Rate-limiting Step Of Reaction Research Articles

Strengthening the metal-support interaction over Pt/SiO2-TiO(OH)2 by defect engineering for efficient dehydrogenation of dodecahydro-N-ethylcarbazole

Liquid organic hydrogen carriers (LOHC) are considered as the promising candidates for large-scale hydrogen storage. The N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NECZ/12H-NECZ) system has received increasing attention due to its excellent comprehensive properties in the hydrogen storage candidates. In this work, the Pt/SiO2-TiO(OH)2 catalysts are synthesized and show good activity, selectivity and stability for 12H-NECZ dehydrogenation reaction. Among them, the 2.5 wt% Pt/SiO2-TiO(OH)2 catalyst shows the best dehydrogenation performance with 5.75 wt% H2 release amount and 98 % selectivity of NECZ. Combined with XRD, HRTEM, ATR-FTIR, XPS and EPR analysis, it is found that the oxygen vacancy concentration in Pt/SiO2-TiO(OH)2 is significantly enhanced due to the formation of Si-O-Ti species compared with Pt/SiO2 and Pt/TiO(OH)2, which strengthens the SMSI (strong metal-supporting interaction) effect between metal Pt and support SiO2-TiO(OH)2. The optimized d-band center of catalyst is beneficial for accelerating the sluggish kinetics of the rate-limiting step of the whole dehydrogenation reaction. Furthermore, compared with the results by replacing SiO2 with Al2O3 or CeO2, it is indicated that the introduction of oxides mainly plays the role of regulating the surface electronic state of TiO(OH)2 and increasing the oxygen vacancy concentration.

A Piezo-Fenton System with Rapid Iron Cycling and Hydrogen Peroxide Self-Supply Driven by Ultrasound.

The piezo-Fenton system has attracted attention not only because it can enhance the Fenton reaction activity by mechanical energy input, but also because it is expected to realize a class of stimuli-responsive advanced oxidation systems by regulating energy input and hydrogen peroxide self-supply, thus greatly enriching the application possibilities of Fenton chemistry. In this work, a series of Fe-doped g-C3 N4 (g-C3 N4 -Fe) as a piezo-Fenton system were synthesized where the iron stably immobilized through Fe-N interaction. The piezo-induced electrons generate on g-C3 N4 matrix support the conversion of Fe(III) to Fe(II) and promote rate-limiting step of Fenton reaction. With the optimal Fe loading, g-C3 N4 -0.5Fe can achieve methylene blue (MB) degradation under ultrasonic treatment with first-order kinetic rate constants of 75×10-3 min-1 . Most importantly, the g-C3 N4 -Fe can maintain good catalytic activity in a wide pH range (pH=2.0∼9.0) and be cyclic used without iron leaching to solution (<0.001 μg ⋅ L-1 ), overcoming the disadvantage of traditional Fe-based Fenton catalysts that can only be applied under acidic conditions and prone to secondary pollution. In addition, g-C3 N4 -0.5Fe also exhibits antibacterial properties of Escherichia coli and Staphylococcus aureus under ultrasound. Hydroxyl radicals mainly contribute to the degradation of MB and the sterilization process. Our work is an attempt to clarify the role of g-C3 N4 -Fe in the conversion of mechanical energy to ROS and provide inspirations for the piezo-Fenton system design.

The effects of biologically important divalent and trivalent metal cations on the cyclization step of dopamine autoxidation reaction: A quantum chemical study

