Key Reaction Research Articles

Regulatory Mechanisms and Applications of Rare Earth Elements‐Based Electrocatalysts†

Comprehensive SummaryAmidst the pressing environmental challenges posed by the prevalent reliance on fossil fuels, it becomes imperative to seek sustainable alternatives and prioritize energy efficiency. Electrocatalysis, which is renowned for its high efficiency and environmental friendliness, has garnered significant attention. Rare earth elements (REEs), distinguished by their unique electronic and orbital structures, play a crucial role in electrocatalysis. The strategic integration of REEs into catalysts allows for the fine‐tuning of atomic structures, which in turn, significantly boosts catalytic performance. Despite substantial advancements in rare earth‐based materials for electrocatalysis, a comprehensive overview of the regulatory mechanisms involving REEs is lacking. In this mini‐review, we systematically explore the regulatory mechanisms of REEs within electrocatalysts and their pivotal roles in essential electrocatalytic processes such as the CO2 reduction reaction, oxygen reduction reaction, and hydrogen evolution reaction. We commence with an elucidation of REEs, proceed to delineate their regulatory impacts on electrocatalysts and delve into their applications in key electroreduction reactions. We conclude with discussions on current limitations and prospects for further advancements in this burgeoning field of research. Key Scientists

Synthesis of Pyrrolidine‐fused β‐lactams as Potential β‐lactamase Inhibitors

AbstractA synthetic protocol for the preparation of novel 3,4‐pyrrolidine‐fused β‐lactams was developed. The proposed 2,6‐diazabicyclo[3.2.0]heptan‐7‐one scaffolds were constructed through an amido group‐induced, potassium tert‐butoxide‐promoted intramolecular ring closure of 3‐acylamino‐4‐oxiranyl‐β‐lactams as the key reaction step. Alternatively, the desired cyclization was also effected by means of a scandium triflate‐mediated catalytic approach. In this way, a set of stereodefined 3,4‐pyrrolidine‐fused β‐lactams was synthesized, which were preliminary evaluated as β‐lactamase inhibitors. These first‐line biological assessments led to the identification of a 2‐benzoyl‐6‐(4‐methoxyphenyl)‐substituted diazabicyclo structure as an eligible starting point for further β‐lactamase inhibitor optimization studies.

Not all cytochrome b5s are created equal: How a specific CytB5 boosts forskolin biosynthesis in Saccharomyces cerevisiae

Cytochrome B5s, or CytB5s, are small heme-binding proteins, ubiquitous across all kingdoms of life that serve mainly as electron donors to enzymes engaged in oxidative reactions. They often function as redox partners of the cytochrome P450s (CYPs), a superfamily of enzymes participating in multiple biochemical processes. In plants, CYPs catalyze key reactions in the biosynthesis of plant specialized metabolites with their activity dependent on electron donation often from cytochrome P450 oxidoreductases (CPRs or PORs). In eukaryotic microsomal CYPs, CytB5s frequently participate in the electron transfer process although their exact role remains understudied, especially in plant systems. In this study, we assess the role of CytB5s in the heterologous biotechnological production of plant specialized metabolites in yeast. For this, we used as a case-study the biosynthesis of forskolin - a bioactive diterpenoid produced exclusively from the plant Coleus forskohlii. The complete biosynthetic pathway for forskolin is known and includes three CYP enzymes. We reconstructed the entire forskolin pathway in the yeast Saccharomyces cerevisiae, and upon co-expression of the three CytB5s - identified in C. forskohlii transcriptomes - alleviation of a CYP-related bottleneck step was noticed only when a specific CytB5, CfCytB5A, was used. Co-expression of CfCytB5A in yeast, in combination with forskolin pathway engineering, resulted in forskolin production at titers of 1.81 g/L in a bioreactor. Our findings demonstrate that CytB5s not only play an important role in plant specialized metabolism but also, they can interact with precision with specific CYPs, indicating that the properties of CytB5s are far from understood. Moreover, our work highlights how CytB5s may act as indispensable components in the sustainable microbial production of plant metabolites, when their biosynthetic pathways involve CYP enzymes.

