Chemical Catalysis Research Articles

Co-Catalyzed P-H Activation and Related Cp*Co(III) Phosphine Complexes.

This study reports that the well-known Co(III) precursor Co(η5-Cp*)I2(CO) (1) is an effective precatalyst for dehydrocoupling reactions of phosphines. Reaction monitoring by NMR, complemented by ESI-MS and EPR, suggests that Co(III) complexes containing secondary and primary phosphine ligands play an important role in this catalysis but that redox chemistry is also facile for these complexes, resulting in paramagnetic species. Representative examples of the mono(phosphine) complexes Co(η5-Cp*)I2(PR2H) (2) and Co(η5-Cp*)I2(PRH2) (4) and bis(phosphine) complexes [Co(η5-Cp*)I(PR2H)2] I (3) have been prepared. The characterization of these complexes through structural, computational, spectroscopic, and electrochemical analysis is reported and serves as a foundation for considering their mechanistic significance in the observed catalytic dehydrocoupling chemistry.

Fluorescence Lifetime Imaging Microscopy (FLIM) as a Tool to Understand Chemical Reactions and Catalysis

Fluorescence Lifetime Imaging Microscopy (FLIM) as a Tool to Understand Chemical Reactions and Catalysis

Endomelanconiopsis endophytica Lipase Immobilized in Calcium Alginate for Production of Biodiesel from Waste Cooking Oil

The increasing global demand for biodiesel is due to the urgent need to replace fossil diesel with a fuel based on renewable energy sources. Although chemical catalysis is widely used to produce biodiesel, it uses harsh operating conditions, has high energy consumption, and generates unwanted byproducts. In this scenario, biocatalysis stands out as an efficient and environmentally friendly alternative to chemical catalysis. In biocatalysis, the use of immobilized enzymes plays an important role in the reduction in costs. In this sense, we investigated the use of the lipase produced by an Amazonian endophytic fungus in an immobilized form in the transesterification of waste cooking oil for biodiesel production. The fungus Endomelanconiopsis endophytica QAT_7AC demonstrated a high production of lipase. The lipolytic extract was precipitated in ethanol, which increased the specific enzyme activity. The lipolytic extract and the precipitated lipolytic extract were immobilized in calcium alginate beads. Immobilization efficiency was over 89%. The immobilized biocatalysts showed thermal stability and were used in the production of biodiesel using waste cooking oil and ethanol. It was possible to reuse them for up to four reaction cycles, with yields greater than 70%. These results prove the efficiency of immobilized biocatalysts in the production of biodiesel from waste oils.

Microwave-Assisted Acid and Alkali Pretreatment of Napier Grass for Enhanced Biohydrogen Production and Integrated Biorefinery Potential

Napier grass, a promising lignocellulosic energy crop, presents a complex composition that limits its bioconversion into fermentable products. To address this challenge, we applied microwave (MW) pretreatment assisted by acid and alkali, using varying chemical concentrations (0.5–1% w/v) and pretreatment times (3–10 min). Acid-catalyzed MW pretreatment achieved a maximal hemicellulose removal of 69.8%, while alkali-catalyzed MW pretreatment resulted in significant lignin removal of 65.5%. Without chemical catalysis, the pretreated hydrolysate significantly increased hydrogen yield to 38.0 ± 2.9 mL H2/g volatile solid (VS), five times greater than that obtained from untreated biomass. Hydrogen yield was further enhanced when the MW-pretreated solid underwent simultaneous saccharification and fermentation. The highest hydrogen yield of 89.2 ± 7.2 mL H2/g VS was achieved from alkali-catalyzed MW pretreated solid (0.5% w/v NaOH, 5 min), with a chemical oxygen demand (COD) solubilization of 62.6%. Increasing the NaOH concentration to 1% (w/v) slightly decreased hydrogen yield but significantly increased COD solubilization to 85.8%. The high carbohydrate content facilitated rapid cellulase hydrolysis, producing and accumulating a high concentration of fermentable sugars. However, this accumulation subsequently led to a shift towards lactic acid formation. The improved hydrogen yield and increased COD solubilization, along with the shift towards lactic acid production, suggest the possibility of optimizing this process for simultaneous production of multiple valuable products in an integrated biorefinery approach, potentially enhancing the economic viability of biomass conversion.

