Dehydrogenation Of NH3 Research Articles

Study on N2 selectivity of iron-manganese ore catalysts in NH3-SCR process

Natural iron-manganese ores exhibit a good deNOx activity at low temperatures after a simple treatment, but the reason for its low N2 selectivity requires further in-depth study. This work conducted deNOx performance and characterization tests on iron-manganese ore catalysts. Based on the experimental results, a simplified computational model of the iron-manganese ore catalyst (Fe2O3/MnO2 (110) surface) was constructed, and the density functional theory (DFT) method was used to investigate the mechanism of N2 formation in the NH3-SCR process. Fe and Mn in the iron-manganese ore play an important role in the deNOx activity, and NH3 forms the stable chemical adsorption on its surface, especially on the Fe site, where the adsorption capacity of NH3 is stronger than that of Mn site. The Fe site exhibits better ability than the Mn site in the dehydrogenation reaction of NH3. However, in a comprehensive comparison, the capability of iron-manganese ore catalyst to promote NH3 dehydrogenation is not high. In addition, the key NH2NO intermediate prefers to form on the Mn site over the Fe2O3/MnO2 (110) surface. Among them, the Mn site is better than the Fe site in promoting the decomposition of NH2NO intermediate to form N2. The study can further understand the microscopic mechanism of iron-manganese ore catalysts in N2 formation, which lays a foundation for improving the N2 selectivity of iron-manganese ore deNOx catalysts.

Unveiling facet engineering of ultrathin Pt overlayers for enhanced ammonia oxidation reaction

Utilizing ammonia for hydrogen production via ammonia oxidation reaction (AOR) remains a challenge owing to insufficient electrode performance and high cost of noble metal. Herein, we performed repeated self-terminated electrodeposition (SED) of Pt on Ni substrate to obtain Pt/Ni electrodes. The electron-deficient Ni sites prefer *OH adsorption and serve as a reservoir for NH3 dehydrogenation, thereby promoting NH3 adsorption on Pt sites. Additionally, this iterative process enabled precise regulation of the Pt loading mass. Pt5/Ni electrode exhibited the highest catalytic activity for AOR. Subsequently, immersing this electrode in various acid solutions resulted in surface morphologies with numerous well-defined pits, driven by the adsorption of different electrolyte ions. Specifically, etching in HNO3 led to a higher Pt(100) density, further enhancing the electrode’s catalytic performance for AOR. Thus, this study offers a simple, fast, and spontaneous method for facet engineering ultrathin Pt overlayers on Ni substrate under ambient conditions.

New insights and reaction mechanisms in the design of catalysts for the synergistic removal of NOx and VOCs from coke oven flue gas: Dual regulation of oxidative properties and acidic sites

The acid and redox sites of the MnCo catalysts are simultaneously fine-tuned by the addition of V. A dual-function catalyst, designated as V0.5Mn5Co5, has been constructed for the synergistic removal of NOx and volatile organic compounds under coke-oven flue gas conditions, which exhibits > 95 % NOx conversion and > 80 % N2 selectivity at 180–300 °C. Meanwhile, it removes 70 % of ethylene at 240 °C. Besides it has excellent sulfur and water resistance. The characterization results indicate that this acid-redox dual sites modulation strategy appropriately weakens the oxidation capacity of the catalysts while increasing the surface acidity of the catalysts. The catalyst mainly performs SCR reaction through the E-R mechanism, and N2O is generated through the transition dehydrogenation of NH3 and NSCR reaction. Ethylene is first adsorbed on the catalyst surface then oxidized to form carbonate species, and finally decomposed to CO2. Ethylene oxidation follows the MvK mechanism. There is a competitive adsorption between NH3 and C2H4, and a mutual inhibition between the SCR reaction and the ethylene oxidation reaction. V0.5Mn5Co5 exhibits excellent synergistic removal of NOx and VOCs in coke oven flue gas compared with commercial VWTi catalysts, which indicates great promise for industrial application.