The characteristics and mechanism of NaHCO3 compound fly ash in suppressing gas explosions in pipeline networks

Gas has been widely concerned due to its importance in the industrial and energy fields. In order to improve the inhibition effect of gas explosion, under the self-constructed pipe network system, the inhibition of gas explosion by composite inhibitor of fly ash and NaHCO3 with different ratios was investigated, and the microscopic inhibition mechanism of the two kinds of powders on the explosion of gas was investigated based on the method of density functional theory and transition state theory from the perspective of molecular dynamics. The results show that: the composite powder explosion suppression is better than a single powder, explosion suppression effect with the increase in the proportion of the mass of NaHCO3 significantly improve the 5 groups of conditions NaHCO3 loading of 40% (by mass) is the best, this time, the explosion of the peak overpressure, the peak flame propagation velocity, the peak flame temperature compared to the maximum reduction in the percentage of the measures taken for the maximum of 74.42%, 81.93%, 68.71%. In addition, NaHCO3, fly ash effectively inhibit the key primitive reaction of gas explosion. When the temperature reaches a certain point, the two and O*, O2, OH* and H* reaction rate higher than the rate of CH4 oxidation chain reaction, the dominant reaction, the maximum difference in rate constants of 70.95, 58.81, 60.06, 44.94. The study of the transition from the macro-scale to the molecular level of the study, in-depth understanding of the mechanism of explosion suppression, to reduce the risk of explosion from the ground up, and enriches the Gas explosion prevention and control of the theoretical system, for the operators to provide a strong technical guarantee for safe production.

Governing chemical reactions and mechanisms of hydrogen generation during in-situ combustion gasification of heavy oil

The global push for sustainable energy solutions has highlighted the importance of producing carbon-zero hydrogen (H2) directly from petroleum reservoirs. In-situ combustion gasification (ISCG) presents a groundbreaking method to harness the potential of heavy oil reserves for clean hydrogen production. Although simulations have demonstrated the considerable promise of ISCG, the key reactions controlling hydrogen generation require experimental validation, and the underlying mechanisms remain largely unexplored. This research aims to describe the chemical reactions and mechanisms responsible for hydrogen generation during the ISCG of heavy oil. Using a specially designed kinetic cell, we conducted combustion and gasification experiments with heavy oil and coke. The findings revealed that clay minerals in the reservoir sand act as catalysts in the oxidation reactions of heavy oil by shifting reactions to lower temperatures by approximately 20 °C. Hydrogen production began at 450 °C and peaked at 900 °C, with coke gasification and the water-gas shift reaction being the primary mechanisms. Additionally, methane was produced due to hydrogen consumption via methanation reactions, and minerals in the reservoir sands were found to inhibit hydrogen production by increasing hydrogen consumption and methane generation at temperatures above 800 °C. Controlling the reservoir temperature within an optimal range between 450 and 800 °C can enhance hydrogen generation by managing the process mechanisms. This study provides a detailed examination of the ISCG process for heavy oil, paving the way for future development of kinetic models to simulate hydrogen production through ISCG. It also emphasizes the significance of mechanistic control in enhancing hydrogen generation and suppressing hydrogen consumption reactions.

Ni-Metalized Covalent Organic Cage as a Photocatalyst for Selective Photoreduction of CO2 to CO.

Metal complex-based photocatalysts are promising for CO2 reduction. Their catalytic performances greatly rely on the synergy of ligands and metal ions. Here, we demonstrate an assembly of covalent organic cage (COC) and metal ions for photocatalytic CO2 reduction. The coordinated metal serves as catalytically active site for CO2 reduction, while the cage not only chelates the metal site, but also enhances the local concentration of CO2 around metal site, and decreases the key intermediate reaction energy barrier, thereby promoting the CO2 reduction reaction kinetically and thermodynamically. Accordingly, a Ni metalized COC exhibited outstanding photocatalytic performance in CO2-to-CO conversion under visible light irradiation. This study highlights the feasibility and advantage of organic cages for the construction of photocatalysts for artificial photosynthesis.

