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Catalytic conversion of carbon dioxide (CO2) into value-added chemicals is of pivotal importance, well the cost of capturing CO2 from dilute atmosphere is super challenge. One promising strategy is combining the adsorption and transformation at one step, such as applying alkali solution that could selectively reduce carbonate (CO3 2-) as consequences of CO2 adsorption. Due to complexity of this system, the mechanistic details on controlling the hydrogenation have not been investigated in depth. Herein, Ru/TiO2 catalyst was applied as a probe to elucidate the mechanism of CO3 2- activation, in which with thermodynamic and kinetic investigations, a compact Langmuir-Hinshelwood reaction model was established which suggests that the overall rate of CO3 2- hydrogenation was controlled by a specific C-O bond rupture elementary step within HCOO- and the Ru surface was mainly covered by CO3 2- or HCOO- at independent conditions. This assumption was further supported by negligible kinetic isotope effects (kH/kD≈1), similarity on reaction barriers of CO3 2- and HCOO- hydrogenation (ΔH≠ hydr,Na2CO3 and ΔH≠ hydr,HCOONa) and a non-variation of entropy (ΔS≠ hydr≈0). More interestingly, the alkalinity of the solution is certainly like a two sides in a sword and could facilitate the adsorption of CO2 while hold back catalysis during CO3 2- hydrogenation.

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Reduction of carbon dioxide (CO2) by renewable electricity to produce multicarbon chemicals, such as ethylene (C2H4), continues to be a challenge because of insufficient Faradaic efficiency, low production rates, and complex mechanistic pathways. Here, we report that the rate-determining steps (RDS) on common copper (Cu) surfaces diverge in CO2 electroreduction, leading to distinct catalytic performances. Through a combination of experimental and computational studies, we reveal that C─C bond-making is the RDS on Cu(100), whereas the protonation of *CO with adsorbed water becomes rate-limiting on Cu(111) with a higher energy barrier. On an oxide-derived Cu(100)-dominant Cu catalyst, we reach a high C2H4 Faradaic efficiency of 72%, partial current density of 359 mA cm-2, and long-term stability exceeding 100 h at 500 mA cm-2, greatly outperforming its Cu(111)-rich counterpart. We further demonstrate constant C2H4 selectivity of >60% over 70 h in a membrane electrode assembly electrolyzer with a full-cell energy efficiency of 23.4%.

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Photoconvertible fluorescent proteins (pcFPs) undergo a slow photochemical transformation when irradiated with blue light. Since their emission is shifted from green to red, pcFPs serve as convenient fusion tags in several cutting-edge biological imaging technologies. Here, a pcFP termed the Least Evolved Ancestor (LEA) was used as a model system to determine the rate-limiting step of photoconversion. Perdeuterated histidine residues were introduced by isotopic enrichment and chromophore content was monitored by absorbance. pH-dependent photoconversion experiments were carried out by exposure to 405-nm light followed by dark equilibration. The loss of green chromophore correlated well with the rise of red, and maximum photoconversion rates were observed at pH 6.5 (0.059 ± 0.001 min-1 for red color acquisition). The loss of green and the rise of red provided deuterium kinetic isotope effects (DKIEs) that were identical within error, 2.9 ± 0.9 and 3.8 ± 0.6, respectively. These data indicate that there is one rate-determining step in the light reactions of photoconversion, and that CH bond cleavage occurs in the transition state of this step. We propose that these reactions are rate-limited on the min time scale by the abstraction of a proton at the His62 beta-carbon. A conformational intermediate such as a twisted or isomerized chromophore is proposed to slowly equilibrate in the dark to generate the red form. Additionally, His62 may shuttle protons to activate Glu211 to serve as a general base, while also facilitating beta-elimination. This idea is supported by a recent X-ray structure of methylated His62.

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This work focuses on the comparison of H2 evolution in the hydrolysis of boron-containing hydrides (NaBH4, NH3BH3, and (CH2NH2BH3)2) over the Co metal catalyst and the Co3O4-based catalysts. The Co3O4 catalysts were activated in the reaction medium, and a small amount of CuO was added to activate Co3O4 under the action of weaker reducers (NH3BH3, (CH2NH2BH3)2). The high activity of Co3O4 has been previously associated with its reduced states (nanosized CoBn). The performed DFT modeling shows that activating water on the metal-like surface requires overcoming a higher energy barrier compared to hydride activation. The novelty of this study lies in its focus on understanding the impact of the remaining cobalt oxide phase. The XRD, TPR H2, TEM, Raman, and ATR FTIR confirm the formation of oxygen vacancies in the Co3O4 structure in the reaction medium, which increases the amount of adsorbed water. The kinetic isotopic effect measurements in D2O, as well as DFT modeling, reveal differences in water activation between Co and Co3O4-based catalysts. It can be assumed that the oxide phase serves not only as a precursor and support for the reduced nanosized cobalt active component but also as a key catalyst component that improves water activation.

