Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

Synergistic effect of RuNi alloy supported by carbon nanohorns for boosted hydrogen evolution from ammonia borane hydrolysis

The present study addresses the critical challenges associated with hydrogen production from ammonia borane (AB) hydrolysis, focusing on the development of cost-effective, high efficient, and stable catalysts. A promising strategy to achieve superior catalytic performance in AB hydrolysis involves alloying noble and non-precious metals. Herein, RuNi bimetallic nanoparticles were successfully deposited onto carbon nanohorns (CNHs) through a facial hydrothermal-reduction processes. The optimized Ru0.6Ni0.4-CNHs catalyst demonstrates a remarkably high turnover frequency (TOF) of 144  [Formula: see text]  molRu-1 min-1, approximately twice that of Ru-CNHs. The synergistic effect between CNHs and the RuNi alloy enhances the anchoring and dispersion of metal particles, leading to reduced particle size and a narrow distribution, along with exceptional stability. Experimental results reveal that the incorporation of the RuNi alloy enables precise regulation of the electron distribution in Ru. Furthermore, density functional theory (DFT) calculations demonstrate that the RuNi alloy significantly reduces the activation and dissociation energies of AB and H2O on the Ru site of Ru0.6Ni0.4 compared to those on a monometallic Ru site. This work provides valuable insights for designing efficient and economical bimetallic nanocatalysts for AB hydrolysis.

Ultrasound-assisted green synthesis of functionalised xanthene derivatives: Advancing sustainable sonochemical strategies

Xanthenes are an important class of heterocycles in medicinal chemistry due to their diverse pharmacological properties. These tricyclic aromatic compounds, characterised by a dibenzo[b,e]pyran core with an oxygen atom at their central position, have gained significant attention for their extensive applications. Beyond pharmaceuticals, xanthenes are widely used in textiles, food industries, electro-optical devices, dyes, and bioimaging agents. Xanthene derivatives, particularly 9-substituted xanthenes, exhibit a wide range of biological activities, including antiparasitic, antibacterial, antileishmanial, cytotoxic, neuroprotective, and photophysical effects, making them valuable in drug discovery. The xanthene scaffold is present in various bioactive natural compounds such as mulgravanols A and B, hermannol, (+)-myrtucommulone D, homapanicones A and B, blumeaxanthene II, and acrotrione. Clinically relevant xanthene-based drugs include propantheline bromide (antimuscarinic), methantheline (antispasmodic), and phloxine B (photosensitiser in antimicrobial therapy). Thus, various synthetic approaches have been developed for the construction of xanthenes, with ultrasound-assisted green methodologies gaining prominence. Ultrasound technique offers advantages over conventional methods, including higher yields, faster reaction rates, and improved selectivity under milder conditions. This review comprehensively explores the ultrasound-assisted synthesis of functionalised xanthene derivatives as an eco-friendly alternative. To the best of our knowledge, this is the first in-depth review focusing on the green methodology under ultrasound irradiation.

Direct Synthesis of Polyesterether from Ethylene Glycol

We report here a method for making polyesterether from ethylene glycol. The reaction is catalyzed by a ruthenium complex and liberates H2 gas and H2O as byproducts. Mechanistic studies conducted through experiments and DFT computations suggest that the chain growth of the polymerization process involves both dehydrogenation and dehydration pathways stemming from a hemiacetal intermediate, leading to the formation of esters and ethers, respectively. Investigations into the polymerization of other diols have also been conducted, showing that diols with a lower number of carbons between the alcohol groups (propylene glycol, glycerol, and 1,3-propanediol) lead to the formation of polyesterether whereas α,ω-diols containing a higher number of carbons (1,6-hexanediol and 1,10-decanediol) lead to the formation of polyester.

Dihydrolevoglucosenone (CyreneTM) as a Bio-derived Liquid Organic Hydrogen Carrier

Organic hydrides can store hydrogen via chemical bonding under ambient conditions, enabling the safe storage and transportation of hydrogen gas using the same infrastructure for gasoline. However, in previous research, most organic hydrides have been produced from petroleum, and therefore replacing them with earth-abundant or renewable compounds is essential to ensure sustainability. This study demonstrates dihydrolevoglucosenone (CyreneTM), which is a biodegradable liquid ketone produced from cellulose (a typical biomass) on an industrial scale, as a new renewable organic hydride. CyreneTM (hydrogen acceptor) is hydrogenated under ambient hydrogen pressure with a highly durable metal complex catalyst to produce 1,6-anhydro-3,4-dideoxy-β-D-threo-hexopyranose (Cyrene-OH, hydrogen adduct). Cyrene-OH stores hydrogen via chemical bonding under ambient conditions, and is dehydrogenated by heating in the presence of the same catalyst to release hydrogen gas and reproduce CyreneTM. This study reports the first attempt to apply compounds, which can be produced directly from biomass on an industrial scale, to organic hydrides, and promotes the development of earth-abundant biomass for sustainable hydrogen storage.

Study of the Photoinduced Charge Injection in the Reaction Intermediate of the Dehydrogenation of Formic Acid on Palladium

The production rate of hydrogen from formic acid on palladium is enhanced in the presence of an Au nanorod by irradiating the system at its plasmon frequency. Taking inspiration from this, we study here the effect of the shape of the Pd cluster (from Pd(111)) on the photoinduced charge injection into the HCOO moiety and adsorbed H, which are the reaction intermediates of the dehydrogenation of formic acid, upon irradiation with a pulse with a carrier frequency equal to the plasmon resonance of a (not included) Au nanorod. We simulate the electron/hole dynamics at frozen nuclei by propagating the time-dependent Schrödinger equation in the space of time-dependent density-functional-theory pseudo-eigenstates in the tight-binding approximation. We have taken into account a cluster with two layers of Pd and3 × 3 $$ 3\times 3 $$ and4 × 4 $$ 4\times 4 $$ atoms per layer (2L3 and 2L4, respectively) or with three layers and3 × 3 $$ 3\times 3 $$ atoms per layer (3L3). For all the systems, a net negative charge on HCOO has been found, according to a photoinduced direct charge-transfer mechanism. For 3L3, an indirect charge-transfer mechanism, occurring after 50 fs and inducing a hole injection into HCOO, has also been found. Moreover, we also used a tailored pulse to populate the antibonding molecular orbital localized on the C-H bond for 3L3.

Outer-Sphere CO Release Mechanism in the Methanol-to-Syngas Reaction Catalyzed by a Ru-PNP Pincer Complex

Methanol can be used as a surrogate molecule for CO and H2 in the synthesis of a large variety of chemicals. In this work, the mechanism for the methanol-to-syngas reaction catalyzed by a Ru-PNP complex was studied using density functional theory. In the proposed mechanism, the CO is directly released from the methyl formate intermediate, forming a Ru-OCH3 species. The preference for this pathway compared to others proposed in literature was supported by a microkinetic model constructed from the computed Gibbs free energies and coupled to a liquid-vapor batch reactor describing the gas phase composition. After including energy corrections of ≤6 kcal mol-1 to three organic intermediates and CO, our model could reproduce the experimental CO and H2 turnover numbers over the time previously reported. Further, this model was used to evaluate the influence of solvent polarity and methanol concentration on the formation of products and catalyst resting states. These results suggest that in methanol, CO formation is limited by the organic reaction thermodynamics, whereas in toluene, it is limited by Ru-CO formation. Overall, this work shows the potential of microkinetic models to benchmark reaction mechanisms and computational methods and provide the relevant information required for catalyst design.

