Biomass valorisation over metal-based solid catalysts from nanoparticles to single atoms

Earth-Abundant 3d-Transition Metal Metasilicates As Effective Electrocatalysts For Alkaline HER: CuZnSiO3 Outperforms CuSiO3 and ZnSiO3

Hydrogen evolution reaction (HER) is a key reaction in electrochemical water splitting for hydrogen production leading to the development of potentially sustainable energy technology. Importantly, the catalysts required for HER must be earth-abundant for their large-scale deployment; silicates representing one such class. Herein, we have synthesized a series of transition mono- and bi- metal metasilicates (with SiO3 2- group) using facile wet-chemical method followed by calcination at a higher temperature. The structural and morphological studies show their unique crystal structure and distinctive morphology, as well as the surface texture, with the band gap ranges of 1.49-2.24 eV. Interestingly, CuZnSiO3, with all earth-abundant elements, exhibits a band gap of 1.67 eV, shows impressive electrocatalytic properties. We show that CuZnSiO3 exhibits HER activity with much lower overpotential (η=151 mV) at 10 mA cm-2 under alkaline conditions. The CuZnSiO3 electrode also shows good electrocatalytic stability (ΔE=24 mV) even after 25 hours of chronoamperometric stability test and the performance is comparable to the commercial Pt/C catalyst under similar conditions. Finally, detailed electronic structure studies employing density functional theory (DFT) as well as electronic transport studies were performed to understand and elucidate the superior performance of CuZnSiO3 over the CuSiO3 and ZnSiO3 electrocatalysts.

Active Hydroxyl-Mediated Preferential Cleavage of Carbon-Carbon Bonds in Electrocatalytic Glycerol Oxidation

Electrocatalytic glycerol oxidation reaction (GOR) to produce high-value formic acid (FA) is hindered by high formation potential of active species and sluggish C-C bond cleavage kinetics. Herein, Ni single-atom (NiSA) and Co single-atom (CoSA) dual sites anchored on nitrogen-doped carbon nanotubes embedded with Ni0.1Co0.9 alloy (Ni0.1Co0.9@NiSACoSA-NCNTs) are constructed for electrochemical GOR. Remarkably, it can reach 10 mA cm-2 at a low potential of 1.15 V versus the reversible hydrogen electrode (vs. RHE) and realize a high formate selectivity of 93.27 % even at high glycerol conversion of 98.81 % at 1.45 V vs. RHE. The GOR mechanism and pathway are systematically elucidated via experimental analyses and theoretical calculations. It is revealed that the active hydroxyl (*OH) can be produced during the GOR. The NiSA, CoSA, and Ni0.1Co0.9 synergistically optimizes the electronic structure of CoSA active sites, reducing the energy barriers of *OH-mediated cleavage of C-C bonds and dehydrogenation of C1 intermediates. This decreases the number of reaction intermediates and reaction steps of GOR-to-FA, thus increasing the formate production efficiency. After coupling GOR with hydrogen evolution reaction in a membrane electrode assembly cell, 14.26 g of formate and 23.10 L of H2 are produced at 100 mA cm-2 for 108 h.

Balancing Competitive Adsorption on Co3O4@P, N-Doped Porous Carbon to Enhance the Electrocatalytic Upgrading of Biomass Derivatives

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) represents an environmentally friendly approach to generate high-value-added chemicals from biomass. The successful electrochemical transformation of HMF during the oxidation reaction (HMFOR) necessitates an ideal adsorption interaction between HMF and OH- on the electrode surface. Yet, catalysts with a singular active site offer limited flexibility in managing the competitive adsorption of HMF and OH-. To this end, different active sites are customized in this work to construct a P and N co-doped porous carbon that wrapped Co3O4 (Co3O4@PNC). Co-doping with these two heteroatoms generates C3P = O and pyrrolic N as adsorption sites to better balance the adsorption of HMF and OH-, respectively, rather than promoting competition between the HMF and OH- on a single active site. With this design strategy, Co3O4@PNC demonstrates significant HMFOR activity, the conversion rate of HMF surpassed 99% with a 2,5-furandicarboxylic acid (FDCA) yield exceeding 95% after 2 h of electrolysis. Furthermore, it shows universal applicability in the electrooxidation of other alcohol/aldehyde substrates, yielding efficiencies of 90-99%. This work not only provides guidance for advanced electrocatalysts design toward alcohol/aldehyde oxidation but also offers insights into the utilization of biomass-derived platform chemicals.

Thermally stable high-loading single Cu sites on ZSM-5 for selective catalytic oxidation of NH3

Rigorous comparisons between single site- and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst.

