FeS2 Surface Research Articles

Construction of dual sites on FeS2 surface for enhanced electrocatalytic reduction of nitrite to ammonia

Cost-effective iron sulfides (FeS2) hold great potential as high-performance catalysts for NO2− electroreduction to NH3 (NO2ER), which is hindered by the weak NO2 activation. Herein, the design of nonmetal-doped FeS2 electrocatalysts was initially conducted by density functional theory (DFT) computations. We found that doping with different nonmetal atoms effectively not only regulates the electronic structures of the d-electrons of Fe atoms but also creates the unique p-d hybridized dual active sites, thereby boosting the efficient NO2 activation. Owing to the optimal NO2 adsorption strength, N–doped FeS2 demonstrates a low limiting potential for the NO2−–to–NH3 conversion, thus significantly improving NO2ER activity. Direct experimental evidence was provided afterward: an NH3 yield rate of 424.5 μmol/hcm−2 with a 92.4 % Faradaic efficiency was achieved. Our findings not only suggest a promising NO2ER catalyst through theoretical computations to guide experiments but also provide a comprehensive understanding of the structure-properties relationship.

Sulfur defect engineering boosted nitrogen activation over FeS2 for efficient electrosynthesis of ammonia

Electrocatalytic nitrogen (N2) reduction to ammonia (NH3) reaction (eNRR) supplies a promising alternative to the Haber-Bosch technology. However, the dissociation of NN bond hinders its development. Herein, sulfur vacancies are introduced into FeS2 for promoting N2 activation and thus stimulating the eNRR progress. Experimental investigations and density functional theory (DFT) calculations reveal that the electrons could transfer from Fe 3d orbits to N2 2π* orbital, thus facilitating the cracking of inert N2 molecules. And the electron transfer is easier for those Fe atoms with S vacancies in adjacent positions. Furthermore, we find that eNRR process on the FeS2 surface follows the distal and alternating hybrid pathway. Also, the water molecules in the electrolyte facilitate the first hydrogenation of N2 (*N2 → *NNH). Notably, FeS2 with rich sulfur vacancies exhibits an excellent NH3 yield rate of 67.5 μg h−1 mgcat.−1, which outperforms most of the reported eNRR activities of Fe-based catalysts.

Formation of Methanol via Fischer-Tropsch Catalysis by Cosmic Iron Sulphide.

Chemical reactions in the gas phase of the interstellar medium face significant challenges due to its extreme conditions (i. e., low gas densities and temperatures), necessitating the presence of dust grains to facilitate the synthesis of molecules inaccessible in the gas phase. While interstellar grains are known to enhance encounter rates and dissipate energy from exothermic reactions, their potential as chemical catalysts remain less explored. Here, we present mechanistic insights into the Fischer-Tropsch-type methanol (FTT-CH3OH) synthesis by reactivity of CO with H2 and using cosmic FeS surfaces as heterogeneous catalysts. Periodic quantum chemical calculations were employed to characterize the potential energy surface of the reactions on the (011) and (001) FeS surfaces, considering different Fe coordination environments and S vacancies. Kinetic calculations were also conducted to assess catalytic capacity and allocate reaction processes within the astrochemical framework. Our findings demonstrate the feasibility of FeS-based astrocatalysis in the FTT-CH3OH synthesis. The reactions and their energetics were elucidated from a mechanistic standpoint. Kinetic analysis demonstrates the temperature dependency of the simulated processes, underscoring the compulsory need of energy sources considering the astrophysical scenario. Our results provide insights into the presence of CH3OH in diverse regions where current models struggle to explain its observational quantity.

Deciphering the Catalytic Mechanism of Peroxidase-like Activity of Iron Sulfide Nanozymes.

