High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone

Atomically dispersed Pt1Ir1 pair for synergetic hydrogenation of levulinic acid to γ-valerolactone

Atomically dispersed metal catalysts have attracted considerable attention in various important reactions owing to their high atom utilization and specific coordination environment. However, monometallic single sites sometimes present undesirable catalytic performance, which usually need a synergistic effect with the neighboring metal atoms, such as dimers or trimers. Different metal pairs on various solid carriers have been reported; nonetheless, huge challenges remain to precisely prepare a metal pair-site. Herein, we present a versatile strategy to synthesize an atomically dispersed Pt1Ir1 pair via strong metal-sulfur interaction over porous sulfur-doped carbons. Pt1Ir1 pair sites presented high activity and stability for the hydrogenation of levulinic acid to γ-valerolactone.

Bimetallic nanozymes synergize to regulate the behavior of oxygen intermediates and substrate HMF adsorption

We have constructed a bimetallic (CoNiP) nanozyme, leveraging the synergistic effect of cobalt and nickel, which efficiently catalyzes the oxidation of TMB from colorless to ox-TMB (blue). Density functional theory (DFT) calculations further highlight the pivotal role of this synergistic effect in improving the adsorption energy of oxygen intermediates, accelerating the catalytic process.

Enhancing reductive conversion of levulinic acid and levulinates to γ-valerolactone: Role of oxygen vacancy in MnOx catalysts

Oxygen vacancies (Ov) in metal oxides play a crucial role in modifying the electronic and acidic properties of catalysts, thereby influencing their catalytic activity. This study explores the impact of Ov in MnOx catalysts on their acidic and catalytic properties for the Meerwein-Ponndorf-Verley reduction of levulinic acid (LA) and levulinate to γ-valerolactone (GVL). Various characterization techniques demonstrate that surface Ov significantly modulate the acidic properties of MnOx catalysts, positively correlating with Lewis/Brønsted acid ratio and GVL yield. In situ DRIFTS and DFT calculations further unveil the reaction mechanism, revealing that Ov facilitate the activation and dehydrogenation of isopropanol and subsequent hydrogen transfer and hydrogenation of LA, leading to enhanced GVL production. These insights underscore the pivotal role of Ov in MnOx catalysts for the efficient conversion of LA to GVL, highlighting their importance in improving catalytic performance.

3D Oxide-Derived Ru Catalyst for Ultra-Efficient Hydrogenation of Levulinic Acid to γ-Valerolactone

γ-valerolactone (GVL) is a key value-added chemical catalytically produced from levulinic acid (LA), an important biomass derivative platform chemical. Here an ultra-efficient 3D Ru catalyst generated by in situ reduction of RuZnOx nanoboxes is reported; the catalyst features a well-defined structure of highly dispersed in situ oxide-derived Ru (IOD-Ru) clusters (≈1 nm in size) spatially confined within the 3D nanocages with rich mesopores, which guarantees a maximized atom utilization with a high exposure of Ru active sites as well as a 3D accessibility for substrate molecules. The IOD-Ru exhibits ultrahigh performance for the hydrogenation of LA into GVL with a record-breaking turnover frequency (TOF) up to 59400 h-1 , 14 times higher than that of the ex situ reduction of RuZnOx nanoboxes catalyst. Structural characterizations and theoretical calculations collectively indicate that the defect-rich and coordination-unsaturated IOD-Ru sites can boost the activation of the carbonyl group in LA with a significantly lowered energy barrier of hydrogenation.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

Hydrogenation of Carboxylic Acids, Esters, and Related Compounds over Heterogeneous Catalysts: A Step toward Sustainable and Carbon-Neutral Processes

The catalytic hydrogenation of esters and carboxylic acids represents a fundamental and important class of organic transformations, which is widely applied in energy, environmental, agricultural, and pharmaceutical industries. Due to the low reactivity of the carbonyl group in carboxylic acids and esters, this type of reaction is, however, rather challenging. Hence, specifically active catalysts are required to achieve a satisfactory yield. Nevertheless, in recent years, remarkable progress has been made on the development of catalysts for this type of reaction, especially heterogeneous catalysts, which are generally dominating in industry. Here in this review, we discuss the recent breakthroughs as well as milestone achievements for the hydrogenation of industrially important carboxylic acids and esters utilizing heterogeneous catalysts. In addition, related catalytic hydrogenations that are considered of importance for the development of cleaner energy technologies and a circular chemical industry will be discussed in detail. Special attention is paid to the insights into the structure-activity relationship, which will help the readers to develop rational design strategies for the synthesis of more efficient heterogeneous catalysts.