Dopamine is the most essential monoaminergic neurotransmitter involved in the pathophysiology of neurodegenerative disorders, and its autoxidation has been recognized as one of the potential trigger factors for dopaminergic neuron loss. The cyclization of dopamine o -quinone was shown to be the irreversible and rate-limiting step of the autoxidation reaction at physiologic pH values. Furthermore, various metal ions such as Al 3+ , Fe 3+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Pb 2+ , and Mn 2+ have been clinically associated with neurodegeneration, especially Parkinsonism and dementia. It has been proposed that these metal ions could increase the rate of the dopamine autoxidation reaction; however, the exact mechanism has not yet been fully understood. Using advanced quantum chemical calculations with the inclusion of solvent effects we showed that except for Mn 2+ , the studied metal cations could form complexes with dopamine o -quinone and significantly increase the dopamine o -quinone cyclization rate in aqueous solution; first, by enabling the cyclization to proceed spontaneously without the attack of the unprotonated amino group by hydroxide ion; second, by decreasing the intrinsic activation energy; and third, by decreasing the free energy of protonated amino group deprotonation. The latter also decreases the protective effect of acidic pH on dopamine autoxidation found in synaptic vesicles. The results are fully consistent with experimental data and provide deeper understanding of the effects of metal cations on the dopamine autoxidation reaction at physiologic pH values.

Oxygen Healing and CO2 /H2 /Anisole Dissociation on Reduced Molybdenum Oxide Surfaces Studied by Density Functional Theory.

Reduced molybdenum oxides are versatile catalysts for deoxygenation and hydrodeoxygenation reactions. In this work, we have performed spin-polarized DFT calculations to investigate oxygen healing energies on reduced molybdenum oxides (reduced α-MoO3 , γ-Mo4 O11 and MoO2 ). We find that Mo+4 on MoO2 (100) is the most active for abstracting an oxygen from the oxygenated compounds. We further explored CO2 adsorption and dissociation on reduced α-MoO3 (010) and MoO2 (100). In comparison to reduced α-MoO3 (010), CO2 adsorbs more strongly on MoO2 (100). We find that CO2 dissociates on MoO2 (100) via a two-step process, the overall barrier for which is 0.6 eV. This barrier is 1.7 eV lower than that on reduced α-MoO3 (010), suggesting a much higher activity for deoxygenation of CO2 to CO. As H2 dissociation is shown to be the rate-limiting step for hydrodeoxygenation reactions, we also studied activation barriers for H2 chemisorption on MoO2 (100). We find that the chemisorption barriers are 0.7 eV lower than that reported on reduced α-MoO3 (010). Finally, we have studied the dissociation (C-O cleavage) of anisole (a lignin-based biofuel model compound) on MoO2 (100). We find that anisole binds very strongly on MoO2 (100) with an adsorption energy of -1.47 eV. According to Sabatier's principle, strongly adsorbing reactants poison the catalyst surface, which may explain the low activity of MoO2 observed during experiments for hydrodeoxygenation of anisole.

Critical role of Cs doping in the structure and NH3 decomposition performance of Ru/MgO catalysts

The NH3 decomposition activity of Ru/MgO catalysts for the production of H2 decreases with increasing calcination temperature. Here, we found that this decrease in activity was the result of the interaction between the Ru and MgO support becoming stronger, causing formation of cationic Ru species. To mitigate this decrease in activity, we investigated the use of doping Ru/MgO catalysts with rare earth, alkali, or alkaline earth metals and found that Cs was particularly effective at enhancing catalytic activity, even at high calcination temperatures. Further examination revealed that doping with Cs weakened the interaction between the Ru and MgO support, resulting in the production of metallic Ru species. The metallic Ru produced by the doping of Cs enhanced the associative desorption of N atoms, which is the rate-limiting step of the NH3 decomposition reaction.

Understanding of Etching Mechanism of Si3N4 Film in H3PO4 Solution For The Fabrication of 3D NAND Devices

