O2 Dissociation Research Articles

Entropy in catalyst dynamics under confinement.

Entropy during the dynamic structural evolution of catalysts has a non-trivial influence on chemical reactions. Confinement significantly affects the catalyst dynamics and thus impacts the reactivity. However, a full understanding has not been clearly established. To investigate catalyst dynamics under confinement, we utilize the active learning scheme to effectively train machine learning potentials for computing free energies of catalytic reactions. The scheme enables us to compute the reaction free energies and entropies of O2 dissociation on Pt clusters with different sizes confined inside a carbon nanotube (CNT) at the timescale of tens of nanoseconds while keeping ab initio accuracy. We observe an entropic effect owing to liquid-to-solid phase transitions of clusters at finite temperatures. More importantly, the confinement effect enhances the structural dynamics of the cluster and leads to a lower melting temperature than those of the bare cluster and cluster outside the CNT, consequently facilitating the reaction to occur at lower temperatures and preventing the catalyst from forming unfavorable oxides. Our work reveals the important influence of confinement on structural dynamics, providing useful insight into entropy in dynamic catalysis.

Oxidation behavior of Fe-Ni Invar alloy under high pressure: A ReaxFF molecular dynamics study

The Fe-Ni Invar alloy is often employed under extreme conditions such as high temperatures, high pressures, and corrosive environments, making it susceptible to oxidation and subsequent failure. Hence, a thorough understanding of its oxidation behavior is crucial. We performed ReaxFF-based molecular dynamics (MD) simulations to study the oxidation behaviour of Fe-Ni Invar alloy at the atomic scale under extreme conditions. The initial stage of oxidation involves the preferential adsorption and dissociation of O2, demonstrating its surface-site selectivity. The initial oxidation kinetics follows a logarithmic law, and the whole oxidation process results in dominant low-coordinated clusters configurations in the oxide film. Simultaneously, Fe atoms tend to donate more electrons to O atoms than Ni atoms. Moreover, the O2 consumption rate were found to increase with pressure and amorphous oxides formed more readily under high pressure. Our results indicate that adjusting the pressure may enhance the oxidation resistance of the Fe-Ni alloy, which is significant for the design and application of alloys in extreme conditions.

Morphology and crystal–plane dependent catalytic activity of α-Fe2O3 for NH3-SCR de-NOx: Experimental and DFT study

Three kinds of α-Fe2O3 catalysts, each having a distinct morphology and crystal planes, were synthesized and applied for NH3-SCR reaction. The morphology and crystal-plane effects for the activity of α-Fe2O3 were investigated by a combined study of experiment and density functional theory. The experiment findings reveal that the α-Fe2O3-S, α-Fe2O3-R, and α-Fe2O3-C display the shuttle (predominantly exposed (110) and (012) crystal planes), rod (predominantly exposed (110), (104), and (012) crystal planes), and cube (only exposed (104) crystal plane) shapes, respectively. Furthermore, the α-Fe2O3-S yields the best catalytic performance because of its moderate surface acidity, the best redox capacity, and the highest contents of surface Fe3+ and chemisorbed oxygen, which may result from the morphology and crystal plane effects. Additionally, the activity of different crystal planes is significantly different. The NO and NH3 are more apt to be adsorbed on the (110) and (012) surfaces and O2 dissociation is more likely to happen on the (110) surface. Besides these, the (110) surface owns the lowest energy barrier to the decomposition of intermediate NH2NO. All of the mentioned above collectively enhance the efficiency of the SCR process. Finally, the (110) and (012) surfaces facilitate the rapid SCR process, while the (104) surface is the most difficult. The α-Fe2O3-S predominately exposes high activity of (110) and (012) surfaces, therefore, it can yield the highest catalytic activity.