The Role of Copper in the Hydrogenation of Furfural and Levulinic Acid

Currently, there is a great interest in the development of sustainable and green technologies for production of biofuels and chemicals. In this sense, much attention is being paid to lignocellulosic biomass as feedstock, as alternative to fossil-based resources, inasmuch as its fractions can be transformed into value-added chemicals. Two important platform molecules derived from lignocellulosic sugars are furfural and levulinic acid, which can be transformed into a large spectrum of chemicals, by hydrogenation, oxidation, or condensation, with applications as solvents, agrochemicals, fragrances, pharmaceuticals, among others. However, in many cases, noble metal-based catalysts, scarce and expensive, are used. Therefore, an important effort is performed to search the most abundant, readily available, and cheap transition-metal-based catalysts. Among these, copper-based catalysts have been proposed, and the present review deals with the hydrogenation of furfural and levulinic acid, with Cu-based catalysts, into several relevant chemicals: furfuryl alcohol, 2-methylfuran, and cyclopentanone from FUR, and γ-valerolactone and 2-methyltetrahydrofuran from LA. Special emphasis has been placed on catalytic processes used (gas- and liquid-phase, catalytic transfer hydrogenation), under heterogeneous catalysis. Moreover, the effect of addition of other metal to Cu-based catalysts has been considered, as well as the issue related to catalyst stability in reusing studies.

Insight into Key Parameters for Fabricating Stable Single-Atom Pt-Nix Alloy by Reduction Environment-Induced Anti-Ostwald Effects

Developing single-atom catalysts with superior stability under reduction conditions is essential for hydrogenation/dehydrogenation catalysis and green hydrogen generation. In this contribution, single-atom Pt catalysts were achieved via a reduction environment-induced anti-Ostwald approach in the highly confined Ni species (Pt-Ni_x ) on nonreducible Al₂ O₃ matrix. In-situ X-ray absorption spectroscopy indicated that the isolated Pt-Ni_x metallic bonds, generated at high reduction temperature, dominated the formation of single Pt atoms. A relatively large cluster of metallic Ni would benefit the stabilization of Pt single atom as observed via high-angle annular dark-field scanning transmission electron microscopy and validated by density functional theory simulation. Excellent performance on cellulose hydrogenolysis was demonstrated under harsh reductive and hydrothermal conditions, potentially expandable to other hydrogen involved reactions like CO₂ hydrogenation, green hydrogen production from different hydrogen carriers, and beyond.

Facile Synthesis of Highly Dispersed and Well-Alloyed Bimetallic Nanoparticles on Oxide Support

Supported alloy catalysts play a pivotal role in many heterogeneous catalytic processes of socioeconomic and environmental importance. But the controlled synthesis of supported alloy nanoparticles with consistent composition and tight size distribution remains a challenging issue. Herein, a simple yet effective method for preparation of highly dispersed, homogeneously alloyed bimetallic nanoparticles on oxide supports is reported. This method is based on solid solution of metal cations in parent oxide and strong electrostatic adsorption of a secondary metal species onto the oxide surface. In the reductive annealing process, hydrogen spillover occurs from the surface metal with a higher reduction potential to the solute metal in solid solution, leading to metal exsolution and homogenous alloying of the metals on the oxide surface. The ceria-supported Ni-Pt alloy is chosen as a model catalyst and hydrazine monohydrate decomposition is chosen as a probe reaction to demonstrate this method, and particularly its advantages over the conventional impregnation and galvanic replacement methods. A systematic application of this method using different oxides and base-noble metal pairs further elucidates its applicability and generality.