Insights into the hydrogenation reaction degradation mechanisms of lignin model compound using density functional theory methods

Lignin through pyrolysis results in a liquid byproduct that contains a significant proportion of phenolic compounds, which can be subsequently enhanced into aromatic hydrocarbons using hydrogenation methods. To comprehend the reaction mechanism of the lignin hydrogenation process, we conducted theoretical investigations on the hydrogenation reaction process of different phenolic lignin model compounds by theoretical calculation method M06-2X/6–31++G(d,p). Different potential reaction routes were developed for the hydrogenation process of lignin model compounds, and the thermodynamic and kinetic properties of key reaction steps in each pathway were computed. The calculated results indicate that the hydrogenation reaction process of lignin model compounds, the aromatic compound, CH2O, H2O, and CH3OH may be the products that emits firstly in lignin hydrogenation reaction process. And the presence of methoxyl and hydroxyl substituents on the benzene ring does not significantly impact the hydrogenation process of lignin model compounds. Furthermore, the hydrogenation reaction in lignin model compounds exhibits a high energy barrier of approximately 300.0 kJ/mol. Thus, the hydrogenation process of lignin necessitates either appropriate modifications to the depolymerization conditions or the introduction of a catalyst. This work offers a theoretical foundation for advancing the research on lignin of hydrogenation and achieving optimal resource utilization.

Diversity Oriented Strategy (DOS) for the Efficient Synthesis of Benzofuro[2,3-b]pyridine Derivatives with Anticancer Activity.

Benzofuropyridines (BFP) are polycyclic compounds with known applications in neuronal diseases. However, its derivatization patterns and anticancer potential remains unexplored. Leveraging the idea of diversity-oriented synthesis (DOS), we developed a highly efficient synthetic route for BFP to increase the library of available analogs producing three compounds in one reaction set up, including the 2O-, 6O-, and the 1N-substituted species, also producing the unusual 2-pyridone derivatives. Key bromination reaction of the BFP moiety was successfully described which can widen the available variation in the compounds' structure. The cytotoxic activity of the compounds was assessed against SH-SY5Y (neuroblastoma), HepG2 (hepatocellular carcinoma), Kb (human oral epidermoid), HeLa (cervical) and MCF-7 (breast) cancer cell lines. In the series, the m-bromobenzyl (5b), methylcyano (5g) and propargyl (5h) 2O-derivatives demonstrated good selectivity against cancer cells with selectivity index (SI) of >71 for 5g against HeLa over the normal cells, as compared to the standard drug, Doxorubicin (SI = 6.7). The quantitative structure-activity relationship (QSAR) analysis revealed an impressive correlation of the defined descriptors with the bioactivity having an R2 value of 0.971 and 0.893 for Kb and HeLa respectively. Altogether, our work highlighted new information on the synthesis of BFP derivatives with potent cytotoxic activity.

Ni- and Co-Based MOF-Derived NixCo3-xO4 Materials: As an Efficient Anode for Direct Methanol Fuel Cell Application.

Finding inexpensive and efficient anode materials is crucial for the oxidation of methanol in the direct methanol fuel cell (DMFC), which is the key electrode reaction. Herein, we report metal-organic framework (MOF)-derived Co3O4, NiO, and NixCo3-xO4 (where x = 1.5, 1, and 0.6) materials deposited on nickel foam as efficient anode material for methanol oxidation. Among them, NiCo2O4 exhibited the highest methanol oxidation activity, owing to its lowest charge-transfer resistance (0.097 Ω) and high electrochemically active surface area (1950 cm2), resulting in the lowest onset potential of 0.35 V vs Hg/HgO. The optimized Ni-to-Co ratio and synergistic effect between Ni and Co metals enable NiCo2O4 to achieve the highest mass activity of 151 mA mg-1 and geometric current density of 288 mA cm-2, demonstrating excellent durability over 14 h at 0.6 V. In addition, to optimize methanol concentration, all the electrocatalysts were tested in a range of methanol concentrations, showing 0.5 M methanol as the optimal concentration. This study focuses on optimizing the metal ratio and methanol concentration to achieve the highest catalytic activity. Additionally, this lays the foundation for developing diverse MOF-derived electrocatalysts and advancing DMFCs.

