Adsorption Energy Of NH3 Research Articles

Hf3C2O2 MXene: A promising NH3 gas sensor with high selectivity/sensitivity and fast recover time at room temperature

Owing to metallic conductivity, tunable surface chemistry, mechanical flexibility, high surface area and chemical stability, MXenes have emerged as promising candidates for room-temperature gas sensors. In this study, gas sensing performances of the newly synthesized Hf3C2 MXene with oxygen termination toward a wide range of common molecules (NH3, H2O, H2S, H2, CO2, CO, CH4, N2 and NO) were investigated by first-principles density functional calculations. With the most negative adsorption energy, the highest charge transfer and the shortest adsorption distance, the adsorption of NH3 among the investigated gases causes the most significant changes in electrical conductivity and work function of Hf3C2O2 substrate, thus holds the biggest gas response. Only the NH3 exhibits strong chemical interactions with Hf3C2O2, and other gas molecules are weakly chemisorbed or physisorbed. All these indicate that Hf3C2O2 exhibits high selectivity and sensitivity to NH3. The adsorption energy of NH3 falls within the appropriate range for room-temperature gas sensors, enabling Hf3C2O2 to maintain NH3 sensitivity while also achieving a fast recovery time. Furthermore, giving that human exhaled breath does not affect, and may even enhance, the selectivity and sensitivity of Hf3C2O2 towards NH3, Hf3C2O2 can serve effectively as an NH3 sensor in human disease detection.

Exploring the joint influence of SO2 and alkali metal on FeW mixed oxides catalyst for NOx elimination

The coexistence of multiple substances in the flue gas, such as alkali metal and SO2, results in the NH3-SCR catalysts suffering from serious deactivation. Therefore, we systematically studied the effects of coexisting SO2 and Na on the FeW oxides for NOx elimination. This study elucidates that the joint influence mechanism of these substances on SCR activity was regulated by reaction temperatures. When the temperature was below 300 °C, the catalyst suffered a double whammy. The addition of SO2 in process of NH3-SCR resulted in a decrease in the activity of Na-poisoned FeW catalyst. It was largely due to the formation of inorganic SO42-, which not only consumed the NH3 but also blocked active sites. With the increase of reaction temperatures above 300 °C, the SO2 could interact with Na2O to construct a ternary electron interaction of SO42--Na+-FeW, contributing to the improvement of alkali metal resistance. This sulfate adjusted the D-band center energy of the catalyst closer to the Fermi level, thereby boosting the adsorption energies of NH3 and NO, increasing their adsorption abilities. Furthermore, sulfate binding broke the Na-O-Fe and Na-O-W bonds, resulting in the restoration of Fe-O-W and Fe-O-Fe active sites and accumulation of Na+ species. Precise characterizations and theoretical calculations shed light on the joint mechanism of SO2 and alkali metals which provide guidance to the design SCR catalyst with excellent resistance to SO2 and alkali metal poisoning.

The Effect of Ligand Field on Enhanced Electrocatalytic Performance of NO Reduction Under Applied Potential

We employed density functional theory to investigate Co-N4/Gra single-atom catalysts, focusing on the modification of axial ligand (X=-F, -CN and -C3H4N2) and examined the influence of ligand field and electric potential on eNORR. Our results demonstrate that Co-N4[X]/Gra exhibit favorable thermodynamic adsorption (ΔG *NO < 0) and remarkable activation activity toward NO molecules. Co-N4/Gra demonstrates a limiting potential of −0.13 V with the potential-determining step (PDS) of *NH3 → * + NH3(g). Notably, under the introduction of ligands, Co-N4[F]/Gra achieves the most favorable overpotential of −0.07 V, superior to most of NORR electrocatalysts, and meanwhile shows an exceptional selectivity of 99.99% for eNORR compared to competitive hydrogen evolution reaction. Under the solvent environment, Co-N4/Gra features the triggering potentials of −0.33 V for a pH of 1, −0.71 V for a pH of 7, and −1.10 V vs RHE for a pH of 13, respectively. Additionally, the potential reduces the desorption energy and adsorption energy of NH3, facilitating the accessibility of the NH3 desorption step (PDS) and promoting NO reduction. Thus, under realistic conditions, the Co ion’s active site displays variable valence electrons and forms a dynamic interplay with the ligand field effect, rendering a crucial effect on the adsorption of reaction species during the eNORR.