Deep eutectic solvent assisted fabrication of zirconium phytate thin nanosheets for important biomass transformations

Utilization of naturally occurring resources to construct functional catalytic materials is significantly important, and facile and environmental-benign strategies are highly desired to afford the materials having a specific structure and good catalytic activity. Herein, we reported an innovative deep eutectic solvent (DES)-assisted strategy to synthesize zirconium phytate with a thin nanosheet structure (denoted as Zr-Phy-DES) using plant-originated phytic acid (PhyA) as the renewable building block. This strategy was eco-friendly and adjustable owing to the designability of DESs. The Zr-Phy-DES as an acidic catalyst showed high activity on two important biomass transformations, i.e., dehydration of carbohydrates and Meerwein-Ponndorf-Verley reduction of ethyl levulinate. Interestingly, Zr-Phy-DES showed higher catalytic performance than the zirconium phytates prepared in ethylene glycol and N,N-dimethylformamide, confirming the advantage of DESs for preparing functional materials. Notably, the unique feature of this proposed strategy is that renewable catalysts are prepared in an environmental-benign solvent for efficiently catalyzing biomass transformation.

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An eco-friendly strategy for preparing catalytic materials with a specific structure

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The catalytic activity of the prepared materials varied with the type of solvents

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The material prepared in deep eutectic solvent showed better performance

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Catalytic materials from natural resources and green solvents to convert biomass

Strong Metal Phosphide-Phosphate Support Interaction for Enhanced Non-Noble Metal Catalysis

Strong metal-support interaction (SMSI) is crucial for supported catalysts in heterogeneous catalysis. Here is the first report on strong metal phosphide-phosphate support interaction (SMPSI). The key to SMPSI is the activation of P species on the support, which leads to simultaneous generation of metal phosphide nanoparticles (NPs) and core-shell nanostructures formed by support migration onto the NPs. The encapsulation state of metal phosphide and charge transfer are identical to those of classical SMSIs and can be optimally regulated. Furthermore, the strong interactions of Co₂ P_L /MnP-3 not only significantly enhance the anti-oxidation and anti-acid capability of non-noble metal but also exhibit excellent catalytic activity and stability toward hydrogenating a wide range of compounds into value-added fine chemicals with 100% selectivity, which is even better than Pd/C and Pt/C. The SMPSI construction can be generally extended to other systems such as Ni₂ P_L /Mn₃ (PO₄ )₂ , Co₂ P_L /LaPO₄ , and CoP_L /CePO₄ . This study provides a new approach for the rational design of advanced non-noble metal catalysts and introduce a novel paradigm for the strong interaction between NPs and support.

Ligand assisted hydrogenation of levulinic acid on Pt(111) from first principles calculations

In this study, we investigate the hydrogenation reaction of levulinic acid to 4-hydroxypentanovic acid on a ligand-modified Pt(111) using DFT. Modifying nanoparticle surfaces with ligands can have beneficial effects on...

Insights into Cascade and Sequential one pot pathways for reductive amination of aldehydes paired with bio-derived levulinic acid to N-substituted pyrrolidones using molecular hydrogen

This work aims to explore cascade and sequential one pot syntheses pathways for N-substituted pyrrolidones from aryl aldehydes and bio-derived levulinic acid (LA) using molecular hydrogen and ammonia. This process...

Zeolite-Tailored Active Site Proximity for the Efficient Production of Pentanoic Biofuels

Biofuel production can alleviate reliance on fossil resources and thus carbon dioxide emission. Hydrodeoxygenation (HDO) refers collectively to a series of important biorefinery processes to produce biofuels. Here, well-dispersed and ultra-small Ru metal nanoclusters (ca. 1 nm), confined within the micropores of zeolite Y, provide the required active site intimacy, which significantly boosts the chemoselectivity towards the production of pentanoic biofuels in the direct, one-pot HDO of neat ethyl levulinate. Crucial for improving catalyst stability is the addition of La, which upholds the confined proximity by preventing zeolite lattice deconstruction during catalysis. We have established and extended an understanding of the "intimacy criterion" in catalytic biomass valorization. These findings bring new understanding of HDO reactions over confined proximity sites, leading to potential application for pentanoic biofuels in biomass conversion.

