How Catalysts and Experimental Conditions Determine the Selective Hydroconversion of Furfural and 5-Hydroxymethylfurfural

CNN pincer ruthenium complexes for efficient transfer hydrogenation of biomass-derived carbonyl compounds

The ligand HCNNOMe (6-(4-methoxyphenyl)-2-aminomethylpyridine) is easily prepared from the commercially available 6-(4-methoxyphenyl)pyridine-2-carbaldehyde by the reaction of hydroxylamine and hydrogenation (H2, 1 atm) with Pd/C. The pincer complexes cis-[RuCl(CNNOMe)(PPh3)2] (1) and [RuCl(CNNOMe)(PP)] (PP = dppb, 2; and dppf, 3) are synthesized from [RuCl2(PPh3)3], HCNNOMe and PP (for 2 and 3) in 2-propanol with NEt3 at reflux and are isolated in 85-93% yield. Carbonylation of 1 (CO, 1 atm) gives [RuCl(CNNOMe)(CO)(PPh3)] (4) (79% yield) which cleanly reacts with Na[BArf4] and PCy3, affording the cationic trans-[Ru(CNNOMe)(CO)(PCy3)(PPh3)][BArf4] (5) (92% yield). These robust pincer complexes display remarkably high catalytic activity in the transfer hydrogenation (TH) of lignocellulosic biomass carbonyl compounds, using 2-propanol at reflux in a basic medium (NaOiPr or K2CO3). Thus, furfural, 5-(hydroxymethyl)furfural and Cyrene are reduced to the corresponding alcohols with 2 and 3, at S/C in the range of 10 000-100 000, within minutes or hours (TOF up to 1 500 000 h-1). The monocarbonyl complex 5 was found to be extremely active in the TH of cinnamaldehyde, vanillin derivatives and ethyl levulinate at S/C in the range of 10 000-50 000. Vanillyl alcohol is also obtained by the TH of vanillin with 5 (S/C = 500) in 2-propanol in the presence of K2CO3.

Self-tuned properties of CuZnO catalysts for hydroxymethylfurfural hydrodeoxygenation towards dimethylfuran production

CuZnO is used as robust, efficient and self-tuned catalyst for the conversion of 5-hydroxymethylfurfural (5-HMF) into 2,5-dimethylfuran (DMF) or 2,5-bishydroxymethylfuran (BHMF) depending on the preparation method and the reaction environment.

Metal organic frameworks for biomass conversion

This review narrates the recent developments on the catalytic applications of pristine metal–organic frameworks (MOFs), functionalized MOFs, guests embedded over MOFs and MOFs derived carbon composites for biomass conversion into platform chemicals.

Heterogeneous iron-containing nanocatalysts – promising systems for selective hydrogenation and hydrogenolysis

Bimetallic catalytic systems Fe–Me (Pt, Pd, Cu) demonstrate synergy in the activity/selectivity pattern in reactions involving hydrogen: selective hydrogenation of CC bonds, NO₂ and carbonyl groups and hydrogenolysis of C–O bonds.

Mechanistic understanding of humin formation in the conversion of glucose and fructose to 5-hydroxymethylfurfural in [BMIM]Cl ionic liquid

This study provided a new mechanistic understanding of humin formation during 5-HMF production from hexose in ionic liquids.

Recent advances in photoelectrochemical cells (PECs) for organic synthesis

The application of PECs in organic synthesis reactions and their reaction mechanisms are highlighted.

Access to N-unprotected 2-amide-substituted indoles from Ugi adducts via palladium-catalyzed intramolecular cyclization of o-iodoanilines bearing furan rings

A variety of N-unprotected 2-amide-substituted indoles were synthesized from readily available furfural-based Ugi adducts in moderate to good yields via palladium-catalyzed intramolecular cyclization of o-iodoanilines bearing furan rings. These reactions involved a cascade sequence consisting of dearomatizing arylation, opening of the furan ring, and deprotection of the N atom.

A variety of N-unprotected 2-amide-substituted indoles were synthesized from readily available furfural-based Ugi adducts in moderate to good yields via palladium-catalyzed intramolecular cyclization of o-iodoanilines bearing furan rings.