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Traditional cathode recycling methods have become outdated amid growing concerns for high-value output and environmental friendliness in spent Li-ion battery (LIB) recycling. Our study presents a closed-loop approach that involves selective sulfurization roasting, water leaching, and regeneration, efficiently transforming spent ternary Li batteries (i.e., NCM) into high-performance cathode materials. By combining experimental investigations with density functional theory (DFT) calculations, we elucidate the mechanisms within the NCM-C-S roasting system, providing a theoretical foundation for selective sulfidation. Utilizing in situ X-ray diffraction techniques and a series of consecutive experiments, the study meticulously tracks the evolution of regenerating cathode materials that use transition metal sulfides as their primary raw materials. The Li-rich regenerated NCM exhibits exceptional electrochemical performance, including long-term cycling, high-rate capabilities, reversibility, and stability. The closed-loop approach highlights the sustainability and environmental friendliness of this recycling process, with potential applications in other cathode materials, such as LiCoO2 and LiMn2O4. Compared with traditional methods, this short process approach avoids the complexity of leaching, solvent extraction, and reverse extraction, significantly increasing metal utilization and Li recovery rates while reducing pollution and resource waste.

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Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

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The mixed ionic and electronic oxide LaNi0.6Fe0.4O3-δ (LNF) is a promising ceramic cathode material for solid oxide fuel cells. Since the reaction rate of oxygen interaction with the cathode material is extremely important, the present work considers the oxygen exchange mechanism between O2 and LNF oxide. The kinetic dependence of the oxygen/oxide interaction has been determined by two isotopic methods using 18O-labelled oxygen. The application of the isotope exchange with the gas phase equilibrium (IE-GPE) and the pulsed isotope exchange (PIE) has provided information over a wide range of temperatures (350-800 °C) and oxygen pressures (10-200 mbar), as each method has different applicability limits. Applying mathematical models to treat the kinetic relationships, the oxygen exchange rate (rH, atom × cm-2 × s-1) and the diffusion coefficient (D, cm2/s) were calculated. The values of rH and D depend on both temperature and oxygen pressure. The activation energy of the surface exchange rate is 0.73 ± 0.05 eV for the PIE method at 200 mbar, and 0.48 ± 0.02 eV for the IE-GPE method at 10-20 mbar; for the diffusion coefficient, the activation energy equals 0.62 ± 0.01 eV at 10-20 mbar for the IE-GPE method. Differences in the mechanism of oxygen exchange and diffusion on dense and powder samples are observed due to the different microstructure and surface morphology of the samples. The influence of oxygen pressure on the ratio of contributions of different exchange types to the total oxygen exchange rate is demonstrated. For the first time, the rate-determining step in the oxygen exchange process for LNF material has been identified. This paper discusses the reasons for the difference in the mechanisms of oxygen exchange and diffusion.

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The electrocatalytic reduction of CO2 towards CO is one of the most desirable routines to reduce atmospheric CO2 concentration and maintain a global carbon balance. In this work, a novel porous NiCu-embedded ZIF-derived N-doped carbon nanoparticle (NiCu@NCNPs) catalyst has been identified as an active, highly selective, stable, and cost-effective catalyst in CO2 reduction. A CO selectivity as high as 100% has been achieved on NiCu@NCNPs which is the highest reported to date. The particle current density of CO on NiCu@NCNPs is around 15 mA cm-2 under the optimized potential at -0.9 V vs. RHE. The NiCu@NCNPs electrode also exhibits excellent stability during the five sequential CO2 electroreduction experiments. The superior catalytic performance of NiCu@NCNPs in CO2RR can be related to its microstructure with high electrochemical surface area and low electron transfer resistance. Furthermore, a kinetic analysis has shown the formation of intermediate *COOH is the rate-determining step in CO2RR towards CO. According to the results of density functional theory (DFT) calculations, a low Gibbs-free energy change (∆G) for the rate-determining step leads to the enhanced catalytic performance of CO2RR on NiCu@NCNPs.