Iron sulfide nanomaterials represented by FeS2 and Fe3S4 nanozymes have attracted increasing attention due to their biocompatibility and peroxidase-like (POD-like) catalytic activity in disease diagnosis and treatments. However, the mechanism responsible for their POD-like activities remains unclear. Herein, taking the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by H2O2 on FeS2(100) and Fe3S4(001) surfaces, the catalytic mechanism was investigated in detail using density functional theory (DFT) calculations and experimental characterizations. Our experimental results showed that the catalytic activity of FeS2 nanozymes was significantly higher than that of Fe3S4 nanozymes. Our DFT calculations indicated that the surface iron ions of iron sulfide nanozymes could effectively catalyze the production of HO• radicals via the interactions between Fe 3d electrons and the frontier orbitals of H2O2 in the range of -10 to 5 eV. However, FeS2 nanozymes exhibited higher POD-like activity due to the surface Fe(II) binding to H2O2, forming inner-orbital complexes, which results in a larger binding energy and a smaller energy barrier for the base-like decomposition of H2O2. In contrast, the surface iron ions of Fe3S4 nanozymes bind to H2O2, forming outer-orbital complexes, which results in a smaller binding energy and a larger energy barrier for the base-like decomposition of H2O2. The charge transfer analysis showed that FeS2 nanozymes transferred 0.12 e and Fe3S4 nanozymes transferred 0.05 e from their surface iron ions to H2O2, respectively. The simulations were consistent with the experimental observations that the FeS2 nanozymes had a greater affinity for H2O2 compared to that of Fe3S4 nanozymes. This work provides a theoretical foundation for the rational design and accurate preparation of iron sulfide functional nanozymes.

Efficiently activate peracetic acid by FeS2-anchored molybdenum species for the rapid degradation of sulfamethazine

Peracetic acid (PAA) based advanced oxidation processes are increasingly used as alternative strategies for sulfonamide antibiotics (SAs) degradation. In this study, molybdenum (Mo) species were successfully anchored on the FeS2 surface. This catalyst (Mo-FeS2) could be used as an excellent PAA activator for the removal of sulfamethazine (SMT). Electrochemical measurements revealed that anchored Mo species lowered the electron transfer resistance on the FeS2 surface, and density functional theory (DFT) calculation suggested more electrons can be shifted from FeS2 to Mo, which is prone to transfer electrons for PAA activation. After 30 min reaction, 87.6 % of SMT could be removed by Mo-FeS2/PAA at pH 4, and reactive species (RSs) including HO•, CH3COO• and Fe(IV) were responsible for the SMT degradation. Increasing the dosages of PAA (0.02 – 0.5 mM) or Mo-FeS2 (0.1 – 0.4 g/L) facilitated the SMT degradation. DFT calculation results suggest that the aniline ring of SMT is vulnerable to attack induced by RSs. The degradation pathways of SMT, including Smiles rearrangements, hydroxylation of aniline ring, oxidation of the –NH2 group and coupling reaction, were proposed according to the identified oxidation products. Sulfamethoxazole, sulfadiazine, sulfanilamide and sulfathiazole could also be degraded by Mo-FeS2/PAA (>50 %), suggesting that the Mo-FeS2/PAA would be a competitive strategy for the remediation of SAs-contaminated water.

Simultaneous removal of As(V) and sulfamethazine from water in FeS2-H2O2 system

Sulfamethazine (SMT) and organic arsenic are usually used as feed additives in animal husbandry and aquaculture, which will produce severe compound pollution after metabolism and discharge. In this work, the FeS2-H2O2 system was used to simultaneously remove As(V) and SMT. Under 0.8 g/L of FeS2, 40 mM of H2O2, the simultaneous removal efficiency of SMT and As(V) was up to 97 %. The initial concentration of As(V) was unfavourable for SMT degradation, while the effect of initial concentration of SMT on As(V) removal could be ignored. Meanwhile, increasing FeS2 and H2O2 dosages enhanced removal efficiency of SMT and As(V). However, excessive FeS2 was detrimental to the removal of As, and the ·OH, ·O2−, and 1O2 were generated to degrade SMT. As was adsorbed on the surface of positively charged FeS2 firstly and then reacted with Fe(III) on the surface of FeS2 or released by Fenton reaction to form FeAsO4. No As(III) was detected during the simultaneous removal process in the FeS2-H2O2 system. This study revealed that SMT and As(V) could be removed simultaneously in the FeS2-H2O2 system, which produced new insight into animal husbandry and aquaculture wastewater treatments.

