Adsorption Of O2 Molecules Research Articles

Inhibition Mechanism of MgO Addition on High‐Temperature Oxidation of Magnetite: Density Functional Theory and Ab Initio Molecular Dynamics Methods Joint Research and Experimental Verification

In order to investigate and analyze the effect of MgO gangue on the surface adsorption and oxidation behavior of magnetite, the physicochemical properties of substances in the magnetite oxidation process are investigated in this study by using thermogravimetric experiments, density functional theory, and ab initio molecular dynamics methods (AIMD) methods. The oxidation mechanism of magnetite and the inhibition mechanism of magnesium oxide on the oxidation properties of magnetite are elucidated. The results of the thermogravimetric experimental study show that the initial oxidation temperature of magnetite tends to increase with the increase of MgO content. At the same time, the presence of MgO leads to the migration of oxidation reactions to the high‐temperature region. AIMD study shows that the presence of the gangue element Mg prolongs the adsorption and dissociation time of O2 molecules on the surface and reduces the interfacial chemical reaction rate of Fe3O4. Moreover, the chemical bonds formed in the system after doping Mg atom are more stable, which is not conducive to the migration of oxygen atoms between Fe3O4 crystal structures, thus affecting the comprehensive oxidation performance of minerals.

Copper nanoparticles incorporated nitrogen-rich carbon nitride as laccase-like nanozyme for colorimetric detection of bisphenol a released from microplastics

Herein, a new strategy for laccase-like nanozyme is proposed by utilizing copper nanoparticles (Cu NPs) as the active center, carbon nitride as the skeleton and triazole groups as the cofactor. Cu NPs incorporated nitrogen-rich carbon nitride (Cu-g-C3N5) nanocomposites are found to possess excellent laccase-like activity, which can catalyze the oxidation of bisphenol A (BPA) to produce a color change in the presence of 4-aminoantipyrine. The catalytic efficiency of Cu-g-C3N5 nanocomposites is 4-fold higher than their analogue (Cu-g-C3N4 nanocomposites) without triazole groups. Cu-g-C3N5 nanocomposites also display robust catalytic activity with high temperature stability, resistance to acid and alkalinity, and long term stability. Density functional theory calculations indicate that triazole groups are beneficial to improve the stability of Cu NPs via additional Cu-N bonds and facilitate the activation of the adsorbed O2 molecules. There is a linear relationship between the absorbance and BPA concentration over the range of 0.25–25 mg L−1 with the limit of detection of 0.09 mg L−1. Finally, Cu-g-C3N5 nanocomposites are successfully applied for colorimetric detection of BPA released from polycarbonate microplastics. To the best of our knowledge, this is the first example to utilize laccase-like nanozyme for colorimetric detection of BPA.

Dual P-doped-site modified porous g-C3N4 achieves high dissociation and mobility efficiency for photocatalytic H2O2 production

Organic semiconductor under photoexcitation could generate abundant strong-binding Frenkel excitons and inevitably suffer from low dissociation efficiency (<1%) and poor mobility ability, which severely suppresses the efficient utilization of photogenerated charges and corresponding activity. Herein, a dual P-doping strategy is proposed in bay and corner sites implanted polymeric carbon nitride (PCN-D) for visible-driven H2O2 production. The dual P doping breaks localized electron state around original symmetric heptazine units and weakens the binding energy between electrons and holes, increasing dissociation efficiency to reach 11.9% with 20-fold improvement. In addition, the conductivity ability of PCN-D, including formed carrier charge concentration and mobility, achieves 13-fold and 7-fold improvement, which facilitates the charge transfer and separation. The proposed dual doped-P-site strategy, with the blessing of porous structure, provides plentiful active center for effective adsorption and activation of O2 molecule, further accelerating reaction progress and achieving six-times increase of photocatalytic H2O2 production rate. This work provides in-depth insight into the importance of dual P-doping to optimize kinetic behavior of photogenerated charges and opens an avenue to the multiscale doping-modulation of semiconductor with high efficiency solar energy conversion.

Core-shell Bi-containing spheres and TiO2 nanoparticles co-loaded on kaolinite as an efficient photocatalyst for methyl orange degradation

Improving the efficiency/cost ratio is the key to the practical application of photocatalysts. Using cheap minerals as carriers is an effective means to improve the efficiency/cost ratio of photocatalysts. Here, kaolinite was used to co-load TiO2 nanoparticles and Bi containing core-shell spheres forming the composites with excellent photocatalytic performance. The rate constant per unit mass of TiO2 in the optimal sample reached 18 times that of TiO2. Kaolinite plays important roles in promoting photocatalytic activity by improving the dispersion of TiO2 and the adsorption of O2 molecules and MO anions, besides the type-II energy band alignment of TiO2 and BixOy.