Development of Triphenylamine Derived Photosensitizers for Efficient Hydrogen Evolution from Water

A series of new (donor)₂-donor-π-acceptor (D2-D-π-A) and (acceptor)₂-donor-π-acceptor (A2-D-π-A) organic photosensitizers based on the framework of (Z)-2-cyano-3-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)acrylic acid have been synthesized and characterized. By incorporating groups with different electron-donating or withdrawing abilities, such as dibenzothiophene (DBT), dibenzofuran (DBF), and triazine (TA), into the triphenylamine segment, their photophysical properties have been regulated. Theoretical calculations were used to explore how various donor-acceptor combinations influence their hydrogen production performance. Notably, DBF-CN achieved the highest turnover number (TON) of 10,202 and an initial turnover frequency (TOFi) of 151.6 h-1 under green light irradiation, with an initial activity (Activityi) of 113,532 μmol g-1 h-1 and an apparent quantum yield (AQYi) of 0.76 %. This dye-sensitized-TiO2-Pt system is recognized as one of the most efficient and durable systems for photocatalytic hydrogen production under green light irradiation, as described in the literature, when compared using TOF and TON values. Experimental results indicate that the D2-D-π-A system significantly enhances photocatalytic hydrogen evolution (PHE) performance more effectively than the A2-D-π-A system, while also maintaining stability under prolonged light exposure.

Ion-induced Effect of Ce, Ni Dual Site Doped LaCoO3 Catalyst for Efficient Electrocatalytic Water Oxidation

Perovskite oxides exhibit excellent performance in water oxidation, but still lacks a precise regulation strategy for the active sites, while the reaction mechanism is poorly understood. Herein, an ion-induced effect (IIE) is proposed of Ce, Ni dual site doped LaCoO3(CeNi-LaCoO3), where Ni2+ induces the binding of Co species into bimetallic sites, and Ce4+ induces the activation of Co species and reduces the Co-O binding energy. Benefiting from the IIE of Ni2+ and Ce4+, the optimized Ce0.15La0.85Ni0.3Co0.7O3 exhibits excellent OER performance with an overpotential of only 330 mV when the current density reached 10 mA cm-2, the Tafel slope of 70.93 mV dec-1 as well as good stability. Theoretical calculations further reveal that the OER occurring on CeNi-LaCoO3 follows the LOM mechanism, and IIE caused by the doping of the Ce, Ni dual site induces the conversion of Co2+ to Co3+, optimizes the electron arrangement, modulates the electron transfer capacity of the Co site, promotes the conversion of lattice oxygen to OH-, lowers the energy barrier for the participation of bulk oxygen in the OER, and thus promotes the OER performance. This work is expected to provide reliable support for the application of high-efficiency perovskite-based OER catalysts.

Temperature-Dependent Stepwise Dissociation of Methanol on Co(0001)

An atomic-level understanding of the elementary steps of catalytic reactions is crucial for a more molecularly driven catalyst design. Herein, we present a comprehensive study of temperature-dependent stepwise decomposition of methanol on a single-crystal Co(0001) surface using a series of surface science techniques and density functional theory calculation. Visualization of surface products was realized by scanning tunneling microscopy. The first step of methanol dissociation is cleavage of the OH bond to the methoxy group and H atom, showing clover-like and honeycomb structures, respectively. Further dissociation to CO through C-H cleavage was ascertained by infrared reflection absorption spectroscopy, and no intermediates, such as CH2O or CHO, were observed. The final product CO molecules showed versatile configurations with different periodicities on the surface under heating or tip-manipulation conditions.

Palladium Membrane Applications in Hydrogen Energy and Hydrogen-Related Processes

In recent years, increased attention has been paid to environmental issues and, in connection with this, to the development of hydrogen energy. In turn, this requires the large-scale production of ultra pure hydrogen. Currently, most hydrogen is obtained by converting natural gas and coal. In this regard, the issue of the deep purification of hydrogen for use in fuel cells is very relevant. The deep purification of hydrogen is also necessary for some other areas, including microelectronics. Only palladium membranes can provide the required degree of purification. In addition, the use of membrane catalysis is very relevant for the widely demanded processes of hydrogenation and dehydrogenation, for which reactors with palladium membranes are used. This process is also successfully used for the single-stage production of high-purity hydrogen. Polymeric palladium-containing membranes are also used to purify hydrogen and to remove various pollutants from water, including organochlorine products, nitrates, and a number of other substances.

Rising Opportunities in Catalytic Dehydrogenative Polymerization

This article gives a perspective on various types of catalytic dehydrogenative polymerization reactions (including organic and main group polymers) while introducing "hydrogen-borrowing polymerization" and "acceptorless dehydrogenative polymerization" to this class. Limitations and future opportunities of each method have been discussed.

Selective PNP Pincer-Ir-Promoted Acceptorless Transformation of Glycerol to Lactic Acid and Hydrogen

The catalytic transformation of glycerol (GLY) using [(iPr2PNHP)Ir(COD)]Cl [iPr2PNHP = κ3-(iPr2PCH2CH2)2NH] affords hydrogen and lactic acid (LA), trapped as its sodium salt (Na[LA]) with high yield (96%) and selectivity (99%) in the presence of an equivalent of in situ generated NaOEt at 140 °C within 4 h. A diminution in activity was observed when the PNMeP ligand was used instead of PNHP, or when Cl- was replaced by [BArF4]-. An Ir to Rh substitution also resulted in poor activity. Kinetic studies show a first-order dependence of the initial rate of turnovers on the concentrations of [(iPr2PNHP)Ir(COD)]Cl, NaOEt, and glycerol. An outer-sphere mechanism does not explain the activity of [(iPr2PNMeP)Ir(COD)]Cl, and DFT studies support an inner-sphere mechanism, with oxidative addition of glycerol to the 14-electron intermediate [(iPr2PNHP)Ir]Cl determined as the rate-determining step (RDS). A kH/kD of 2.7 obtained with glycerol-d8 shows a major contribution from O-H activation in the RDS. The kinetics of the reaction become favorable (ΔG140⧧ = 27.01 kcal/mol) when one of the terminal O-H's of glycerol is hydrogen bonded to the N-H of the pincer backbone, in contrast to cases where no hydrogen bonds are invoked (ΔG140⧧ = 31.96 kcal/mol) or are not possible [(iPr2PNMeP)Ir]Cl (ΔG140⧧ = 30.36 kcal/mol).