Steering Selectivity in Electrocatalytic Furfural Reduction via Electrode-Electrolyte Interface Modification

Electrocatalytic reduction of biomass-derived furfural (FF) represents a sustainable route to produce furfuryl alcohol (FA) and 2-methylfuran (MF) as a value-added chemical and a biofuel, respectively. However, achieving high selectivity for MF as well as tuning the selectivity between FA and MF within one reaction system remain challenging. Herein, we have reported an electrode-electrolyte interface modification strategy, enabling FA and MF selectivity steering under the same reaction conditions. Specifically, by modifying copper (Cu) electrocatalysts with butyl trimethylammonium bromide (BTAB), we achieved a dramatic shift in selectivity from producing FA (selectivity: 83.8%; Faradaic efficiency, FE: 68.9%) to MF (selectivity: 80.1%; FE: 74.8%). We demonstrated that BTAB adsorption over Cu modulates the electrical double layer (EDL) structure, which repels interfacial water and weakens the hydrogen-bond (H-bond) network for proton transfer, thus impeding FF-to-FA conversion by suppression of the hydrogen atom transfer (HAT) process. On the contrary, FF-to-MF conversion was less affected. This work shows the potential of engineering of the electrode-electrolyte interface for selectivity control in electrocatalysis.

Nanoparticles as an antidote for poisoned gold single-atom catalysts in sustainable propylene epoxidation

The development of sustainable and anti-poisoning single-atom catalysts (SACs) is essential for advancing their research from laboratory to industry. Here, we present a proof-of-concept study on the poisoning of Au SACs, and the antidote of Au nanoparticles (NPs), with trace addition shown to reinforce and sustain propylene epoxidation. Multiple characterizations, kinetics investigations, and multiscale simulations reveal that Au SACs display remarkable epoxidation activity at a low propylene coverage, but become poisoned at higher coverages. Interestingly, Au NPs can synergistically cooperate with Au SACs by providing distinct active sites required for H2/O2 and C3H6 activations, as well as hydroperoxyl radical to restore poisoned SACs. The difference in reaction order between C3H6 and H2 (nC3H6-nH2) is identified as the descriptor for establishing the volcano curves, which can be fine-tuned by the intimacy and composition of SACs and NPs to achieve a rate-matching scenario for the formation, transfer, and consumption of hydroperoxyl. Consequently, only trace addition of Au NPs antidote (0.3% ratio of SACs) stimulates significant improvements in propylene oxide formation rate, selectivity, and H2 efficiency compared to SACs alone, offering a 56-fold, 3-fold, and 22-fold increase, respectively, whose performances can be maintained for 150 h.

Preparation and Application of Single-Atom Cobalt Catalysts in Organic Synthesis and Environmental Remediation

The development of high-performance catalysts plays a crucial role in facilitating chemical production and reducing environmental contamination. Single-atom catalysts (SACs), a class of catalysts that bridge the gap between homogeneous and heterogeneous catalysis, have garnered increasing attention because of their unique activity, selectivity, and stability in many pivotal reactions. Meanwhile, the scarcity of precious metal SACs calls for the arrival of cost-effective SACs. Cobalt, as a common non-noble metal, possesses tremendous potential in the field of single-atom catalysis. Despite their potential, reviews about single-atom Co catalysts (Co-SACs) are lacking. Accordingly, this review thoroughly summarized various preparation methodologies of Co-SACs, particularly pyrolysis; its application in the specific domain of organic synthesis and environmental remediation is discussed as well. The structure-activity relationship and potential catalytic mechanism of Co-SACs are elucidated through some representative reactions. The imminent challenges and development prospects of Co-SACs are discussed in detail. The findings and insights provided herein can guide further exploration and development in this charming area of catalyst design, leading to the realization of efficient and sustainable catalytic processes.

Atomically precise Au and Ag nanoclusters doped with a single atom as model alloy catalysts

Gold and silver nanoclusters (NCs) composed of <200 atoms are novel catalysts because their catalytic properties differ significantly from those of the corresponding bulk surface and can be dramatically tuned by the size (number of atoms). Doping with other metals is a promising approach for improving the catalytic performance of Au and Ag NCs. However, elucidation of the origin of the doping effects and optimization of the catalytic performance are hampered by the technical challenge of controlling the number and location of the dopants. In this regard, atomically precise Au or Ag (Au/Ag) NCs protected by ligands or polymers have recently emerged as an ideal platform because they allow regioselective substitution of single Au/Ag constituent atoms while retaining the size and morphology of the NC. Heterogeneous Au/Ag NC catalysts doped with a single atom can also be prepared by controlled calcination of ligand-protected NCs on solid supports. Comparison of thermal catalysis, electrocatalysis, and photocatalysis between the single-atom-doped and undoped Au/Ag NCs has revealed that the single-atom doping effect can be attributed to an electronic or geometric origin, depending on the dopant element and position. This minireview summarizes the recent progress of the synthesis and catalytic application of single-atom-doped, atomically precise Au/Ag NC catalysts and provides future prospects for the rational development of active and selective metal NC catalysts.