Mechanistic investigation of ammonia adsorption and reforming over Ni, Ru loaded catalysts toward green H2 production of marine engines: DFT calculation and experimental evaluation

Highly active catalysts suitable for ammonia reforming reactions have been comprehensively investigated by density functional theory (DFT) calculations and experimental tests. Non-precious metal Ni, precious metal Ru and Ru-Ni composite metal are selected as catalytic activity surfaces, and a series of three-dimensional metal-packed catalyst models are constructed parallelly. Then, to elucidate the rate-determining step of reforming reaction, in-depth analysis of microscopic reaction mechanisms for amino groups (including H and NHx, x=0–3) adsorption, dissociation, recombination and desorption are carried out by simulation parameters and experimental data. The results indicate that NH3 exhibits highly stable adsorption configurations (Bridge site) on both Ni, Ru-based catalyst surfaces, with the adsorption position having a relatively minor effect on adsorption energy. It is worth noting that Ni-based catalyst exhibits better adsorption behaviors towards NH3 compared to Ru. Whereas, during stepwise dehydrogenation of NH3 and subsequent N2 and H2 recombination and desorption processes, the reaction energy barriers confirm experimental observations of higher activity displayed by Ru-based catalyst in low-temperature range of 400–500 °C. Interestingly, N2 synthesis behavior of innovative Ru-Ni bimetallic tandem catalyst surface possesses the lowest reaction energy barrier than other models, which is attributed to the adsorption capability of Ni layers and the catalytic activity of Ru atoms. The experimental results also demonstrate that under typical engine exhaust conditions, the H2 production efficiency of 1 %Ru-3 %Ni/Al2O3 surpasses that of 1 %Ru/Al2O3 by 6.2 %, showcasing exceptional stability.

Advancing highly selective low-temperature ammonia oxidation: Hydrophobic silicalite-1 shell confining silver nanoparticles on Cu/ZSM-5 core

A judiciously devised core–shell NH3-SCO catalyst featuring a Cu/ZSM-5 core enveloped by an Ag/silicalite-1 shell (Cu/ZSM-5@Ag/S-1) was rationally constructed. Integrating the silicalite-1 shell effectively suppresses the migration of Ag into Cu/ZSM-5 core, conserving the active Cu2+ sites for the catalytical conversion of byproducts NOx. Concurrently, the shell averts the formation of positively charged Ag species, facilitating the generation of abundant Ag0 nanoparticles encapsulated in the S-1 shell. Comprehensive characterizations reveal abundant Ag0 species within the core–shell Cu/ZSM-5@Ag/S-1 catalyst, boosting O2 activation and NH3 dehydrogenation and thereby contributing to superior low-temperature activity in NH3-SCO reactions. Furthermore, the hydrophobic S-1 shell effectively reinforces the hydrothermal stability of the core–shell Cu/ZSM-5@Ag/S-1. DRIFTS coupled with DFT studies elucidate that the core–shell sample follows the imide mechanism, while the shell-free sample adheres to the hydrazine mechanism. This work advances our understanding of catalyst design and presents a promising solution with practical implications for ammonia oxidation processes.

Insight into the regulation effect of steam dilution on oxygen-enriched ammonia combustion characteristics

NH3/O2/H2O combustion technology combines oxygen enrichment to enhance NH3 combustion and steam dilution to control flame temperature and emissions, which can achieve clean and efficient power generation. Steam dilution strategies necessitate a balance between flame speed, temperature, and emissions. The key lies in kinetic investigation into the regulation effects of steam dilution on NH3/O2/H2O flames. An adaptive kinetic model is developed and validated against the measured flame speed and NO distribution. Experimental and numerical investigations are conducted to analyze the steam dilution effect on NH3/O2/H2O flame at varying Φs and Tus. Fuel-lean NH3/O2/H2O flames (Φ = 0.8–0.9) possess the highest flame speeds and a 25 % steam dilution results in a 39–45 % reduction (67.63–82.09 cm/s) in SL. H/O radical pools and NH3 primary decomposition (NH3 → NH2 + H) are the keys to the SL, and steam dilution significantly decreases the key radical accumulation. As ZH2O increases from 0 to 0.25, the stoichiometric flame temperature decreases to approximately 2600 K (a reduction of about 200 K). The staged dehydrogenation of NH3 always dominates the heat release, while the conversions of the H/O radical pool are the main endothermic reactions ·H2O dilution reduces the reactant concentration, and the high specific heat capacity of H2O also further reduces the flame temperature. ZH2O of 0.25 can reduce NO emissions to the order of magnitude of 100, while steam dilution may turn to promote NO emissions at Φ < 0.75 because steam dilution accelerates the generation of H and OH and promotes NO formation at fuel-lean conditions. ZH2O needs to be increased to more than 30 %, controlling the flame temperature not to exceed 2000 K and improving the fluid work efficiency. To further reduce NO emissions to 50 ppmv@15 %O2, it is necessary to adopt staged combustion nozzle/chamber structure designs, such as co-flow or secondary injection.