Silicon nitride (Si3N4) has been widely used as an insulating or etch stop layer in the semiconductor devices [1]. For example, in a 3D V-NAND flash memory manufacturing process, Si3N4 is alternately stacked with silicon oxide (SiO2) to form a NAND structure. Here, it is necessary to selectively etch Si3N4 avoiding etching of SiO2 in the repeated Si3N4/SiO2 multi-stack layers. In general, phosphoric acid (H3PO4) is used to selectively etch Si3N4 against SiO2 [2]. However, since the concentration of H3PO4 solution changes with the evaporation of H2O, it is not easy to determine the concentration dependence of Si3N4 etching rate in H3PO4 solution. In order to properly control the shape of the 3D V-NAND structure, it is necessary to extensively understand the effect of H3PO4 concentration on the Si3N4 etching. The study of Si3N4 etching has been mainly focused on the effect of additives in H3PO4 on the behavior of Si3N4 etching to solve the issue such as oxide regrowth so far [3, 4]. Fundamental study of the Si3N4 etching reaction mechanism in H3PO4 is lacking. In this study, the Si3N4 etching mechanism in H3PO4 solution is elucidated systematically.For the investigation of Si3N4 etching reaction mechanism, LPCVD Si3N4 blanket wafer and Si3N4/SiO2 multi-stack layered trench wafer were used. Etching experiments of of Si3N4 were conducted in 10-95 wt% H3PO4 solutions at 160 °C. Spectroscopic ellipsometry and field emission scanning electron microscopy were used to measure the etching rate of Si3N4 after etching process.First, the changes in etching rate of Si3N4 in the various concentrations of H3PO4 solution were investigated. As shown in Fig. 1, according to our kinetic calculation and experiments, etching rate of Si3N4 increased as the H3PO4 concentration increased until the concentration of H3PO4 reaches a certain concentration that produced the highest etching rate. However, etching rate of Si3N4 decreased with the concentration of H3PO4 beyond the critical H3PO4 concentration. According to the results, there may be two concentrations of H3PO4 solution which produce an identical etching rate of Si3N4. It is also suggested that not only H3PO4 but also H2O plays an important role in the Si3N4 etching kinetics.To investigate the role of H2O and H3PO4 in the etching reaction of Si3N4, kinetic isotope effect (KIE) of Si3N4 etching reaction in H3PO4 solution was used. KIE provides information about which reactant determines the rate-limiting step. In this study, each reactant of Si3N4 etching reaction, H2O or H3PO4, was substituted with D2O and D3PO4, respectively. Then, etching of Si3N4 was conducted in four different solutions. As shown in Fig. 2, when H3PO4 was replaced by D3PO4, the Si3N4 etching rate was not significantly changed. However, when H2O was replaced by D2O, the Si3N4 etching rate decreased by 30 %. Therefore, it is thought that rate-limiting step of the Si3N4 etching reaction is determined by an elementary reaction related to H2O rather than H3PO4.Based on the above results, Si3N4 etching reaction mechanism was suggested. First, the Si3N4 surface termination (-NH2) is substituted with H2PO4 -, which is a weak nucleophile, by an SN1-like reaction. When H2PO4 - binds to Si, the backbone of Si3N4 is weakened because the electronegativity of O (3.44) is greater than N (3.04). Next, the Si-N of the weakened backbone of Si3N4 is substituted with Si-OH by an SN2-like reaction of H2O. This SN2-like reaction is considered as a rate-limiting step. It is believed that understanding of etching mechanism of Si3N4 in H3PO4 solution will improve selective etching process of Si3N4 for the integration of 3D V-NAND.

Analyses of pre-steady-state kinetics and isotope effects of the γ-elimination reaction catalyzed by Citrobacter freundii methionine γ-lyase

Methionine γ-lyase (MGL) is a pyridoxal 5′-phosphate–dependent enzyme catalyzing γ-elimination in l-methionine. Pyridoxal 5′-phosphate–dependent enzymes have unique spectral properties that allow to monitor sequential formation and decomposition of various intermediates via the detection of absorbance changes. The kinetic mechanism of the γ-elimination reaction catalyzed by Citrobacter freundii MGL was elucidated here by fast stopped-flow kinetic analysis. Single-wavelength detection of characteristic absorbance changes enabled us to compare transformations of intermediates in the course of the reaction with different substrates. The influence of various γ-substituents in the substrate on the formation of key intermediates was estimated. Kinetic isotope effects of α- and β-protons were determined using deuterium-substituted l-methionine. Contributions of amino acid residues Tyr113 and Tyr58 located in the active site on the formation and decomposition of reaction intermediates were identified too. α-Aminocrotonate formation is the rate-limiting step of the enzymatic γ-elimination reaction. Kinetic isotope effects strongly support concerted reaction mechanisms of transformation between an external aldimine and a ketimine intermediate as well as a ketimine intermediate and an unsaturated ketimine.