A Comprehensive Review on Imperative Role of Ionic Liquids in Pharmaceutical Sciences.

Ionic liquids (ILs) are poorly-coordinated ionic salts that can exist as a liquid at room temperatures (or <100 °C). ILs are also referred to as "designer solvents" because so many of them have been created to solve particular synthetic issues. ILs are regarded as "green solvents" because they have several distinctive qualities, including better ionic conduction, recyclability, improved solvation ability, low volatility, and thermal stability. These have been at the forefront of the most innovative fields of science and technology during the past few years. ILs may be employed in new drug formulation development and drug design in the field of pharmacy for various functions such as improvement of solubility, targeted drug delivery, stabilizer, permeability enhancer, or improvement of bioavailability in the development of pharmaceutical or vaccine dosage formulations. Ionic liquids have become a key component in various areas such as synthetic and catalytic chemistry, extraction, analytics, biotechnology, etc., due to their superior abilities along with highly modifiable potential. This study concentrates on the usage of ILs in various pharmaceutical applications enlisting their numerous purposes from the delivery of drugs to pharmaceutical synthesis. To better comprehend cuttingedge technologies in IL-based drug delivery systems, highly focused mechanistic studies regarding the synthesis/preparation of ILs and their biocompatibility along with the ecotoxicological and biological effects need to be studied. The use of IL techniques can address key issues regarding pharmaceutical preparations such as lower solubility and bioavailability which plays a key role in the lack of effectiveness of significant commercially available drugs.

Ultrafine Mo2N Quantum Dots Embedded in N-Doped Graphene Sheets Enable Efficient Adsorption-Catalytic Transformation of Polysulfides.

Because of the high theoretical energy density of 2600 Wh kg-1, lithium-sulfur batteries (LSBs) are anticipated to be among the next generation of high-energy-density storage technologies. However, the practical application of LSBs has been severely hampered by the significant shuttle effect and slow redox kinetics of polysulfides (LiPSs). To address the above problems, in this paper, the concept of quantum dots (QDs) was introduced to design and synthesize Mo2N QD-modified N-doped graphene nanosheets (marked as Mo2N-QDs@NG), which were used as separator modification materials for LSBs. The experimental results demonstrated that the introduction of Mo2N QDs avoids stacking of graphene sheets and provides more active sites for the conversion of LiPSs. Moreover, Mo2N enhances the chemical fixation and catalyzes the liquid-solid conversion of soluble LiPSs by forming Mo-S and Li-N bonds with LiPSs. Additionally, establishing Mo-C bonds with Mo2N, N-doped graphene sheets can facilitate the transport of electrons and ions and physically prevent the diffusion of LiPSs, thus creating a highly conducting carbon structure to support electrochemical reactions. Benefiting from the synergistic effect of chemical immobilization and catalysis of Mo2N QDs with the physical confinement of NG, Mo2N-QDs@NG-PP batteries exhibit enhanced electrochemical performance.

1,3‐Propanediol, An Exemplary Bio‐Renewable Organic Platform Chemical.

This opinionated review underlines the increasing production of 1,3‐propanediol (1,3‐PDO) by whole cell biocatalytic fermentation of biomass and highlights how production has transitioned from petrochemicals to bio‐renewables. Current uses of 1,3‐PDO are listed. Some future prospects for evolving the current technology and expanding the chemical uses of 1,3‐PDO use are discussed, with emphasis on catalytic and atom efficient chemistries. Lessons from the success of biomass derived 1,3‐PDO are noted that may be applied to other bio‐based organic platform chemicals.