Theoretical study on K poisoning resistance of M-doped Ce/TiO2 (001) surface (M=Cu, Co, Zr, Sb, Mo, Nb, W)

Enhancing the resistance of SCR (Selective Catalytic Reduction) catalyst to K poisoning can be effectively achieved through modification. This study investigated the impact of transition metal modification on improving the ability of Ce/TiO2 (CT) catalysts to resist K poisoning by DFT (Density functional theory) calculations. Mo-, Nb-, and W-doping could effectively suppress the adsorption of K. Ov (oxygen vacancy) formation and hydrogenation reactions were both facilitated due to the modification of Cu, Co and Sb. The Cu-doping had a significant contribution to the adsorption of NH3 and NO, and showed the best resistance to K poisoning in the adsorption of reactive species. Additionally, Cu-doping decreased the energy barriers for NH3 dehydrogenation, NH2NO generation and decomposition, and NO2 formation on CT catalyst, and weakened the inhibition effect of K on the above elementary reactions. Consequently, this provided an effective improvement in the k-poisoning tolerance of the CT catalysts.

Insight into hydroxyl groups in anchoring Ir single–atoms on vacancy–deficient rutile TiO2 supports for selective catalytic oxidation of ammonia

High–performance catalysts are extremely required for controlling NH3 emission via selective catalytic oxidation (SCO), and the anchoring structural feature of active sites is a key prerequisite for developing them. This study confirms the importance of hydroxyl groups on vacancy–deficient reducible oxides as active groups. On the one hand, spontaneous atomic dispersion of active metal Ir is promoted by the abundant terminal hydroxyl groups. On the other hand, Ir cations anchor on the TiO2 surface through exchange with H+ in Ti–OH groups, and thus occupy the Brönsted acid sites. The adsorption strength of NH3 is another key factor affecting the reaction rate–determining step, namely NH3 dehydrogenation, which occurs at a faster rate in the coordinated L–NH3 rather than the ionic B–NH4+. Meanwhile, the coordinated L–NH3 significantly avoids the competitive adsorption of water vapor in the NH3–SCO reaction by reducing the number of hydrogen bonding. The TOF of preferred 0.8Ir/TiO2 sample is significantly higher than 0.2Ir/TiO2 sample, although Ir is almost always atomic dispersed. Finally, NH3 conversion is 85% in a wet circumstance (5% H2O) at 240 °C (GHSV = 85 000 h–1), with a N2 selectivity of up to 65% on 0.8Ir/TiO2 sample.

Adsorption and dehydrogenation of ammonia on Ru55, Cu55 and Ru@Cu54 nanoclusters: role of single atom alloy catalyst.

Hydrogen production by the catalytic decomposition of ammonia (NH3) is an important process for several important applications, which include energy production and environment-related issues. The role of single Ru-atom substitution in a Cu55 nanocluster (NC) has been illustrated using the NH3 decomposition reaction as a model system. The structural stability of Ru@Cu54 NC has been evaluated using Ru55 and Cu55 NCs for comparison. Ru@Cu54 prefers an icosahedron structure (Ih), like Ru55 and Cu55 NCs, with almost comparable average binding energies of -5.55 eV per atom. The adsorption of NHx (x = 0-3) on different adsorption sites of the icosahedron Ru@Cu54 NC has also been studied and the corresponding adsorption energies have been estimated. The site-preference investigation suggested that NH3 prefers to adsorb vertically to the Ru@Cu54. The stable geometries of the N and H atoms on the high symmetry adsorption sites of Ru@Cu54 NC have been studied. Although the N atom favours top and hollow sites, the H atom prefers to stay in the Ru-Cu bridge site along with the hollow sites. The adsorption energy of N on the Ru@Cu54 NC fcc site is found to be -5.42 eV, which is very close to the optimal value (-5.81 eV) of the ammonia decomposition volcano curve. The reaction energies for stepwise H atom elimination from an adsorbed NH3 molecule have been estimated. Finally, NH3 adsorption and decomposition on Ru@Cu54 have been illustrated in terms of electronic structure analysis. The energetics calculations for the dehydrogenation of NH3 suggest that Ru@Cu54 NC can be a suitable catalyst.