Photo-promoted in situ reduction and stabilization of Pd nanoparticles by H2 at photo-insensitive Sm2O3 nanorods

Controlled synthesis of noble metal nanoparticles with well-defined size and good dispersion on supports has been a long-standing challenge in heterogeneous catalysis. Here we report a facile photo-assisted H₂in situ reduction process to synthesize monodispersed Pd nanoparticles with 2-4 nm size on photo-insensitive Sm₂O₃ rare-earth metal oxide with nanorod morphology. Thanks to the contribution of UV irradiation, the photoelectrons generation in the Sm₂O₃ support accelerates the H₂ reduction of Pd²⁺ ions into Pd⁰ and stabilize the growth of very small Pd nanoparticles homogeneously dispersed on the support. The homogeneous distribution of the Pd NPs on the surface of Sm₂O₃ is most likely attributed to the profuse nucleation sites created by the UV irradiation and the abundance of hydroxyl groups on the support. The hydrogenation of styrene to ethylbenzene was studied as a model reaction. As a result, the UV radiated sample shows an excellent TOF value of 7419 h^-1, which is quadruple of the sample without UV irradiation, under the condition of 0.1 MPa H₂ at a content of 1.0 wt% Pd. Besides, UV radiated sample shows a negligible performance degradation during the repeated cycling process. This photo-promoted H₂ reduction process provides a convenient and straightforward route for assembling materials with novel structures and functions for nanotechnology applications.

Atomic Pyridinic Nitrogen Sites Promoting Levulinic Acid Hydrogenations over Double-Shelled Hollow Ru/C Nanoreactors

Nitrogen-doped nanocarbons are widely used as supports for metal-heterogeneous catalytic conversions. When nitrogen-doped nanocarbon supports are used to disperse metallic nanoparticles (MNPs), the nitrogen dopant can enhance MNPs electron density to reach higher catalytic activity and promote MNPs stability through anchoring effects. However, the precise identification of active nitrogen species between N-dopants and reactants is rarely reported. Herein, a proof-of-concept study on the active N species for levulinic acid hydrogenation is reported. A double-shell structured carbon catalyst (DSC) is designed with selectively locating ultrafine Ru NPs only on inner carbon shell, specifically, different N species on the external carbon shell. Through the design of such a nanostructure, it is demonstrated that the alkaline pyridinic N species on the outer shell serves as an anchor point for the spontaneous binding of the acidic reactant. The pyridinic N content can be modulated from 7.4 to 29.2 mg g_cat^-1 by selecting different precursors. Finally, the Ru-DSC-CTS (using chitosan as the precursor) catalyst achieves a 99% conversion of levulinic acid under 70 °C and 4 MPa hydrogen pressure for 1 h. This work sheds light on the design of nanoreactors at the atomic scale and investigates heterogeneous catalysis at the molecular level.

MoOx-Decorated Co-Based Catalysts toward the Hydrodeoxygenation Reaction of Biomass-Derived Platform Molecules

Catalytic conversion of a biomass derivative (levulinic acid, LA) to a high value-added product (γ-valerolactone, GVL) has attracted much attention, in which the control of catalytic selectivity plays an important role. Herein, a stepwise method was developed to prepare Co-MoO_x catalysts via topological transformation (calcination reduction) from layered double hydroxide (Mo/CoAl-LDH) precursors. X-ray diffraction, high-resolution transmission electron microscopy, and hydrogen temperature-programmed reduction demonstrate the formation of MoO_x-decorated Co structures of Co-MoO_x samples. Remarkably, the sample that is reduced at 500 °C is featured with the most abundant interfacial Co^δ+ (denoted as Co-MoO_x-500), which exhibits an excellent catalytic performance toward the hydrodeoxygenation (HDO) reaction of several biomass-derived platform molecules (furfural, FAL; succinic acid, SA; 5-hydroxymethyl-furfural, HMF; and levulinic acid, LA). Especially, this optimal catalyst displays a high yield (99%) toward the HDO reaction of LA to GVL, which stands at the highest level among non-noble metal catalysts. The combination of in situ FT-IR characterization and theoretical calculation further confirms that interfacial Co^δ+ sites in Co-MoO_x-500 act as adsorption active sites for the polarization of a C═O bond in an LA molecule, which simultaneously promotes C═O hydrogenation and C-O cleavage. Moreover, the MoO_x overlayer suppresses the formation of byproducts by covering the Co⁰ sites. This work offers a cost-effective and efficient catalyst, which can be potentially applied in catalytic conversion of biomass-derived platform molecules.