Dealuminated Beta zeolite reverses Ostwald ripening for durable copper nanoparticle catalysts

Copper nanoparticle-based catalysts have been extensively applied in industry, but the nanoparticles tend to sinter into larger ones in the chemical atmospheres, which is detrimental to catalyst performance. In this work, we used dealuminated Beta zeolite to support copper nanoparticles (Cu/Beta-deAl) and showed that these particles become smaller in methanol vapor at 200°C, decreasing from ~5.6 to ~2.4 nanometers in diameter, which is opposite to the general sintering phenomenon. A reverse ripening process was discovered, whereby migratable copper sites activated by methanol were trapped by silanol nests and the copper species in the nests acted as new nucleation sites for the formation of small nanoparticles. This feature reversed the general sintering channel, resulting in robust catalysts for dimethyl oxalate hydrogenation performed with supported copper nanoparticles for use in industry.

Advances in Heterogeneous Catalysts for Lignin Hydrogenolysis

Lignin is the main component of lignocellulose and the largest source of aromatic substances on the earth. Biofuel and bio-chemicals derived from lignin can reduce the use of petroleum products. Current advances in lignin catalysis conversion have facilitated many of progress, but understanding the principles of catalyst design is critical to moving the field forward. In this review, the factors affecting the catalysts (including the type of active metal, metal particle size, acidity, pore size, the nature of the oxide supports, and the synergistic effect of the metals) are systematically reviewed based on the three most commonly used supports (carbon, oxides, and zeolites) in lignin hydrogenolysis. The catalytic performance (selectivity and yield of products) is evaluated, and the emerging catalytic mechanisms are introduced to better understand the catalyst design guidelines. Finally, based on the progress of existing studies, future directions for catalyst design in the field of lignin depolymerization are proposed.

Direct C-C Double Bond Cleavage of Alkenes Enabled by Highly Dispersed Cobalt Catalyst and Hydroxylamine

The utilization of a single-atom catalyst to break C-C bonds merges the merits of homogeneous and heterogeneous catalysis and presents an intriguing pathway for obtaining high-value-added products. Herein, a mild, selective, and sustainable oxidative cleavage of alkene to form oxime ether or nitrile was achieved by using atomically dispersed cobalt catalyst and hydroxylamine. Diversified substrate patterns, including symmetrical and unsymmetrical alkenes, di- and tri-substituted alkenes, and late-stage functionalization of complex alkenes were demonstrated. The reaction was successfully scaled up and demonstrated good performance in recycling experiments. The hot filtration test, catalyst poisoning and radical scavenger experiment, time kinetics, and studies on the reaction intermediate collectively pointed to a radical mechanism with cobalt/acid/O2 promoted C-C bond cleavage as the key step.

Facile Hydrogenolysis of Sugars to 1,2-Glycols by Ru@PPh3/OPPh3 Confined Large-Pore Mesoporous Silica

Tandem hydrogenation vis-à-vis hydrogenolysis of xylose to 1,2-glycols remains a major challenge. Although one-pot conversion of xylose to 1,2-glycols requires stringent conditions, a sustainable approach would be quite noteworthy. We have developed a microwave route for the one-pot conversion of pentose (C5) and hexose (C6) sugars into glycol and hexitol, without pressurized hydrogen reactors. A pronounced hydrogenolysis of sugars to glycols is observed by Ru single atom (SA) on triphenylphosphine/phosphine oxide-modified silica (Ru@SiP), in contrast to Ru SA on pristine (Ru@SiC) and 3-aminopropyl-modified silica (Ru@SiN). A promising "ligand effect" was observed through phosphine modification of silica that presents a 70% overall yield of all reduced sugars (xylitol + glycols) from a 99% conversion of xylose with Ru@SiP. A theoretical study by DFT depicts an electronic effect on Ru-SA by triphenylphosphine that promotes the catalytic hydrogenolysis of sugars under mild conditions. Hence, this research represents an important step for glycols from biomass-derived sources.

Recent Progress and Opportunity of Metal Single-Atom Catalysts for Biomass Conversion Reactions

The conversion of lignocellulosic biomass into platform chemicals and fuels by metal single atoms is a new domain in solid catalysis research. Unlike the conventional catalysis route, single-atom catalysts (SACs) proliferate maximum utilization efficiency, high catalytic activity, and good selectivity to the desired product with an ultralow loading of the active sites. More strikingly, SACs show a unique cost-effective pathway for the conversion of complex sugar molecules to value-added chemicals in high yield and selectivity, which may be hindered by conventional metal nanoparticles. Primarily, SACs having adjustable active sites could be easily modified using sophisticated synthetic techniques based on their intended reactions. This review covers current research on the use of SACs with a strong emphasis on the fundamentals of catalyst design, and their distinctive activities in each type of reaction (hydrogenation, hydrogenolysis, hydrodeoxygenation, oxidation, and dehydrogenation). Furthermore, the fundamental insights into the superior actions of SACs within the opportunity and prospects for the industrial-scale synthesis of value-added products from the lignocelluloses are covered.