Design of Cu-based bimetals for ammonia catalytic combustion via DFT-based microkinetic modeling

Copper and its oxides possess excellent performance for ammonia catalytic combustion, but further improving the catalytic performance is still impeded by the limited understanding of the reaction mechanism. Herein, a density functional theory-based microkinetic study by considering the adsorbate-adsorbate interactions was performed to uncover the reaction mechanism under experimental conditions and further design the superior Cu-based bimetal catalysts. Our calculations demonstrate that the partially oxidized Cu(111) covered by oxygen atoms is the active phase. The ammonia consumption rate is not only constrained by strong adsorption of NH and O species but also suppressed by elementary reactions of NH coupling and O-assisted NH3 dehydrogenation from 400 to 800 K. Subsequently, two Cu-based bimetal catalysts, CuAg3 and CuAu3, cautiously designed by weakening the adsorption of NH and O species and reducing the activation barriers of the two rate-determining steps, possess superior catalytic performance than the copper in ammonia catalytic combustion. Overall, our studies not only reveal the reaction mechanism of ammonia catalytic combustion on Cu(111) but also provide important insights for the design of optimal catalysts including two predicted Cu-based bimetal catalysts.

Promoting mechanism of Mn doping on the NH3-SCR reaction over the Fe/γ-Al2O3 catalyst surface

To verify the superiority of Mn-Fe dual-component doped catalysts in terms of deNOx performance, the differences of mechanisms in selective catalytic reduction with ammonia (NH3-SCR) between Fe/γ-Al2O3 and Mn-Fe/γ-Al2O3 catalysts were investigated by using the density functional theory (DFT). On the surface of the Fe/γ-Al2O3 catalyst, the NH2 group generated by NH3 dehydrogenation can react with NO and NO2 to form NH2NO and NH2NO2, respectively. The decomposition process of NH2NO is established as the rate-determining step in the reaction between NH3 and NO, while the rate-determining step in the reaction between NH3 and NO2 is the decomposition of NHNO2. Mn doping significantly enhances the catalyst's adsorption performance for O2 and oxidation ability toward NO, thereby promoting the production of NO2. Additionally, Mn doping markedly reduces the reaction barriers, facilitating the dissociation of NH2NO and NHNO2 on the Mn-Fe/γ-Al2O3 catalysts. These findings may elucidate the reasons of the effective enhancement of deNOx performance in the Mn-doped Fe/γ-Al2O3 catalysts, which establishes a foundation for the subsequent development and application of Mn-Fe bimetallic-doped SCR deNOx catalysts.

Enhanced alkaline ammonia oxidation reaction activity using PtW alloy catalysts with tungsten as built-in competitor reservoir

Direct ammonia anion exchange membrane fuel cells (DA-AEMFCs) have drawn great attention recently with the recognition that liquid ammonia (NH3), as a carbon-free hydrogen storage medium, is easy to store, transport, and distribute. However, its practical application is significantly limited by the anodic ammonia oxidation reaction (AOR), which not only is kinetically sluggish, but also suffers from competitive adsorption of oxidizing agent, OH–. Herein, we tackle the above challenges simultaneously by alloying the highly active platinum with electron-deficient tungsten. The W sites would preferentially adsorb *OH to serve as the reservoir and supply for the dehydrogenation of NH3. The Pt sites are thus liberated and free for the targeting adsorption of NH3. Moreover, density functional theory calculations suggest that, with the pre-adsorption of *OH, the d band center of PtW alloy experiences a positive shift toward the Fermi level, which would contribute to stronger adsorption of the reaction intermediates and thus benefit the whole AOR process. As expected, the synthesized alloy with the optimum ratio exhibits a low onset potential of 0.46 V versus reversible hydrogen electrode and a large peak current density of 11.70 mA cm−2. When subjected to practical application, the DA-AEMFCs assembled with such electrocatalyst deliver an excellent peak power density of 22.47 mW cm−2, indicating its potential feasibility in the next-generation energy devices.

