Hydroxymethylfurfural

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-bishydroxymethyltetrahydrofuran (BHMTHF), a vital fuel precursor and solvent, is crucial for biomass refining. Herein, we report highly selective and stable PdNi nanoalloy catalysts for this deep hydrogenation process. A CO2-assisted green method was developed for the controllable synthesis of various bimetallic and monometallic catalysts. The PdNi/SBA-15 catalysts with various Pd/Ni ratios exhibited a volcano-like trend between BHMTHF yield and Pd/Ni ratio. Among all catalysts tested, Pd2Ni1/SBA-15 achieved the best performance, converting 99.0 % of HMF to BHMTHF with 96.0 % selectivity, surpassing previously reported catalysts. Additionally, the Pd2Ni1/SBA-15 catalyst maintained excellent stability even after five recycling runs. Catalyst characterizations (e. g., HAADF-STEM) and density functional theory (DFT) calculations confirmed the successful formation of the alloy structure with electron transfer between Ni and Pd, which accounts for the remarkable performance and stability of the catalyst. This work paves the way for developing highly selective and stable alloy catalysts for biomass valorization.

The Use of 5-Hydroxymethylfurfural (5-HMF) in Multi-Component Hantzsch Dihydropyridine Synthesis

The renewable 5-hydroxymethylfurfural (5-HMF) has gained a wide interest from the chemistry community as a valuable biobased platform opening the way to many applications. Despite an impressive number of publications reporting either its preparation or its functionalization, its direct use in fine chemistry, and especially in multi-component reaction (MCR), is less reported. Here, we report a complete study of the use of 5-HMF in the Hantzsch dihydropyridines synthesis. The strategy was applied to a scope of β-dicarbonyl molecules (including β-ketoesters and 1,3-diketones) in a 3-component procedure leading to a series of symmetrical 1,4-dihydropyridines derived from 5-HMF in excellent yields. The study was extended to the 4-component protocol using one equivalent of a β-ketoester and one equivalent of 5,5-dimethyl-1,3-cyclohexanedione (dimedone), which efficiently provided the corresponding unsymmetrical dihydropyridines.

Precursor-Driven Catalytic Performances of Al2O3-Supported Earth-Abundant Ni Catalysts in the Hydrogenation of Levulinic Acid and Hydroxymethylfurfural into Added-Value Chemicals

It has been shown that the nature of the metal precursor and the thermal effects during calcination determine the physicochemical properties of the catalysts and their catalytic activity in the levulinic acid (LA) and 5-hydroxymethylfurfural (HMF) hydrogenation reactions. The endothermic effect during calcination of the inorganic nickel precursor promoted higher metal dispersion and stronger interaction with the alumina surface. In contrast, the exothermic effects during the calcination of organic nickel precursors resulted in smaller metal dispersion and lower interaction with the support surface. A clear relationship was found between the size of the metal crystallites and the yield of LA hydrogenation reaction. The smaller crystallites were more active in the LA hydrogenation reaction. In turn, the size of the metal particles and their nature of interaction with the surface of the alumina influence the hydrogenation pathways of the HMF.

Au-Based Bimetallic Catalysts for Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid under Base-Free Reaction Conditions

The aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) plays a pivotal role in the synthesis of renewable, biodegradable plastics and sustainable chemicals. Although supported gold nanoclusters (NCs) exhibit significant potential in this process, they often suffer from low selectivity. To address this challenge, a series of gold-M (M means Ni, Fe, Cu, and Pd) bimetallic NCs catalysts were designed and synthesized to facilitate the selective oxidation of HMF to FDCA. Our findings indicate that the introduction of doped metals, particularly Ni and Pd, not only improves the reaction rates for HMF tandem oxidation but also promotes high yields of FDCA. Various characterizations techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS), and temperature-programmed desorption of oxygen (O2-TPD), were employed to scrutinize the structural and electronic properties of the prepared catalysts. Notably, an electronic effect was observed across the Au-based bimetallic catalysts, facilitating the activation of reactant molecules and enhancing the catalytic performance. This study provides valuable insights into the alloy effects, aiding in the development of highly efficient Au-based bimetallic catalysts for biomass conversions.

Modular Synthesis of Fluoro-Substituted Furan Compounds via Controllable Fluorination of Biomass-Based 5-HMF and Its Derivatives

5-Hydroxymethylfurfural (5-HMF) is regarded as one of the most promising platform feedstocks for producing valuable chemicals, fuels, and materials. In this study, we present a controllable fluorination technique for biomass-based 5-HMF and its oxygenated derivatives. This technique allows us to synthesize mono-fluoromethyl, difluoromethyl, and acylfluoro-substituted furan compounds by adjusting experimental conditions such as different fluorine sources and mole ratio. To gain a deeper understanding the reactivity order, we conducted intermolecular and intramolecular competition experiments. The results revealed that the hydroxyl group exhibited the highest reactivity, followed by the aldehyde group. This finding provides important theoretical support and opens up the possibility of selective fluorination. The reaction offers several advantages, including mild conditions, no need for inert gas protection, and easy operation. Furthermore, the fluoro-substituted furan compounds can be further transformed for the preparation of drug analogs, offering a new route for the high-value utilization of biomass molecules.