MOF-Based Dual-Layer Pickering Emulsion: Molecular-Level Gating of Water Delivery at Water-Oil Interface for Efficient Photocatalytic Hydrogenation Using H2O as a Hydrogen Source

Biphasic system not only presents a promising opportunity for complex catalytic processes, but also is a grand challenge in efficient tandem reactions. As an emerging solar-to-chemical conversion, the visible-light-driven and water-donating hydrogenation combines the sustainability of photocatalysis and economic-value of hydrogenation. However, the key and challenging point is to couple water-soluble photocatalytic hydrogen evolution reaction (HER) with oil-soluble hydrogenation. Herein, we employed metal-organic frameworks (MOFs) and CdS nanorods to construct a MOF-CdS dual-layer Pickering emulsion (water in oil, W/O), which compartmented aqueous phase for photocatalytic HER and oil phase for hydrogenation. The hydrophobic MOF and hydrophilic CdS were isolated at the inner and outer layers of W/O emulsion, respectively. The molecularly regulated hydrophobicity of MOF controlled the water delivery onto CdS photocatalysts, which realized the synergistic regulation of HER and hydrogenation. In the photocatalytic hydrogenation of cinnamaldehyde, the highest yield of MOF-CdS Pickering emulsion reached 187.37 mmol ⋅ g-1 ⋅ h-1, 30 times that of the counterpart without emulsion (6.44 mmol ⋅ g-1 ⋅ h-1). Its apparent quantum yield reached 43.24 % without co-catalysts. To our knowledge, this performance is at a top-level so far. Our work realized the precise regulation of water-oil interface to effectively couple two reactions in different phases, providing new perspective for challenging tandem catalysis.

Salen-Pd(II)-Modified Stereoregular Polyisocyanides for Efficient Cooperative Catalysis of Suzuki Coupling Reaction

The development of high activity catalysts is crucial for improving industrial efficiency and mitigating environmental pollution. Polyisocyanides, with their pendant groups capable of forming ordered adjacent structures, offer a promising framework for designing cooperative catalysts that mimic the functionality of bimetallic centers. This unique structural arrangement is anticipated to significantly enhance catalytic activity in cooperative reactions. A novel approach to enhance the Suzuki coupling reaction using polymer-supported catalysts is presented. In this study, stereoregular polyisocyanides with Salen-Pd are functionalized to produce the Pd(II) metalized polyisocyanide (P1-Pd). The rigid backbone of the polymer facilitates the parallel alignment of Salen-Pd pendants, enabling double activation of the two substrates at an average distance of ≈1.2 nm. Catalytic efficiency is evaluated through Suzuki coupling reactions using various aryl halides. P1-Pd demonstrates high activity, yielding the desired products with excellent conversion rates. Conversely, the irregular polymer counterpart P2-Pd. P3-Pd and the small molecule control C1-Pd exhibit lower performance due to the absence of cooperative catalysis. To showcase the applicability of this strategy, Suzuki coupling is successfully conducted with outstanding yields for key drug intermediates, while also offering innovative insights for conjugated polymer synthesis.

Research progress in the preparation of sodium-ion battery anode materials using ball milling

Sodium-ion batteries are regarded as one of the most promising alternatives to lithium-ion batteries due to the greater abundance and lower cost of sodium compared to lithium. However, sodium-ion batteries have not yet been widely adopted. The main reason is that, compared to lithium-ion batteries, sodium-ion batteries have lower energy density and shorter cycle life, with the performance of anode materials directly affecting the energy density and cycle stability of sodium-ion batteries. Notably, ball milling, as an efficient material processing technique, has been widely applied in the preparation and modification of sodium-ion battery anode materials in recent years. This paper reviews the recent progress in the preparation of sodium-ion battery anode materials using ball milling. The process is categorized into ball milling mixing, ball milling exfoliation, ball milling synthesis, and ball milling doping. First, the basic principles and mechanisms of ball milling technology are introduced. Then, the preparation of different types of sodium-ion battery anode materials is discussed based on four specific categories. For various material systems, the effects of ball milling on the structure, morphology, and electrochemical performance are discussed. Additionally, the advantages and challenges of using ball milling in the preparation of sodium-ion battery anode materials are summarized. Finally, the future directions and development trends in the preparation of sodium-ion battery anode materials using ball milling are forecasted, aiming to provide insights and references for further research in this field.

State-of-the-art advances in homogeneous molecular catalysis for the Guerbet upgrading of bio-ethanol to fuel-grade bio-butanol

The upgrading of ethanol to n-butanol marks a major breakthrough in the field of biofuel technology, offering the advantages of compatibility with existing infrastructure while simultaneously offering potential benefits in terms of transport efficiency and energy density. With its lower vapour pressure and reduced corrosiveness compared to ethanol, n-butanol is easier not only to manage but also to transport, eliminating the need for costly infrastructure changes. This leads to improved fuel efficiency and reduced fuel consumption. These features position n-butanol as a promising alternative to ethanol in the future of biodiesel. This review article delves into the cutting-edge advancements in upgrading ethanol to butanol, highlighting the critical importance of this transformation in enhancing the value and practical application of biofuels. While traditional methods for making butanol rely heavily on fossil fuels, those that employ ethanol as a starting material are dominated by heterogeneous catalysis, which is limited by the requirement of high temperatures and a lack of selectivity. Homogeneous catalysts have been pivotal in enhancing the efficiency and selectivity of this conversion, owing to their unique mode of operation at the molecular level. A comprehensive review of the various homogeneous catalytic processes employed in the transformation of feedstock-agnostic bio-ethanol to fuel-grade bio-n-butanol is provided here, with a major focus on the key advancements in catalyst design, reaction conditions and mechanisms that have significantly improved the efficiency and selectivity of these Guerbet reactions.

Advances in Catalysts for Hydrogen Production: A Comprehensive Review of Materials and Mechanisms

This review explores the recent advancements in catalyst technology for hydrogen production, emphasizing the role of catalysts in efficient and sustainable hydrogen generation. This involves a comprehensive analysis of various catalyst materials, including noble metals, transition metals, carbon-based nanomaterials, and metal-organic frameworks, along with their mechanisms and performance outcomes. Major findings reveal that while noble metal catalysts, such as platinum and iridium, exhibit exceptional activity, their high cost and scarcity necessitate the exploration of alternative materials. Transition metal catalysts and single-atom catalysts have emerged as promising substitutes, demonstrating their potential for enhancing catalytic efficiency and stability. These findings underscore the importance of interdisciplinary approaches to catalyst design, which can lead to scalable and economically viable hydrogen production systems. The review concludes that ongoing research should focus on addressing challenges related to catalyst stability, scalability, and the integration of renewable energy sources, paving the way for a sustainable hydrogen economy. By fostering innovation in catalyst development, this work aims to contribute to the transition towards cleaner energy solutions and a more resilient energy future.

Efficient Nitrate to Ammonia Conversion on Bifunctional IrCu4 Alloy Nanoparticles

Electrochemical nitrate reduction (NO3RR) to ammonia presents a promising alternative strategy to the traditional Haber-Bosch process. However, the competitive hydrogen evolution reaction (HER) reduces the Faradaic efficiency toward ammonia, while the oxygen evolution reaction (OER) increases the energy consumption. This study designs IrCu4 alloy nanoparticles as a bifunctional catalyst to achieve efficient NO3RR and OER while suppressing the unwanted HER. This is achieved by operating the NO3RR at positive potentials using the IrCu4 catalyst, which allows a Faradaic efficiency of 93.6% for NO3RR. When applied to OER catalysis, the IrCu4 alloy also shows excellent results, with a relatively low overpotential of 260 mV at 10 mA cm-2. Stable ammonia production can be achieved for 50 h in a 16 cm2 flow electrolyzer in simulated working conditions. Our research provides a pathway for optimizing NO3RR through bifunctional catalysts in a tandem approach.