Synthesis and reactivity of a heteroleptic magnesium hydride on a dearomatized picolyl-based NNN-chelator.

Heteroleptic magnesium hydrides are important for their stoichiometric and catalytic reduction chemistry. Their primary nucleophilic site is typically the hydride, while the ancillary ligands commonly used are mostly spectators. Chemically non-innocent ligands in comparison are rarely applied on MgH as their reactivity can be complex. Milstein et al. have recently reported Mg-mediated alkyne hydrogenation by using their metal-ligand cooperation (MLC) concept on a dearomatized picolyl-based PNP pincer that is non-innocent with a nucleophilic nature. A '(PNP)MgH' is noted as the active catalyst in hydrogenation but without structural validation. Inspired by the same, we report herein a novel NNN-chelator (MesL) with a dearomatized picolyl moiety and its well-defined MgH. Having two prominent nucleophilic sites, the present MgH shows metal-ligand competition while reacting with certain electrophiles. It also distinguishes nonpolar alkynes and polar carbonyls by cleanly inserting itself into the former but not the latter. The nucleophilicities of the two sites are also probed by DFT methods and compared with Milstein's (PNP)MgH. Although the present system shows no MLC-type H2 activation, the addition of a CS2 molecule in that way is realized.

Trace MnFe2O4 Boosts Polyphenol-Maillard Reaction and Humification Process for Value-Added Composting: Integrated Effect of Chemical and Enzymatic Catalysis

Trace MnFe₂O₄ Boosts Polyphenol-Maillard Reaction and Humification Process for Value-Added Composting: Integrated Effect of Chemical and Enzymatic Catalysis

From Catalysis of Evolution to Evolution of Catalysis.

ConspectusThe mystery of the origins of life is one of the most difficult yet intriguing challenges to which humanity has grappled. How did biopolymers emerge in the absence of enzymes (evolved biocatalysts), and how did long-lasting chemical evolution find a path to the highly selective complex biology that we observe today? In this paper, we discuss a chemical framework that explores the very roots of catalysis, demonstrating how standard catalytic activity based on chemical and physical principles can evolve into complex machineries. We provide several examples of how prebiotic catalysis by small molecules can be exploited to facilitate polymerization, which in biology has transformed the nature of catalysis. Thus, catalysis evolved, and evolution was catalyzed, during the transformation of prebiotic chemistry to biochemistry. Traditionally, a catalyst is defined as a substance that (i) speeds up a chemical reaction by lowering activation energy through different chemical mechanisms and (ii) is not consumed during the course of the reaction. However, considering prebiotic chemistry, which involved a highly diverse chemical space (i.e., high number of potential reactants and products) and constantly changing environment that lacked highly sophisticated catalytic machinery, we stress here that a more primitive, broader definition should be considered. Here, we consider a catalyst as any chemical species that lowers activation energy. We further discuss various demonstrations of how simple prebiotic molecules such as hydroxy acids and mercaptoacids promote the formation of peptide bonds via energetically favored exchange reactions. Even though the small molecules are partially regenerated and partially retained within the resulting oligomers, these prebiotic catalysts fulfill their primary role. Catalysis by metal ions and in complex chemical mixtures is also highlighted. We underline how chemical evolution is primarily dictated by kinetics rather than thermodynamics and demonstrate a novel concept to support this notion. Moreover, we propose a new perspective on the role of water in prebiotic catalysis. The role of water as simply a "medium" obscures its importance as an active participant in the chemistry of life, specifically as a very efficient catalyst and as a participant in many chemical transformations. Here we highlight the unusual contribution of water to increasing complexification over the course of chemical evolution. We discuss possible pathways by which prebiotic catalysis promoted chemical selection and complexification. Taken together, this Account draws a connection line between prebiotic catalysis and contemporary biocatalysis and demonstrates that the fundamental elements of chemical catalysis are embedded within today's biocatalysts. This Account illustrates how the evolution of catalysis was intertwined with chemical evolution from the very beginning.