Superior room temperature ammonia gas sensing of copper selenide nanoflowers

Facile wet chemical synthesis was utilized to synthesize nanoflowers of copper selenide (CuSe) that exhibited exceptional room temperature ammonia (NH3) gas sensing capability. Observations of surface morphology revealed the presence of petal-like structures arranged in a flower-like pattern. The layered materials have been analyzed for their crystalline structure, phase, composition, and band gap by utilizing X-ray diffraction, Transmission Electron Microscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy, UV-Vis, respectively. At ambient conditions, CuSe nanoflowers-based sensor demonstrated exceptional sensitivity, reaching up to 79% (200 ppm NH3) with short response and recovery time of 12.9 s and 6.3 s, respectively, at 5 ppm gas concentration. The sensor exhibited rapid response and recovery times, a broad concentration range, long-term stability over extended periods, exceptional specificity towards NH3, and good repeatability owing to its distinct flower-shaped structures assembled in thin layers. Density Functional Theory simulations were conducted to investigate the interactions between NH3 and CuSe. Our findings revealed an increase in the adsorption energy of NH3 on CuSe, indicating a stronger binding affinity. We observed a higher charge transfer from CuSe to NH3, which suggests an increase in conductivity. This increase in conductivity enhances the superior sensing capability observed in the experimental results.

Insights into the diffusion coefficient and adsorption energy of NH3 in MgCl2 from molecular simulation, experiments, and machine learning

Molecular models were developed to evaluate the adsorption behavior between NH3 and MgCl2. These models were utilized to assess the diffusion coefficient and adsorption energy at different temperatures and pressures through the application of molecular dynamics (MD) simulations. Subsequently, a comprehensive dataset comprising the diffusion coefficient and adsorption energy was established. The analysis of the relative diffusion and adsorption mechanisms involved calculating the radius distribution function, coordination numbers, and energy values within the primary solvent layer. The molecular simulation results revealed that the highest values for the diffusion coefficient and adsorption energy of NH3 in MgCl2 were observed at a temperature of 348 K and a pressure of 0.2 MPa. Moreover, the experimental findings exhibited good agreement with the computational simulation conclusions. The preparation of Magnesium hydroxide (MH) under the aforementioned temperature and pressure conditions resulted in a concentrated particle size distribution, effective dispersion, and a complete hexagonal sheet morphology. Furthermore, machine learning predictions were performed using significant features (i.e., molarity(M), temperature(T), pressure(P), volume(V), density(D), and total energy(E)). The results demonstrated that the decision tree regression (DTR) model exhibited superior performance in predicting the diffusion coefficient, while the k-nearest Neighbors (KNN) regression model achieved the best performance in predicting the adsorption energy.

Computational design and experimental validation of monometallic-doped SnO2 catalysts for selective catalytic oxidation of ammonia

Due to the intricate structure of catalysts, traditional catalyst design relies on iterative trial-and-error experiments. We have systematically established a catalyst design strategy to evaluate the performance of NH3-SCO reactions from the perspective of DFT calculations. Specifically, we used the catalyst formation energy as a stability descriptor and the adsorption energies of NH3, NH2, and O p-band center as performance descriptors, we identified the four most promising catalysts among 45 kinds of doped SnO2 catalysts. Subsequently, experimental validation was performed to demonstrate the outstanding consistency between the DFT-driven descriptors and the stability and catalytic performance of the catalyst. Particularly, the Ce doping resulted in a 175 °C reduction in the T90 compared to the SnO2 catalyst. It is noteworthy that Ce doping promotes the cycling between oxygen vacancies and lattice oxygen, which contributes primarily to the enhancement of O2 activation capability and, consequently, the improvement in catalytic activity.