Mechanism study of Na poisoning on Ce/TiO2(001) surface based on adsorption of reaction species and elementary reaction pathways

The presence of alkali metal Na in flue gas can significantly impair the reactivity of Ce/TiO2 (CT) SCR (Selective Catalytic Reduction) catalyst. This study investigates the deactivation mechanism of Na on the Ce/TiO2 catalyst using Density Functional Theory (DFT) calculations, focusing on the adsorption of surface species and the pathway of elementary reaction. Due to the high affinity between Na atom and the catalyst surface, Na poisoning readily occurs on Ce/TiO2 (001) surface. The presence of Na on the catalyst surface hampers hydrogenation, oxygen vacancy formation, and NH3 adsorption, while also reducing the catalyst's acidity and reducibility. Additionally, Na impedes the NH3 dehydrogenation reaction, as well as the formation and decomposition of NH2NO and the dissociation of O2 on the catalyst surface, thereby inhibiting the NH3-SCR reaction. The inhibition of NO2 formation further affects the fast SCR reaction, which may explain the low-temperature deactivation of the catalyst.

Recognizing zeolite topologies for Cu2+ localizations with effective activities for selective catalytic reduction of nitrogen oxide

Cu-loaded zeolites are widely investigated in selective catalytic reduction of nitrogen oxide, but effects of zeolite topologies on formed active species and the changing tendency remain unexplored. In this work, catalytic turnover frequencies (TOF) of Cu loaded ZSM-5, Beta, MOR, and SSZ-13 were first determined. The topology-localized Cu species in these zeolites were analyzed by temperature-programmed reduction of H2. Then Multiple Linear Regression distinguished TOF contributions (kj, s−1·mol−1) of the Cu species. Density functional theory calculated NH3 dehydrogenation energy of the Cu species. As a result, topologies with more node atoms showed bigger kj and lower dehydrogenation energies simultaneously. The best topology in each zeolite was 10-membered ring (ZSM-5), 6-membered ring facing a 12-membered ring (Beta), 8-membered ring (MOR), and cha cage (SSZ-13). Moreover, cha cage-localized Cu2+ exhibited the largest kj and the lowest dehydrogenation energy among all the Cu species. This work reveals topology-catalysis relationships in the zeolite, which benefits zeolite design for enhanced catalytic performances.

Adiabatic laminar burning velocities and NO generation paths of NH3/H2 premixed flames

NH3/H2 is an important hydrogen fuel without carbon emissions. In order to know the fundamental flame characteristics of NH3/H2, the adiabatic laminar burning velocity (SL,0) and overall activation energy (Ea) were measured simultaneously by the flat flame method. Four combustion mechanisms were evaluated to clarify the NO generation paths. It was found that SL,0 shows a monotonic nonlinear increase from 10.69 cm/s to 39.99 cm/s with the increasing of equivalent ratio (Φ = 0.6–1.0) and hydrogen mixing ratio (0.2–0.5 vol%). The four mechanisms have a good prediction for SL,0, but an unsatisfactory prediction for Ea. Among them, S-Mech has the best prediction for SL,0 and Ea. Detailed kinetic analysis shows that NNH-reaction (R700, R795, and R801 in S-Mech) simultaneously play an important role in SL,0 and NO generation. Under lean conditions, NO generation is mainly related to H2NO →OH HNO →HO2 NO, and NO reduction is mainly from NO converted to NNH, which is related to NHi generated by NH3 dehydrogenation. This work identified critical reactions of NO generation and systematically explained the path tendency of NH3 combustion at lean conditions.

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.