Regulation of magnetism on Fe- and Ni-doped SnO2 (1 1 0) surfaces by oxygen vacancy and adsorbed O2 molecule

We investigated the ferromagnetism of Fe- and Ni-doped SnO2 (110) surfaces and the regulation of the ferromagnetism on doped surfaces by the oxygen vacancy and adsorbed O2 molecule. The introduction of Fe/Ni dopant can make the nonmagnetic SnO2 (110) surface have a magnetic moment of 3.45 µB/1.97 µB and exhibit stable ferromagnetic coupling. After forming oxygen vacancy under oxygen-deficient conditions, a fraction of the remaining electrons provided by vacancy is acquired by the doped atom, which reduces the number of unpaired electrons in the doped atom d shell, thereby reducing the surface magnetic moment by about 0.6 µB. The oxygen vacancy reduces the magnetization of the bound magnetopolaron, which leads to the weakening of the surface ferromagnetic coupling. The free O2 molecule can exothermically adsorb on the defect surface and fill the oxygen vacancy, forming a magnetic cluster with the doped atom. Although the magnetic moment of the spontaneously adsorbed O2 molecule decreases due to obtaining a small number of electrons from the surface, the magnetic moment of the O2-adsorbed surface increases about 1.0 µB. The magnetic coupling of the O2-adsorbed surface is determined by the competition mechanism of antimagnetic coupling between O2 molecules and ferromagnetic coupling between magnetopolarons.

Effects of A‐site replacement (Sm, Y, and Pr) on catalytic performances of mullite catalysts for NO oxidation

Mullite was one of the most promising catalysts that used in the selective catalytic oxidation of NO (NO-SCO), and deciphering its intrinsic properties that affect the catalytic performance was a great challenge but critical to the development of mullite catalysts. Herein, a series of Mn-based mullite nanofibers with different A-site cations were synthesized by electrospinning method and used for catalytic NO oxidation. Activity tests showed that SmMn2O5 exhibited a better NO conversion rate (77.8 %) than those of PrMn2O5 (63.3 %) and YMn2O5 (57.5 %) under typical experimental conditions (GHSV = 120 000 h−1, T = 325 °C). To investigate the factors influencing the catalytic activity, various techniques including XRD, N2 adsorption, SEM, TEM, EDX, XPS, H2-TPR, and O2-TPD were employed, and the results showed that abundant surface adsorbed oxygen species and good reducibility contributed greatly to the catalytic performance of SmMn2O5. DFT calculations revealed that A-site cation played the decisive role in the Fermi level relative to the Mn 3d-band centre, thus affecting the adsorption and dissociation of O2 molecule. The present synthetic strategy offered a new viable route for the large-scale preparation of metal oxide catalysts with remarkable NO oxidation performance for practical application.

Role of External Electric Field in Carrier Mobility of Graphene/ZnO Heterojunction Adsorbed H2O and O2 Molecules

AbstractThe density functional theory is performed to investigate the energy band structure, effective mass and carrier mobility of Graphene/ZnO (G/ZnO) heterojunction. The intrinsic G/ZnO heterojunction has higher electron mobility (4.323 m2/V⋅s) as compared to Graphene and ZnO. The adsorption of H2O and O2 molecules significantly reduces the carrier mobility of the G/ZnO heterojunction. Then, the number of H2O and O2 molecules is changed from 1 to 4. The results show that electron mobility of the G/ZnO heterojunction increase with increasing number of H2O, but the opposite is true for O2. Therefore, both strain and external electric field (Eext) are used to regulate the electronic properties. The carrier mobility are significantly enhanced under appropriate Eext. In this work, under the strain and Eext, the calculation about the adsorption of H2O and O2 will play an important role in monitoring the stability of G/ZnO heterojunction based microelectronic devices in the external environment.