Transition Metal as Template: Reversing the Synthesis Logic in the Preparation of Pincer Complexes

The conventional synthetic approach to transition metal pincer complexes calls for the preparation of the tridentate pincer (pro)ligand first, with subsequent introduction of the transition metal center as the last step. This work demonstrates that the alternative synthetic logic, where the central main group element is introduced last, can be applicable to a number of PEP pincer complexes (E=B, Al, Si, P) derived from phosphinophenols and phosphinopyrroles. This approach obviates the need to isolate well-behaved propincer precursors, and instead relies on the formation of phosphine-metal adducts first, whose nature determines the stoichiometry of the needed main group reagent to complete the synthesis.

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

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

Manganese(I)-Catalyzed Enantioselective Alkylation To Access P-Stereogenic Phosphines

This work introduces a novel Mn(I)-catalyzed enantioselective alkylation methodology that efficiently produces a wide array of P-chiral phosphines with outstanding yields and enantioselectivities. Notably, the exceptional reactivity of Mn(I) complexes in these reactions is demonstrated by their effective catalysis with both typically reactive alkyl iodides and bromides, as well as with less reactive alkyl chlorides. This approach broadens the accessibility to various P-chiral phosphines and simplifies the synthesis of chiral tridentate pincer phosphines to a concise 1-2 step process, contrary to conventional, labor-intensive multistep procedures. Importantly, the development significantly expands the applicability of earth-abundant Mn(I)-based complexes beyond their recently established roles in catalytic hydrogenative and conjugate addition reactions, emphasizing the catalytic potential of Mn(I) complexes as a viable alternative to noble metal chemistry and, in some cases, even surpassing their performance.

Direct Photocatalytic Oxidation of Methane to Formic Acid with High Selectivity via a Concerted Proton-Electron Transfer Process

Light-driven direct conversion of methane to formic acid is a promising approach to convert methane to value-added chemicals and promote sustainability. However, this process remains challenging due to the complex requirements for multiple protons and electrons. Herein, we report the design of WO3-based photocatalysts modified with Pt active sites to address this challenge. We demonstrate that modulating the dimensional effect of Pt on the WO3 support is key to enhancing the catalytic performance of selective CH4-to-HCOOH conversion. The Pt nanoparticles on WO3 exhibit superior conversion rate, selectivity and durability in the production of HCOOH compared to the Pt-free sample and WO3 decorated with Pt single atoms. The optimal PtNPs-WO3 catalyst achieves a HCOOH conversion rate of 17.7 mmol g-1, with 84% selectivity and stability maintained for up to 48 h. Mechanistic studies show that the protonation of O2 to hydroxyl radicals is the limiting step for HCOOH yield. Pt nanoparticles can facilitate electron transfer and promote O2 dissociation, generating hydroxyl radicals via a proton-coupled electron transfer process. This process provides sufficient protons to lower the formation barrier for •OH radicals, thereby promoting the activation of CH4. In addition, Pt nanoparticles regulate the adsorption of oxygenated hydrocarbon intermediates, increasing the selectivity of the reaction. This work advances our understanding of catalyst design for methane conversion and the effective regulation of complex reaction pathways.

Sulfate salt assistant fabrication of Fe-doped Ni2P modified with SO42-/carbon as highly efficient oxygen evolution reaction electrocatalyst

The incorporation of oxyanion groups offers a greater potential for enhancing the activity of oxygen evolution reaction (OER) electrocatalysts compared to traditional metal cations doping, owing to their unique configurations and high electronegativity. However, the incorporation of oxyanion groups that differ from those derived from the oxidation of anions in transition metal monoxides poses significant challenges, thereby limiting further applications of oxyanion group modification approach. Herein, we present a novel sulfate salt assistant approach to fabricate Fe-doped Ni2P modified with SO42-/carbon (Fe-Ni2P-S/C) nanofibers as highly efficient OER electrocatalyst. The optimized Fe-Ni2P-S/C nanofibers display superb OER activity, requiring low overpotentials of 266, 323, and 357 mV at 100, 500, and 1000 mA cm-2, respectively. Theoretical calculations reveal that the co-adsorption of PO43- and SO42- on the surface of reconstructed electrocatalyst can reduce the energy barrier of rate-determining step, thereby resulting in enhanced OER activity. The present study emphasizes the crucial role played by anion groups in OER activity as well as proposes a novel approach for incorporating anion groups into electrocatalysts.

Metal-Ligand Cooperation in Dihydrogen Activation by a Cationic Metallogermylene: Enhanced Activity from Tungsten to Molybdenum

Dihydrogen activation by metallogermylenes was investigated experimentally and theoretically. A neutral NHC-coordinated chlorometallogermylene was synthesized and converted to a cationic base-free metallogermylene of molybdenum via chloride abstraction. The cationic molybdogermylene showed enhanced reactivity toward H2 compared to the tungsten analog. The reaction mechanism was investigated by theoretical calculations, which revealed a novel route that proceeds via a new type of metal-ligand cooperative activation between the metal and divalent germanium moiety. The activation energy of this route is much lower than that of the alternative route via an "oxidative addition" type of reaction on the single Ge(II) center, which is generally proposed for organotetrylenes. The features of the frontier orbitals and the origin of the metal effect on the H2 activation are also described.

Transition Metal-Gallium Intermetallic Compounds with Tailored Active Site Configurations for Electrochemical Ammonia Synthesis

Gallium (Ga) with a low melting point can serve as a unique metallic solvent in the synthesis of intermetallic compounds (IMCs). The negative formation enthalpy of transition metal-Ga IMCs endows them with high catalytic stability. Meanwhile, their tunable crystal structures offer the possibility to tailor the configurations of active sites to meet the requirements for specific catalytic applications. Herein, we present a general method for preparing a range of transition metal-Ga IMCs, including Co-Ga, Ni-Ga, Pt-Ga, Pd-Ga, and Rh-Ga IMCs. The structurally ordered CoGa IMCs with body-centered cubic (bcc) structure are uniformly dispersed on the nitrogen-doped reduced graphene oxide substrate (O-CoGa/NG) and deliver outstanding nitrate reduction reaction (NO3RR) performance, making them excellent catalysts to construct highly efficient rechargeable Zn-NO3 - battery. Operando studies and theoretical simulations demonstrate that the electron-rich environments around the Co atoms enhance the adsorption strength of *NO3 intermediate and simultaneously suppress the formation of hydrogen, thus improving the NO3RR activity and selectivity.