Towards the Accurate Thermodynamic Characterization of Enzyme Reaction Mechanisms.

We employed QM/MM molecular dynamics (MD) simulations to characterize the rate-limiting step of the glycosylation reaction of pancreatic α-amylase with combined DFT/molecular dynamics methods (PBE/def2-SVP : AMBER). Upon careful choice of four starting active site conformations based on thorough reactivity criteria, Gibbs energy profiles were calculated with umbrella sampling simulations within a statistical convergence of 1-2 kcal ⋅ mol-1 . Nevertheless, Gibbs activation barriers and reaction energies still varied from 11.0 to 16.8 kcal ⋅ mol-1 and -6.3 to +3.8 kcal ⋅ mol-1 depending on the starting conformations, showing that despite significant state-of-the-art QM/MM MD sampling (0.5 ns/profile) the result still depends on the starting structure. The results supported the one step dissociative mechanism of Asp197 glycosylation preceded by an acid-base reaction by the Glu233, which are qualitatively similar to those from multi-PES QM/MM studies, and thus support the use of the latter to determine enzyme reaction mechanisms.

Effect of Tethered, Axially Coordinated Ligands (TACLs) on Dirhodium(II,II) Catalyzed Cyclopropanation: A Linear Free Energy Relationship Study.

Hammett correlation experiments were used to determine the influence of dirhodium(II,II) paddlewheel complexes with tethered, axially coordinated ligands (TACLs) on the selectivity of rhodium carbenoids in competitive cyclopropanation reactions. The results suggest that dirhodium(II,II) paddlewheel complexes with TACLs are less sensitive to changes in electronics and reduce selectivity in cyclopropanation reactions with acceptor-substituted rhodium carbenoids. Also, Hammett plots with aryl diazoacetates resulted in a nonlinear downward curvature, suggesting a change in the rate-limiting step of the carbene transfer reaction.

Structure and Mechanism of a Cold-Adapted Bacterial Lipase.

The structural origin of enzyme cold-adaptation has been the subject of considerable research efforts in recent years. Comparative studies of orthologous mesophilic–psychrophilic enzyme pairs found in nature are an obvious strategy for solving this problem, but they often suffer from relatively low sequence identity of the enzyme pairs. Small bacterial lipases adapted to distinctly different temperatures appear to provide an excellent model system for these types of studies, as they may show a very high degree of sequence conservation. Here, we report the first crystal structures of lipase A from the psychrophilic bacterium Bacillus pumilus, which confirm the high structural similarity to the mesophilic Bacillus subtilis enzyme, as indicated by their 81% sequence identity. We further employ extensive QM/MM calculations to delineate the catalytic reaction path and its energetics. The computational prediction of a rate-limiting deacylation step of the enzymatic ester hydrolysis reaction is verified by stopped-flow experiments, and steady-state kinetics confirms the psychrophilic nature of the B. pumilus enzyme. These results provide a useful benchmark for examining the structural basis of cold-adaptation and should now make it possible to disentangle the effects of the 34 mutations between the two enzymes on catalytic properties and thermal stability.

Role of water coordination at zinc binding site and its catalytic pathway of dizinc creatininase: insights from quantum cluster approach.

Creatininase is a key enzyme of creatinine-metabolizing pathway in mammals, and has a great potential for diagnostic application. It catalyzes the reversible conversion of creatinine to creatine. Here, we investigated its reaction mechanism with density functional theory in conjunction with the quantum cluster approach. Three reaction pathways in which several possible proton transfers assisted by either His178 or a water ligand to Zn1 (Wat2) or both were considered. DFT calculations reveal, depending on Wat2 coordination mode at Zn1, two competitive ring-opening pathways where His178 playing a central role as a proton shuttle or both His178 and Wat2 serving as a dual catalytic role as a base and an acid, respectively. Three elementary steps were proposed for the reaction: the first involves nucleophilic attack by a bridging hydroxide to the substrate and forms a gem-diolate intermediate, followed by a proton transfer from the gem-diolate to His178 (His178 protonation is a required step for efficient proton transfers). Finally, the second proton transfer from the protonated His178 or Wat2 to the amide of substrate leads to the ring opening. The first proton transfer is the rate-limiting step of the whole reaction, in consistent with previous experimental and computational studies. A detailed understanding of the reaction mechanism of the creatininase enzyme family will also be helpful for developing a biosensor for kidney function.