Reduced sulfur accelerates Fe(III)/Fe(II) recycling in FeS2 surface for enhanced electro-Fenton reaction

FeS2 is well-known for its role in redox reactions. However, the mechanism within heterogeneous electron-Fenton (Hetero-EF) systems remains unclear. In this study, a novel FeS2 based three-dimensional system (GF/Cu–FeS2) with self-generation of H2O2 was investigated for Hetero-EF degradation of sulfamethazine (SMZ). The results revealed that SMZ could be completely removed in 1.5 h, accompanying with the mineralization efficiency of 96% within 4 h. This system performed excellent stability, evidenced by consistently eliminated 100% of SMZ within 2 h over 4 cycles. The generated Reactive Oxygen Species (ROS) of •OH and •O2− in every degradation cycle were quantitatively measured to confirm the stability of the GF/Cu–FeS2 system. Additionally, the redox reaction mechanism on the surface of FeS2 was thoroughly analyzed in detail. The accelerated reduction of Fe(III) to Fe(II), triggered by S22− on the surface of FeS2, promoted the iron cycling, thereby quickening the Fenton process. Density Functional Theory (DFT) results illustrated the process of S22− to be oxidized to in detail. Therefore, this work provides deeper insight into the mechanistic role of S22− in FeS2 for environmental remediation.

First‐principles study on the effect of arsenic impurity on oxidation of pyrite surfaces

AbstractArsenic (As) frequently exists in pyrite (FeS2) in the form of impurities. The oxidation behavior of As in FeS2 is important in environmental science, mineral processing, and other related fields. The adsorption behaviors of H2O and O2 molecules on the As‐bearing pyrite (100) surface (AsFeS2(100)) are studied using the density functional theory (DFT). The results show that As prefers the S site on the pyrite (100) surface (FeS2(100)). In the absence of O2, an isolated H2O molecule does not dissociate when adsorbed at an iron (Fe) site and is repelled at an As site. Furthermore, the surface area around the As atoms exhibits a hydrophobic behavior. Adsorption energy analysis reveals that the presence of As atoms is unfavorable for the adsorption of H2O molecules on the pure FeS2 surface, and that the adsorption of H2O molecules on the AsFeS2(100) is physical adsorption. In the absence of H2O, it is suggested that the O2 molecule easily dissociates on both the pure FeS2(100) and AsFeS2(100). The adsorption of O2 on the As‐bearing surface is weaker than that on the pure FeS2(100). For the co‐adsorption of H2O and O2, the adsorption energy on the As‐bearing surface is more negative than that on the pure surface. This indicates that the presence of As promotes surface oxidation. Additionally, two OH and O (AsO or SO) or O (FeO) species are formed on the surface of pyrite when the H2O molecule is dissociated.

Adsorption and dissociation of CH3SH on FeS surface: A DFT study

Methyl mercaptan (CH3SH) is a common sulfide in oil and natural gas, easily corroded in transportation pipes and storage containers. In this paper, the adsorption and dissociation processes of CH3SH on FeS (0 0 1), (0 1 1), (1 0 0) and (1 1 1) surfaces have been studied by the density functional theory (DFT). And the characteristics of the adsorption and dissociation processes were elucidated. The calculated surface energies show that the order of surface stability is (0 0 1) > (0 1 1) > (1 0 0) > (1 1 1). The stability of CH3SH adsorption is (1 1 1) > (1 0 0) > (0 1 1) > (0 0 1) by the adsorption energy, and the most stable adsorption configurations are obtained. Compared with the changes in electron density and the partial density of states (PDOS) before and after adsorption, there is an obvious electron orbital hybrid phenomenon between CH3SH and FeS (1 0 0), (1 1 1) surface, and its adsorption is stronger than that of the other two surfaces. It can be seen from the calculation of the transition state that the dissociation reaction of CH3SH is endothermic on the (0 0 1) and (0 1 1) surfaces, while the exothermic reaction on the (0 1 1) and (0 0 1) surfaces. CH3SH will dissociate preferentially on the FeS (1 0 0) surface because the reaction of Ea and ΔE on this surface is the smallest. Overall, the adsorption and dissociation processes are exothermic, the increase in temperature makes the crystal surface unstable and susceptible to spontaneous combustion, and the phenomenon occurs first on the FeS (1 0 0) and FeS (1 1 1) surfaces. These findings increase the understanding of the electronic structure and energy of the sulfides' action on the FeS surface and also have a reference value for flame retardant research.