Cobalt Phosphide-Supported Single-Atom Pt Catalysts for Efficient and Stable Hydrogen Generation from Ammonia Borane Hydrolysis

Ammonia borane (AB) has emerged as a promising chemical hydrogen storage material. The development of efficient, stable, and cost-effective catalysts for AB hydrolysis is the key to achieving hydrogen energy economy. Here, cobalt phosphide (CoP) is used to anchor single-atom Pt species, acting as robust catalysts for hydrogen generation from AB hydrolysis. Thanks to the high Pt utilization and the synergy between CoP and Pt species, the optimized Pt/CoP-100 catalyst exhibits an unprecedented hydrogen generation rate, giving a record turnover frequency (TOF) value of 39911mo l H 2 mo l Pt - 1 mi n - 1 ${\mathrm{mo}}{{{\mathrm{l}}}_{{{{\mathrm{H}}}_{\mathrm{2}}}}}{\mathrm{\ mo}}{{{\mathrm{l}}}_{{\mathrm{Pt}}}}^{{\mathrm{ - 1}}}{\mathrm{\ mi}}{{{\mathrm{n}}}^{{\mathrm{ - 1}}}}$ and turnover number of 2926829mo l H 2 mo l Pt - 1 ${\mathrm{mo}}{{{\mathrm{l}}}_{{{{\mathrm{H}}}_{\mathrm{2}}}}}{\mathrm{\ mo}}{{{\mathrm{l}}}_{{\mathrm{Pt}}}}^{{\mathrm{ - 1}}}$ at room temperature. These metrics surpass those of all existing state-of-the-art supported metal catalysts by an order of magnitude. Density functional theory calculations reveal that the integration of single-atom Pt onto the CoP substrate significantly enhances adsorption and dissociation processes for both water and AB molecules, thereby facilitating hydrogen production from AB hydrolysis. Interestingly, the TOF value is further elevated to 54878mo l H 2 mo l Pt - 1 mi n - 1 ${\mathrm{mo}}{{{\mathrm{l}}}_{{{{\mathrm{H}}}_{\mathrm{2}}}}}{\mathrm{\ mo}}{{{\mathrm{l}}}_{{\mathrm{Pt}}}}^{{\mathrm{ - 1}}}{\mathrm{\ mi}}{{{\mathrm{n}}}^{{\mathrm{ - 1}}}}$ under UV-vis light irradiation, which can be attributed to the efficient separation and mobility of photogenerated carriers at the Pt-CoP interface. The findings underscore the effectiveness of CoP as a support for single-atom metals in hydrogen production, offering insights for designing high-performance catalysts for chemical hydrogen storage.

A catalytic approach for the dehydrogenative upgradation of crude glycerol to lactate and hydrogen generation

The ambiguous nature of non-innocent ligand catalysts provides an excellent strategy for developing an efficient catalyst system featuring extended applicability in sustainable catalysis. In this study, we unveil the catalytic activity of an NNN-Ru catalyst for lactic acid synthesis from a mixture of glycerol, ethylene glycol, and methanol. The developed strategy was also implemented to synthesize lactate (up to 80% yield) with good selectivity via the dehydrogenative upgradation of a crude glycerol and ethylene glycol mixture. As an extended utility, the method was utilized for lactate synthesis from triglyceride directly with hydrogen gas generation.

Well-defined cobalt(II)-catalyzed synthesis of perimidine derivatives via acceptorless dehydrogenative annulation

The versatility of the perimidine moiety offers a rich playground for researchers in fields ranging from medical science to industrial chemistry. Herein, we describe the first Co-catalyzed synthesis of 2,3-dihydro-1H-perimidine via acceptorless dehydrogenative annulation (ADA). Apart from featuring benzyl alcohol having different functionalities, heteroaryl and aliphatic alcohols also provide good yields. Our catalytic protocol is also suitable for different fatty alcohols for furnishing perimidine derivatives, keeping distal unsaturation intact. Several kinetic and control tests were carried out in order to understand the reaction sequence.

Thermal and Sono-Aqueous Reforming of Alcohols for Sustainable Hydrogen Production

Hydrogen is a clean-burning fuel with water as its only by-product, yet its widespread adoption is hampered by logistical challenges. Liquid organic hydrogen carriers, such as alcohols from sustainable sources, can be converted to hydrogen through aqueous-phase reforming (APR), a promising technology that bypasses the energy-intensive vaporization of feedstocks. However, the hydrothermal conditions of APR pose significant challenges to catalyst stability, which is crucial for its industrial deployment. This review focuses on the stability of catalysts in APR, particularly in sustaining hydrogen production over extended durations or multiple reaction cycles. Additionally, we explore the potential of ultrasound-assisted APR, where sonolysis enables hydrogen production without external heating. Although the technological readiness of ultrasound-assisted or -induced APR currently trails behind thermal APR, the development of catalysts optimized for ultrasound use may unlock new possibilities in the efficient hydrogen production from alcohols.

Exchange coupling states of cobalt complexes to control proton-coupled electron transfer

The electrochemical proton reactivity of transition metal complexes receives significant attentions. A thorough understanding of proton-coupled electron transfer (PCET) pathways is essential for elucidating the mechanism behind a proton reduction reaction, and controlling the pathway is a key focus in the field of the catalyst development. Spin interactions within complexes, which arise during electron transfer, can affect significantly the PCET pathway. Herein, we explore the phenomenon of spin rearrangement during the electrochemical reorganization of high-spin cobalt complexes. Our findings reveal that opposing spin interactions, induced by different coordination environments, can alter the PCET pathway. Finally, detailed analysis of the PCET pathway allows us to propose mechanisms for proton reduction in high-spin cobalt complexes.

Recent developments of artificial intelligence in MXene-based devices: from synthesis to applications

Two-dimensional transition metal carbides, nitrides, or carbonitrides (MXenes) have garnered remarkable attention in various energy and environmental applications due to their high electrical conductivity, good thermal properties, large surface area, high mechanical strength, rapid charge transport mechanism, and tunable surface properties. Recently, artificial intelligence has been considered an emerging technology, and has been widely used in materials science, engineering, and biomedical applications due to its high efficiency and precision. In this review, we focus on the role of artificial intelligence-based technology in MXene-based devices and discuss the latest research directions of artificial intelligence in MXene-based devices, especially the use of artificial intelligence-based modeling tools for energy storage devices, sensors, and memristors. In addition, emphasis is given to recent progress made in synthesis methods for various MXenes and their advantages and disadvantages. Finally, the review ends with several recommendations and suggestions regarding the role of artificial intelligence in fabricating MXene-based devices. We anticipate that this review will provide guidelines on future research directions suitable for practical applications.