Numerical investigation on the combustion characteristics and NOx emission of non-premixed H2/NH3/air in vase-shaped micro combustor

Hydrogen and ammonia, as currently popular zero carbon fuels, have received widespread attention. These two fuels have complementary advantages in combustion characteristics, cost, safety, etc. Based on the vase shaped micro combustor, a new structure proposed for application in micro thermophotovoltaic systems in our previous work. This article numerically investigated the combustion characteristics and NOx emission of non-premixed H2/NH3/Air in vase shaped micro combustor which proposed in our previous work. The variation patterns of flame temperature, wall temperature, flammability limit, and NOx emission with the blended ratio of NH3 and equivalence ratio were obtained. It was found that the flame cannot move and stabilize when the mixing ratio is 0.6. The rate of production (ROP) and sensitivity of NO and N2O were analyzed. Four precursors of NO, HNO, NH, N, N2 have been discovered. Under the conditions of this article, HNO is the key component affecting NO emissions. When the blending ratio is greater than 0.3, the lower reaction rate of HNO leaded to a decrease in NO. The elementary reaction R63: NH + NON2O + H is the key elementary reaction that affects NO consumption and N2O generation. The blending ratio of 0.4 and the equivalence ratio of 1.2 are the optimized operating conditions with the highest comprehensive performance.

Numerical Study on the Explosion Reaction Mechanism of Multicomponent Combustible Gas in Coal Mines

Combustible gases, such as CO, CH4, and H2, are produced during spontaneous coal combustion in goaf, which may cause an explosion under the stimulation of an external fire source. It is of great significance to study the influence of combustible gases, such as CO and H2, on the characteristics of a gas explosion. In this study, CHEMKIN software (Version 17.0) and the GRI-Mech 3.0 reaction mechanism were used to study the influences of different concentration ratios between CO and H2 on the ignition delay time, free radical concentration, and key reaction step of a gas explosion. The results show that the increase in the initial CH4 and CO concentrations prolonged the ignition delay time, while the increase in the H2 concentration shortened the time and accelerated the explosion reaction. The addition of H2 promoted the generation of free radicals (H⸱, O⸱, ⸱OH) and accelerated the occurrence of the gas explosion. CO generated ⸱OH free radicals and dominated the methane consumption through the R119 and R156 reactions. As the concentrations of CO and H2 increased, the R38 reaction gradually became the main driving factor of the gas explosion.

Tandem Electrochemical Redox/Condensation Reaction Between 2‐Amino Nitrobenzenes and Aliphatic Alcohols: An Approach to Benzimidazoles

AbstractTandem reactions via electrocatalytic annulations have emerged as a strategy for the construction of heterocycles. Herein, a two‐component electrochemical annulation via sequential reduction, oxidation, and condensation steps to synthesize valuable benzimidazoles motifs is reported. This reaction, which utilizes electricity as both the oxidants and reductants, tolerates a broad range of functional groups. Detailed mechanistic studies including control experiments, cyclic voltammetry (CV) analysis, and key reaction intermediate characterization, reveals an intermolecular electrochemical redox/cyclization pathway.

Unraveling the Fundamentals of Axial Coordination FeN4+1 Sites Regulating the Peroxymonosulfate Activation for Fenton-Like Activity.

Precise modulation of the axial coordination microenvironment in single-atom catalysts (SACs) to enhance peroxymonosulfate (PMS) activation represents a promising yet underexplored approach. This study introduces a pyrolysis-free strategy to fabricate SACs with well-defined axial-FeN4+1 coordination structures. By incorporating additional out-of-plane axial nitrogen into well-defined FeN4 active sites within a planar, fully conjugated polyphthalocyanine framework, FeN4+1 configurations are developed that significantly enhance PMS activation. The axial-FeN4+1 catalyst excelled in activating PMS, with a high bisphenol A (BPA) degradation rate of 2.256 min-1, surpassing planar-FeN4/PMS systems by 6.8 times. Theoretical calculations revealed that the axial coordination between N and the Fe sites forms an optimized axial FeN4+1 structure, disrupting the electron distribution symmetry of Fe and optimizing the electron distribution of the Fe 3d orbital (increasing the d-band center from -1.231 to -0.432eV). Consequently, this led to an enhanced perpendicular adsorption energy of PMS from -1.79 to -1.82eV and reduced energy barriers for the formation of the key reaction intermediate (O*) that generates 1O2. This study provides new insights into PMS activation through the axial coordinated engineering of well-defined SACs in water purification processes.

