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Stabilization of Atomically Dispersed Metallic Catalysts for Electrochemical Energy Applications
Published in Wei Yan, Xifei Li, Shuhui Sun, Xueliang Sun, Jiujun Zhang, Atomically Dispersed Metallic Materials for Electrochemical Energy Technologies, 2023
Junjie Li, Xiaozhang Yao, Yi Guan, Kieran Doyle-Davis, Xueliang Sun
Since the OER is a multiple-step reaction, the intermediates, such as *O, *OH, and *OOH, directly affect the reaction rate. Among these steps, the slowest step ultimately determines the whole reaction velocity, named the rate-determining step. From Figure 10.9a, the whole reaction Gibbs energy of ideal catalysts is 1.23 V, and under this circumstance, the overpotential is zero.68 However, the relationship of the absorption energy of three intermediates is linearly correlated, and some researchers suggested that the discrepancy of *OOH and *OH absorption energy stabilized at 3.2 V, as shown in Figure 10.9b.68 Thus, we can calculate one intermediate absorption energy rather than calculating every single one. Additionally, the reaction rate could be simplified to two intermediates: *O and *OH absorption energy. Figure 10.9c indicates the volcano shape of metal oxide catalysts for OERs. We found that IrO2 and RuO2 exhibit the best performance for OER due to their medium bonding energy.
Electrochemistry of Fuel Cells
Published in Xianguo Li, Principles of Fuel Cells, 2005
Since it is generally a difficult task to determine a complex mechanism for a given electrode reaction under various conditions, the concept of rate-determining step of an overall reaction has been frequently used for the calculation of electrode reaction rate. The rate-determining step may be defined as the reaction step that determines the rate of the overall reaction. This concept holds both in the case of consecutive and of parallel reactions or a combination of the two types of the reactions. Further, it is known that many electrochemical reactions proceed by a consecutive mechanism, and few by a parallel-path mechanism. In other word, it may be regarded that the rate of an overall reaction is mainly influenced, or determined, by one step among many elementary reactions, called the rate-determining step. Such a concept considerably simplifies the analysis and calculation of the rate of an overall electrode reaction, and have been used extensively in fuel cell literature, although it is over-simplistic in the description of the complex electrode reactions. It is known that the most important factor in determining the power and efficiency of electrochemical energy conversion is the reaction rate of the rate-determining step, although other factors may be also important such as the adsorptive properties of reactants and intermolecular forces among the species adsorbed on the electrode.
Enzymatic Reaction Kinetics
Published in Debabrata Das, Debayan Das, Biochemical Engineering, 2019
The product-formation step is the slower reaction step; hence, it is the rate-determining step. The rate of the reaction can be expressed as () vP=dCPdt=k5CES
Transesterification of the ethyl ester of trifluoroacetic acid to its methyl ester using Amberlyst-15: reaction and purification
Published in Chemical Engineering Communications, 2023
Reshma R. Devale, Amit M. Katariya, Yogesh S. Mahajan
Data obtained during kinetic runs was used to obtain a mathematical expression for the system, using the data for catalyst loading, temperature effect, and mole ratio. The reaction of the adsorbed molecules on catalyst surface is the rate determining step. The model equation is derived based on this assumption and is reported as Equation (2). LHHW type rate expression was found to represent data reasonably well for fitting (Equation (2)). Model was represented in terms of activities of components. where Wcat is the mass of catalyst and the constant kc is the forward rate constant:
Mechanisms of N2 Formation from Armchair Configurations with Different Dinitrogen Active Sites During Coal Pyrolysis
Published in Combustion Science and Technology, 2023
Tingting Jiao, Pengzheng Shi, Wenguang Du, Shoujun Liu, Ju Shangguan
According to the transition state theory, the elementary reaction with the highest activation energy (rate-determining step) determines the overall rate of the reaction. The rate-determining steps of R1 and R2 during pyrolysis are IM4 → IM5（ΔE = 273.26 kJ·mol −1）and IM6 → IM7（ΔE = 273.13 kJ·mol −1）. Both of which are the conversion of the dinitrogen six-membered ring to the dinitrogen four-membered ring and the energy barriers of the two reactions are comparable.
Synthesis, structure and catalytic promiscuity of a napthyl-pyrazole Mn(II) complex and structure–activity relationships
Published in Journal of Coordination Chemistry, 2019
Abhimanyu Jana, Paula Brandão, Harekrishna Jana, Atish Dipankar Jana, Gopinath Mondal, Pradip Bera, Ananyakumari Santra, Ajit Kumar Mahapatra, Pulakesh Bera
To know the extent of the catalytic efficiency of the complexes, kinetic studies are performed. For this purpose, a 1 × 10−5 M solution of 1–5 is allowed to react with about 10-fold concentrated OAPH solution to meet a pseudo-first-order rate law. All the experiments are performed at 25 °C under aerobic conditions. The initial rate of reaction of 1–5 shows rate saturation kinetics as shown in Supplementary Figure S7. This observation indicates the formation of substrate-catalyst intermediate and the rate-determining step is the decomposition step of the intermediate. Michaelis–Menten enzymatic kinetics is used to understand the kinetics of PHS [48]. The observed and simulated initial rates versus substrate concentrations of the non-linear plot and the Lineweaver–Burk plot for 1–5 are shown in Supplementary Figure S8. The value of Michaelis binding constant (Km) and Vmax, and the turnover number (Kcat) of the complexes, are listed in Table 4. A linear relationship for the initial rates is obtained varying the complex concentration which gives first-order reaction kinetics. As shown in Table 4, the turnover number (Kcat) for the oxidation of OAPH follows the order 3 > 4 > 5 > 1 > 2. The higher reactivity of 3 and 4 is due to the dinuclearity in the molecule, which confirms stable binding with molecular O2 in the labile copper centers of the complex. Relatively lower Kcat values of mononuclear complexes 1, 2, and 5 than dinuclear 3 and 4 are probably due to steric crowding arising from the napthyl/pyridine group around the metal center of 1, 2, and 5 (ORTEP of 2 and 5 in Supplementary Figures S4 and S5). The steric effect resists the oxygen binding to the metal center. However, the same steric effect somehow is less in the dinuclear complex (ORTEP of 3 and 4 in Supplementary Figures S2 and S3) as the metal centers are sufficiently separated by bridged bonds. The greater the steric repulsion in the system, the lesser is the formation of substrate binding property.