Toward the Rational Design of More Efficient Mo2C Catalysts for Hydrodeoxygenation-Mechanism and Descriptor Identification

Viable alternatives to scarce and expensive noble-metal-based catalysts are transition-metal carbides such as Mo and W carbides. It has been shown that these are active and selective catalysts in the hydrodeoxygenation of renewable lipid-based feedstocks. However, the reaction mechanism and the structure-activity relationship of these transition-metal carbides have not yet been fully clarified. In this work, the reaction mechanism of butyric acid hydrodeoxygenation (HDO) over molybdenum carbide (Mo2C) has been studied comprehensively by means of density functional theory coupled with microkinetic modeling. We identified the rate-determining step to be butanol dissociation: C4H9*OH + * → C4H9* + *OH. Then we further explored the possibility to facilitate this step upon heteroatom doping and found that Zr- and Nb-doped Mo2C are the most promising catalysts with enhanced HDO catalytic activity. Linear-scaling relationships were established between the electronic and geometrical descriptors of the dopants and the catalytic performance of various doped Mo2C catalysts. It was demonstrated that descriptors such as dopants' d-band filling and atomic radius play key roles in governing the catalytic activity. This fundamental understanding delivers practical strategies for the rational design of Mo2C-based transition-metal carbide catalysts with improved HDO performance.

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.

Fine-Tuning of Ni/NiO over H-NbOx for Enhanced Eugenol Hydrogenation through Enhanced Oxygen Vacancies and Synergistic Participation of Active Sites

The hydrogenation of lignin-derived phenolics to produce valuable chemicals is a promising but challenging task. This study successfully demonstrates the use of sustainable transition metal-based catalysts to hydrogenate lignin-derived phenolics. A defect-induced oxygen vacancy containing H-NbOx prepared from commercial Nb2O5 was employed as a catalyst. H-NbOx exhibited higher oxygen vacancies (158.21 μmol/g) than commercial Nb2O5 (39.01 μmol/g), evaluated from O2-TPD. Upon supporting 10 wt % Ni, a Ni/NiO interface was formed over H-NbOx, which was intrinsically active for the hydrogenation of phenolics. 10Ni/H-NbOx exhibited a two-fold increase in activity than 10Ni/Nb2O5, achieving >99% eugenol conversion and affording ∼94% 4-propyl cyclohexanol selectivity, wherein ∼63% eugenol conversion and ∼73% 4-propyl cyclohexanol selectivity were obtained over 10Ni/Nb2O5. The Ni/NiO formation was confirmed by X-ray photoelectron spectroscopy, HR-TEM, and H2-TPR analysis, while the oxygen vacancies were verified by Raman spectroscopy and O2-TPD analysis. The resulting interface enhanced the synergy between Ni and H-NbOx and facilitated hydrogen dissociation, confirmed by H2-TPD. Remarkably, 10Ni/H-NbOx maintained its catalytic activity for five tested cycles and demonstrated exceptional activity with various phenolics. Our findings highlight the potential of a sustainable transition metal catalyst for the hydrogenation of lignin-derived phenolic compounds, which could pave the path to producing valuable chemicals in an environmentally friendly manner.

Facile and Eco-Friendly Approach To Produce Confined Metal Cluster Catalysts

Zeolite-supported metal nanocluster catalysts have attracted significant attention due to their broad application in heterogeneously catalyzed reactions. The preparation of highly dispersed metal catalysts commonly involves the use of organic compounds and requires the implementation of complicated procedures, which are neither green nor deployable at the large scale. Herein, we present a novel facile method (vacuum-heating) which employs a specific thermal vacuum processing protocol of catalysts to promote the decomposition of metal precursors. The removal of coordinated H₂O via vacuum-heating restricts the formation of intermediates (metal-bound OH species), resulting in catalysts with a uniform, metal nanocluster distribution. The structure of the intermediate was determined by in situ Fourier transform infrared, temperature-programmed decomposition, and X-ray absorption spectroscopy (XAS) measurements. This alternative synthesis method is eco-friendly and cost-effective as the procedure occurs in the absence of organic compounds. It can be widely used for the preparation of catalysts from different metal species (Ni, Fe, Cu, Co, Zn) and precursors and is readily scaled-up.