Accelerating the Activation of NO x − on Ru Nanoparticles for Ammonia Production by Tuning Their Electron Deficiency

Accelerating the Activation of NO _x ⁻ on Ru Nanoparticles for Ammonia Production by Tuning Their Electron Deficiency

Mechanistic Insights into Pyridine Ring Degradation Catalyzed by 2,5-Dihydroxypyridine Dioxygenase NicX.

2,5-Dihydroxypyridine dioxygenase (NicX) from Pseudomonas putida KT2440 is a mononuclear non-heme iron oxygenase that can catalyze the oxidative pyridine ring cleavage. Recently, the reported crystal structure of NicX has lent support to an apical dioxygen catalytic mechanism, while the mechanistic details remain unclear. In this work, we constructed a Fe(II)-O2-substrate complex model and performed a series of combined quantum mechanics/molecular mechanics (QM/MM) calculations to illuminate the catalysis of NicX. Our results reveal that although the substrate does not directly coordinate with the central iron ion, there is an electron transfer from the substrate to the Fe-coordinated dioxygen, and the active form of the reactant complex can be described as DHP•+-Fe(II)-O2•-, which is different from other similar mononuclear non-heme iron. The NicX-catalyzed pyridine ring degradation contains three parts, including the attack of Fe(II)-superoxo on the activated pyridine ring, the dissociation of the Op-Od bond, and the ring-opening of the seven-membered-ring lactone. Owing to the radical characteristic of the pyridine ring, the first attack of Fe(II)-superoxo on the C6 of the pyridine ring was calculated to be quite easy. In the second step of the reaction, the dissociation of the Op-Od bond leads to the incorporation of the first oxygen atom into the substrate, which is the rate-limiting step of the overall reaction with an energy barrier of 18.0 kcal/mol. The resultant intermediate then undergoes an arrangement by the intramolecular attack of Od• on the carbonyl C5, forming the seven-membered-ring lactone. Finally, the Fe(III)-oxo attacks the carbonyl C5 of lactone, accompanied by the ring-opening to generate N-formylmaleamic acid. His105 can promote reactivity by donating a proton to Fe(III)-oxo, but it is not a necessary residue. In addition to the ligated residues of iron, other pocket residues such as Glu177, His189, and His105 mainly play roles in anchoring the substrate.

Effect of oxygen vacancies on the photocatalytic CO2 reduction performance of Bi2WO6: DFT and experimental studies

In order to improve the photocatalytic activity of Bi2WO6 (BWO) under solar light irradiation, the introduction of oxygen vacancies has attracted wide attention owing to its simple synthesis method. However, the intrinsic link between oxygen vacancies and photocatalytic CO2 reduction performance is still elusive. In this work, density functional theory (DFT) calculations combining with experimental measurements verify that oxygen vacancies are inclined to generate in [Bi2O2]2+ layers on BWO (010) surface, which results in narrowed band gap and improved electron-hole pair separation efficiency arising from the formation of Bi 6p impurity level. To the best of our knowledge, the reduction product CO is obtained via the reaction of CO2 with •H, and the intermediate species include •COOH, •CO, •OH, and H2O. Owing to BWO (010) surface chemical state variations, such as charge accumulation and depletion upon the introduction of oxygen vacancies, CO2 and intermediate species change remarkably in adsorption configuration, and so do the reaction energy barriers with or without oxygen vacancies. Apparently, the rate-limiting step for the overall reaction is the transition from •COOH to •CO and •OH, and the corresponding activation barrier value is reduced from 2.83 eV to 1.91 eV, because C–O bond breaks more easily after the introduction of oxygen vacancies. This work provides a new enlightenment and insight into the role of oxygen vacancies in the process of reducing CO2, and paves ways to design defective systems with higher photocatalytic activity.