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Limited comprehension of the reaction mechanism has hindered the development of catalysts for CO2 reduction reactions (CO2 RR). Here, the bimetallic AgCu nanocatalyst platform is employed to understand the effect of the electronic structure of catalysts on the selectivity and activity for CO2 electroreduction to CO. The atomic arrangement and electronic state structure vary with the atomic ratio of Ag and Cu, enabling tunable d-band centers to optimize the binding strength of key intermediates. Density functional theory calculations confirm that the variation of Cu content greatly affects the free energy of *COOH, *CO (intermediate of CO), and *H (intermediates of H2 ), which leads to the change of the rate-determining step. Specifically, Ag96 Cu4 reduces the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction(HER), thus achieving the best CO selectivity. While Ag70 Cu30 shows relatively low formation energy of both *COOH and *H, the compromised thermodynamic barrier and product selectivity allows Ag70 Cu30 the best CO partial current density. This study realizes the regulation of the selectivity and activity of electrocatalytic CO2 to CO, which provides a promising way to improve the intrinsic performance of CO2 RR on bimetallic AgCu.

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Photo-thermo catalysis utilizing light has been a promising strategy to improve the conventional thermal catalytic activity and attracts great attention nowadays. However, how heat works in synergy with light radiation is still unclear. This Concept article is trying to clarify the specific contents via summarizing the kinetic studies including 1) proposing elementary steps through pressure dependence studies, 2) estimating reaction barriers through measuring the apparent activation energies and 3) assigning the kinetically relevant step(s) with kinetic isotope effects (KIE) as well as 4) exploring the relationship of the reaction rate with the light excitation wavelength and light intensity. The challenges in kinetic studies such as describing the light-induced carrier transfer process, the surface temperature under light illumination as well as reaction intermediates were discussed at the same time. Finally, an outlook about kinetic studies in clarifying the photo-thermo catalysis reaction mechanism was proposed.

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Uptake of Cu by Thalassiosira oceanica requires that Cu(II) is reduced to Cu(I) prior to transport across the cell membrane. The reduction step is mediated biochemically by cellular reductases active with a broad range of Cu chemical species. Here, we report on the cellular Cu(II) reduction and Cu(I) uptake of a diatom under saturating and subsaturating irradiance. An increase in growth irradiance, from 50 to 400 µmol photons m-2 s-1, increased the rate of extracellular Cu(II) reduction and steady-state Cu uptake. Under these conditions, Cu-limited cells acquired Cu more efficiently and maintained faster rates of growth than Cu-limited cells in low light. Pseudo-first-order reaction rate constants were about 70-fold faster for Cu(I) uptake than for Cu(II) reduction so that reduction was the rate-determining step in Cu acquisition. Accordingly, steady-state Cu uptake rates predicted from the reduction rate constants agreed well with measured rates of Cu uptake obtained from cultures growing at low nanomolar Cu concentrations. Transcript abundance of putative Cu(II) reductases followed a similar pattern to cupric reductase activity, increasing in Cu-limited cells and with increasing growth irradiance. The results are significant in showing Cu(II) reduction as the rate-determining step in Cu uptake: they suggest that biologically mediated Cu(II) reduction may be an important part of the Cu cycle in surface waters of the open sea.

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Exploring catalyst reconstruction under the electrochemical condition is critical to understanding the catalyst structure-activity relationship as well as to design effective electrocatalysts. Herein, a PbF2 nanocluster is synthesized and its self-reconstruction under the CO2 reduction condition is investigated. F- leaching, CO2 -saturated environment, and application of a cathodic potential induce self-reconstruction of PbF2 to Pb3 (CO3 )2 (OH)2 , which effectively catalyze the CO2 reduction to formate. The in situ formed Pb3 (CO3 )2 (OH)2 discloses >80% formate Faradaic efficiencies (FEs) across a broad range of potentials and achieves a maximum formate FE of ≈90.1% at -1.2 V versus reversible hydrogen electrode (RHE). Kinetic studies show that the CO2 reduction reaction (CO2 RR) on the Pb3 (CO3 )2 (OH)2 is rate-limited at the CO2 protonation step, in which proton is supplied by bicarbonate (HCO3 - ) in the electrolyte. To improve the CO2 RR kinetics, the Pb3 (CO3 )2 (OH)2 is further doped with Pd (4 wt%) to enhance its HCO3 - adsorption, which leads to accelerated protonation of CO2 . Therefore, the Pd-Pb3 (CO3 )2 (OH)2 (4 wt%) reveals higher formate FEs of >90% from -0.8 to -1.2 V versus RHE and reaches a maximum formate FE of 96.5% at -1.2 V versus RHE with a current density of ≈13 mA cm-2 .