Computational evaluation of sensing properties of a novel 2D diboron dinitride for detecting toxic gas molecules

2D materials have the potential for superior sensing performance due to their distinctive surface properties. In this study, the sensing properties of a novel 2D diboron dinitride (n-BN) material for detecting four toxic gas molecules (H2S, NH3, SO2, and NO2) with and without an external electric field are investigated by the first-principles calculation method. The results show that the NO2 molecule has excellent trapping characteristics and sensing properties on the n-BN monolayer due to its significant adsorption energy (−2.06eV) and significant changes in conductance. It has a medium affinity for H2S, NH3, and SO2 molecules and a feasible recovery time for NH3 and SO2 molecules at room temperature. Meanwhile, the adsorption energy of NH3 is approximately linearly increased with the magnitude of the external electric field along the adding direction, which is different from the parabolic form of the other three gas molecules. The recovery time of H2S can be adjusted more suitable by adjusting the external electric field at room temperature. Combining these sensing properties, the 2D n-BN monolayer is expected to be an excellent sensitive gas detection material for H2S, NH3, and SO2 gas molecules, and a scavenger for NO2 gas molecules.

Mechanism of NO removal in selective catalytic reduction based on γ‐Fe2O3 catalyst doped with Mg element

AbstractThe doping of different elements will make the Fe2O3 catalyst show different catalytic characteristics and improve the activity of the Fe2O3 catalyst in selective catalytic reduction (SCR), mainly by increasing the types of reactive oxygen species and the specific surface area of the catalyst. In this paper, density functional theory (DFT) was used to reveal the reaction path and adsorption behaviour of the Mg‐doped γ‐Fe2O3 catalyst. The results show that the doping of Mg ions can contribute electrons and lead to electron migration on the catalyst surface, which changes the acidity of some sites on the catalyst surface. The adsorption energy of NH3 is related to the binding sites of N atoms on the catalyst surface, and different adsorption sites will be enhanced or weakened due to Mg doping. NH2 reacts with NO to form N2 and H2O, so the dehydrogenation of NH3 to the NH2 radical is a key step in SCR. With doping, this process becomes more likely to occur. In addition, the activation energy barrier of NH2 formation in the aerobic environment is lower than that in the anaerobic condition, which contributes to NH3 dehydrogenation. Therefore, doping Mg on the surface of γ‐Fe2O3 catalyst can improve the catalytic activity of NO removal.

Effects of Vacancy Defects and the Adsorption of Toxic Gas Molecules on Electronic, Magnetic, and Adsorptive Properties of g−ZnO: A First-Principles Study

Using first principles based on density functional theory (DFT), the CO, NH3, NO, and NO2 gas adsorbed on intrinsic Graphite-like ZnO (g−ZnO) and vacancy-deficient g−ZnO were systematically studied. For intrinsic g−ZnO, the adsorption energy of NH3, NO, and NO2 adsorption defective g−ZnO systems increased significantly due to the introduction of Zn vacancy (VZn). Especially, for NH3, NO, and NO2 adsorbed Zn-vacancy g−ZnO (VZn/g−ZnO) systems increased to 1.366 eV, 2.540 eV and 2.532 eV, respectively. In addition, with the introduction of vacancies, the adsorption height of the gases adsorbed on VZn/g−ZnO system is significantly reduced, especially the adsorption height of the NH3 adsorbed on VZn/g−ZnO system is reduced to 0.686 Å. It is worth mentioning that the introduction of O-vacancy (VO) significantly enhances the charge transfer between NO or NO2 and VO/g−ZnO. This suggest that the defective g−ZnO is more suitable for detecting NH3, NO and NO2 gas. It is interesting to note that the adsorption of NO and NO2 gases gives rise to magnetic moments of 1 μB and 0.858 μB for g−ZnO, and 1 μB and 1 μB for VO/g−ZnO. In addition, VZn induced 1.996 μB magnetic moments for intrinsic g−ZnO, and the CO, NH3, NO and NO2 change the magnetic of VZn/g−ZnO. The adsorption of NO2 causes the intrinsic g−ZnO to exhibit metallic properties, while the adsorption of NH3 gas molecules causes VZn/g−ZnO also to show metallic properties. The adsorption of NO and NO2 causes VZn/g−ZnO to display semi-metallic properties. These results facilitate the enrichment of defect detection means and the design of gas detection devices.