In Situ Synthesis of Copper-Based Metal-Organic Frameworks with Ligand Defects for Electrochemical Reduction of CO2 into C2 Products.

Electrochemical reduction of CO2 into high-value-added products is a potential approach to solving environmental problems but is limited by poor product selectivity and low efficiency. Metal-organic framework (MOF) materials have been considered one of the most promising catalysts, but their application is limited by complicated preparation processes, especially during the synthesis of organic ligands. In this work, a new three-dimensional Cu-MOF (JXUST-301) with high porosity was constructed based on the naphthalene diimide (NDI) ligand. Furthermore, JXUST-301 with ligand defects (JXUST-301D) originating from the missing NDI unit was synthesized via an in situ reaction. The presence of ligand defects endows JXUST-301D with a better CO2RR performance with a FEC2 of 56.7% and a jC2 of -162.4 mA cm-2. Mechanistic studies revealed that the hierarchical pore structure and amino sites are created from the absence of the NDI unit, which promotes the exposure of catalytically active sites and CO2 enrichment. Furthermore, the electronic structure of the Cu sites is modulated to upshift the d-band center, facilitating chemical adsorption and activation of key reaction intermediates. This work provides new insight into the in situ preparation of efficient Cu-MOF catalysts by introducing defects for the CO2RR.

Recovery of Magnetic Ni Particles from Spent Catalyst Leachate by Direct Cementation

An alternative method based on cementation for the recovery of nickel from spent Ni/Al2O3 reforming catalyst pregnant leach solution (PLS) was proposed to overcome the limitations of traditional two-step extraction and precipitation processes. Thermodynamic analysis was used to evaluate the potential interference of key reactions, such as nickel and sacrificial metal leaching, with the selective cementation of nickel from the PLS. Key variables in the cementation process were optimized using response surface methodology (RSM) combined with Box–Behnken design (BBD). Under optimal conditions—pH 2.2 ± 0.1, processing time of 15 min, and Al/Ni molar ratio of 2.65—a maximum nickel recovery of 73.2% was achieved. Extensive characterization confirmed the high quality of the cemented nickel product: (i) ICP-OES indicated nickel purity of 99.47%, (ii) XRD patterns verified the presence of pure face-centered cubic nickel, (iii) SEM-EDS and vibrating sample magnetometry confirmed the high purity of the metallic nickel particles.

Simultaneous construction of Zr-β zeolite with high content and high accessibility of framework Zr sites in the conversion of ethanol to 1,3-butadiene: Mechanisms and synergistic effects

Metallosilicate zeolites, represented by Zr-β zeolite, possess unique porosity and tunable acidity, showing great potential in the conversion of ethanol to 1,3-butadiene. However, there still remains potential for further improvement of catalytic activity and stability by breaking the bottleneck framework metal site content and microporosity diffusion. In this paper, a novel Zr-β zeolite with both high content and high accessibility of framework Zr sites was successfully synthesized via the combination strategy of “Improved Decomposition Reconstruction” and “Silanization.” Based on the activity evaluation experiments of key reaction steps and in situ DRIFTS in the conversion of ethanol to 1,3-butadiene, the enhanced activity and stability are due to the synergistic effects of the content and accessibility of framework Zr sites, which both facilitate reactant conversion and inhibit the covering of active sites or the plugging of pore channels by polymerized heavy compounds. The prepared zeolite demonstrates excellent performance with a total conversion of 66 % and a 1,3-butadiene selectivity above 67 % in 100 h, along with good regenerability.