Study on the flotation mechanism of cobalt-bearing pyrite: A DFT calculation

The adsorption mechanism of flotation collector methyl xanthate on the pure and Co-doped FeS2 (100) crystal plane was investigated by density functional theory (DFT) calculation. For the purpose of comprehensive calculation, the top sites on the two nearest neighbor Fe atoms (TFe-Fe-I) of the FeS2 (100) crystal plane, and on the one Co atom and one nearest neighbor Fe (TFe-Co) as well as on the top sites on the two nearest neighbor Fe atoms (TFe-Fe-II) of the Co-doped FeS2 (100) crystal plane are taken into account, respectively. The adsorption energy analysis showed that the TFe-Co sites on the Co-doped FeS2 (100) crystal plane were more favorable for methyl xanthate adsorption. Furthermore, From the charge density difference and Bader charge analysis results of the most stable adsorption configuration of methyl xanthate on TFe-Co sites of the Co-doped FeS2 (100) crystal plane, it can be clearly seen that the direction of charge transfer is S to Fe and Co after methyl xanthate adsorption on mineral surfaces. The results of projected density of states (PDOS) and crystal orbital Hamilton population (COHP) in terms of the complex interactions atomic orbitals and chemical bonds further reveal that Co substitution of Fe in FeS2 promoted the adsorption of methyl xanthate onto the Co-doped FeS2 (100) surface.

Symmetry dependent activation and reactivity of peroxysulfates on FeS2(0 0 1) surface

Symmetry dependent activation and reactivity of peroxysulfates on FeS2(0 0 1) surface

Theoretical Research on the Reduction of CO2 with H2S on Pyrite FeS2 Surfaces

Understanding the reduction of CO2 and the origin and evolution of early life on Earth is an important research endeavor. Pyrite, due to its semiconductor properties, is believed to play a pivotal role as a reactant or catalyst in converting reducing gases, such as CO2, into organic matter. In this study, we employed density functional theory (DFT) to investigate the reduction of CO2 in the presence of H2S on the surface of pyrite. Our findings reveal that the presence of sulfur vacancies enhances the adsorption of H2S and CO2 molecules onto the pyrite surface. Interestingly, we observed the generation of the HCOOH molecule on the defective pyrite surface. Additionally, the transition state analysis indicates that H2S and CO2 molecules require the overcoming of an energy barrier (Ea) of 36.93 kJ/mol to form the HCOOH molecule. This study sheds light on the role of pyrite in the early creation of life on Earth by elucidating its impact on the reduction of carbon dioxide.

Controlled p-Type Doping of Pyrite FeS2.

Pyrite FeS2 has extraordinary potential as a low-cost, nontoxic, sustainable photovoltaic but has underperformed dramatically in prior solar cells. The latter devices focus on heterojunction designs, which are now understood to suffer from problems associated with FeS2 surfaces. Simpler homojunction cells thus become appealing but have not been fabricated due to the historical inability to understand and control doping in pyrite. While recent advances have put S-vacancy and Co-based n-doping of FeS2 on a firm footing, unequivocal evidence for bulk p-doping remains elusive. Here, we demonstrate the first unambiguous and controlled p-type transport in FeS2 single crystals doped with phosphorus (P) during chemical vapor transport growth. P doping is found to be possible up to at least ∼100 ppm, inducing ∼1018 holes/cm3 at 300 K, while leaving the crystal structure and quality unchanged. As the P doping is increased in crystals natively n-doped with S vacancies, the majority carrier type inverts from n to p near ∼25 and ∼55 ppm P, as detected by Seebeck and Hall effects, respectively. Detailed temperature- and P-doping-dependent transport measurements establish that the P acceptor level is 175 ± 10 meV above the valence band maximum, explain details of the carrier inversion, elucidate the relative mobility of electrons and holes, reveal mid-gap defect levels, and unambiguously establish that the inversion to p-type occurs in the bulk and is not an artifact of hopping conduction. Such controlled bulk p-doping opens the door to pyrite p-n homojunctions, unveiling new opportunities for solar cells based on this extraordinary semiconductor.