Recent advances in catalytic synthesis of 2,5-furandimethanol from 5-hydroxymethylfurfural and carbohydrates

5-Hydroxymethylfurfural (HMF) is a versatile platform chemical derived from the dehydration of renewable carbohydrates (typically glucose/fructose-based monosaccharides, oligosaccharides, and polysaccharides). Some useful compounds, such as 2,5-furandimethanol (FDM), 2,5-dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF), have been synthesized by reduction of HMF. Among these, FDM is a promising diol and can be further converted towards fine chemicals, liquid fuels and polymer materials. In this review, some typical catalytic systems for the synthesis of FDM from both HMF and carbohydrates were summarized. The discussion focused on controlling the reaction networks for the reduction of HMF. The reaction mechanisms and the stability of the catalysts were introduced briefly. Last but not least, the prospects of effective production of FDM were discussed as well.

Design of Bifunctional Nanocatalysts Based on Zeolites for Biomass Processing

Bifunctional catalysts consisting of metal-containing nanoparticles (NPs) and zeolite supports have received considerable attention due to their excellent catalytic properties in numerous reactions, including direct (biomass is a substrate) and indirect (platform chemical is a substrate) biomass processing. In this short review, we discuss major approaches to the preparation of NPs in zeolites, concentrating on methods that allow for the best interplay (synergy) between metal and acid sites, which is normally achieved for small NPs well-distributed through zeolite. We focus on the modification of zeolites to provide structural integrity and controlled acidity, which can be accomplished by the incorporation of certain metal ions or elements. The other modification avenue is the adjustment of zeolite morphology, including the creation of numerous defects for the NP entrapment and designed hierarchical porosity for improved mass transfer. In this review, we also provide examples of synergy between metal and acid sites and emphasize that without density functional theory calculations, many assumptions about the interactions between active sites remain unvalidated. Finally, we describe the most interesting examples of direct and indirect biomass (waste) processing for the last five years.

Enantioselective transformations of 5-hydroxymethylfurfural via catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

A catalytic asymmetric 1,3-dipolar cycloaddition between iminoesters derived from 5-hydroxymethylfurfural (HMF) and different activated alkenes is reported. Excellent levels of diastereo and enantioselectivity were obtained when Fesulphos/Cu^I complex was used as catalyst. This metodology provides an effective and sustainable access to challenging enantioenriched heterocyclic scaffolds and represents one of the rare examples of catalytic asymmetric transformations using HMF as a starting material.

Bio-Derived Furanic Compounds with Natural Metabolism: New Sustainable Possibilities for Selective Organic Synthesis

Biomass-derived C6-furanic compounds have become the cornerstone of sustainable technologies. The key feature of this field of chemistry is the involvement of the natural process only in the first step, i.e., the production of biomass by photosynthesis. Biomass-to-HMF (5-hydroxymethylfurfural) conversion and further transformations are carried out externally with the involvement of processes with poor environmental factors (E-factors) and the generation of chemical wastes. Due to widespread interest, the chemical conversion of biomass to furanic platform chemicals and related transformations are thoroughly studied and well-reviewed in the current literature. In contrast, a novel opportunity is based on an alternative approach to consider the synthesis of C6-furanics inside living cells using natural metabolism, as well as further transformations to a variety of functionalized products. In the present article, we review naturally occurring substances containing C6-furanic cores and focus on the diversity of C6-furanic derivatives, occurrence, properties and synthesis. From the practical point of view, organic synthesis involving natural metabolism is advantageous in terms of sustainability (sunlight-driven as the only energy source) and green nature (no eco-persisted chemical wastes).

A Diamine-Oriented Biorefinery Concept Using Ammonia and Raney Ni as a Multifaceted Catalyst

Diamines are important industrial chemicals. In this paper we outline the feasibility of lignocellulose as a source of diol-containing molecules. We also illustrate the possibility of turning these diols into their diamines in good to excellent yields. Central to these transformations is the use of commercially available Raney Ni. For diol formation, the Raney Ni engages in hydrogenation and often also demethoxylation, that way funneling multiple components to one single molecule. For diamine formation, Raney Ni catalyzes hydrogen-borrowing mediated diamination in the presence of NH₃.