Reclaiming Ti-bearing blast furnace slag into wide-temperature and sulfur-resistant catalyst to boost flue gas demercuration

Elimination of neurotoxic mercury from coal-fired flue gas is imperative to the global environment. This work reclaimed waste Ti-bearing blast furnace slags (TBFS) into perovskite-type catalyst for efficient flue gas demercuration (DeHg). Through mild impregnation with Mn and Ce, the TBFS-based catalyst exhibited desirable DeHg performance at wide-range temperatures (50 ∼ 300 °C), good tolerance to varied SO2 concentrations (400 ∼ 1200 ppm), and long-term DeHg stability (30 h, > 85 % DeHg efficiency) under typical coal-fired flue gas conditions, thereby outperforming existing Mn- and Ce-containing catalysts (perovskites, spinels, and other synthetic oxides). Mn-Ce interplay was well characterized to facilitate O2 dissociation and mitigate SO2 competition by modulating the redox activity of MnCe/TBFS catalyst. DFT calculations revealed in-depth that Hg0 oxidation over MnCe/TFBS was rate-determined by O2 dissociation and significantly promoted by the activated oxygens. Our attempt herein has exemplified a feasible strategy to deal with waste slag disposal and Hg emission synergistically.

Sulfur modified N-doped carbocatalysts promote the selectivity for H2S selective oxidation

Sulfur element is widely applied as a non-metallic dopant into carbon framework for the modulation of their chemical activities. An interesting question is whether the intrinsic catalytic performances for the H2S selective oxidation to sulfur can be manipulated by sulfur element introduction into carbocatalysts. In this study, we employ a simple solvent-free method to introduce S atoms into framework of N-doped carbocatalysts, resulting in a notable enhancement of the product S selectivity with negligible loss of H2S selective oxidation. The experimental results show that the as-synthesized N-S-C-2 catalyst exhibits a H2S conversion of 97.5 % and sulfur selectivity of >80 % at a high O2-to-H2S ratio (2.5) under continuous mode (over the dew point temperature of sulfur, c.a. 210 °C), while also demonstrating robust stability (> 100 h), anti-CO2 (up to 50 vol%) and anti-oxidation properties. Kinetic analysis and H2S/O2-TPD-MS results reveal that S introduction attenuates the adsorption and dissociation of H2S and O2 by the N-doped carbon catalyst. Furthermore, density functional theory calculations elucidate that S doping elevates the adsorption energies of H2S and O2 at the pyridinic N site, thereby moderately reducing the adsorption of H2S and O2, consequently preventing the over-oxidation of H2S to SO2 and enhancing S selectivity. The double doping promotion effect of carbon materials reported in this investigation offers an alternative insight for the development of highly selective carbon desulfurization catalysts.

Atomic-scale mechanistic study of oxygen reduction mechanism for B-site doped Pr(Ba,Sr)Co2O5+δ by density functional theory calculations

Pr(Ba,Sr)Co2O5+δ is a promising cathode material for solid oxide fuel cell (SOFC) due to its high oxygen ion transport capability and oxygen reduction activity. Density functional theory (DFT) calculations were performed to elucidate the oxygen reduction mechanism of B-site doped Pr(Ba,Sr)(Co,M)2O5+δ (M = Fe, Ni, Cu, and Zn) materials. First, we investigated the formation of O vacancies. The results indicate that Cu and Zn doping facilitate O vacancy formation, resulting in lower O vacancy formation energies. Furthermore, the interaction between oxygen and the (0 0 1) surfaces of B-site doped Pr(Ba,Sr)(Co,M)2O5+δ has been comprehensively discussed, involving both perfect and defective surfaces. The results demonstrate that the presence of O vacancies enhances the catalytic activity for oxygen reduction, by reducing the energy required for O2 dissociation. Zn-doped Pr(Ba,Sr)(Co,M)2O5+δ exhibits a low O vacancy formation energy, resulting in a stable adsorption configuration upon oxygen dissociation, indicating its potential as a cathode material for SOFC.

Highly catalytic performance for the selective C–H bond oxidation of p-chlorotoluene over Co, Cr co-doped OMS-2 catalyst

Using O2 as an oxidant, developing a non-noble metal catalyst for the selective catalytic C–H bond oxidation of p-chlorotoluene is desirable and challenging. In this work, a series of Co, Cr co-doped OMS-2 (Octahedral Molecular Sieve-2) catalysts were prepared by a conventional refluxing method. It was found that the incorporation of Co and Cr improved the catalytic activity for the selective oxidation of p-chlorotoluene to p-chlorobenzaldehyde. Among these catalysts, CoCr/OMS-2 (Co: Cr = 1: 1, mass ratio), the best catalyst, shows that the conversion and the selectivity of p-chlorobenzaldehyde is 94.8 % and 94.3 %, respectively. The enhanced catalytic activity was due to the larger specific surface area and even dispersion of active components. The characterization results also disclosed that the co-doping of Co and Cr increased the oxygen vacancy and enhanced the ability to activate the surface lattice oxygen. Additionally, density functional theory calculations demonstrated that co-doping of Co and Cr promoted the adsorption of p-chlorotoluene and O2, and decreased the energy barrier of rate-determining step (the conversion of p-chlorobenzyl alcohol to p-chlorobenzaldehyde). Besides, when H2O was added to the reaction system as the second solvent, the activation and dissociation of O2, and the formation of p-chlorobenzaldehyde were facilitated, in agreement with the experimental results. This work demonstrated the promotional effect of Co, Cr co-doped into OMS-2 catalyst and the role of H2O for the selective oxidation of p-chlorotoluene.