On the Interplay Between Force, Temperature, and Electric Fields in the Rupture Process of Mechanophores.

The use of oriented external electric fields (OEEFs) shows promise as an alternative approach to chemical catalysis. The ability to target a specific bond by aligning it with a bond-weakening electric field may be beneficial in mechanochemical reactions, which use mechanical force to selectively rupture bonds. Previous computational studies have focused on a static description of molecules in OEEFs, neglecting to test the influence of thermal oscillations on molecular stability. Here, we performed ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) to investigate the behaviour of a model mechanophore under the simultaneous influence of thermal and electric field effects. We show that the change in bond length caused by a strong electric field is largely independent of the temperature, both without and with mechanical stretching forces applied to the molecule. The amplitude of thermal oscillations increases with increasing field strength and temperature, but at low temperatures, the application of mechanical force leads to an additional increase in amplitude. Our research shows that methods for applying mechanical force and OEEFs can be safely combined and included in an AIMD simulation at both low and high temperatures, allowing researchers to computationally investigate mechanochemical reactions in realistic application scenarios.

Cobalt-doped molybdenum sulfide as an interlayer facilitates polysulfide conversion to obtain high-performance lithium−sulfur batteries

Lithium–sulfur (Li–S) batteries are considered to be a promising energy storage system due to their theoretical specific capacity. However, the “shuttle effect” of polysulfides (LiPSs) and the slow redox kinetics of LiPSs in the conversion reaction have hindered their large−scale application. In this study, the Co-MoS2 is prepared and coated on the polypropylene (PP) separator of Li–S batteries. The Co elements are successful addition and uniform distribution in the Co-MoS2. This coating is designed to provide chemical adsorption and catalysis for LiPSs. Consequently, Li–S batteries with a Co-MoS2 interlayer exhibit outstanding long-cycle and high-rate performance. After 500 cycles at 0.5C, the reversible capacity is found to be 561 mAh g−1, with only a low-capacity reduction of 0.097 % per cycle. Furthermore, 602 mAh g−1 is delivered even at 4C. The results of electrochemical measurements and first principles calculations demonstrate that the high performance of Li–S batteries is attributed to the chemical adsorption and electrocatalysis roles of the Co-MoS2 interlayer, which inhibit the “shuttle effect” and enable fast redox reaction kinetics. In addition, the introduction of cobalt doping results in the formation of the 1T phase of MoS2, which enhances the conductivity of the Co-MoS2. The presence of plentiful cobalt-doped MoS2 defects provides abundant catalytic sites for the electrochemical reaction of LiPSs.

Machine learning the electric field response of condensed phase systems using perturbed neural network potentials

The interaction of condensed phase systems with external electric fields is of major importance in a myriad of processes in nature and technology, ranging from the field-directed motion of cells (galvanotaxis), to geochemistry and the formation of ice phases on planets, to field-directed chemical catalysis and energy storage and conversion systems including supercapacitors, batteries and solar cells. Molecular simulation in the presence of electric fields would give important atomistic insight into these processes but applications of the most accurate methods such as ab-initio molecular dynamics (AIMD) are limited in scope by their computational expense. Here we introduce Perturbed Neural Network Potential Molecular Dynamics (PNNP MD) to push back the accessible time and length scales of such simulations. We demonstrate that important dielectric properties of liquid water including the field-induced relaxation dynamics, the dielectric constant and the field-dependent IR spectrum can be machine learned up to surprisingly high field strengths of about 0.2 V Å−1 without loss in accuracy when compared to ab-initio molecular dynamics. This is remarkable because, in contrast to most previous approaches, the two neural networks on which PNNP MD is based are exclusively trained on molecular configurations sampled from zero-field MD simulations, demonstrating that the networks not only interpolate but also reliably extrapolate the field response. PNNP MD is based on rigorous theory yet it is simple, general, modular, and systematically improvable allowing us to obtain atomistic insight into the interaction of a wide range of condensed phase systems with external electric fields.