Adsorption of ammonia on ZrOx-modified graphene nanoribbon: a first-principle investigation

Ammonia (NH3) is a main environmental pollutant related to global warming, and reduction of its emission is the subject of multiple international agreements and regulations. Accordingly, the development of highly precise detectors to monitor its content in the environment is essential to track and limit its emission. This work examines the influence of modifying of armchair–graphene nanoribbon (AGNR) by zirconium (Zr) and its oxides on its adsorption for NH3 gas. Density functional theory (DFT) computations are utilized to investigate the band structure, adsorption energy ({E}_{d}), adsorption length (D), charge transferred (Delta Q), and density of states (DOS) of pristine and modified structures with ZrOx (x=0, 1, mathrm{or }2). ZrOx is presented to AGNR nanostructure by two pathways: substitution of carbon atoms (doping) and introduction on top of the AGNR surface (decoration). The findings of the investigation illustrate great improvement of NH3 adsorption on AGNR due to its modification. Although the adsorption energy is enhanced in general upon modification, AGNR structures where ZrOx substitute carbon atoms exhibit greater adsorption energy as compared with the decoration scheme. The maximum energy of adsorption is for the AGNR structure doped with ZrO2, followed by that doped with Zr. The adsorption energy of NH3 on the ZrO2-doped AGNR is − 10.05 eV with an adsorption length of 2.4 Å and − 0.214e charge transferred. As compared to the pristine structure, the adsorption energy for NH3 on AGNR doped with ZrO2 increases 22.2 times. Therefore, AGNR nanostructure doped with ZrOx can be considered for practical sensors for the applications of detection and control of ammonia emission.

Adsorption mechanisms of different toxic molecular gases on intrinsic C2N and Ti-C2N-V monolayer: a DFT study.

Recently, the excessive emission of chemical toxic gases such as nitrogen trifluoride (NF3), ammonia (NH3), phosgene (COCL2), and benzene (C6H6) has caused serious environmental problems. Adsorption of these chemical toxic gas molecules is a promising method to reduce environmental pollution. In this work, density functional theory (DFT) calculations are used to investigate the adsorption properties of these chemical toxic molecules on intrinsic C2N and Ti-C2N-V monolayer. The results show that NF3, NH3, C6H6, and COCL2 can all be adsorbed to the intrinsic C2N monolayer with weak adsorption energy, while the adsorption properties of these gas molecules were greatly improved after doping Ti atom. The adsorption energy of NH3, C6H6, COCL2, and NF3 increased from - 0.585, - 0.432, - 0.633, and - 0.362eV to - 2.214, - 1.699, - 1.822, and - 0.799eV, respectively, which increased by 2 ~ 4 times compared with that before doping. Besides, the results of the electron distribution, work function, the total density of states (TDOS), and the partial density of states (PDOS) analysis indicate that the doped Ti atom can be used as a bridge to connect the adsorbed molecules with the C2N-V monolayer, strengthen their interaction, and significantly improve the adsorption capacity. Therefore, Ti-doped C2N-V (Ti-C2N-V) monolayer is a promising adsorbent for the enrichment and utilization of harmful gases.