Ag nanoparticles on arginine-cyanoguanidine functionalized magnetic g-C3N4: A catalyst for nitroaromatic hydrogenation and regioselective click reactions

This study describes the development of a novel hybrid nanocatalyst that was obtained by doping magnetic g-C3N4 with Ag nanoparticles and modifying it with arginine and cyanoguanidine (Ag@Fe3O4-g-C3N4-Arg-CG). Comprehensive characterization of the nanocatalyst using techniques such as FTIR, XRD, SEM, and TGA confirmed its structural and morphological properties. The catalytic efficiency of the synthesized nanostructure was evaluated in two key reactions: the reduction of nitroaromatic compounds and a click reaction for 1,2,3-triazole synthesis. The results demonstrate that Ag@Fe3O4-g-C3N4-Arg-CG effectively reduced various nitroaromatic compounds to substituted anilines at room temperature using NaBH4 as the reducing agent. Nitrobenzene reduction did not proceed in aprotic solvents such as acetonitrile, CH2Cl2, and dimethylformamide, whereas it exhibited a high reaction yield in protic solvents such as ethanol and water. The highest yield (100 %) was observed in water at 50 °C using H2O solvent. Additionally, the nanohybrid exhibited significant potential for “green” click chemistry by efficiently synthesizing 1,2,3-triazoles under mild conditions, with low catalyst loading. Its magnetic properties facilitated easy recovery, and the catalyst maintained high activity over six cycles, making it suitable for sustainable applications in organic transformations.

Effect of mesh aluminum alloy on hydrogen and propane explosion characteristics

In order to explore the effect of mesh aluminum alloy (MAA) on the explosion characteristics of different types of gases, experiments were conducted by filling MAA in hydrogen and propane explosion pipes. The explosion characteristic parameters of hydrogen and propane with different volume fractions under the action of MAA were obtained. The chain reaction process and thermodynamic reaction mechanism of hydrogen and propane explosions were studied using the numerical simulation software CHEMKIN-PRO and Materials Studio. The experimental results show that MAA significantly promotes hydrogen explosions but inhibits propane explosions. Simulation results show that ·H, ·O, and ·OH are key radicals in the hydrogen explosion process. As the hydrogen volume fraction increases, the number of radicals in the reaction system also increases. When MAA is filled in the hydrogen explosion test pipe, the turbulence of the flame structure inside the pipe increases the collision probability between key radicals such as ·H, ·O, and ·OH, sharply increasing the temperature of the explosion reaction system, resulting in a promoting effect of MAA on hydrogen explosions. When MAA is introduced into the propane explosion test pipe, it creates a barrier and wall effect. This reduces the number of key radicals in the reaction system and lowers the likelihood of radical collisions, which slows down the rates of multiple chain reactions and inhibits the propane explosion. Thermodynamically, it can be seen that propane requires more energy than hydrogen for key elementary reactions to explode, making it more difficult to react.

In Situ Construction of Highly Dispersed Pd on Cobalt Nanoparticle on Hollow Functional Cubic Graphene by Double Framework for ORR.

Developing advanced functional carbon materials is essential for electrocatalysis, caused by their vast merits for boosting many key energy conversion reactions. Herein, the covalent organic frameworks (COFs) is utilized on metal-organic frameworks (MOFs) as the template, under the controllable metal atoms thermal migration process successfully in situ constructs Pd-Co alloy nanoparticles on hollow cubic graphene. The electrocatalytic oxygen reduction reaction (ORR) evaluation showed excellent performances with a half-wave potential of 0.866V, and a limited current density of 4.975mA cm-2, that superior to the commercial Pt/C and Co nanoparticles. The contrast experiments and X-ray absorption spectrum demonstrated the aggregated electrons at highly dispersed Pd atoms on Co nanoparticle that promoted the main activities. This work not only enlightens the novel carbon materials designing strategies but also suggests heterogeneous electrocatalysis.

Short DNAzymes for Efficient Catalysis of "Click" Reactions in Solution and on Surface.

We have systematically investigated and found surprising superior catalytic activities of very short DNAzymes for copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), both in solution and on surface. As a key reaction of the "click chemistry" class, CuAAC is a highly efficient and specific covalent conjugation tool with demonstrated applications in organic synthesis, bioconjugation, and surface functionalization; however, it requires the presence of the Cu(I) catalyst, which is an unstable species in aqueous solutions. We show here that one ultrashort, 14-nucleotide-truncated fragment of an earlier in vitro selected DNAzyme (CLICK-17) shows a striking and superior catalytic activity toward the in trans CuAAC reaction in solution and on surface in the presence of either Cu(I) or Cu(II), at significantly lowered concentrations. These results obviate the need for long-sequence DNAzymes, selected out of the homogeneous solution phase, for application in complex surface environments.