First-Principles Study of Hg0 Immobilization on a Defective Pyrite Surface

The formation of defects over a crystal surface could significantly improve the elemental mercury (Hg0) removal performance of pyrite (FeS2). Herein, the role of surface defects in Hg0 immobilization over FeS2(100) was investigated by adopting quantum chemistry. The contribution of surface defects to mercury immobilization over pyrite was mainly manifested in facilitating Hg0 adsorption. Compared with a perfect pyrite surface, a defective pyrite surface exhibited a higher affinity to Hg0, whose adsorption energy was up to −53.03 kJ/mol. In addition, surface defects could induce the dissociation of HCl, a common component in coal combustion flue gas, which provided active chlorine (Cl*) for subsequent Hg0 oxidation. The Langmuir–Hinshelwood mechanism is responsible for Hg0 oxidation over the defective FeS2(100) surface. First, Hg0 and HCl were simultaneously adsorbed over the defective surface, and the presence of defects could promote Hg0 adsorption and HCl dissociation. Subsequently, adsorbed Hg0 would combine with the adjacent active Cl* site, whose energy barrier was 92.60 kJ/mol. Eventually, HgCl could spontaneously react with another Cl* site to form a HgCl2 molecule. Thus, the formation of a HgCl intermediate was the rate-determining step for Hg0 oxidation over a defective pyrite surface. This work reveals the role of defects in Hg0 immobilization over a pyrite surface, which provides a scientific basis for the design and modification of natural mineral sulfide sorbents.

H2O2 mediated oxidation mechanism of pyrite (0 0 1) surface in the presence of oxygen and water

Pyrite (FeS2) is the most common metal sulfide in nature. The oxidation mechanism of the pyrite has attracted intensive research attentions. It has been determined that this process involves multi-step electron transfer reactions between the FeS2 surface and the adsorbed O2 and H2O. In this process, sulfoxide (such as S2O32−, SO42−) and ferrous (Fe2+) are released into solution, and intermediate by-products, such as hydrogen peroxide (H2O2) and other reactive oxygen species (ROS), are produced. However, our understanding of the formation and transformation of these transient species is still limited. In this study, oxidation pathways by O2 and H2O on the pyrite (001) surface are explored by means of density functional theory (DFT) simulation. The oxidation pathway including the H2O2 forms as the intermediate is reported for the first time. It is found that the H2O2 molecule forms with low activation energy barriers when the O2 and H2O are co-absorbed on the pyrite surface. The H2O2 dissociates and releases the O atom to promote the sulfur oxidation. The product distribution resulted by the H2O2 mediated oxidation pathway agrees with the isotopic composition experiment that a minor amount of O2 is permanently incorporated into SO42– during pyrite oxidation (O in SO42– is mainly derived from water).

Depression mechanisms of sodium humate and 3-mercaptopropionic acid on pyrite in fine coal flotation

Pyrite in coal causes serious environmental pollution in the utilization of coal. Flotation is an appropriate method to remove pyrite present in fine coal. Sodium humate (HA-Na) and 3-mercaptopropionic acid (3-MPA) were used as depressants for pyrite removal in the flotation of fine coal, and their depression mechanisms were investigated by molecular dynamics simulation. The results showed that a relatively lower concentration of HA-Na solution can effectively reduce the sulfur content of flotation cleaned coal, whereas 3-MPA had little effect on its desulfurization. This difference in the desulfurization effect can be attributed to the modification effect of depressants on the surface wettability of pyrite. HA-Na molecules were adsorbed on the FeS2 (100) surface mainly by van der Waals forces, while 3-MPA molecules were adsorbed by hydrogen bonds, with a strong directionality. The –COO– groups in the HA-Na molecules formed strong hydrogen bonds with the water molecules. The –SH groups in the 3-MPA molecules pointed to the water layer and had weak interactions with the water molecules. Therefore, 3-MPA had a stronger selectivity than HA-Na, while HA-Na had a better effect on enhancing the surface wettability. These results are beneficial to the development of depressants for pyrite removal from fine coal.

Evaluation of pyrite/sodium hypochlorite for activating purification of arsenic from fractured-bedrock groundwater

In this work, the effectiveness of pyrite/sodium hypochlorite (FeS2/NaClO) treatment to eliminate arsenic (As) from fractured-bedrock groundwater via oxidative adsorption was evaluated. The As concentration in the tested reactors decreased sharply during the initial 5 min, as the addition of NaClO effectively increased the As removal efficiency, attaining 98.6% removal within 60 min in the presence of 0.05 M NaClO. There was no coexisting anion effect (Cl−, CO3−, HCO3−, NO3−, and F−) on the As removal capacity of FeS2/NaClO, except for the PO43− which resulted in less removal of As. X-ray spectroscopy analysis of As(III)-sorbed FeS2 surfaces revealed that a portion of As(III) was oxidized into As(V) during the adsorption process. Scanning electron microscopy-energy-dispersive spectrometer results of FeS2 exhibited the distribution of adsorbed As on the newly formed iron (oxy) hydroxide surfaces, with an As element ratio of 1.27%. A continuous flow-bed column study further demonstrated the efficiency of FeS2/NaClO treatment to lower the contamination level of As at the removal rates of 0.66–3.02 mg/L·day for 160 h. These results suggest that FeS2/NaClO treatment can be considered an effective strategy for removing As in groundwater of bedrock aquifers.