Efficient Hydrogenation of Xylose and Hemicellulosic Hydrolysate to Xylitol over Ni-Re Bimetallic Nanoparticle Catalyst

A disadvantage of the commercial Raney Ni is that the Ni active sites are prone to leaching and deactivation in the hydrogenation of xylose to xylitol. To explore a more stable and robust catalyst, activated carbon (AC) supported Ni-Re bimetallic catalysts (Ni-Re/AC) were synthesized and used to hydrogenate xylose and hemicellulosic hydrolysate into xylitol under mild reaction conditions. In contrast to the monometallic Ni/AC catalyst, bimetallic Ni-Re/AC exhibited better catalytic performances in the hydrogenation of xylose to xylitol. A high xylitol yield up to 98% was achieved over Ni-Re/AC (nNi:nRe = 1:1) at 140 °C for 1 h. In addition, these bimetallic catalysts also had superior hydrogenation performance in the conversion of the hydrolysate derived from the hydrolysis reaction of the hemicellulose of Camellia oleifera shell. The characterization results showed that the addition of Re led to the formation of Ni-Re alloy and improved the dispersion of Ni active sites. The recycled experimental results revealed that the monometallic Ni and the bimetallic Ni-Re catalysts tended to deactivate, but the introduction of Re was able to remarkably improve the catalyst's stability and reduce the Ni leaching during the hydrogenation reaction.

Heterogeneous Nickel Catalysts Derived from 2D Metal-Organic Frameworks for Regulating the Selectivity of Furfural Hydrogenation

Hydrolysis of the biomass platform compound furfural can produce a bulk of fine chemicals because of its multiple functional groups. Developing an efficient catalytic system to regulate the process toward some desirable products has always been a hot research area. Herein, the novel Ni-based catalysts (Ni-MFC-X, X = 300, 400...800) synthesized by pyrolysis of the 2D Ni-based metal-organic framework (MOF) in the temperature range 300-800 °C show good performance for selective hydrogenation of furfural (FUR). Interestingly, the calcination temperature of the MOF precursor plays an important role in hydrogenation of furfural with controllable selectivity toward furfuryl alcohol (FOL) and tetrahydro FOL (THFOL). Ni-MFC-500 affords us 92.5% conversion of furfural and 59.5% selectivity of FOL. Ni-MFC-700 can promote hydrogenation of furfural with 91.8% conversion and 51.0% selectivity of THFOL. Furthermore, the stability of as-obtained Ni-MFC-500 and Ni-MFC-700 was also very impressive in this reaction system.

Capping Agent Effect on Pd-Supported Nanoparticles in the Hydrogenation of Furfural

The catalytic performance of a series of 1 wt % Pd/C catalysts prepared by the sol-immobilization method has been studied in the liquid-phase hydrogenation of furfural. The temperature range studied was 25–75 °C, keeping the H2 pressure constant at 5 bar. The effect of the catalyst preparation using different capping agents containing oxygen or nitrogen groups was assessed. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly (diallyldimethylammonium chloride) (PDDA) were chosen. The catalysts were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization data suggest that the different capping agents affected the initial activity of the catalysts by adjusting the available Pd surface sites, without producing a significant change in the Pd particle size. The different activity of the three catalysts followed the trend: PdPVA/C > PdPDDA/C > PdPVP/C. In terms of selectivity to furfuryl alcohol, the opposite trend has been observed: PdPVP/C > PdPDDA/C > PdPVA/C. The different reactivity has been ascribed to the different shielding effect of the three ligands used; they influence the adsorption of the reactant on Pd active sites.

Facile Preparation of Pd/UiO-66-v for the Conversion of Furfuryl Alcohol to Tetrahydrofurfuryl Alcohol under Mild Conditions in Water

The hydrogenation of furan ring in the biomass-derived furans is of great importance for the conversion of biomass to valuable chemicals. Fabrication of high activity and selectivity catalyst for this hydrogenation under mild conditions was one of the focuses of this research. In this manuscript, UiO-66-v, in which vinyl bonded to the benzene ring, was first prepared. Then, the uniformly distributed vinyl was used as the reductant for the preparation of Pd/UiO-66-v. The catalyst was characterized by X-ray diffraction, thermogravimetric, N₂ physical adsorption/desorption, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, energy dispersive spectrometer elemental mappings, and inductively coupled plasma atomic emission spectroscopy to find the Pd/UiO-66-v had a narrow palladium nanoparticles size of 3–5 nm and maintained the structure and thermal stability of UiO-66-v. The Pd/UiO-66-v was used for the hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol in water. 99% conversion of furfuryl alcohol was obtained with 90% selectivity to tetrahydrofurfuryl alcohol after reacted at 0.5 MPa H₂, 303 K for 12 h. The Pd/UiO-66-v was proved to be effective for the hydrogenation of furan ring in furans and could be used for at least five times.