TaIrTe4 Monolayer with Topological Insulator Characteristic: A New and Highly Efficient Electrocatalyst toward Oxygen Reduction Reaction

Topological materials with robust topological surface states can be a class of very promising catalysts in electrocatalysis. In this study, a freestanding 2D topological insulator (TI) nanomaterial, namely, TaIrTe4 monolayer with low Ir-loading, which can be exfoliated from the bulk phase with the layered structure, is demonstrated to be dynamically, mechanically, and thermodynamically stable under the first-principles calculations. More intriguingly, coupled with good conductivity, a 2D TaIrTe4 monolayer can be considered as an alternative to noble metal Pt-based electrocatalyst for the oxygen reduction reaction (ORR). Our calculations revealed that on the surface of the TaIrTe4 monolayer, the adsorbed O2 molecules can be effectively activated and dissociated into two separated O* species through a very small energy barrier (0.28 eV, even lower than that of Pt(111)). When the four-electron (4e) dissociation path of ORR occurs on the TaIrTe4 monolayer, a very small overpotential of 0.47 V can be observed, which can be even comparable to the Pt(111) surface. In addition, the 2D TaIrTe4 monolayer can also exhibit high selectivity, effectively inhibiting the formation of byproduct H2O2. It can be revealed that the TI topological states can have an important effect on the excellent ORR catalytic activity of the 2D TaIrTe4 monolayer. Undoubtedly, the design of ORR electrocatalysts based on the fascinating topological materials can be a new and effective way to replace the precious metal Pt-based ORR electrocatalysts.

A computational insight into the intrinsic, Si-decorated and vacancy-defected γ-graphyne nanoribbon towards adsorption of CO2 and O2 molecules

In this study, the effects of decorating a silicon (Si) atom and applying a single vacancy defect on an armchair γ-graphyne nanoribbon (A-γ-GyNR) are investigated toward CO2 and O2 molecules adsorption. The magnetic and electronic transport properties, including the calculation of adsorption energy, charge transfer, magnetic moment, band structure, phonon dispersion and density of state (DOS), have been studied using the spin-polarized density functional theory (DFT) method. The stability of the proposed substrates is measured and different positions for gas molecules are considered. The results reveal that the highest amounts of adsorption energy of CO2 (0.63 eV) and O2 (2.2 eV) molecules belong to the substrate decorated with the Si atom in the 12-membered ring (H1) and acetylene linkage (B3), respectively. In addition, the removal of a carbon atom with sp hybridization improves the O2 molecule adsorption by 3.34 times compared to the primary substrate (P-GyNR). According to the recovery time calculations, the most appropriate desorption time is related to T1-M1 model. The current–voltage characteristic confirms that the resistance of the introduced sensors fully changed after sensing. This work can be considered as an effective step toward understanding and developing A-γ-GyNR-based gas sensors.

The construction of conjugated organic polymers containing phenanthrenequinone redox centers for visible-light-driven H2O2 production from H2O and O2 without any additives

Photocatalytic preparation of hydrogen peroxide (H2O2) by visible light irradiation is a promising approach to achieve the conversion of solar-to-chemical energy. But it still faces a huge challenge with the development of efficient and environmentally friendly catalytic system which is applied to H2O2 production from H2O and O2 without any additives. Hereby, we present a conjugated organic polymer (PQTEE-COP) by Sonogashira cross-coupling reaction between 2,7-dibromophenanthrenequinone (PQ) with 1,1,2,2-tetrakis(4-ethynylphenyl)ethene (TEE), which contains phenanthrenequinone redox centers and can efficient photocatalysis the production of H2O2 from H2O and O2 without any additives. The extended two-dimensional π-conjugated framework with electron-donor tetrakis(4-ethynylphenyl)ethene and electron-acceptor phenanthrenequinone moieties can not only improve visible light harvesting, but also accelerate photo-induced charges separation and migration. In addition, the phenanthrenequinone moieties can serve as redox centers to accept photo-induced electrons and transfer to adsorbed O2 molecule for subsequent H2O2 production through electron-coupled hydrogenation reaction (PQ to PQH2). The PQTEE-COP exhibits efficient photocatalytic production of H2O2 with initial rate of 3009 μmol g-1h−1 from H2O and O2 under visible light (λ ≥ 400 nm) irradiation without any additives. This work provides a scheme for the rational design of conjugated organic polymer based materials for efficient solar-to-chemical energy conversion.