Vanadium selective separation enhancement from iron in black shale using oxalic acid due to FeS2 (1 0 0) surface passivation: A theoretical and experimental study

Iron impurity tends to precipitate and reduces vanadium product purity during vanadium extraction from black shale. Oxalic acid is an eco-friendly leachant which can enhance vanadium selective separation from iron impurity. In this paper, the separation mechanism was systematically investigated. The mineral phases transformations and thermodynamics analysis indicate that the FeS2 in black shale can react with H2C2O4, HC2O4-, C2O42- and O2, as a result, the pyrite surface was coated by ferrous oxalate passivation layer, which can depress pyrite dissolution reaction. Meanwhile, the density functional theory (DFT) calculations show that the H2C2O4, HC2O4- and C2O42- can reconstruct FeS2 (100) surface by adsorption, and the adsorption energy can be as low as −3.73 eV for C2O42- adsorption configuration. The electrons in Fe atoms were transferred to O atoms and the stable Fe-O bands together with closed seven/eight-membered rings structures were formed as passivation layer, which can weaken and reduce Fe atoms reactive activation for the FeS2 during oxalic acid leaching. This study reveals vanadium separation from iron due to pyrite passivation in presence of oxalic acid at an atomic level.

Adsorption/dissociation process of H2S on different FeS2(1 0 0) surfaces

Interactions between H2S and an FeS2(100) surface significantly affect the corrosion of carbon steel, and effects of pre-adsorbed atoms on the H2S adsorption/dissociation process remain unclear. Herein, we adopted the Hubbard U-corrected GGA + U method of density functional theory and considered the effect of spin polarization. The stability order of different FeS2 low-dimensional surfaces was calculated. The adsorption/dissociation mechanism of H2S on perfect and pre-adsorbed FeS2(100) surfaces was explored, and the theoretical basis of the improved hydrogen barrier effect in FeS2 was revealed. The stability order of different FeS2 low-dimensional surfaces was (100) > (110) > (111). The adsorption capacity of H2S on the surface of the pre-adsorbed FeS2(100) was stronger and dissociated spontaneously. Pre-adsorbed oxygen atoms significantly promoted the H2S adsorption/dissociation process. Owing to the ETS1H of H atoms and interaction energy between H and SH, the dissociated Ea on the pre-adsorbed surface decreased. Hydrogen atoms are prone to overflowing of H2 molecules on the perfect surface of FeS2(100), and FeS2 had better hydrogen barrier properties. This study enhances our understanding of structural properties of FeS2 and the interaction of H2S with different FeS2(100) surfaces, providing guidance for developing corrosion protection, hydrogen barrier materials, and catalytic systems.

Design of S-vacancy FeS2 as an electrocatalyst for NO reduction reaction: A DFT study

Electrocatalytic reduction is an effective method to remove harmful gas NO. In the process of reduction, NH3, one of the most important chemical raw materials in industrial production, can also be produced. However, large-scale practical application of NO electrocatalytic reduction is still a challenge, and to find the efficient, low-cost and stable catalysts is a problem that needs to be solved at present. By use of density functional theory calculation, we systematically studied that the potential of FeS2 (100) containing S vacancy (S-vacancy FeS2) as catalyst for NO electrocatalytic reduction. Our results revealed that NO can be chemisorbed stably at the S vacancy of FeS2 (100) surface and consequent reduction of NO molecular can generate NH3 and H2O. The S-vacancy FeS2 as catalyst has an excellent electrocatalytic activity of NO under ambient conditions. More interestingly, when the O atom of NO molecule is loaded in the S vacancy and side-on is adsorbed, all the steps in the reduction process are exothermic reactions. Our work provides a deep understanding for the search of efficient and low-cost NO reduction catalysts.