A theoretical insight into furfural conversion catalyzed on the Ni(111) surface

Biomass-derivatives, e.g., furfural, have been widely reported to become new-generation renewable sources of chemicals and fuels. However, it is too complicated to understand the product selectivity of furfural conversion in diverse reactions. Accordingly, by using density functional theory calculations, both the hydrodeoxygenation and decarboxylation of furfural on the Ni(111) surface to form furan, 2-methylfuran, furfuryl alcohol, tetrahydrofuran, and tetrahydrofurfuryl alcohol have been thoroughly investigated. On the basis of the minimum energy path, furfural decarbonylation leads to the formation of furan via F-CHO + 2H → F + CO + 2H → F + CO + H → F-H, and then tetrahydrofuran forms via sequential hydrogenation on the carbon atoms of the furan ring, while furfuryl alcohol (F-CHO + 2H → F + CHOH + H → F-CH₂OH) can be obtained via furfural hydrogenation. More importantly, 2-methylfuran tends to form through the hydrodeoxygenation reaction, and tetrahydrofurfuryl alcohol is generated via furfural hydrogenation, which is realized with furfuryl alcohol identified as the likely intermediate. Overall, among all these products, furan is a dominant product. More importantly, it has been found that different types of metal doping will also lead to different adsorption configurations of the reactants. These findings should provide guidance in catalyst design for converting furfural to value-added products.

Selective Arene Hydrogenation for Direct Access to Saturated Carbo- and Heterocycles

Arene hydrogenation provides direct access to saturated carbo- and heterocycles and thus its strategic application may be used to shorten synthetic routes. This powerful transformation is widely applied in industry and is expected to facilitate major breakthroughs in the applied sciences. The ability to overcome aromaticity while controlling diastereo-, enantio-, and chemoselectivity is central to the use of hydrogenation in the preparation of complex molecules. In general, the hydrogenation of multisubstituted arenes yields predominantly the cis isomer. Enantiocontrol is imparted by chiral auxiliaries, Brønsted acids, or transition-metal catalysts. Recent studies have demonstrated that highly chemoselective transformations are possible. Such methods and the underlying strategies are reviewed herein, with an emphasis on synthetically useful examples that employ readily available catalysts.

Biorefinery via Achmatowicz Rearrangement: Synthesis of Pentane-1,2,5-triol from Furfuryl Alcohol

A new scalable synthesis of pentane-1,2,5-triol from the furanics platform has been developed. Excellent yields of up to 92 % are obtained under flow conditions by using readily available catalysts from the existing pool. The strategy exploits the highly functionalized Achmatowicz product as a key intermediate, thus circumventing problems related to the low reactivity of the parent furfural and furfuryl alcohol. Besides expanding the portfolio of biomass-derived C₅ alcohols, this strategy may also be further applied for the establishment of a versatile bio-based chemical platform.

Ni Promotion by Fe: What Benefits for Catalytic Hydrogenation?

Metallic nickel is known to efficiently catalyze hydrogenation reactions, but one of its major drawbacks lies in its lack of selectivity, linked to side-reactions of hydrogenolysis and over-hydrogenation. More selective hydrogenations can be obtained upon the introduction of a second metal in combination with Ni. Fe is an interesting choice, as it is a cheap and abundant metal. This review aims at discussing the advantages and constraints brought by the preparation procedures of bimetallic supported Ni–Fe nanoparticles, and at analyzing the benefits one can draw by substituting Ni–Fe supported catalysts for Ni monometallic systems for the catalytic hydrogenation of organic molecules. Specific formulations, such as Ni75Fe25, will be singled out for their high activity or selectivity, and the various hypotheses behind the roles played by Fe will be summarized.

An electrocatalytic route for transformation of biomass-derived furfural into 5-hydroxy-2(5H)-furanone

An electrocatalytic route was developed for the first time for conversion of biomass-derived furfural to bioactive 5-hydroxy-2(5H)-furanone over CuS nanosheets using H₂O as the oxygen source.