Electrodeposited Ni-Rich Ni-Pt Mesoporous Nanowires for Selective and Efficient Formic Acid-Assisted Hydrogenation of Levulinic Acid to γ-Valerolactone

In pursuit of friendlier conditions for the preparation of high-value biochemicals, we developed catalytic synthesis of γ-valerolactone by levulinic acid hydrogenation with formic acid as the hydrogen source. Both levulinic and formic acid are intermediate products in the biomass transformation processes. The objective of the work is twofold: the development of a novel approach for milder synthesis conditions to produce γ-valerolactone and the reduction of the economic cost of the catalyst. Ni-rich Ni-Pt mesoporous nanowires were synthesized in an aqueous medium using a combined hard-soft-template-assisted electrodeposition method, in which porous polycarbonate membranes controlled the shape and the Pluronic P-123 copolymer served as the porogen agent. The electrodeposition conditions selected favored nickel deposition and generated nanowires with nickel percentages above 75 atom %. The increase in deposition potential favored nickel deposition. However, it was detrimental for the porous diameter because the mesoporous structure is promoted by the presence of the platinum-rich micelles near the substrate, which is not favored at more negative potentials. The prepared catalysts promoted the complete transformation to γ-valerolactone in a yield of around 99% and proceeded with the absence of byproducts. The coupling temperature and reaction time were optimized considering the energy cost. The threshold operational temperature was established at 140 °C, at which, 120 min was sufficient for attaining the complete transformation. Working temperatures below 140 °C rendered the reaction completion difficult. The Ni₇₈Pt₂₂ nanowires exhibited excellent reusability, with minimal nickel leaching into the reaction mixture, whereas those with higher nickel contents showed corrosion.

Thermal Stability of Ru–Re NPs in H2 and O2 Atmosphere and Their Activity in VOCs Oxidation: Effect of Ru Precursor

The thermal stability of Ru–Re NPs on γ-alumina support was studied in hydrogen at 800 °C and in air at 250–400 °C. The catalysts were synthesized using Cl-free and Cl-containing Ru precursors and NH4ReO4. Very high sintering resistance of Ru–Re NPs was found in hydrogen atmosphere and independent of Ru precursors and Re loading, the size of them was below 2–3 nm. In air, metal segregation occurred at 250 °C, leading to formation of RuO2 and highly dispersed ReOx species. Ruthenium agglomeration was hindered at higher Re loading and in presence of residual Cl species. Propane oxidation rate was higher with the Ru(N)–Re catalysts than with Ru(N) and that containing Cl species. The Ru(N)–Re (3:1) catalyst exhibited the highest activity and the lowest activation energy (91.6 kJ mol−1) what is in contrast to Ru(Cl)–Re (3:1) which had the lowest activity and the highest activation energy (119.3 kJ mol−1). Thus, the synergy effect was not observed in Cl-containing catalysts.

Graphic Abstract

Electrocatalytic synthesis of heterocycles from biomass-derived furfuryl alcohols

It is very attractive yet underexplored to synthesize heterocyclic moieties pertaining to biologically active molecules from biomass-based starting compounds. Herein, we report an electrocatalytic Achmatowicz reaction for the synthesis of hydropyranones from furfuryl alcohols, which can be readily produced from biomass-derived and industrially available furfural. Taking advantage of photo-induced polymerization of a bipyridyl ligand, we demonstrate the facile preparation of a heterogenized nickel electrocatalyst, which effectively drives the Achmatowicz reaction electrochemically. A suite of characterization techniques and density functional theory computations were performed to aid the understanding of the reaction mechanism. It is rationalized that the unsaturated coordination sphere of nickel sites in our electrocatalyst plays an important role at low applied potential, not only allowing the intimate interaction between the nickel center and furfuryl alcohol but also enabling the transfer of hydroxide from nickel to the bound furfuryl alcohol.

