Theoretical study on the reduction reactions from solid char(N): The effect of the nearby group and the high-spin state

Zhang, Hai; Luo, Lei; Liu, Jiaxun; Jiao, Anyao; Liu, Jianguo; Jiang, Xiumin

doi:10.1016/j.energy.2019.116286

Cited by 24 publications

(9 citation statements)

References 49 publications

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“…A first-principles study based on the density functional theory (DFT) can help researchers determine the reaction mechanism at the molecular level . Accordingly, the DFT is also one of the important methods to study the heterogeneous reduction mechanism of NO, which has been widely used. − , Based on the DFT method, the effects of nitrogen, carbon monoxide, and oxygen on the heterogeneous reduction of NO–char interaction were studied by Zhang et al − The results showed that the NO chemisorption behavior on the char(N) surface is barrierless and highly exothermic, carbon monoxide can lower the energy barrier to facilitate the reaction, and two different oxygen enhancement mechanisms during the NO–char interaction were found, respectively. Besides, thermodynamic and kinetic evaluation of the reaction between NO and char(N) showed that the reaction rate accelerated with the increasing temperature.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the Heterogeneous Reduction of NO on a Sodium-Doped Char Surface: A First-Principles Study

et al. 2021

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Sodium in high-alkali coal facilitates the heterogeneous reduction of nitrogen oxides on char surfaces. However, the reaction mechanism is unclear. In this paper, the effect of sodium on the reaction path of the char heterogeneous reduction of NO was analyzed based on the first-principles study using an armchair char model and a zigzag char model separately. Four reaction paths were obtained, and the most likely reaction path was found by comparison. The highest energy barriers of the reduction reactions were reduced to some extent by doping with the sodium atom. The doped sodium atom had a significant effect on the heterogeneous reduction reactions on the surface of the armchair char and had little effect on the surface of the zigzag char. However, a comprehensive analysis showed that the reactivity of the zigzag model is better than that of the armchair model. From the thermodynamic analysis, the addition of the sodium atom could change the reaction from nonspontaneous to spontaneous. After the completion of the reaction, the oxygen atom would be immobilized on the char structure surface, which will have an effect on the subsequent reaction. This study revealed the effect of the sodium atom on the reaction mechanism of the char heterogeneous reduction of NO and helped perfect the mechanism of the char heterogeneous reduction of NO.

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Section: Introductionmentioning

confidence: 99%

Mechanism of the Heterogeneous Reduction of NO on a Sodium-Doped Char Surface: A First-Principles Study

et al. 2021

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“…In this research, the DFT method was employed to reveal the combustion mechanisms of char derived from oxidizing torrefaction. It is widely known that the reactivity of char is relevant to the type of reacting edge, and that the zigzag edges are more active than armchair edges [ 29 , 30 , 31 ]. Therefore, a single layer of graphite consisting of seven rings with zigzag edges was selected to simulate the initial model of preheated char (as shown in Figure 2 a).…”

Section: Experiments and Calculationsmentioning

confidence: 99%

Experimental and DFT Research on the Effects of O2/CO2 and O2/H2O Pretreatments on the Combustion Characteristics of Char

Zhang

Sun

et al. 2023

Molecules

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The use of a coal-based energy structure generates a large amount of CO2 and NOx. The numerous emissions from these agents result in acid rain, photochemical smog, and haze. This environmental problem is considered one of the greatest challenges facing humankind in this century. Preheating combustion technology is considered an essential method for lowering the emissions of CO2 and NO. In this research, the char prepared from O2/CO2 and O2/H2O atmospheres was employed to reveal the effects of the addition of an oxidizing agent on the combustion characteristics of char. The structural features and combustion characteristics of preheated chars were determined by Raman, temperature-programmed desorption (TPD), and non-isothermal, thermo-gravimetric (TGA) experiments. According to the experimental results, the addition of oxidizing agents promoted the generation of smaller aromatic ring structures and oxygen-containing functional groups. The improvement in the surface physicochemical properties enhanced the reactivity of char and lowered its combustion activation energy. Furthermore, the combustion mechanisms of the char prepared from the O2/CO2 and O2/H2O atmospheres were investigated using the density functional theory (DFT). The simulation results illustrated that the combustion essence of char could be attributed to the migration of active atoms, the fracture of the benzene ring structure, and the reorganization of new systems. The addition of oxidizing agents weakened the conjugated components of the aromatic ring systems, promoting the successive decomposition of CO and NO. The results of this study can provide a theoretical basis for regulating the reaction atmosphere in the preheating process and promoting the development of clean combustion for high-rank coals.

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“…Further examination of the groups shown in Figure 6 gives the reason for the better oxidation performance of the TM model. Group A is directly 27 Therefore, the difference in electronegativity between Group B and Group C will be responsible. The electronegativity X G is evaluated by 42…”

Section: Effect Of the Model On The Oxidation Mechanismsmentioning

confidence: 99%

“…In addition, the effect of the spin state is another focus of the reported works. 26,27 The analysis of the DFT results shows that the reaction with the high-spin excited states is much more competitive than that with the low-spin ground states. 27 To sum up, most of the reported DFT studies are associated with the potential energy surface of the oxidation and reduction reactions from char and/or char(N) with the emphasis on its temperature-, spin-, and group-dependent reactivity.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Model-Dependent Reactivity of the Char-Bound Nitrogen Surface: A DFT Study

et al. 2023

Self Cite

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The concern of energy and the environment provides great inducement for fundamental research on the mechanisms of oxidation of char-bound nitrogen (char(N)). In the present study, based on the armchair(N) model, we investigated its reaction mechanism at an atomistic level and with a comprehensive study of the effect of the model surface. Several pathways are found by density functional theory (DFT) calculations for the oxidation of armchair(N). The main gaseous species released during the oxidation are NO, HCN, CO, and CO2. The evaluated optimal reaction pathways are selected to investigate the model-dependent reactivity. According to our calculations, the oxidation of the simplified top armchair(N) model (TM) will be much more competitive than that of the simplified edge armchair(N) model (EM). In the route giving NO, the decreased stability of the intermediates makes the reaction of TM more favorable. In the route giving HCN, the described reduced mechanism and the larger exothermicity and lower highest-energy transition state will be responsible for the priority. Further analysis of the kinetics gives the evidence for the competitiveness: the rate constants for most of the steps of the TM, such as HCN desorption, surface bond dissociation, ring closure and opening, and oxygen insertion and migration, are higher than that of the EM. Therefore, a conclusion can be drawn that the oxidation of the armchair(N) will mainly take place from the top surface rather than the edge surface. The results can be used to supplement present understanding of the oxidation of armchair structure, which is extremely crucial for the development of the kinetics model to better predict the NO x emissions during the air-staged combustion.

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Theoretical study on the reduction reactions from solid char(N): The effect of the nearby group and the high-spin state

Cited by 24 publications

References 49 publications

Mechanism of the Heterogeneous Reduction of NO on a Sodium-Doped Char Surface: A First-Principles Study

Mechanism of the Heterogeneous Reduction of NO on a Sodium-Doped Char Surface: A First-Principles Study

Experimental and DFT Research on the Effects of O2/CO2 and O2/H2O Pretreatments on the Combustion Characteristics of Char

Investigation of the Model-Dependent Reactivity of the Char-Bound Nitrogen Surface: A DFT Study

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