First principle study on the interactions of NH3, NOx and O2 with Fe3O4 (1 1 1) surfaces

The interactions of NH3, NOx and O2 with two Fe3O4 (111) surfaces named Fetet- and Feoct-tet-terminated, respectively, were investigated by first principle calculation. The results indicated that the Feoct-tet-terminated surface had a stronger effect on the adsorption and activation of these small molecules overall. Specifically, NH3, NO and O2 tend to be stably adsorbed on the octahedral Fe site on the Feoct-tet-terminated surface. The energy released by O2 adsorption is the most among them, and it is easy to form abundant surface adsorbed oxygen on the catalyst surface, which further co-adsorb or combine with NO to form nitrate and nitrite species with various coordination structures. The chelated and bridged bidentate-coordinated nitrate species with the highest adsorption energies are important reaction intermediates in NH3 selective catalytic reduction (NH3-SCR). In addition, due to the horizontal adsorption configuration, NH3 is significantly affected by the nearest lattice oxygen, which makes the oxidative dehydrogenation reaction more likely to occur, although the adsorption energy of NH3 on Feoct-tet-terminated surface is relatively lower. These results provide a basis for understanding the interactions of NH3, NOx and O2 on Fe3O4 (111) surfaces in NH3-SCR reaction.

Theoretical insight into the reaction mechanism of ammonia dehydrogenation on iron-based clusters

Ammonia (NH3) molecule decomposition is a promising approach for H2 production with COx-free. Density functional theory (DFT) calculations are employed to investigate the NH3 molecule stepwise dehydrogenation on Fe6M (M = Fe, Mo, Ni, and Co) clusters. The stability of these clusters has been investigated, and the result shows that the stability of Fe-based clusters is enhanced with doping of other metals. The catalytic activity of metal clusters for ammonia decomposition is systematically investigated by analyzing the adsorption property and reaction barriers. NH3 prefers to bind to the atop metal atom through the N end, which is agreement with the electrostatic potential analysis. Moreover, the adsorption energies of NH3 are related to the d-band center of Fe-based clusters. The reaction energy barriers show that the last dehydrogenation step (NH* + * ⇌ N* + H*) is the rate-determining step for most investigated clusters. The overall dehydrogenation process is exothermic reaction, and by comparing the rate-determining step, the Fe6Mo(l) and the Fe6Ni(l) clusters can efficiently promote the NH3 dissociation reaction.

N-p-Conductor Transition of Gas Sensing Behaviors in Mo2CTx MXene.

It is highly important to implement various semiconducting, such as n- or p-type, or conducting types of sensing behaviors to maximize the selectivity of gas sensors. To achieve this, researchers so far have utilized the n-p (or p-n) two-phase transition using doping techniques, where the addition of an extra transition phase provides the potential to greatly increase the sensing performance. Here, we report for the first time on an n-p-conductor three-phase transition of gas sensing behavior using Mo2CTx MXene, where the presence of organic intercalants and film thickness play a critical role. We found that 5-nm-thick Mo2CTx films with a tetramethylammonium hydroxide (TMAOH) intercalant displayed a p-type gas sensing response, while the films without the intercalant displayed a clear n-type response. Additionally, Mo2CTx films with thicknesses over 700 nm exhibited a conductor-type response, unlike the thinner films. It is expected that the three-phase transition was possible due to the unique and simultaneous presence of the intrinsic metallic conductivity and the high-density of surface functional groups of the MXene. We demonstrate that the gas response of Mo2CTx films containing tetramethylammonium (TMA) ions toward volatile organic compounds (VOCs), NH3, and NO2 is ∼30 times higher than that of deintercalated films, further showing the influence of intercalants on sensing performance. Also, DFT calculations show that the adsorption energy of NH3 and NO2 on Mo2CTx shifts from -0.973, -1.838 eV to -1.305, -2.750 eV, respectively, after TMA adsorption, demonstrating the influence of TMA in enhancing sensing performance.