Carbonized MOF-Coated Zero-Valent Cu Driving an Efficient Dual-Reaction-Center Fenton-like Water Treatment Process through Utilizing Pollutants and Natural Dissolved Oxygen

Excessive consumption of resources and energy is inevitable in a classical Fenton reaction due to the demand for electron donors or electron acceptors (H2O2) and the existence of reaction rate-limiting steps. In this work, we propose an innovative strategy to solve this key scientific problem by utilizing the organic pollutants and the dissolved oxygen (DO) naturally present in the wastewater through a newly developed carbonized metal–organic framework-coated zero-valent Cu catalyst (ZVC@CMOF). It has been found that the formation of a C–O–Cu bond bridge on the catalyst induces electron polarization distribution to form a non-equilibrium surface with electron-rich or electron-poor microareas based on a series of characterization techniques. This typical non-equilibrium surface feature leads to excellent performance for pollutant conversion and a new interfacial reaction mechanism. Various types of refractory organic pollutants can be rapidly degraded in a few minutes in the ZVC@CMOF Fenton-like systems, accompanied by good stability and a wide pH adaptation range. The interfacial reaction processes are revealed by experimental analysis and theoretical calculations, in which pollutants and DO act as electron donors and electron acceptors in the electron-poor and electron-rich microareas, respectively, which greatly reduce the consumption of H2O2 and improve the reaction efficiency and catalytic performance for pollutant removal.

Biodegradation of tetramethylammonium chloride wastewater and inorganic nitrogen removal by a mixed culture

The disposal of wastewater containing tetramethylammonium chloride (TMAC) generated from the semiconductor and photoelectric industries is a challenging problem due to the limited information is available regarding its treatability. This study aims to investigate the feasibility of using biological processes to treat TMAC. An activated sludge collected from a lake near the Southern Taiwan Science Park was used. Various operational parameters, including operating temperature, pH conditions and TMAC dosages were evaluated for the optimal condition. Results showed that the activated sludge could successfully degrade TMAC, and subsequently achieve simultaneous nitrification and denitrification (SND) of the nitrogen-containing intermediates under mild conditions (pH at a range of 3–7 and temperature at a range of 20–40 °C). Besides, more than 60% of the nitrogen-containing intermediates were converted into gaseous nitrogen (N2). TMAC biodegradation was found to follow first-order kinetics. The observed rate constant of TMAC biodegradation increased from 0.64 ╳ 10−4 to 9.57 ╳ 10−4 1/min as the concentration of TMAC decreased. In addition, TMAC demethylation was identified as the rate-limiting step of the entire reaction. Major functional organisms of the activated sludge were identified as Mycobacterium, Ochrobactrum and Arthrobacter species which are aerobic and acidophilic strains. This study can be an important reference for future researches attempting to treatment TMAC wastewater by biological processes.

Rate-Limiting Step of Epoxidation Reaction of the Oxoiron(IV) Porphyrin π-Cation Radical Complex: Electron Transfer Coupled Bond Formation Mechanism.

Epoxidation reactions catalyzed by high-valent metal-oxo species are key reactions in various biological and chemical processes. Because the redox potentials of alkenes are higher than those of most high-valent metal-oxo species, the electron transfer (ET) from the alkene to the high-valent metal-oxo species in the epoxidation reaction is endergonic and must be coupled with another exergonic process. To reveal the mechanism of the ET, we performed a Marcus plot analysis for the epoxidation reaction of the oxoiron(IV) porphyrin π-cation radical complex (compound I) with alkene. The Marcus plots can be simulated with a linear line with the gradient of 0.50 when the redox potential of compound I varies and 0.07 when the redox potential of alkene varies. These results indicate that the ET process is involved in the rate-limiting step and coupled with the following O-C bond formation process: ET coupled bond formation mechanism. The DFT calculations support this conclusion and disclose the details of the mechanism. As the alkene comes close to the oxo ligand, the energy of the highest occupied molecular orbital (HOMO) of the alkene increases and the energy for the ET becomes small enough to allow the ET. Finally, the ET occurs from the HOMO of the alkene to the porphyrin π-radical orbital. The shift of one electron from the HOMO of the alkene by the ET simultaneously results in the O-C half bond formation between the oxo ligand and the alkene. The ET process itself is still endergonic and reversible, but the bond formation coupled with the ET changes the overall process to exergonic and irreversible. We also discuss the similarity with the aromatic hydroxylation reaction and the relevance to the epoxidation reactions of other metal-oxo complexes and peracid.