Sulfonic Derivatives as Recyclable Acid Catalysts in the Dehydration of Fructose to 5-Hydroxymethylfurfural in Biphasic Solvent Systems

Biphasic systems have received increasing attention for acid-catalyzed dehydration of hexoses to 5-hydroxymethylfurfural (HMF) because of their high efficiency in in situ extraction and stabilization of HMF. Different organic solvents and acid catalysts were applied in these systems, but their effects on the dehydration activity and HMF yield, and the recycling of homogeneous acid catalysts remain largely unexplored. Here, we tested different solvent systems containing a wide range of organic solvents with low boiling points to study the effects of their chemical structures on fructose dehydration and provided stable H₂O-dioxane and H₂O-acetonitrile biphasic systems with high HMF yields of 76-79% using water-soluble sulfonic derivatives as homogeneous acid catalysts under mild conditions (383 K). By analyzing the partition coefficients of HMF and sulfonic derivatives, 94.3% of HMF and 87.1% of NH₂SO₃H were, respectively, restrained in the dioxane phase and aqueous phase in the H₂O-dioxane biphasic system and easily divided by phase separation. The effects of the adjacent group in sulfonic derivatives and reaction temperature on fructose conversions and HMF yields suggest that in a specific biphasic system, the catalysts' acidity and reaction conditions significantly affect the fructose dehydration activity but hardly influence the optimal yield of HMF, and an almost constant amount of carbon loss was observed mainly due to the poor hydrothermal stability of fructose. Such developments offer a promising strategy to address the challenge in the separation and recycling of homogeneous acid catalysts in the practical HMF production.

Heterogeneous Ru Catalysts as the Emerging Potential Superior Catalysts in the Selective Hydrogenation of Bio-Derived Levulinic Acid to γ-Valerolactone: Effect of Particle Size, Solvent, and Support on Activity, Stability, and Selectivity

Catalytic hydrogenation of a biomass-derived molecule, levulinic acid (LA), to γ-valerolactone (GVL) has been getting much attention from researchers across the globe recently. This is because GVL has been identified as one of the potential molecules for replacing fossil fuels. For instance, GVL can be catalytically converted into liquid alkenes in the molecular weight range close to that found in transportation fuels via a process that does not require an external hydrogen source. Noble and non-noble metals have been used as catalysts for the selective hydrogenation of LA to GVL. Of these, Ru has been reported to be the most active metal for this reaction. The type of metal supports and solvents has been proved to affect the activity, selectivity, and yields of GVL. Water has been identified as a potential, effective “green” solvent for the hydrogenation of LA to GVL. The use of different sources of H2 other than molecular hydrogen (such as formic acid) has also been explored. In a few instances, the product, GVL, is hydrogenated further to other useful products such as 1,4-pentanediol (PD) and methyl tetrahydrofuran (MTHF). This review selectively focuses on the potential of immobilized Ru catalysts as a potential superior catalyst for selective hydrogenation of LA to GVL.

Robust Ruthenium Catalysts Supported on Mesoporous Cyclodextrin-Templated TiO2-SiO2 Mixed Oxides for the Hydrogenation of Levulinic Acid to γ-Valerolactone

In this paper, we present a versatile template-directed colloidal self-assembly method for the fabrication in aqueous phase of composition-tuned mesoporous RuO2@TiO2-SiO2 catalysts. Randomly methylated β-cyclodextrin/Pluronic F127 supramolecular assemblies were used as soft templates, TiO2 colloids as building blocks, and tetraethyl orthosilicate as a silica source. Catalysts were characterized at different stages of their synthesis using dynamic light scattering, N2-adsorption analysis, powder X-ray diffraction, temperature programmed reduction, high-resolution transmission electron microscopy, high-angle annular bright-field and dark-field scanning transmission electron microscopy, together with EDS elemental mapping. Results revealed that both the supramolecular template and the silica loading had a strong impact on the pore characteristics and crystalline structure of the mixed oxides, as well as on the morphology of the RuO2 nanocrystals. Their catalytic performance was then evaluated in the aqueous phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) under mild conditions (50 °C, 50 bar H2). Results showed that the cyclodextrin-derived catalyst displayed almost quantitative LA conversion and 99% GVL yield in less than one hour. Moreover, this catalyst could be reused at least five times without loss of activity. This work offers an effective approach to the utilization of cyclodextrins for engineering the surface morphology of Ru nanocrystals and pore characteristics of TiO2-based materials for catalytic applications in hydrogenation reactions.