Multiple pollutants control of NO, benzene and toluene from coal-fired plant by Mo/Ni impregnated TiO2-based NH3-SCR catalyst: A DFT supported experimental study

There was a dearth of understanding regarding the mechanism of MPC catalyst activity and the creation of effective MPC catalysts for industrial low oxygen and high SO2 concentration environments. Herein, Mo/Ni was utilized to modify the commonly used WVTiOX catalyst to investigate the role and reaction mechanism of Mo/Ni in the MPC process. Mo/Ni doping greatly improved the MPC performance of the WVTiOX catalyst, increased the number of Brønsted and Lewis acid sites on the surface, promoted surface active oxygen Oα ratio, and intensified metal oxide synergy. The TiO2 (001) models of WVTiOX and NiWVTiOX catalysts were built, and the adsorption energies of NH3, O2, NO, C6H6, and C7H8 gaseous molecules on the surfaces of the two catalysts were calculated by density functional theory (DFT). The DFT and in situ DRIFTS results proved that NH3-SCR process of the catalyst was mainly governed by the L-H mechanism, while the E-R mechanism also worked to a certain extent. The following are possible benzene and toluene oxidation pathways on NiWVTiOX: C6H6 → C6H4O2 → C4H2O3 → CO2 + H2O and C7H8 → C6H5CH2OH → C6H5CHO → C6H5COOH → C4H2O3 → CO2 + H2O.

A DFT-based method to determine the ammonium-induced activation and sulfidation pathway of tenorite

BackgroundThe ammonia modification of minerals surfaces has been successfully applied to obtain a successful flotation performance and plays an important role in the sulfidation flotation of copper oxides. First principle calculations based on density functional theory (DFT) are able to provide information on the electronic structures, properties, adsorption energies, and electron transfer of the mineral surface and floatation reagents, thus helping to understand the interaction mechanisms of reagents with copper oxides. MethodsThe DFT was explored to discuss the mechanisms underlying the HS– species and NH3 direct and activated sulfidation of tenorite (1 1 1) surfaces. The relationship between Cu–S–NH3 species distribution and pH value in the solution was simulated by visual MINTEQ. Significant findingsThe Cu 3d orbital peak was observed to be stronger at the Fermi level than that of the O 2p orbit on the tenorite (1 1 1) surface, and the negative adsorption energy and adsorption effect of HS– get better results through calculations, while the Cu 3d and 4 s peaks overlapped the corresponding S 3 s and 3p peaks at the HS– adsorption on tenorite (1 1 1) surface. The maximum adsorption energy of NH3 and HS– on the tenorite (1 1 1) surface was determined as –19.63 eV, which is more negative than that with just the adsorption of HS– on the tenorite (1 1 1) surface. Herein, we combined Visual MINTEQ and DMOL3 models to indicate that the addition of NH3 ions catalyzes the formation of CuS(s), ie., NH3 mainly catalyzes the interaction between HS– species and Me(OH)2 on the hydroxylated oxidized ore surface or solution, that is, Me(OH)2 first dehydroxylates to metal ions, and then forms sulfide species with HS–. The flotation experiment was consistent with the DFT calculation results.

The interplay between acid-base properties and Fermi level pinning of a nano dispersed tungsten oxide - titania catalytic system

A series of WO3/TiO2 catalysts were synthesized, characterized, and evaluated for the NO selective catalytic reduction (SCR) with NH3. Based on a wide range of characterization techniques, a detailed model was developed that describes the interfacial electron transfer between WO3 and TiO2 and defines a relationship between the acid-base properties of the catalytic surface and electronic structure modification. The electronic interactions at the WO3/TiO2 interface were quantified using variations in the system's electronic structure. Altering the dispersion and size of the WO3 nanostructures results to drastic changes in titania's surface electron distribution, which are reflected in the pinning of Fermi level through an electron transfer process between WO3 and TiO2. The variations in the Fermi level were further related to changes in the point of zero charge (PZC) values and the activity towards NO SCR with NH3, which was used as a test reaction. Temperature Programmed Surface Reaction (TPSR) was employed to study the catalytic activity at temperatures ranging from 30 °C to 500 °C and was quantitatively correlated to changes in coverage and interfacial charge transfer. We demonstrate that higher WO3 loading on TiO2 results in a stronger electronic interaction and a higher catalytic activity. This is because electron transfer increases the surface electron density, which enhances the surface basicity of TiO2. The concomitant decrease in the adsorption energy of NH3 results in a decrease in the activation energy, which is reflected in the SCR temperature onset.