Mechanism and kinetic study of Paal-Knorr reaction based on in-situ MIR monitoring

An in-depth understanding of reaction processes is beneficial to the development and quality control of chemical products. In this work, the mechanism and kinetics of the Paal-Knorr reaction for pyrrole derivatives are thoroughly studied using in-situ Fourier transform infrared (FTIR) spectroscopy. The hemiacetal amine intermediate, reactants, and products were identified and quantified by the treatment of real-time infrared spectra via chemometrics method and two-dimensional correlation spectroscopy (2DCOS) technique. Based on the IR quantitative models, influences of operating conditions on reaction processes were investigated, and the reaction kinetic model was built with kinetic parameters of two rate-limiting reaction steps calculated. This approach of analysis on the in-situ FTIR data demonstrated the ability to extract useful information on reaction components, especially the intermediate spectrum, from the confounding real-time IR data. The in-situ FTIR monitoring combined with the IR analysis methods is proved as a powerful tool for revealing the reaction mechanism and kinetics.

Probing the Mechanism of Plasmon-Enhanced Ammonia Borane Methanolysis on a CuAg Alloy at a Single-Particle Level

Plasmon-enhanced ammonia borane (AB) methanolysis, as an efficient, controllable, and safe method for hydrogen release, has attracted increasing attention. However, the mechanism remains controversial since it is difficult to directly observe the interface interaction in the plasmonic field. Here, CuAg alloy nanoparticles (NPs) with controlled compositions are synthesized and exhibit an excellent H2 yield (17.1 μmol min–1) under light illumination. Theories and experiments show that both hot carriers and photoinduced local-field enhancement contribute to the improved catalytic activity under light irradiation. More impressively, plasmon-induced interfacial charge transfer between single CuAg NPs and reactant molecules was explored in situ by a single-particle confocal microscope system, and a complete photoluminescence (PL) quenching phenomenon of CuAg NPs was observed when immersed in a methanol solution, not ammonia borane. The PL quenching indicates the transfer of hot electrons to methanol, which is the rate-limiting step of the AB dehydrogenation reaction. In contrast, charge transfer from the plasmonic NP to AB (the most widely proposed path to date) does not work here. This work provides direct evidence for the hot electron transfer from CuAg to methanol via single-particle PL measurement and provides insights for plasmon-enhanced AB methanolysis.

Carbothermic Reduction and Nitridation Mechanism of Vanadium-Bearing Titanomagnetite Concentrate

In this study, the carbothermic reduction and nitridation mechanism of vanadium-bearing titanomagnetite concentrate are investigated in terms of phase transformation, microstructure transformation, and thermodynamic analyses. The differences in the reaction behavior of titanomagnetite and ilmenite in vanadium-bearing titanomagnetite concentrate, as well as the distribution characteristic of V in the roasted products, are emphatically studied. It is observed that the reaction sequences of titanomagnetite and ilmenite transformations into nitride are as follows: Fe3−xTixO4→Fe2TiO4→FeTiO3→M3O5→(Ti, V)(N, C); FeTiO3→M3O5→Ti(N, C). The reduction of M3O5 to TiN is the rate-limiting step of the entire reaction, and metal iron is an important medium for transferring C for the reduction of M3O5. Titanomagnetite is faster to convert into nitride than ilmenite is, and the reasons for this are discussed in detail. During the entire roasting process, V mainly coexists with Ti and seems to facilitate the conversion of titanium oxides into (Ti, V)(N, C).