Molybdenum-Catalyzed Deoxygenation Coupling of Lignin-Derived Alcohols for Functionalized Bibenzyl Chemicals

With the growing demand for sustainability and reducing CO₂ footprint, lignocellulosic biomass has attracted much attention as a renewable, carbon-neutral and low-cost feedstock for the production of chemicals and fuels. To realize efficient utilization of biomass resource, it is essential to selectively alter the high degree of oxygen functionality of biomass-derivates. Herein, we introduced a novel procedure to transform renewable lignin-derived alcohols to various functionalized bibenzyl chemicals. This strategy relied on a short deoxygenation coupling pathway with economical molybdenum catalyst. A well-designed H-donor experiment was performed to investigate the mechanism of this Mo-catalyzed process. It was proven that benzyl carbon-radical was the most possible intermediate to form the bibenzyl products. It was also discovered that the para methoxy and phenolic hydroxyl groups could stabilize the corresponding radical intermediates and then facilitate to selectively obtain bibenzyl products. Our research provides a promising application to produce functionalized aromatics from biomass-derived materials.

Falling Leaves Return to Their Roots: A Review on the Preparation of γ-Valerolactone from Lignocellulose and Its Application in the Conversion of Lignocellulose

γ-Valerolactone (GVL), derived from renewable lignocellulosic biomass, has been considered as a cost-competitive and green platform chemical. With the increasingly prominent environmental problems, a deep understanding of the preparation and transformation of GVL is highly needed. Based on the latest progress made with GVL, preparation and applications of GVL are summarized and discussed in this Review. In particular, the state-of-the-art in catalytic production of GVL is described based on the use of noble-metal and non-noble-metal catalysts. The application of GVL for the valorization of lignocellulose would improve the yield of target products such as sugar monomers and furfural. Thus, GVL can be produced from lignocellulose and simultaneously it can also be used for the valorization of lignocellulose, just as in the sustainable and renewable cycle, "the falling leaves returns to their roots". This Review is expected to provide valuable reference and new proposal for the further development and better utilization of GVL.

Nickel phosphide nanoalloy catalyst for the selective deoxygenation of sulfoxides to sulfides under ambient H2 pressure

Exploring novel catalysis by less common, metal-non-metal nanoalloys is of great interest in organic synthesis. We herein report a titanium-dioxide-supported nickel phosphide nanoalloy (nano-Ni2P/TiO2) that exhibits high catalytic activity for the deoxygenation of sulfoxides. nano-Ni2P/TiO2 deoxygenated various sulfoxides to sulfides under 1 bar of H2, representing the first non-noble metal catalyst for sulfoxide deoxygenation under ambient H2 pressure. Spectroscopic analyses revealed that this high activity is due to cooperative catalysis by nano-Ni2P and TiO2.

High-Temperature Synthesis of Small-Sized Pt/Nb Alloy Catalysts on Carbon Supports for Hydrothermal Reactions

Catalytic biomass conversions are sustainable processes to produce value-added fuels and chemicals but need stable catalysts that can tolerate harsh hydrothermal conditions. Herein, we report a hydrothermally stable catalyst by alloying Pt with a high-melting-point metal Nb. The Pt/Nb alloy catalysts are prepared by H₂ reduction at a high temperature of 900 °C with a high-surface-area carbon black support, which can suppress metal sintering at high temperatures and thus lead to small-sized alloyed Pt/Nb particles of only 2.2 nm. Taking the advantages of surface acid property provided by the Nb sites and the size effect, the prepared C-supported small-sized Pt/Nb alloy catalysts exhibit attractive activities for the hydrogenation of levulinic acid into γ-valerolactone and the water-gas shift reaction. More significantly, benefiting from the inherent stability of high-melting-point Nb, the Pt/Nb alloy catalysts show much enhanced hydrothermal stability compared to commercial Pt/C and Ru/C catalysts.