Adsorption of O2 molecule on the transition metals (TM(II) = Sc2+, Ti2+, V2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) porphyrins induced carbon nanocone (TM(II)PCNC)

In this work, the adsorption of the O2 molecule on the transition metals (TM(II) = Sc2+, Ti2+, V2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) porphyrins induced carbon nanocone (TM(II)–PCNC) were investigated using density functional theory (DFT) in terms of stabilities, energetic, structural, and electronic properties. It has been found that the O2 molecule is adsorbed on the TM(II)–PCNC with adsorption energies in the range of 0.29 to −98.32 kcal/mol. The interaction between the O2 gas and the Sc-PCNC molecule from the outer site is the strongest. The interaction of the O2 gas over the Ni–PCNC molecule from both outer and inner sites is the weakest. It can be concluded that the suitable interaction energy (Eg) for sensing ability attributed to the Zn–PCNC because an effective and physical interaction between Zn–PCNC and the O2 gas leads to short recovery time. DFT calculations also clarified that the high %ΔEg of Zn–PCNC and hence the high sensitivity to the O2 gas confirm that the Zn–PCNC molecule is a promising candidate for having a good sensing ability to the O2 gas.

A density functional theory study of the CO oxidation on Pt1 supported on PtX2 (X = S, Se, Te)

The geometric stability, electronic structure and catalytic properties towards CO oxidation of a single Pt atom supported on PtS2, PtSe2, PtTe2 with a S, Se, and Te vacancies (Pt1/PtX2) were systematically explored by density functional theory calculations. The results showed that the single Pt atom can be located at the vacancy site stably, providing accessible active sites for CO oxidation. Both the Langmuir-Hinshelwood (LH) mechanism and the termolecular Eley-Rideal (TER) mechanism were considered comprehensively. By comparing the rate-determining step (RDS) of CO oxidation process, we found that the LH mechanism is easier to achieve. Meanwhile, as the X atom changes from S to Te, the RDS energy barrier gradually decreases, which is attributed to promoted adsorption and activation of O2 molecules on Pt1/PtX2. The results show that Pt1/PtTe2 is the most active catalysts with a low RDS barrier of 0.41 eV. This work provides an important reference for the design of single atom catalysts (SACs) based on transition metal dichalcogenides (TMDs), and has profound implications for the use of supported SACs on defective TMDs for CO oxidation or other reactions.

Stitching electron localized heptazine units with “carbon patches” to regulate exciton dissociation behavior of carbon nitride for photocatalytic elimination of petroleum hydrocarbons

The electron localized heptazine units make it difficult to separate photoinduced electeron-hole pairs for graphitic carbon nitride (g-C3N4), which limits the application prospect of graphitic-like carbon nitride. Changing inherent N-(C)3 bridging mode of in-plane heptazine units and built more electron channel could be a reasonable strategy. Herein, “carbon patches” were introduced to stitch heptazine units, high speed electron transfer path were thus constructed due to delocalized p orbital electron in “carbon patches” as a result. Simultaneously, interlayers’ high speed electron transfer channel was also constructed by distorted molecular layer because of presence of large electronegative interstitial phosphorus atoms. Such photoinduced electron-holes’ spatial separation in-plane and interlayers were built concurrently and confirmed by XANES and DFT calculation for the first time. The resulted PCCNv series photocatalysts exhibited superior photon absorption capability, excellent charge carriers’ separation kinetics, good O2 molecule adsorption as well as activation capability, the resulted abundant reactive radicals contributed to petroleum hydrocarbons photocatalytic degradation significantly. This work shed light on efficient separation of photoinduced excition for carbon nitride in photocatalysis, simultaneously presented a promising candidate non-metal photocatalytic environmental material for marine oil spill remediation.

The adsorption mode and evolution of O2 molecules on the SnO2 (221) crystal plane

Density functional theory (DFT) and electrochemical impedance spectroscopy (EIS) techniques are used to investigate the adsorption mode and evolution of O2 molecules on the SnO2 (221) crystal plane in this paper. The study shows that adsorbed O2 molecules on the crystal plane exist in two reversible modes. In the general atmosphere, O2 molecules are preferentially physically adsorbed on the crystal plane in the form of the mono-molecule, namely mode I; when the ambient oxygen concentration increases, it appears as a bi-molecular adsorption mode, namely mode II. Both modes decrease the crystal plane conductivity, but the decrease is more pronounced in mode II, which is also confirmed by EIS. In-depth exploration of the adsorption behavior of O2 molecules is conducive to better understanding and control the surface state of materials and provides a basis for material design.