Review on supported metal catalysts with partial/porous overlayers for stabilization

Heterogeneous catalysts of supported metals are important for both liquid-phase and gas-phase chemical transformations which underpin the petrochemical sector and manufacture of bulk or fine chemicals and pharmaceuticals. Conventional supported metal catalysts (SMC) suffer from deactivation resulting from sintering, leaching, coking and so on. Besides the choice of active species (e.g. atoms, clusters, nanoparticles) to maximize catalytic performances, strategies to stabilize active species are imperative for rational design of catalysts, particularly for those catalysts that work under heated and corrosive reaction conditions. The complete encapsulation of metal active species within a matrix (e.g. zeolites, MOFs, carbon, etc.) or core-shell arrangements is popular. However, the use of partial/porous overlayers (PO) to preserve metals, which simultaneously ensures the accessibility of active sites through controlling the size/shape of diffusing reactants and products, has not been systematically reviewed. The present review identifies the key design principles for fabricating supported metal catalysts with partial/porous overlayers (SMCPO) and demonstrates their advantages versus conventional supported metals in catalytic reactions.

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.

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

Hypervalent aryliodoumiums are intensively investigated as arylating agents. They are excellent surrogates to aryl halides, and moreover they exhibit better reactivity, which allows the corresponding arylation reactions to be performed under mild conditions. In the past decades, acyclic aryliodoniums are widely explored as arylation agents. However, the unmet need for acyclic aryliodoniums is the improvement of their notoriously low reaction economy because the coproduced aryl iodides during the arylation are often wasted. Cyclic aryliodoniums have their intrinsic advantage in terms of reaction economy, and they have started to receive considerable attention due to their valuable synthetic applications to initiate cascade reactions, which can enable the construction of complex structures, including polycycles with potential pharmaceutical and functional properties. Here, we are summarizing the recent advances made in the research field of cyclic aryliodoniums, including the nascent design of aryliodonium species and their synthetic applications. First, the general preparation of typical diphenyl iodoniums is described, followed by the construction of heterocyclic iodoniums and monoaryl iodoniums. Then, the initiated arylations coupled with subsequent domino reactions are summarized to construct polycycles. Meanwhile, the advances in cyclic aryliodoniums for building biaryls including axial atropisomers are discussed in a systematic manner. Finally, a very recent advance of cyclic aryliodoniums employed as halogen-bonding organocatalysts is described.

Effects of throat sizing and gasification agents in a biomass downdraft gasifier: towards CO2-free syngas production

The gasification process in a downdraft biomass gasifier is investigated using Computational Fluid Dynamics (CFD). The aim is to develop a novel approach to reduce CO₂ emissions from producer syngas while increasing the higher heating value (HHV). To this end, the effects of varying the throat diameter of the gasifier and gasifying media (air and oxygen) on the performance of gasification are investigated. The results reveal that as the throat ratio decreases for oxy-gasification, more CO, H₂, and CH₄ are produced, thus resulting in a HHV of 12.1 MJ Nm⁻³. For the same working conditions (ER, MC, and feedstock), the suggested design/optimum throat ratio of 0.14 is found to reduce CO₂ by ∼55% compared to any other higher throat ratios, while simultaneously increasing HHV by ∼20% for both air and oxy-gasification cases. Additionally, the suggested throat ratio increases the gasification efficiency, carbon conversion and producer gas yield by 19%, 33%, and 22% respectively. Therefore, it shows a significant potential for CO₂-free syngas production in the gasification process, demonstrating a promising technique that does not require any solvents, catalysts, absorbers, or additional CO₂ removal. Lower throat ratios further favour the higher yield of syngas, HHV, gasification and conversion efficiencies, with better gasifier performance.

The influence of throat diameter and gasifying medium on gasifier performance is investigated using a CFD model. Lower throat ratios favour higher gasification efficiency, carbon conversion, and producer gas yield, with potential to reduce CO₂ emissions by 50%.

Palladium nanoparticles on chitin-derived nitrogen-doped carbon materials for carbon dioxide hydrogenation into formic acid

Utilizing waste carbon resources to produce chemicals and materials is beneficial to mitigate the fossil fuel consumption and the global warming. In this study, ocean-based chitin biomass and waste shrimp shell powders were employed as the feedstock to prepare Pd loaded nitrogen-doped carbon materials as the catalysts for carbon dioxide (CO₂)/bicarbonate hydrogenation into formic acid, which simultaneously converts waste biomass into useful materials and CO₂ into a valuable chemical. Three different preparation methods were examined, and the two-stage calcination was the most efficient one to obtain N-doped carbon material with good physicochemical properties as the best Pd support. The highest formic acid yield was achieved of ∼77% at 100 °C in water with KHCO₃ substrate under optimal condition with a TON of 610. The nitrogen content and N functionalities of the as-synthesized carbon materials were crucial which could serve as anchor sites for the Pd precursor and assist the formation of well-dispersed and small-sized Pd NPs for boosted catalytic activity. The study puts forward a facile, inexpensive and environmentally benign way for simultaneous valorization of oceanic waste biomass and carbon dioxide into valuable products.