Out-of-Equilibrium Polymorph Selection in Nanoparticle Freezing

The ability to design synthesis processes that are out of equilibrium has opened the possibility of creating nanomaterials with remarkable physicochemical properties, choosing from a much richer palette of possible atomic architectures compared to equilibrium processes in extended systems. In this work, we employ atomistic simulations to demonstrate how to control polymorph selection via the cooling rate during nanoparticle freezing in the case of Ni₃Al, a material with a rich structural landscape. State-of-the-art free-energy calculations allow us to rationalize the complex nucleation process, discovering a switch between two kinetic pathways, yielding the equilibrium structure at room temperature and an alternative metastable one at higher temperature. Our findings address the key challenge in the synthesis of nanoalloys for technological applications, i.e., rationally exploiting the competition between kinetics and thermodynamics by designing a treatment history that forces the system into desirable metastable states.

Recent advances in liquid hydrosilane-mediated catalytic N-formylation of amines with CO2

Carbon dioxide is an ideal raw material for the synthesis of complex organic compounds because of its rich, non-toxic, and good physical properties. It is of great significance to transform CO₂ into valuable fine chemicals and develop a green sustainable cycle of carbon surplus. Based on hydrosilane as a reducing agent, this work summarizes the recent applications of reductive amidation of CO₂ using different catalysts such as organocatalysts, ionic liquids (ILs), salts, transition metal complexes, and solvents. The main factors affecting the reductive amidation of CO₂ and the possible reaction mechanism are discussed. Moreover, the future orientation and catalytic systems of the formylation of amines with CO₂ and hydrosilane are prospected.

This review depicts different types of catalyst systems developed for upgrading of amines and carbon dioxide into N-formylated products in the presence of hydrosilane, with attention on reaction mechanism and process optimization.

Effect of support acidity during selective hydrogenolysis of glycerol over supported palladium-ruthenium catalysts

We report the role of the acidity of support during the selectivity hydrogenolysis of glycerol over supported bimetallic palladium-ruthenium (PdRu) catalysts. The PdRu nanoparticles were supported on a series of metal oxides and zeolitic supports via the modified impregnation method and tested for the liquid-phase hydrogenolysis of glycerol using gaseous hydrogen. The relative acid site densities of selected catalysts were determined by ammonia temperature-programmed desorption and pyridine desorption experiments. Based on these studies, we report a direct correlation between the catalytic activity (conversion and 1,2 propane diol yield) and two different acid sites (strong acid sites and very strong acid sites). Besides zeolite-supported catalysts, TiO₂ supported PdRu nanoparticles exhibit moderate catalytic activity; however, this catalyst shows high selectivity for the desired C-O bond cleavage to produce C3 products over the undesired C-C bond cleavage to produce < C3 products. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Heterogeneous Catalytic Hydrogenation of Levulinic Acid to γ-Valerolactone with Formic Acid as Internal Hydrogen Source

As one of the most promising biomass-based platform molecules, γ-valerolactone (GVL) can be synthesized from a variety of lignocellulosic feedstocks through different hydrogen supply pathways. Among these transformation routes, the hydrogenation of levulinic acid (LA) to GVL by using formic acid (FA) as the internal hydrogen source is regarded as a critical path for the sustainable development of renewable energy systems. Although a large number of studies on the synthesis of GVL have been reported, the FA/LA catalytic system has not been interpreted as thoroughly as it should be. In this Minireview, core concerns are focused on key issues and their effects in this FA/LA catalytic system. The catalytic mechanism, together with competitive adsorption behavior between FA and LA on heterogeneous catalysts, is presented. The effects of active metal species and catalyst supports on the overall catalytic performance are summarized, and the influences of key condition parameters, including the time, temperature, FA/LA molar ratios, and aqueous solvent, are discussed. In particular, impacts and improvements of coke deposition and metal leaching, which could greatly affect the catalyst stability, are analyzed in detail. Additionally, several feasible suggestions for the enhancement of the catalytic efficiency and stability are also proposed.