Electron spins from a molecular perspective: an interview with Song Gao.

Spin chemistry has emerged as an interdisciplinary field that focuses on electron spins in molecules and related applications in physics, chemistry, biology, materials science and information science. It will play a crucial role in technological innovations. The chemistry of spins is deeply related to the essence of chemical bonds, chemical catalysis, enzyme catalysis, optical and electromagnetic properties, quantum computation and quantum precision measurements. The related research is intersectional, cutting-edge and has a wide range of application prospects. National Science Review (NSR) recently interviewed Prof. Song Gao to discuss spin chemistry. Prof. Gao is a renowned inorganic chemist and an academician of Chinese Academy of Sciences. He is the president of Sun Yat-sen University and the founder of the Spin-X Institute of South China University of Technology. He is recognized as a leader in coordination chemistry and molecular magnetism, and has strong academic influence. Since 2008, he has served on the International Advisory Committee of International Conference on Molecule-Based Magnets, and organized and chaired its 2010 conference. Prof. Gao's primary research topics include molecular nanomagnets; the relationship between geometric structures, electronic structures and magnetism of molecules; and the spin states and reactivity of molecules.

Remarkable chemical adsorption and catalysis of 3D self-supporting Zn-doped NiCo2O4 nanowires for high-performance lithium-sulfur batteries

Lithium-sulfur batteries are one of the most potential next-generation energy storage systems with high theoretical energy density and low cost. However, the lithium polysulfides (LiPSs) dissolution and shuttle effect limit their commercial application. Herein, the Zn-doped NiCo2O4 nanowires grown on carbon cloth (ZNCOCC) are prepared by hydrothermal method and as sulfur host. ZNCO nanowires consisting of stacked nanoparticles and abundant mesopores were grown vertically on carbon fibers. The mesoporous structure of ZNCOCC provides more space to accommodate sulfur and its volume change during charging and discharging, is conducive to electrolyte infiltration and maintains strong adsorption of LiPSs to ensure fast ion transport kinetics. The ZNCOCC displays higher Co3+/Co2+ and Ni3+/Ni2+ ratio compared to NCOCC, and the high-valent metal cations can provide more unsaturated electron orbitals for S binding, causing high adsorption of LiPSs. Density functional theory calculations demonstrate that the Zn doping significantly reduces the band gap, improves the conductivity and increases the LiPSs adsorption energy of NCO. The ZNCOCC/Li2S8 displays a high specific capacity of 1184 mAh g−1 (0.1 C) and a low decay of 0.07 %/cycle after 500 cycles (2 C). This research reveals the rational design of a doped bimetal oxide nanostructure for the improvement of lithium-sulfur batteries.

CatchyCFDEM: Open-source microkinetic modeling of heterogeneous catalysis in Eulerian-Lagrangian CFD applied to oxidative coupling of methane

This work introduces catchyCFDEM, an OpenFOAM-based open-source CFD-DEM framework designed for simulating reactive gas–solid fluidized beds with both gas-phase chemistry and heterogeneous catalytic chemistry. A convective gas–solid heat transfer model is implemented and validated using experimental data gathered in a non-reactive pseudo-2D fluidized bed. Catalytic chemistry including different levels of complexity are included: pseudo-homogeneous, heterogeneous without mass transfer, and heterogeneous with diffusive mass transfer. Verification studies are performed by simulating a packed bed reactor using catchyCFDEM and comparing mass fraction profiles to a 1D plug flow simulation in Cantera. To enhance the computational efficiency of the resource-intensive reactive CFD-DEM simulations, speed-up algorithms such as Particle Agglomeration (PA) and in-situ adaptive tabulation (ISAT) are integrated in catchyCFDEM. As a case study, a gas–solid vortex reactor (GSVR) is simulated using the validated framework. The applicability of the GSVR for the oxidative coupling of methane (OCM) is evaluated based on an isothermal analysis evaluating the influence of several operational and geometrical parameters on the process. Finally, a proof-of-concept adiabatic simulation of the GSVR is presented. The catchyCFDEM framework is made publicly available on GitHub.