Superhydrophobic Ru Catalyst for Highly Efficient Hydrogenation of Phenol under Mild Aqueous Conditions

Selective hydrogenations of lignin-derived phenolic compounds represent essential processes in the chemical industry, especially for production of a multitude of fine chemicals. However, selective hydrogenation of phenolic compounds in water phase suffers from low conversion. Here we report a catalyst of well-dispersed Ru clusters fixed in N-doped mesoporous hollow carbon spheres (Ru@N-CS) for enhanced cyclohexanol productivity in phenol hydrogenation at mild aqueous condition. This superhydrophobicity carbon spheres appear to selectively allow diffusion of phenol and hydrogen molecules to the electron-rich coordination unsaturated Ru active sites, while confining the reactants there to enhance its reaction probability. The Ru@N-CS catalyst can selectively hydrogenate phenol at 80 °C and 0.5 MPa of H2 in 30 min in aqueous medium with phenol conversions of 100% and ~100% cyclohexanol selectivity, corresponding to cyclohexanol productivity up to 471 per g of Ru per minute. The TOF value is up to 9980 h−1, which 14 times more than Ru nanoparticles supported on N-doped carbon hollow spheres (Ru/N-CS). This work provides an important catalytic system for upgrading of bio-oil into value-added chemicals under mild aqueous-phase.

A unified view on catalytic conversion of biomass and waste plastics

Originating from the desire to improve sustainability, producing fuels and chemicals from the conversion of biomass and waste plastic has become an important research topic in the twenty-first century. Although biomass is natural and plastic synthetic, the chemical nature of the two are not as distinct as they first appear. They share substantial structural similarities in terms of their polymeric nature and the types of bonds linking their monomeric units, resulting in close relationships between the two materials and their conversions. Previously, their transformations were mostly studied and reviewed separately in the literature. Here, we summarize the catalytic conversion of biomass and waste plastics, with a focus on bond activation chemistry and catalyst design. By tracking the historical and more recent developments, it becomes clear that biomass and plastic have not only evolved their unique conversion pathways but have also started to cross paths with each other, with each influencing the landscape of the other. As a result, this Review on the catalytic conversion of biomass and waste plastic in a unified angle offers improved insights into existing technologies, and more importantly, may enable new opportunities for future advances.

Palladium catalyzed radical relay for the oxidative cross-coupling of quinolines

Traditional approaches for transition-metal catalyzed oxidative cross-coupling reactions rely on sp²-hybridized starting materials, such as aryl halides, and more specifically, homogeneous catalysts. We report a heterogeneous Pd-catalyzed radical relay method for the conversion of a heteroarene C(sp³)–H bond into ethers. Pd nanoparticles are supported on an ordered mesoporous composite which, when compared with microporous activated carbons, greatly increases the Pd d charge because of their strong interaction with N-doped anatase nanocrystals. Mechanistic studies provide evidence that electron-deficient Pd with Pd–O/N coordinations efficiently catalyzes the radical relay reaction to release diffusible methoxyl radicals, and highlight the difference between this surface reaction and C–H oxidation mediated by homogeneous catalysts that operate with cyclopalladated intermediates. The reactions proceed efficiently with a turn-over frequency of 84 h⁻¹ and high selectivity toward ethers of >99%. Negligible Pd leaching and activity loss are observed after 7 catalytic runs.

Traditional approaches for transition-metal catalyzed oxidative cross-coupling reactions rely on sp²-hybridized starting materials. Here the authors report a heterogeneous Pd-catalyzed radical relay method for the conversion of a heteroarene C(sp³)–H bond into ethers.

Advanced Carbon-Based Nanocatalysts and their Application in Catalytic Conversion of Renewable Platform Molecules

The transformation of renewable platform molecules to produce value-added fuels and fine-chemicals is a promising strategy to sustainably meet future demands. Owing to their finely modified electronic and geometric properties, carbon-based nanocatalysts have shown great capability to regulate their catalytic activity and stability. Their well-defined and uniform structures also provide both the opportunity to explore intrinsic reaction mechanisms and the site-requirement for valorization of renewable platform molecules to advanced fuels and chemicals. This Review highlights the progress achieved in carbon-based nanocatalysts, mainly by using effective regulation approaches such as heteroatom anchoring, bimetallic synergistic effects, and carbon encapsulation to enhance catalyst performance and stability, and their applications in renewable platform molecule transformations. The foundation for understanding the structure-performance relationship of carbon-based catalysts has been established by investigating the effect of these regulation methods on catalyst performance. Finally, the opportunities, challenges and potential applications of carbon-based nanocatalysts are discussed.