Insight into the micro-mechanism of Co doping to improve the deNOx performance and H2O resistance of β-MnO2 catalysts

Mn-based catalysts are desirable for selective catalytic reduction (SCR) of NO by NH3 due to their good catalytic activity and environmentally friendliness. However, the deNOx performance of single component MnO2 catalyst fails to meet the requirement and it has poor tolerance to H2O. Co doping can improve the activity and the H2O resistance of the catalysts, but the reaction mechanism remains unclear. Here, the effect of Co doping on the deNOx activity of Mn-based catalysts and the reaction mechanism of gas molecules over the β-MnO2 (110) surface were revealed by combining experimental measurements and DFT simulations. Results show that the optimal proportion of Co can increase the deNOx efficiency of MnO2 catalysts. Doping Co enhances the adsorption and dehydrogenation of NH3 on the β-MnO2 catalyst surface. NH2 can combine with NO to form NH2NO. Co doping promotes the breakdown of NH2NO, and the Langmuir-Hinshelwood mechanism dominates this reaction. Furthermore, Co-doped β-MnO2 catalysts can reduce the competitive adsorption of H2O, which alleviates the poisoning effect of the catalyst.

Study on the mechanism of NOx reduction by NH3-SCR over a ZnXCu1-XFe2O4 catalyst.

Experimental evidence shows that CuFe2O4 exhibits excellent catalytic performance in the SCR reaction. However, there is a lack of in-depth research on its specific reaction mechanism. Our study begins by computing the adsorption model of molecules like NH3 and then goes on to examine the SCR reaction mechanism of NH3 on CuFe2O4 before and after Zn doping. The results indicate that NH3 is chemically adsorbed (-1.26 eV) on the surface and has a strong interaction with the substrate. Importantly, Zn doping provides more favorable reactive sites for NH3 molecules. Subsequent investigation into the NH3 dehydrogenation and SCR reaction processes showed that incorporating Zn can greatly decrease the energy barrier of the most critical step in the reaction (0.58 eV). Additionally, the study also assesses the feasibility of the reaction of adsorbed NO with surface active O atoms to form NO2 (barrier 0.86 eV). Lastly, the sulfur resistance of the catalyst before and after doping is calculated and analyzed, and it is found that Zn doping effectively improves the sulfur resistance. Our study provides valuable theoretical guidance for the development of ferrite spinel and doping modification.

Origin of Ammonia Selective Oxidation Activity of SmMn2O5 Mullite: A First-Principles-Based Microkinetic Study.

Based on first-principles calculations and microkinetic analysis, the reaction routes and origin of the activity of SmMn2O5 mullite for the selective catalytic oxidation of ammonia (NH3-SCO) are systematically investigated on three low-index surfaces under experimentally operating conditions. Key influencing factors and contributions of different iconic intermediate species (NH*, N2H4*, and HNO*) to the overall reaction process have been identified. In detail, Mn4+ serves as the primary active site for NH3 adsorption, while lattice oxygen participates in the dehydrogenation of NH3 on (010)4+ and (001)4+ surfaces. Furthermore, the (010)4+ surface shows both the best activity and the highest N2 selectivity at low temperatures via the synergy effect of exposed Mn-Mn dimers and the most labile O2 atoms. We further evaluate the potential catalytic performances of six A-site doped (010)4+ facets, among which La, Pr, and Nd dopings are predicted to possess better catalytic performances. Our study provides deep insights into the microscope reaction mechanisms and provides the specific optimization strategy for NH3-SCO on mullite oxides.

Density functional theory calculation of reaction pathways for AP decomposition over g-C3N4 surface

The profound understanding of decomposition mechanism of ammonium perchlorate (AP) is significant to the design of AP-based solid propellants. Herein, the possible decomposition reactions of AP over graphitic carbon nitride (g-C3N4) catalyst were investigated by employing density functional theory calculation to explore the reaction network of HClO4 and degradation pathway of NH3 on g-C3N4 surface. The energy barriers of elementary reactions in the network were obtained, the main reaction channels of the decomposition of HClO4 over g-C3N4 catalyst was found out to be HClO4 → ClO3- → ClO2- → ClO− → Cl−. The rate-limiting step along the pathway was the formation of ClO− from ClO2-, with the energy barrier as high as 1.903 eV. The oxidation of g-C3N4 surface would weaken the catalytic capacity of g-C3N4 for the decomposition of HClO4. However, the oxidation of g-C3N4 surface would enhance the catalytic capacity for the adsorption and dehydrogenation of NH3. The pre-adsorbed OH* on g-C3N4 surface would inhibit the adsorption of NH3 but it could promote the dehydrogenation of NH2* and NH*. This work provides new insights about the molecular-level decomposition mechanism of AP over g-C3N4.