Unveiling Inequality of Atoms in Ultrasmall Pt Clusters: Oxygen Adsorption Limited to the Uppermost Atomic Layer

The concept of preferential atomic and molecular adsorption site is of primary relevance in heterogeneous catalysis. In the case of ultrasmall size‐selected clusters, distinguishing the role played by each atom in a reaction is extremely challenging due to their reduced size and peculiar structures. Herein, it is revealed how the inequivalent atoms composing graphene‐supported Pt12 and Pt13 clusters behave differently in the photoinduced dissociation of O2, with only those in the uppermost layer of the clusters being involved in the reaction. In this process, the epitaxial graphene support plays a fundamental active role: its corrugation and pinning induced by the presence of the clusters are crucial for defining the preferential adsorption site on the Pt atomic agglomerates, facilitating the lateral diffusion of physisorbed oxygen at a distance that induces its selective adsorption in the topmost layer of the clusters, and inducing an inhomogeneous charge distribution within the clusters which directly affects the O2 adsorption. The inhomogeneous oxidation of the clusters is resolved by means of synchrotron‐based X‐ray photoelectron spectroscopy and supported by ab initio density functional theory calculations. The possibility to identify the active sites on Pt clusters induced by cluster–support interactions has the potential to enhance the experimentally supported design of nanocatalysts.

Inclusion Strategy for Constructing S/N Orbital Hybridization-Regulated sp3/sp2 Carbon toward Boost Electrocatalysis.

Metal-free carbon-based electrocatalysts have gained significant attention in the field of zinc-air batteries (ZABs) due to their affordability, good conductivity and chemical stability. However, unmodified carbon materials typically fall short in adsorbing and activating the substrates and intermediates involved in oxygen reduction reactions (ORR). Here, a metal-free carbon-based electrocatalyst with S atom p orbital hybrid modified N-sp3/sp2 carbon structure (C/NS) were prepared by cyclodextrins inclusion. The catalyst demonstrates impressive ORR activity (E1/2=0.885 V vs. RHE) and robust ZABs performance with a power density of 171.3 mW cm-2 and a specific capacity of 781.2 mAh g-1. Density functional theory (DFT) calculation reveals that S atom effectively regulates the charge distribution and p-band center of active site carbon atom in the N-sp3/sp2 carbon structure. This modification prompts the adsorption and dissociation of O2 and intermediates, resulting in higher reactive activity. This work provides a valuable and practical strategy for preparing cost-effective metal-free carbon-based electrocatalysts for ORR with high performance.

Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran on Alkali Doped Ru/C Catalysts. Electron Properties of Ruthenium Species as Descriptor of Catalytic Activity.

Selective aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran has been achieved on alkali doped Ru/C catalyst. Optimization of Ru metal nanoparticles, as well as the nature and amount of the alkali dopant have been performed. The results showed that doping the Ru/C catalyst with controlled amount of potassium increases the catalytic activity, 2.5 fold with respect to the non-doped sample. Spectroscopic studies showed that these differences in activity can be attributed to a different oxidation reaction mechanism associated to the presence of electron rich Ru species in the promoted sample that facilitate the dissociation of O2, while prevents the oxidation of the metal. The Ru/C-K doped catalyst resulted very stable against leaching and metal sintering, being possible the reuse over several consecutive runs. Moreover, the catalyst could be successfully applied to the oxidation of different alcohols.