Magnetic Monopole-Like Behavior in Superparamagnetic Nanoparticle Coated With Chiral Molecules.

Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted wide attention due to their promising applications in biomedicine, chemical catalysis, and magnetic memory devices. In this work, the force is measured between a single SPION coated with chiral molecules and a ferromagnetic substrate by atomic force microscopy (AFM), with the substrate magnetized either toward or away from the approaching AFM tip. The force between the coated SPION and the magnetic substrate depends on the handedness of the molecules adsorbed on the SPION and on the direction of the magnetization of the substrate. By inserting nm-scale spacing layers between the coated SPION and the magnetic substrate it is shown that the SPION has a short-range magnetic monopole-like magnetic field. A theoretical framework for the nature of this field is provided.

Leidenfrost Effect-Induced Chaotic Vortex Flow for Efficient Mixing of Highly Viscous Droplets.

Efficiently mixing highly viscous liquids in microfluidic systems is appealing for green chemistry such as chemical synthesis and catalysis, but it is a long-standing challenge owing to the unfavorable diffusion kinetics. In this work, a new strategy is explored for mixing viscous droplets by harnessing a peculiar Leidenfrost state, where the substrate temperature is above the boiling point of the liquid without apparent liquid evaporation. Compared to the control experiment where the droplet stays at a similar temperature but in the contact boiling regime, the mixing time can be reduced significantly. Moreover, it is demonstrated that the liquid mixing originates from the chaotic convection flow in the Leidenfrost droplet, characterized by the internal vortex motion evidenced by the microscale visualization. A correlation between mixing time and droplet volume is also proposed, showing a good agreement with experimental results. It is further shown that Leidenfrost droplets can be used to synthesize nanoparticles of the desired morphology, and it is anticipated that this simple and scalable fabrication approach will find applications in the biological, pharmaceutical, and chemical industries.

Reductive samarium (electro)catalysis enabled by SmIII-alkoxide protonolysis.

Samarium diiodide (SmI2) is a privileged, single-electron reductant deployed in diverse synthetic settings. However, generalizable methods for catalytic turnover remain elusive because of the well-known challenge associated with cleaving strong SmIII-O bonds. Prior efforts have focused on the use of highly reactive oxophiles to enable catalyst turnover. However, such approaches give rise to complex catalyst speciation and intrinsically limit the synthetic scope. Herein, we leveraged a mild and selective protonolysis strategy to achieve samarium-catalyzed, intermolecular reductive cross-coupling of ketones and acrylates with broad scope. The modularity of our approach allows rational control of selectivity based on solvent, pKa (where Ka is the acid dissociation constant), and the samarium coordination sphere and provides a basis for future developments in catalytic and electrocatalytic lanthanide chemistry.

A Radical Revolution in the 21st Century

AbstractThis Special Collection on “Radical Chemistry in Homogeneous Catalysis and Organic Synthesis” organized in collaboration with the European Journal of Organic Chemistry and ChemCatChem showcases the maturity of field. Overall, this Special Collection encompasses 11 reviews and 27 research articles, covering a diverse range of topics. It presents the latest advancements in the controlled generation of radical species using transition metal catalysis, photoredox catalysis, or electrochemistry. It highlights the importance of moving towards more sustainable chemical processes, with particular focus on the development of novel organo(photo)catalysts, or efficient catalyst‐free reactions. It presents new transformations to access complex scaffolds as well as new building blocks and reagents, further simplifying single‐electron disconnection logic. In addition, it also highlights the key advancements in addressing some of the current challenges in radical chemistry, such the development of enantioselective reactions or how to scale‐up radical processes to meet the needs of the fine chemical industry.