PO4 3- Coordinated Robust Single-Atom Platinum Catalyst for Selective Polyol Oxidation

Achieving efficient catalytic conversion over a heterogeneous catalyst with excellent resistance against leaching is still a grand challenge for sustainable chemical synthesis in aqueous solution. Herein, we devised a single-atom Pt₁ /hydroxyapatite (HAP) catalyst via a simple hydrothermal strategy. Gratifyingly, this robust Pt₁ /HAP catalyst exhibits remarkable catalytic selectivity and catalyst stability for the selective oxidation of C₂ -C₄ polyols to corresponding primary hydroxy acids. It is found that the Pt-(O-P) linkages with strong electron-withdrawing function of PO₄ ^3- (Pt₁ -OPO₄ ^3- pair active site) not only realize the activation of the C-H bond, but also destabilize the transition state from adsorbed hydroxy acids toward the C-C cleavage, resulting in the sharply increased selectivity of hydroxy acids. Moreover, the strong PO₄ ^3- -coordination effect provides electrostatic stabilization for single-atom Pt, ensuring the highly efficient catalysis of Pt₁ /HAP for over 160 hours with superior leaching resistance.

Comparative study on the hydrogenolysis performance of solid residues from different bamboo pretreatments

Both alkaline organosolv and formaldehyde stabilization pretreatment can yield high-quality lignin by preventing condensation. For the hydrogenolysis of the pretreated solid residues, the highest yield of C2-C4 chemicals was 66.8% under alkaline organosolv pretreatment for 60 min. Specifically, the crimped fibers and residual lignin and hemicellulose increased the surface roughness of the residue by 40.6%, the crystallinity index decreased to 44.4%, and the crystal size was reduced to 2.15 nm, which in turn promoted hydrogenolysis of the residue. However, the increase of crystallinity and crystal size and the decrease in surface roughness of the formaldehyde stabilization pretreatment residue greatly hindered the conversion of polysaccharides. In addition, residual formaldehyde on the residue may also inhibit catalyst activity. Overall, this study provides novel perspectives on the full utilization of biomass, as well as new insights into the conversion of polysaccharides.

Exploiting the Fracture in Metal-Organic Frameworks: A General Strategy for Bifunctional Atom-Precise Nanocluster/ZIF-8(300 °C) Composites

Atom-precise nanoclusters-metal-organic framework (APNC/MOF) composites, as bifunctional material with well-defined structures, have attracted considerable attention in recent years. Despite the progress made to date, there is an urgent need to develop a generic and scalable approach for all APNCs. Herein, the authors present the Exploiting Fracture Strategy (EFS) and successfully construct a super-stable bifunctional APNC/ZIF-8(300 °C) composite overcoming the limitations of previous strategies in selecting APNCs. The EFS utilizes the fracture of ZnN in ZIF-8 after annealing at 300 °C. This method is suitable for all kinds of S/P protected APNCs with different sizes, including uncharged clusters Au₁ Ag₃₉ , Ag₄₀ , negatively charged Au₁₂ Ag₃₂ , positively charged Ag₄₆ Au₂₄ , Au₄ Cu₄ and P-ligand-protected Pd₃ Cl. Importantly, the generated APNC/MOF show significantly improved performances, for example, the activities of Au₁₂ Ag₃₂ /ZIF-8(300°C), Au₄ Cu₄ /ZIF-8(300°C), and Au₁ Ag₃₉ /ZIF-8(300°C) in the corresponding reactions are higher than those of Au₁₂ Ag₃₂ , Au₄ Cu₄ , and Au₁ Ag₃₉ , respectively. In particular, Au₁₂ Ag₃₂ /ZIF-8(300 °C) shows higher activity than Au₁₂ Ag₃₂ @ZIF-8. Therefore, this work offers guidance for the design of bifunctional APNC/MOF composites with excellent optimization of properties and opens up new horizons for future related nanomaterial studies and nanocatalyst designs.