DFT study of NH3 adsorption on 2D monolayer MXenes (M2C, M = Cr, Fe) via oxygen functionalization: Suitable materials for gas sensors

This work deals with the kind of the interaction of NH3 molecules adsorbed on the MXene layers. The adsorption energies of NH3 on the surface of MXenes (M2C, M = Cr and Fe) and their oxygen-functionalized forms (O-MXenes or M2CO2) were calculated by using the density functional theory. DFT-D4 calculations have revealed that the on-top sites are initiated for adsorption of NH3 on M2C and M2CO2. For the reaction on Cr2CO2, the Ead is found to be −0.29 eV lower than Cr2C and also the same tendency was achieved in Fe2C and its O-terminated MXene. This suggests that the molecule will strongly adsorb on Cr2C than its O-terminated surface. Bader charge analysis in terms of the induced net charges on M2C MXenes suggests that electron density distribution between N of NH3 (negatively charged) and the Cr/Fe (positively charged) surface would play a key role in the adsorption. Furthermore, DOS calculations reveal that the electrical conducting behaviour and magnetic nature of MXenes make them suitable for gas sensors applications.

Adsorption behaviors of NH3 and HCl molecules on Fe-based crystal planes: A DFT study

By adopting the First-principles method based on the density functional theory (DFT), the adsorption properties of NH3 and HCl molecules intermingled in crude oil on the Fe-based crystal planes exposed on the inner surface of a duct in a crude distillation column have been conducted. Specifically, the calculated adsorption energy of NH3 and HCl reveal the most stable adsorption sites on the three planes, and the free energy at different temperatures was corrected. Furthermore, the charge density difference and the Bader charge obviously illustrate the direction of charge transfer and the valence of the atoms after adsorption. The results of projected electron density of states (PDOS), electron localization function (ELF) and the crystal orbital Hamilton population (COHP) reveal the nature of chemical bonds and the influence of specific atomic orbitals. Accordingly, the adsorption type of the two molecules on the Fe-based crystal planes is chemical adsorption. Considering the nature of the chemical bond and the multi-component environment of the distillation column, we infer that the possible causes of corrosion are coordination ions, hydrogen embrittlement and Cl− concentration.

Study on the Mechanism of Selective Catalytic Reduction of NOx by NH3 over Mn-Doped CoCr2O4

In this paper, the first-principles calculation method based on density functional theory is used to calculate the structure of CoCr2O4 and Mn-doped Mn0.1Co0.9Cr2O4 low-refractive-index surface (100) and the adsorption model of NH3 and other molecules. Moreover, the process of the NOx removal reaction with NH3 was studied in detail. The results showed that the adsorption energy of NH3 and the amount of Mulliken charge transfer increased after Mn doping. The projected density of states indicates that the interactions between the adsorbed molecule and the substrate are stronger. It is worth noting that the doped Mn sites are also favorable sites for catalytic reactions. Based on the calculation results, we know that NH3 molecules are easily adsorbed on the surface of the catalyst and then dehydrogenated to produce NH2, NH, and other products. The next major step is the reaction of NH2 with gaseous NO to form an intermediate product of NH2NO, which is then decomposed into N2 and H2O. However, the route of N2O as an intermediate is energetically infeasible. Among them, NH3 dehydrogenation is a rate-determining step, and the activation energy barrier is 1.01 eV. However, under aerobic conditions, the activation energy barrier (0.71 eV) from NH3 to NH2 is significantly reduced. In addition, the adsorbed NO reacts with the active O atoms to generate NO2 on the surface, and NO2 can undergo a “fast selective catalytic reduction” process. To sum up, doping manganese on the surface of the CoCr2O4 catalyst can improve the catalytic activity of denitration, and the Mn0.1Co0.9Cr2O4 catalyst has a good selectivity.