In-situ grown N, S co-doped graphene on TiO2 fiber for artificial photosynthesis of H2O2 and mechanism study

Artificial photosynthesis offers a promising strategy for converting solar energy into environmental-friendly H2O2. Herein, robust photocatalytic H2O2 production through dioxygen reduction is achieved, reaching a high H2O2 yield of 873 μmol L−1 h−1. The photocatalyst was prepared by in-situ chemical vapor deposition of N, S co-doped graphene on TiO2 nanofibers. Thanks to the intimate interface with large area and Schottky junction, the H2O2 yield of the composite can be increased by eight times than that of pristine TiO2. Experimental results and density functional theory calculations clarify that the strong synergistic effect between the doped N and S atoms provides abundant active sites to facilitate the electron transfer, promote the adsorption of O2 molecules, and restrain the decomposition of formed H2O2 by suppressing H2O2 adsorption. This work not only provides a novel approach to build close contact between photocatalyst and co-catalyst, but also develops a highly efficient photocatalyst for H2O2 production.

Regulating directional transfer of electrons on polymeric g-C3N5 for highly efficient photocatalytic H2O2 production

Graphite carbon nitride (g-C3N5) has been widely used in various photocatalytic reactions due to its higher thermodynamic stability and better electronic properties compared to g-C3N4. However, it is still challenging to endow g-C3N5 with high performance on photocatalytic hydrogen peroxide (H2O2) production. Herein, potassium and iodine are co-doped into g-C3N5 (g-C3N5-K, I) for photocatalytic production of H2O2 with high efficiency. As expected, the photocatalytic H2O2 production rate over the g-C3N5-K, I (2933.4 μM h−1) reaches to 84.22 times as that of g-C3N5. The excellent photocatalytic H2O2 production activity is mainly ascribed to the co-doping of K and I, which significantly improves the capacity of oxygen (O2) adsorption, selectivity of two-electrons oxygen reduction reaction (2e− ORR) and separation efficiency of charge carriers. The density functional theory (DFT) calculations reveal that O2 molecules are more conducive to being adsorbed on g-C3N5-K, I. Besides, the result of excited states further indicates that photo-generated electrons can be directionally driven to the adsorbed O2 molecules, which are effectively activated to form H2O2. The findings will contribute to new insights in designing and synthesizing g-C3N5 based photocatalysts for the H2O2 production.

Enhancement of Activity Low-Pt-Content O2-Reduction Catalysts through Formation of Hybrid Systems with Sub-Stoichiometric Cerium Oxide Nanostructures

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, under such condition, O2-reduction reaction (ORR) often proceeds at a less positive potential, and produces higher amounts of undesirable H2O2-intermediate. Recent studies have demonstrated that the rational design of a catalytic system is based on nanostructures of platinum, or carbon-supported platinum (Pt/C), and metal oxide (MOx). By combining the catalytic properties of both components, such hybrid Pt-MOx catalysts are capable of tuning of the activity and durability of Pt. Due to strong interactions of MOx with Pt catalytic nanoparticles leading to the improved activity and durability during ORR, certain nanostructured metal oxides are considered as co-catalysts or active components of supports. The existence of specific interactions between MOx and noble metal (Pt) nanoparticles should improve the stability and activity of the metal catalytic sites due to modification of the Pt electronic structure and diminishing of the oxo (OH) species adsorption on Pt surface, thus promoting centers for the adsorption of oxygen and the cleavage of O=O bonds. The interactions mentioned above would also facilitate dispersion of Pt, inhibit their detachment and further aggregation, and, consequently, prevent or decrease their degradation during the fuel cell operation [1].The catalytic activity of substoichiometric ceria, CeOx (where x < 2) additive results from its unique structure, presence of oxygen vacancies, and other features resulting from the 4f-electronic configuration of cerium. While the oxygen defects are likely to serve as active oxygen adsorption sites, the mixed-valent CeIII/CeIV redox sites should permit the electron shuffling within the lattice of oxygen vacancies and enhancing the ORR activity. The formation of oxygen-defects is accompanied by the localization of electrons left behind in Ce 4f states, thus leading to the formation of CeIII species capable of elongating and reducing the O–O bond strength of the adsorbed O2 molecule; consequently, by increasing the relative ratio of CeIII-to-CeIV, the ORR electrocatalytic activity can be improved [1]. Therefore, in the present study, we consider the intentionally reduced CeOx nanostructured components through subjecting them to high-temperature pretreatment in the presence of argon gas admixed with hydrogen. It is reasonable to expect that, the increased population of CeIII sites on the surfaces of the pretreated ceria particles would stabilize the neighboring active Pt-metal centers, exhibit reductive interactions toward Pt-oxo species, and to improve durability of the catalytic materials. Thus the boundary formed between the Pt-metal and CeOx-metal oxide should facilitate inhibition of the Pt oxide formation by the CeOx layer. Furthermore, our recent studies clearly show that, in the presence of ceria, the oxidative degradation of carbon carriers is also largely decreased. Finally, cerium oxide is known to act as the oxidative scavenger for free radicals such as hydroxyl (HO•) and hydroperoxyl (HOO•), which, once generated, would otherwise lead to the formation of undesirable hydrogen peroxide. Sub-stoichiometric CeOx is capable of rapidly switching between CeIII and CeIV oxidation states, thus inducing the decomposition of both radicals and peroxides. The above observation seems to be very helpful when it comes to designing highly active and durable ORR catalysts containing low platinum loadings.[1] A.Kostuch, I.A. Rutkowska, B. Dembinska, A. Wadas, E. Negro, K. Vezzù, V. Di Noto, P.J. Kulesza, Molecules 26 (2021) 5147. Acknowledgements: This work was supported by the National Science Center (Poland) under Opus Project (2018/29/B/ST5/02627) and under auspices of the European Union EIT Raw Materials ALPE 19247 Project (Specific Grant Agreement No. EIT/RAW MATERIALS/SGA2020/1).