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The identity of the rate-determining step (RDS) in the electrochemical CO reduction reaction (CORR) on Cu catalysts remains unresolved because: 1) the presence of mass transport limitation of CO; and 2) the absence of quantitative correlation between CO partial pressure (pCO ) and surface CO coverage. In this work, we determined CO adsorption isotherms on Cu in a broad pH range of 7.2-12.9. Together with electrokinetic data, we demonstrate that the reaction orders of adsorbed CO at pCO <0.4 and >0.6 atm are 1st and 0th , respectively, for multi-carbon (C2+ ) products on three Cu catalysts. These results indicate that the C-C coupling is unlikely to be the RDS in the formation of C2+ products in the CORR. We propose that the hydrogenation of CO with adsorbed water is the RDS, and the site competition between CO and water leads to the observed transition of the CO reaction order.

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Activation of high-energy triple-bonds of N2 is the most significant bottleneck of ammonia synthesis under ambient conditions. Here, by importing cobalt single clusters as strong electron-donating promoter into the catalyst, the rate-determining step of ammonia synthesis is altered to the subsequent proton addition so that the barrier of N2 dissociation can be successfully overcome. As revealed by density functional theory calculations, the N2 dissociation becomes exothermic over the cobalt single cluster upon the strong electron backdonation from metal to the N2 antibonding orbitals. The energy barrier of the positively shifted rate-determining step is also greatly reduced. At the same time, advanced sampling molecular dynamics simulations indicate a barrier-less process of the N2 approaching the active sites that greatly facilitates the mass transfer. With suitable thermodynamic and dynamic property, a high ammonia yield rate of 76.2 µg h-1 mg[Formula: see text] and superior Faradaic efficiency of 52.9% were simultaneously achieved.

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The multimetallic sulfur-framework catalytic site of biological nitrogenases allows the efficient conversion of dinitrogen (N2 ) to ammonia (NH3 ) under ambient conditions. Inspired by biological nitrogenases, a bimetallic sulfide material (FeWSx @FeWO4 ) was synthesized as a highly efficient N2 reduction (NRR) catalyst by sulfur substitution of the surface of FeWO4 nanoparticles. Thus prepared FeWSx @FeWO4 catalysts exhibit a relatively high NH3 production rate of 30.2 ug h-1 mg-1cat and a Faraday efficiency of 16.4 % at -0.45 V versus a reversible hydrogen electrode in a flow cell; these results have been confirmed via purified 15 N2 -isotopic labeling experiments. In situ Raman spectra and hydrazine reduction kinetics analysis revealed that the reduction of undissociated hydrazine intermediates (M-NH2 -NH2 ) on the surface of the bimetallic sulfide catalyst is the rate-determing step for the NRR process. Therefore, this work can provide guidance for elucidating the structure-activity relationship of NRR catalysts.

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Fluorochemicals are persistent, bioaccumulative, and toxic compounds that are widely tributed in the environment. Developing efficient biodegradation strategies to decompose the fluorochemicals via breaking the inert C-F bonds presents a holistic challenge. As a promising biodegradation enzyme candidate, fluoroacetate dehalogenase (FAcD) has been reported as the only non-metallic enzyme to catalyze the cleavage of the strong C-F bond. Here, we systematically investigated the catalytic actions of FAcD toward its natural substrate fluoroacetate using molecular dynamics simulations and quantum mechanism/molecular mechanism calculations. We propose that the enzymatic transformation involves four elementary steps, (I) C-F bond activation, (II) nucleophilic attack, (III) C-O bond cleavage, and (IV) proton transfer. Our results show that nucleophilic attack is the rate-determining step. However, for difluoroacetate and trifluoroacetate, C-F bond activation, instead of nucleophilic attack, becomes the rate-determining step. We show that FAcD, originally recognized as α-fluorocarboxylic acid degradation enzyme, can catalyze the defluorination of difluoroacetate to glyoxylate, which is captured by our high-resolution mass spectrometry experiments. In addition, we employed amino acid electrostatic analysis method to screen potential mutation hotspots for tuning FAcD's electrostatic environment to favor substrate conversion. The comprehensive understanding of catalytic mechanism will inform a rational enzyme engineering strategy to degrade fluorochemicals for benefits of environmental sustainability.