Development of efficient strategies for biomass valorization is a highly attractive topic. Herein, we conducted the first work on electrocatalytic oxidation of renewable furfural to produce the key bioactive intermediate 5-hydroxy-2(5H)-furanone (HFO). It was demonstrated that using H₂O as the oxygen source and metal chalcogenides (CuS, ZnS, PbS, etc.) as electrocatalysts, the reaction could proceed efficiently, and the CuS nanosheets prepared in this work showed the best performance and provided high HFO selectivity (83.6%) and high conversion (70.2%) of furfural. In addition, the CuS electrocatalyst showed long-term stability. Mechanism investigation showed that furfural was oxidized to HFO via multistep reactions, including C–C cleavage, subsequent ring opening and oxidation, and intramolecular isomerization.

Exploiting the Synergetic Behavior of PtPd Bimetallic Catalysts in the Selective Hydrogenation of Glucose and Furfural

Mono and bimetallic catalysts based on Pt and Pd were prepared by a co-precipitation method. They were tested in liquid phase hydrogenation reactions of glucose and furfural at low temperature and pressure. The bimetallic PtPd/TiO2 catalyst proved to be an efficient material in selectively hydrogenating glucose to sorbitol. Moreover, high furfural conversion was attained under relatively soft conditions, and the furfuryl alcohol selectivity was strongly affected by the chemical composition of the catalysts. Furfuryl alcohol (FA) was the major product in most cases, along with side products such as methylfuran (MF), furan, and traces of tetrahydrofuran (THF). These results showed that the PtPd bimetallic sample was more active relative to the monometallic counterparts. A correlation between the catalytic results and the physicochemical properties of the supported nanoparticles identified key factors responsible for the synergetic behavior of the PtPd system. The high activity and selectivity were due to the formation of ultra-small particles, alloy formation, and the Pt-rich surface composition of the bimetallic particles supported on the TiO2 nanowires.

In situ cryocrystallization and solid-state structures of furfural and some derivatives

The crystal and molecular structures of the bio-based platform chemical furfural (1) and its derivatives furfurylamine (2), 2-furonitrile (3) and 2-methylfuran (4), which are all liquid at ambient temperature, have been determined by in situ cryocrystallography.

Multiple activations of CH bonds in arenes and heteroarenes

Re₂(CO)₈(μ-C₆H₅)(μ-H) reacts with anthracene four times to yield the quadruply CH activated complex [Re₂(CO)₈(μ-H)]₄(μ-η²-1,2-μ-η²-3,4-μ-η²-5,6-μ-η²-7,8-C₁₄H₆).

Photoactive ZnO Materials for Solar Light-Induced CuxO-ZnO Catalyst Preparation

In this work, the solar light-induced redox photoactivity of ZnO semiconductor material was used to prepare Cu_xO-ZnO composite catalysts at room temperature with a control of the chemical state of the copper oxide phase. Cu₂^(I)O-ZnO and Cu^(II)O-ZnO composite catalysts were prepared by using Cu(acac)₂ in tetrahydrofuran-water and Cu(NO₃)₂ in water as metallic precursor, respectively. Prior to the implementation of the photon-assisted synthesis method, the most efficient photoactive ZnO material was selected from among different ZnO materials prepared by the low temperature polyol and precipitation methods with carbonates and carbamates as precipitation agents. The photocatalytic degradation of the 4-chlorophenol compound in water under simulated solar light was taken as a model reaction. The ZnO support materials were characterized by X-ray diffraction (XRD), surface area and porosimetry measurements, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the synthesis method strongly influenced their photoactivity in terms of 4-chlorophenol degradation and of total organic carbon removal. The most photoactive ZnO material was prepared by precipitation with carbonates and calcined at 300 °C, benefitting from a high specific surface area and a small mean crystallite size for achieving a complete 4-chlorophenol mineralization within 70 min of reaction, with minimum Zn²⁺ released to the solution. Besides thermal catalysis applications, this work has opened a new route for the facile synthesis of Cu₂O-ZnO heterojunction photocatalysts that could take place under solar light of the heterojunction built between the p-type semi-conductor Cu₂O with direct visible light band gap and the ZnO semiconductor phase.