Toward Methanol Production by CO2 Hydrogenation beyond Formic Acid Formation

ConspectusThe Paradigm shift in considering CO2 as an alternative carbon feedstock as opposed to a waste product has recently prompted intense research activities. The implementation of CO2 utilization may be achieved by designing highly efficient catalysts, exploring processes that minimize energy consumption and simplifying product purification and separation. Among possible target products derived from CO2, methanol is highly valuable because it can be used in various chemical feedstocks and as a fuel. Although it is currently produced on a plant scale by heterogeneous catalysis using a Cu/ZnO-based catalyst, a limited theoretical conversion ratio at high reaction temperatures remains an issue. In addition, a catalytic system that can be adjusted to accommodate a variable renewable energy source for the synthesis of methanol is more desirable than current continuous-operation systems, which require a reliable energy supply. Recently, significant progress has been made in the field of homogeneous catalysis, which primarily relies on an indirect route to synthesize methanol via the hydrogenation of carbonate or formate derivatives in the presence of additives and solvents. However, homogeneous catalysis is inappropriate for industrial-scale methanol production because of the inefficient separation and purification processes involved.In this Account, we demonstrate a novel approach for methanol production under mild reaction conditions by CO2 hydrogenation catalyzed by multinuclear iridium complexes under heterogeneous gas-solid phase conditions without any additives and solvents. One of the aims of this Account provides insights for overcoming the barriers for efficient CO2 hydrogenation by focusing on catalyst design, specifically by incorporating varying functionalities into the ligand. The fundamental strategy entails activating hydrogen molecule and enhancing the hydricity of the resulting metal-hydride species, which is based on the following two concepts of catalyst design: (i) Activating a metal-hydride by electronic effects; and (ii) accelerating H2 heterolysis. We have elucidated the mechanism for accelerating H2 heterolysis using a state-of-the-art catalyst that contains an actor-ligand that responds to or participates in catalysis as opposed to a classical spectator-ligand.We have also demonstrated a novel heterogeneous catalysis using a molecular catalyst as a key step for the hydrogenation of CO2 to methanol beyond formic acid formation. The dehydrogenation of formic acid as a reverse reaction of formic acid hydrogenation is strongly favored in acidic aqueous solution. To circumvent the equilibrium limitation, we have envisioned an alternative route that both prevents the liberation of formic acid into the reaction medium, and develops a multinuclear complex to facilitate the transfer of multiple reactive hydrides. The unconventional gas-solid phase catalysis is capable of preventing the liberation of formate species and promoting further hydrogenation of formic acid through multihydride transfer.This novel catalytic system, which is the fusion of a molecular catalyst in heterogeneous catalysis, provides high performance for methanol synthesis through a sophisticated catalyst design and straightforward separation processes. A detailed mechanistic analysis of molecular catalysts in the gas phase would lead to significant progress in the field of Surface Organometallic Chemistry (SOMC).

A phosphine-free molecularly-defined Ni(II) complex in catalytic hydrogenation of CO2

The development of base metal catalysts capable of CO2 hydrogenation is a challenge and a necessity to progress from the scarce noble metal catalysts. In this regard, we report herein the first non-phosphine-based Ni complex, supported by a "carbazolato-bis-NHC" pincer ligand framework, for efficient catalytic hydrogenation of CO2 to formate. A tailored combination of the Ni complex as a catalyst, DBU as a base, and Zn(OAc)2 as an additive offered enhanced activity leading to a TON up to 5476 and an excellent yield up to 92% for the formate product from a reaction on ∼27 mmol scale.

Recent Advances in Reversible Liquid Organic Hydrogen Carrier Systems: From Hydrogen Carriers to Catalysts

Liquid organic hydrogen carriers (LOHCs) have gained significant attention for large-scale hydrogen storage due to their remarkable gravimetric hydrogen storage capacity (HSC) and compatibility with existing oil and gas transportation networks for long-distance transport. However, the practical application of reversible LOHC systems has been constrained by the intrinsic thermodynamic properties of hydrogen carriers and the performances of associated catalysts in the (de)hydrogenation cycles. To overcome these challenges, thermodynamically favored carriers, high-performance catalysts, and catalytic procedures need to be developed. Here, significant advances in recent years have been summarized, primarily centered on regular LOHC systems catalyzed by homogeneous and heterogeneous catalysts, including dehydrogenative aromatization of cycloalkanes to arenes and N-heterocyclics to N-heteroarenes, as well as reverse hydrogenation processes. Furthermore, with the development of metal complexes for dehydrogenative coupling, a new family of reversible LOHC systems based on alcohols is described that can release H2 under relatively mild conditions. Finally, views on the next steps and challenges in the field of LOHC technology are provided, emphasizing new resources for low-cost hydrogen carriers, high-performance catalysts, catalytic technologies, and application scenarios.

Unlocking Predictive Capability and Enhancing Sensing Performances of Plasmonic Hydrogen Sensors via Phase Space Reconstruction and Convolutional Neural Networks

This study innovates plasmonic hydrogen sensors (PHSs) by applying phase space reconstruction (PSR) and convolutional neural networks (CNNs), overcoming previous predictive and sensing limitations. Utilizing a low-cost and efficient colloidal lithography technique, palladium nanocap arrays are created and their spectral signals are transformed into images using PSR and then trained using CNNs for predicting the hydrogen level. The model achieves accurate predictions with average accuracies of 0.95 for pure hydrogen and 0.97 for mixed gases. Performance improvements observed are a reduction in response time by up to 3.7 times (average 2.1 times) across pressures, SNR increased by up to 9.3 times (average 3.9 times) across pressures, and LOD decreased from 16 Pa to an extrapolated 3 Pa, a 5.3-fold improvement. A practical application of remote hydrogen sensing without electronics in hydrogen environments is actualized and achieves a 0.98 average test accuracy. This methodology reimagines PHS capabilities, facilitating advancements in hydrogen monitoring technologies and intelligent spectrum-based sensing.

Direct hydrogenation of natural oils to fatty alcohols enabled by an alcoholysis/hydrogenation relay strategy and two-phase solvent system

Direct hydrogenation of natural oils to fatty alcohols was achieved via a relay strategy involving alcoholysis of natural oils followed by hydrogenation of fatty acid esters. A two-phase system was used to avoid catalyst poisoning by glycerol. This protocol is suitable for plant oils, animal fats and waste cooking oil.

A Comprehensive Review of Solar Photocatalysis & Photothermal Catalysis for Hydrogen Production from Biomass: from Material Characteristics to Engineering Application

Biomass photoreforming is a promising way of producing sustainable hydrogen thanks to the abundant sources of biomass feedstocks. Solar energy provides the heat and driven force to initial biomass oxidation coupled with H2 evolution. Currently, biomass photoreforming is still far from plant-scale applications due to the lower solar energy utilization efficiencies, the low H2 yield, and the lack of appropriate photoreactors. The production of H2 from photoreforming of native biomass and platform molecules was summarized and discussed with particular attention to the prospects of scaling up the catalysis technology for mass hydrogen production. The types of photoreforming, including photocatalysis and photothermal catalysis, were discussed, consequently considering the different requirements for photoreactors. We also reviewed the photoreactors that support biomass photoreforming. Numerical simulation methods were implemented for the solid-liquid two-phase flow and inter-particle radiative transfer involved in the reaction process. Developing concentrated photothermal catalytic flowed reactors is beneficial to scale-up catalytic hydrogen production from biomass.