Temperature-Controlled Selectivity of Hydrogenation and Hydrodeoxygenation of Biomass by Superhydrophilic Nitrogen/Oxygen Co-Doped Porous Carbon Nanosphere Supported Pd Nanoparticles

Selective hydrogenation and hydrodeoxygenation (HDO) of biomass to value-added products play a crucial role in the development of renewable energy resources. However, achieving a temperature-controlled selectivity within one catalytic system while retaining excellent hydrogenation and HDO performance remains a great challenge. Here, nitrogen/oxygen (N/O) co-doped porous carbon nanosphere derived from resin polymer spheres is synthesized as the host matrix to in situ encapsulate highly dispersed Pd nanoparticles (NPs). Through N/O co-doping, the defects on the surface of carbon structure can serve as active sites to promote substrate adsorption. After a facile H₂ O₂ post-treatment process, the presence of abundant carboxyl groups on the porous carbon nanospheres can act as acidic sites to replace the use of acidic additives in the HDO process. Additionally, the increased surface oxygen-containing groups improve hydrophilicity to disperse catalysts in aqueous solutions. Owing to the unique highly dispersed Pd NPs and abundant surface defects, the Pd@APF-H₂ O₂ (2.3 nm) catalysts exhibit excellent catalytic activity and temperature-controlled selectivity for hydrogenation and HDO products of biomass-derived vanillin.

Electrochemical Hydrogenation of Furfural in Aqueous Acetic Acid Media with Enhanced 2-Methylfuran Selectivity Using CuPd Bimetallic Catalysts

Herein, we report a series of CuPd catalysts for electrochemical hydrogenation (ECH) of furfural to 2-methylfuran (MF or FurCH₃ where Fur=furyl) in aqueous 0.1 M acetic acid (pH 2.9). The highest faradaic efficiency (FE) for MF reached 75 % at -0.58 V vs. reversible hydrogen electrode with an average partial current density of 4.5 mA cm^-2 . In situ surface-enhanced Raman spectroscopic and kinetic isotopic experiments suggested that electrogenerated adsorbed hydrogen (H_ads ) was involved in the reaction and incorporation of Pd enhanced the surface coverage of H_ads and optimized the adsorption pattern of furfural, leading to a higher FE for MF. Density functional theory calculations revealed that Pd incorporation reduced the energy barrier for the hydrogenation of FurCH₂ * to FurCH₃ *. Our study demonstrates that catalyst surface structure/composition plays a crucial role in determining the selectivity in ECH and provides a new strategy for designing advanced catalysts for ECH of bio-derived oxygenates.

Catalytic Activity Enhancement on Alcohol Dehydrogenation via Directing Reaction Pathways from Single- to Double-Atom Catalysis

To further improve the intrinsic reactivity of single-atom catalysts (SACs), the controllable modification of a single site by coordinating with a second neighboring metal atom, developing double-atom catalysts (DACs), affords new opportunities. Here we report a catalyst that features two bonded Fe-Co double atoms, which is well represented by an FeCoN₆(OH) ensemble with 100% metal dispersion, that work together to switch the reaction mechanism in alcohol dehydrogenation under oxidant-free conditions. Compared with Fe-SAC and Co-SAC, FeCo-DAC displays higher activity performance, yielding the desired products in up to 98% yields. Moreover, a broad diversity of benzyl alcohols and aliphatic alcohols convert into the corresponding dehydrogenated products with excellent yields and high selectivity. The kinetic reaction results show that lower activation energy is obtained by FeCo-DAC than that by Fe-SAC and Co-SAC. Moreover, computational studies demonstrate that the reaction path by DACs is different from that by SACs, providing a rationale for the observed enhancements.

Microwave-Assisted Conversion of Carbohydrates

Catalytic conversion of carbohydrates into value-added products and platform chemicals became a trend in recent years. Microwave activation used in the processes of carbohydrate conversion coupled with the proper choice of catalysts makes it possible to enhance dramatically the efficiency and sometimes the selectivity of catalysts. This mini-review presents a brief literature survey related to state-of-the-art methods developed recently by the world research community to solve the problem of rational conversion of carbohydrates, mostly produced from natural resources and wastes (forestry and agriculture wastes) including production of hydrogen, synthesis gas, furanics, and alcohols. The focus is made on microwave technologies used for processing carbohydrates. Of particular interest is the use of heterogeneous catalysts and hybrid materials in processing carbohydrates.

Magnetic solid sulfonic acid-enabled direct catalytic production of biomass-derived N-substituted pyrroles

Five-membered nitrogen heterocyclic pyrroles have extremely high physiological activity and are widely used in medicine, agriculture, material chemistry, industry, and supramolecular chemistry. Developing a mild and eco-friendly way to synthesize...

N-doped carbon nanotube encapsulated cobalt for efficient oxidative esterification of 5‑hydroxymethylfurfural

The cobalt nanoparticles embedded into graphitic nitrogen-rich carbon nanotube (Co/GCN) was prepared with a facile method and employed as an efficient catalyst for oxidative esterification of 5-hydroxymethylfurfural (HMF). The introduction...

A sustainable pseudo-homogeneous catalyst from renewable biomass: design, development and catalytic applications

Pseudo-homogeneity, sustainability and functional growth in a sustainable raw material derived catalyst.