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Precipitation of arsenic as As2S3 produces little waste sludge, has the potential for low chemical consumption and for selective metal(loid) removal. In this study, arsenic removal from acidic (pH 2), metallurgical wastewater was tested in industrially relevant conditions. Sulfides added at a S:As molar ratio of 2.5 and 5 resulted in removal of 99% and 84% of As(III) and As(V). Precipitation of As2S3 from the As(III) and industrial wastewater containing 17% As(V) was nearly instantaneous. For the synthetic As(V) solution, reduction to As(III) was the rate limiting step. At a S:As ratio of 20 and an observed removal rate (k2 = 4.8 (mol L-1) h-1), two hours were required to remove of 93% of arsenic from a 1 g As L-1 solution. In the case of As(V) in industrial samples this time lag was not observed, showing that components in the industrial wastewater affected the removal and reduction of arsenate. Speciation also affected flocculation and coagulation characteristics of As2S3 particles: As(V) reduction resulted in poor coagulation and flocculation. Selective precipitation of arsenic was possible, but depended on speciation, S:As ratio and other metals present.

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Recently major advances were gained on the designed proteins aimed to generate biomolecular mimics of proteases. Although such enzyme-like catalysts must still suffer refinements for improving the catalytic activity, at the moment, they represent a good example of artificial enzymes to be tested in different fields. Herein, a de novo designed homo-heptameric peptide assembly (CC-Hept) where the esterase activity towards p-nitro-phenylacetate was obtained for introduction of the catalytic triad (Cys-His-Glu) into the hydrophobic matrix, is the object of the present combined molecular dynamics and quantum mechanics/molecular mechanics investigation. Constant pH Molecular Dynamics simulations on the apoform of CC-Hept suggested that the Cys residues are present in the protonated form. Molecular dynamics (MD) simulations of the enzyme-substrate complex evidenced the attitude of the enzyme-like system to retain water molecules, necessary in the hydrolytic reaction, in correspondence of the active site, represented by the Cys-His-Glu triad on each of the seven chains, without significant structural perturbations. A detailed reaction mechanism of esterase activity of CC-Hept-Cys-His-Glu was investigated on the basis of the quantum mechanics/molecular mechanics calculations employing a large quantum mechanical (QM) region of the active site. The proposed mechanism is consistent with available esterases kinetics and structural data. The roles of the active site residues were also evaluated. The deacylation phase emerged as the rate-determining step, in agreement with esterase activity of other natural proteases.

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Increasing attention has been given to amine-copper formate complexes for their use as low-cost printable conductive inks. The structure of amine ligands coordinated to copper centers has been reported to dictate the properties of copper molecular inks, such as stability and printability, thereby influencing the copper reduction pathway during the thermolysis. Yet, the underlying mechanism by which formate is oxidized when complexed with amine ligands is still not fully understood. Here, we propose a mechanistic pathway of copper formate dehydrogenation and decarboxylation and examine the critical role that amine ligands play in their thermal decomposition by employing first-principles electronic structure computations and experimental analyses of thermolysis reactions. Based on the computational characterization of the relevant reaction pathways for a number of primary and secondary amines as well as pyridine ligand complexes, we are the first to show that the hydrogen bonds formed between the amine ligand and formate are the key factors governing the activation energy, providing a design principle for the synthesis of organic ligands that can tune the height of the reaction barriers of the dehydrogenation and decarboxylation reactions. The calculations, confirmed by NMR studies, show that the reduction of Cu(II) to Cu(I) occurs in concert with the release of H2 via the dimerization of Cu(II) hydride. This result suggests that the monomeric elimination of H2 is not favorable for the Cu(II) to Cu(I) reduction and thus identifies dimeric amino copper formate as an important intermediate for copper reduction whose thermodynamic stabilities are also dictated by the nature of the amine ligands.

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Plasmonic photocatalysis has emerged as a new frontier in heterogeneous catalysis due to its promise in harvesting light to drive reactions. Yet many mechanistic aspects remain to be unambiguously defined. Using single-molecule fluorescence imaging, Li et al. studied a fluorogenic and plasmon-enhanced reaction, amplex red oxidation, on single Au nanorods at subturnover resolution and under operando conditions. Both the rate-determining step and its activation energy were identified from the multiple elemental reactions. The results provide insights into the mechanism of plasmonic photocatalysis that may help the rational design of heterogeneous catalysts.