Thermodynamic Modulation of Dihydrogen Activation Through Rational Ligand Design in GeII-Ni0 Complexes

A family of chelating aryl-functionalized germylene ligands has been developed and employed in the synthesis of their corresponding 16-electron Ni0 complexes (PhiPDippGeAr·Ni·IPr; PhiPDipp = {[Ph2PCH2Si(iPr)2](Dipp)N}-; IPr = [{(H)CN(Dipp)}2C:]; Dipp = 2,6-iPr2C6H3). These complexes demonstrate the ability to cooperatively and reversibly activate dihydrogen at the germylene-nickel interface under mild conditions (1.5 atm H2, 298 K). We show that the thermodynamics of the dihydrogen activation process can be modulated by tuning the electronic nature of the germylene ligands, with an increase in the electron-withdrawing character displaying more exergonic ΔG298 values, as ascertained through NMR spectroscopic Van't Hoff analyses for all systems. This is also shown to correlate with experimental 31P NMR and UV/vis absorption data as well as with computationally derived parameters such as Ge-Ni bond order and Ni/Ge NPA charge, giving a thorough understanding of the modulating effect of ligand design on this reversible, cooperative bond activation reaction. Finally, the utility of this modulation was demonstrated in the catalytic dehydrocoupling of phenylsilane, whereby systems that disfavor dihydrogen activation are more efficient catalysts, aligning with H2-elimination being the rate-limiting step. A density functional theory analysis supports cooperative activation of the Si-H moiety in PhSiH3.

Deciphering the Concept of Solubility by Strategically Using the Counterion Effect in Charged Molecules

Solubility is an essential concept in chemistry that describes the ability of a substance to dissolve in a particular solvent. Despite its importance in many fields of science, understanding the basic principles of solubility is challenging for many undergraduate students. Notably, students often encounter difficulties in comprehending the role of counterions when dealing with charged molecules. Here, we bring the opportunity to assimilate the key concepts of solubility regarding the role of counterions by developing a straightforward, cheap, and visually appealing experiment that focuses on the strategic use of counterions to control solubility. A student questionnaire delivered encouraging results with most of students giving positive feedback in both interest and training their hands-on skills. Hence, our experiment offers a proficient understanding of the solubility concept, thus preparing undergraduate students for advanced courses in the various subject areas of chemistry.

Direct synthesis of partially ethoxylated branched polyethylenimine from ethanolamine

We report here a method to make a branched and partially ethoxylated polyethyleneimine derivative directly from ethanolamine. The polymerization reaction is catalysed by a pincer complex of Earth-abundant metal, manganese, and produces water as the only byproduct. Industrial processes to produce polyethyleneimines involve the transformation of ethanolamine to a highly toxic chemical, aziridine, by an energy-intensive/waste-generating process followed by the ring-opening polymerization of aziridine. The reported method bypasses the need to produce a highly toxic intermediate and presents advantages over the current state-of-the-art. We propose that the polymerization process follows a hydrogen borrowing pathway that involves (a) dehydrogenation of ethanolamine to form 2-aminoacetaldehyde, (b) dehydrative coupling of 2-aminoacetaldehyde with ethanolamine to form an imine derivative, and (c) subsequent hydrogenation of imine derivative to form alkylated amines.

Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

Counterintuitive chemoselectivity in the reduction of carbonyl compounds

The reactivity of carbonyl functional groups largely depends on the substituents on the carbon atom. Reversal of the commonly accepted order of reactivity of different carbonyl compounds requires novel synthetic approaches. Achieving selective reduction will enable the transformation of carbon resources such as plastic waste, carbon dioxide and biomass into valuable chemicals. In this Review, we explore the reduction of less reactive carbonyl groups in the presence of those typically considered more reactive. We discuss reductions, including the controlled reduction of ureas, amides and esters to aldehydes, as well as chemoselective reductions of carbonyl groups, including the reduction of ureas over carbamates, amides and esters; the reduction of amides over esters, ketones and aldehydes; and the reduction of ketones over aldehydes.

Metal-Ligand Cooperation with Thiols as Transient Cooperative Ligands: Acceleration and Inhibition Effects in (De)Hydrogenation Reactions

ConspectusOver the past two decades, we have developed a series of pincer-type transition metal complexes capable of activating strong covalent bonds through a mode of reactivity known as metal-ligand cooperation (MLC). In such systems, an incoming substrate molecule simultaneously interacts with both the metal center and ligand backbone, with one part of the molecule reacting at the metal center and another part at the ligand. The majority of these complexes feature pincer ligands with a pyridine core, and undergo MLC through reversible dearomatization/aromatization of this pyridine moiety. This MLC platform has enabled us to perform a variety of catalytic dehydrogenation, hydrogenation, and related reactions, with high efficiency and selectivity under relatively mild conditions.In a typical catalytic complex that operates through MLC, the cooperative ligand remains coordinated to the metal center throughout the entire catalytic process, and this complex is the only catalytic species involved in the reaction. As part of our ongoing efforts to develop new catalytic systems featuring MLC, we have recently introduced the concept of transient cooperative ligand (TCL), i.e., a ligand that is capable of MLC when coordinated to a metal center, but the coordination of which is reversible rather than permanent. We have thus far employed thiol(ate)s as TCLs, in conjunction with an acridanide-based ruthenium(II)-pincer catalyst, and this has resulted in remarkable acceleration and inhibition effects in various hydrogenation and dehydrogenation reactions. A cooperative thiol(ate) ligand can be installed in situ by the simple addition of an appropriate thiol in an amount equivalent to the catalyst, and this has been repeatedly shown to enable efficient bond activation by MLC without the need for other additives, such as base. The use of an ancillary thiol ligand that is not fixed to the pincer backbone allows the catalytic system to benefit from a high degree of tunability, easily implemented by varying the added thiol. Importantly, thiols are coordinatively labile enough under typical catalytic conditions to leave a meaningful portion of the catalyst in its original unsaturated form, thereby allowing it to carry out its own characteristic catalytic activity. This generates two coexisting catalyst populations─one that contains a thiol(ate) ligand and another that does not─and this may lead to different catalytic outcomes, namely, enhancement of the original catalytic activity, inhibition of this activity, or the occurrence of diverging reactivities within the same catalytic reaction mixture. These thiol effects have enabled us to achieve a series of unique transformations, such as thiol-accelerated base-free aqueous methanol reforming, controlled stereodivergent semihydrogenation of alkynes using thiol as a reversible catalyst inhibitor, and hydrogenative perdeuteration of C═C bonds without using D2, enabled by a combination of thiol-induced acceleration and inhibition. We have also successfully realized the unprecedented formation of thioesters through dehydrogenative coupling of alcohols and thiols, as well as the hydrogenation of organosulfur compounds, wherein the cooperative thiol serves as a reactant or product. In this Account, we present an overview of the TCL concept and its various applications using thiols.

Promoter Effect of Pt on Zr Catalysts to Increase the Conversion of Furfural to γ-Valerolactone Using Batch and Continuous Flow Reactors: Influence of the Way of the Incorporation of the Pt Sites

The valorization of biomass and its transformation into fuels are highly interesting due to the abundance of biomass and its almost neutral carbon emissions. In this article, we show the production of γ-valerolactone (GVL), a valuable product, from furfural (FF), a compound that can be easily obtained from biomass. This FF to GVL transformation involves a catalytic cascade reaction with two hydrogenation steps. Pt and/or Zr supported on sepiolite catalysts have been prepared and tested in the FF transformation reaction. A physical mixture of a Zr-based and a Pt-based catalyst has reached a yield to GVL of ca. 50% after 16 h at 180 °C. This performance largely exceeds that obtained by each of the single Pt or single Zr metal catalysts independently, showing a strong synergistic effect. These data suggest that each metal (Pt and Zr) plays an important and complementary role in different reaction steps. Furthermore, the physical mixture appears to be much more efficient than bimetallic Pt/Zr catalysts synthesized with the same amount of metals. The role of the type of acidity and the oxidation state of the surface platinum species on the catalytic performance has been discussed. Moreover, this reaction has been carried out in batch and continuous flow reactors, and a comparative study between the two operation modes has been undertaken. A certain correlation between the catalytic results obtained by both operation modes has been found.