Effects of Zn, Mg and Cu Doping on Oxidation Reaction of Al (111) Surface

Aiming at the performance degradation of lithium-ion batteries due to shell corrosion, the doping of alloy elements Zn, Mg and Cu on Al (111) surface and the effect on oxidation reaction of Al (111) surface were studied by the first-principles calculation method. The results show that Zn, Mg and Cu atoms stably combine with Al atoms, and the surface smoothness is slightly different due to their different radii and electronegativity. The dissociative adsorption of O2 molecules is related to the surface doping atoms and O2 coverage, while the electron tunneling of underlying metal promotes O2 adsorption on the surface. As O2 coverage increases, the O atoms adsorbed on the hcp site gradually migrate to the subsurface layer. Zn, Mg, Cu and vacancy defect hinder the migration of the surrounding O atoms to subsurface layer, resulting in different structures and thicknesses of the oxide film near the doped atoms. At the same time, Zn, Mg, and Cu atoms differ in their ability to gain or lose electrons compared with Al atoms, resulting in their different positions on the surface. In addition, the surface work function rises with the increase of O2 coverage, and Zn and Cu atoms make the work function increase faster. Finally, according to the research results, it can be inferred that Zn and Mg are the unfavorable factors for the oxidation reaction of Al surface.

Theoretical study of metal-free catalytic for catalyzing CO-oxidation with a synergistic effect on P and N co-doped graphene

P and N co-doped graphene (PNxCy-G with x = 1, 2, 3 and y = 0, 1, 2) is designed to enhance graphene reactivity with a synergistic effect of the P and N atoms for the CO oxidation reaction, focusing on the influence of the N dopant concentration on graphene. The calculated results indicate that increasing two or three coordinated N to P can facilitate charge transfer from the surface onto O2 molecules. However, the adsorbed O2 molecule breaks apart on PN3-G surface, affecting CO oxidation performance. Furthermore, PN2C1-G exhibits excellent catalytic activity towards the oxidation of CO via the ER mechanism, which catalyzes CO oxidation with the rate-determining step of only 0.26 eV for the first and 0.25 eV for the second oxidation at 0 K. Additionally, the catalytic oxidation of PN2C1-G via Eley–Rideal mechanism prefers to occur at room temperature (298.15 K), with a rate-determining step of 0.77 eV. The reaction rates at 298.15 K is calculated to be 5.36 × 1016 mol s–1. The rate constants are obtained according to harmonic transition state theory, which could be supportive for catalytic oxidation of CO on the experiment.

The effect of hydrogen reduction of α-MnO2 on formaldehyde oxidation: The roles of oxygen vacancies

A series of α-MnO2 catalysts with various Mn valence states were treated by hydrogen reduction for different periods of time. Their catalytic capacity for formaldehyde (HCHO) oxidation was evaluated. The results indicated that hydrogen reduction dramatically improves the catalytic performance of α-MnO2 in HCHO oxidation. The α-MnO2 sample reduced by hydrogen for 2 h possessed superior activity and could completely oxidize 150 ppm HCHO to CO2 and H2O at 70 °C. Multiple characterization results illustrated that hydrogen reduction contributed to the production of more oxygen vacancies. The oxygen vacancies on the catalyst surface enhanced the adsorption, activation and mobility of O2 molecules, and thereby enhanced HCHO catalytic oxidation. This study provides novel insight into the design of outstanding MnOx catalysts for HCHO oxidation at low temperature.