Balance between FeIV-NiIV synergy and Lattice Oxygen Contribution for Accelerating Water Oxidation

Hydrogen obtained from electrochemical water splitting is the most promising clean energy carrier, which is hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Thus, the development of an efficient OER electrocatalyst using nonprecious 3d transition elements is desirable. Multielement synergistic effect and lattice oxygen oxidation are two well-known mechanisms to enhance the OER activity of catalysts. The latter is generally related to the high valence state of 3d transition elements leading to structural destabilization under the OER condition. We have found that Al doping in nanosheet Ni-Fe hydroxide exhibits 2-fold advantage: (1) a strong enhanced OER activity from 277 mV to 238 mV at 10 mA cm-2 as the Ni valence state increases from Ni3.58+ to Ni3.79+ observed from in situ X-ray absorption spectra. (2) Operational stability is strengthened, while weakness is expected since the increased NiIV content with 3d8L2 (L denotes O 2p hole) would lead to structural instability. This contradiction is attributed to a reduced lattice oxygen contribution to the OER upon Al doping, as verified through in situ Raman spectroscopy, while the enhanced OER activity is interpreted as an enormous gain in exchange energy of FeIV-NiIV, facilitated by their intersite hopping. This study reveals a mechanism of Fe-Ni synergy effect to enhance OER activity and simultaneously to strengthen operational stability by suppressing the contribution of lattice oxygen.

Construction of Ag─Co(OH)2 Tandem Heterogeneous Electrocatalyst Induced Aldehyde Oxidation and the Co-Activation of Reactants for Biomass Effective and Multi-Selective Upgrading

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) provides a feasible way for utilization of biomass resources. However, how to regulate the selective synthesis of multiple value-added products is still a great challenge. The cobalt-based compound is a promising catalyst due to its direct and indirect oxidation properties, but its weak adsorption capacity restricts its further development. Herein, by constructing Ag─Co(OH)2 heterogeneous catalyst, the efficient and selective synthesis of 5-hydroxymethyl-2-furanoic acid (HMFCA) and 2,5-furan dicarboxylic acid (FDCA) at different potential ranges are realized. Based on various physical characterizations, electrochemical measurements, and density functional theory calculations, it is proved that the addition of Ag can effectively promote the oxidation of aldehyde group to a carboxyl group, and then generate HMFCA at low potential. Moreover, the introduction of Ag can activate cobalt-based compounds, thus strengthening the adsorption of organic molecules and OH- species, and promoting the formation of FDCA. This work achieves the selective synthesis of two value-added chemicals by one tandem catalyst and deeply analyzes the adsorption enhancement mechanism of the catalyst, which provides a powerful guidance for the development of efficient heterogeneous catalysts.

Electron-Rich Ru Supported on N-Doped Coffee Biochar for Selective Reductive Amination of Furfural to Furfurylamine

Highly selective synthesis of primary amines from renewable biomass has attracted increasing attention, but it still faces great challenges in chemical industry applications. In this study, an electron-rich Ru catalyst was constructed by doping N into coffee biochar using a one-pot carbonization method (Ru/NCB-600). Ru/NCB-600 showed high catalytic activity and yield for the reductive amination of furfural with green and cheap NH3 and H2. The excellent catalytic performance of Ru/NCB-600 was closely correlated to the formation of electron-rich Ruδ- species (Ruδ--Nxδ+), which endowed Ru/NCB-600 with an enhanced H2 adsorption and activation ability. Ru/NCB-600 showed a high formation rate of 95.6 gfurfurylamine·gRu-1·h-1 and a high yield of furfurylamine (98.6%) at 50 °C. Ru/NCB-600 can also be used for the reductive amination of various carbonyl compounds in good to excellent yield (95.4-99%). This study thus provides a potential pathway for the highly selective reductive amination of carbonyl compounds by regulating the electron density of Ru.

Micropores in Hollow Organic Cage Nanocapsule as a Size Exclusion Gate: Cage Entrapped Pd(II)-Catalyst for Efficient Cross-Coupling Reaction

Hollow porous organic capsules (HPOCs) with an entrapped active catalyst have nanosized cavities, providing the benefits of a nanoreactor, as well as separation of the catalysts from the reaction medium via pores acting as a size-exclusion gate. Such purpose-built HPOCs with desired molecular weight cutoffs offer the advantages of semipermeable membrane separation and a sustainable chemical process that excludes energy-extensive separation. Here, we report a newly synthesized HPOC with an entrapped Pd(PPh3)2Cl2 as the catalyst for demonstrating a Suzuki-Miyaura coupling reaction as a proof of concept.

Unique activity of a Keggin POM for efficient heterogeneous electrocatalytic OER

Polyoxometalates (POMs) have been well studied and explored in electro/photochemical water oxidation catalysis for over a decade. The high solubility of POMs in water has limited its use in homogeneous conditions. Over the last decade, different approaches have been used for the heterogenization of POMs to exploit their catalytic properties. This study focused on a Keggin POM, K6[CoW12O40], which was entrapped in a sol-gel matrix for heterogeneous electrochemical water oxidation. Its entrapment in the sol-gel matrix enables it to catalyze the oxygen evolution reaction at acidic pH, pH 2.0. Heterogenization of POMs using the sol-gel method aids in POM's recyclability and structural stability under electrochemical conditions. The prepared sol-gel electrode is robust and stable. It achieved electrochemical water oxidation at a current density of 2 mA/cm2 at a low overpotential of 300 mV with a high turnover frequency (TOF) of 1.76 [mol O2 (mol Co)-1s-1]. A plausible mechanism of the electrocatalytic process is presented.

Production of hydrogen from alcohols via homogeneous catalytic transformations mediated by molecular transition-metal complexes

Hydrogen obtained from renewable sources such as water and alcohols is regarded as an efficient clean-burning alternative to non-renewable fuels. The use of the so-called bio-H2 regardless of its colour will be a significant step towards achieving global net-zero carbon goals. Challenges still persist however with conventional H2 storage, which include low-storage density and high cost of transportation apart from safety concerns. Global efforts have thus focussed on liquid organic hydrogen carriers (LOHCs), which have shown excellent potential for H2 storage while allowing safer large-scale transformation and easy on-site H2 generation. While water could be considered as the most convenient liquid inorganic hydrogen carrier (LIHC) on a long-term basis, the utilization of alcohols as LOHCs to generate on-demand H2 has tasted instant success. This has helped to draw a road-map of futuristic H2 storage and transportation. The current review brings to the fore the state-of-the-art developments in hydrogen generation from readily available, feed-agnostic bio-alcohols as LOHCs using molecular transition-metal catalysts.