Effects of spatiotemporal plasma power distribution on the modeling of ignition kernel evolution in quiescent and turbulent methane/air mixtures

Abstract The present work improves a phenomenological plasma-assisted combustion model by integrating the spatiotemporal distribution of plasma power density, thereby considering the evolution of plasma streamers in the modeling, and subsequently, better predicting the ignition kernel evolution. The improved phenomenological model is validated against experiments representing the plasma discharge and post-discharge ignition kernel evolution. Specifically, the new model demonstrates a more accurate prediction of ultrafast gas heating and O2 dissociation during the plasma discharge, compared to the original model. In addition, the new model is found to closely match the experimental pressure wave and heated channel profiles post-discharge without the need for tuning the energy deposition (unlike the original model), highlighting its accuracy of post-discharge ignition kernel dynamics. The improved phenomenological model is then employed to investigate ignition kernel evolution for a stoichiometric methane-air discharge across various discharge gap configurations. Simulations reveal a non-uniform temperature and streamer distribution progressing from the electrode tips toward the center, contrasting uniform cylindrical discharges previously described in the original model. Streamer propagation is observed to be faster for larger gaps when maintained at the same average electric field for different discharge gaps. The tendency of smaller gaps to produce detached toroidal ignition kernels is observed, while larger gaps promote cylindrical and attached ignition kernels. Interactions between successive ignition kernels from consecutive discharges varied significantly, with the smallest gap (1 mm) promoting the quenching of the preceding ignition kernel due to the initial kernel–kernel separation. The intermediate gap (2 mm) promotes detached kernel growth. In contrast, in the largest gap (4 mm), kernels consistently combine and expand attached to electrodes. The impact of homogeneous isotropic turbulence is also explored, showing the persistence of ignition kernels early on but eventually quenching due to enhanced radical and heat losses with pronounced turbulence intensity.

Water accelerates parabolic oxidation of Pu-Ga alloy: from mechanism to model

The moisture accelerated oxidation can endanger the safety storage of plutonium, but experiments haven’t provided a complete mechanism explanation, let alone a prediction model. Based on first principles calculations, this work reveals the acceleration mechanism of water on Pu-Ga alloy oxidation in moist air and interprets available experimental findings. Specifically, the OH adsorption after H2O dissociation can promote the O-vacancy formation in PuO2 by the polaron interaction mechanism, and then facilitate the vacancy diffusion of the actual corrosion medium O after O2 dissociation. Therefore, the diffusion kinetics of O in Pu-oxide is decisive, which is correlated to the relative humidity (RH) and temperature (T). Based on the micro mechanisms and the available experiments, we propose a method to modify the oxidation kinetic model by taking into account the coupling effects of RH and T, this model provides a new way to evaluate and predicts the acceleration ratio of RH and T on the oxidation kinetics of Pu-Ga alloy. This work comprehensively reveals the acceleration mechanism of moisture and then proposes the oxidation kinetic model, which is significant to the storage and protective of nuclear materials.

Phosphorus and nitrogen co-doped-graphene: Stability and catalytic activity in oxygen reduction reaction

This study systematically investigated the stable configurations and oxygen reduction reaction (ORR) catalytic activity of PN co-doped graphene using first-principles methods. We found that PN co-doped graphene substrates are generally highly stable. The adsorption energy of adsorbates is linearly positively correlated with the number of electrons obtained from the substrate. The P atoms serve as catalytic activity sites, the co-doping of N significantly enhances the adsorption energies of intermediate species in the ORR process, facilitating the direct dissociation of O2 and O2H. The solvation effect has a non-negligible impact on the adsorption energy of adsorbates, especially for O2. Due to the excessive adsorption of O, it poisons and inhibits the catalytic activity of P active sites for ORR. However, after O adsorption, the C atoms neighboring the PN impurity atoms in the P-Nn-Gra (n=2,3) substrates exhibit better catalytic activity than that of graphene doped with P/N alone. The P-Nn-defect-Gra (n=2,3,4) substrates are potential catalysts with good HER catalytic activity.

Unraveling distinct effects between CuOx and PtCu alloy sites in Pt−Cu bimetallic catalysts for CO oxidation at different temperatures

In situ exploration of the dynamic structure evolution of catalysts plays a key role in revealing reaction mechanisms and designing efficient catalysts. In this work, PtCu/MgO catalysts, synthesized via the co-impregnation method, outperforms monometallic Pt/MgO and Cu/MgO. Utilizing quasi/in-situ characterization techniques, it is discovered that there is an obvious structural evolution over PtCu/MgO from PtxCuyOz oxide cluster to PtCu alloy with surface CuOx species under different redox and CO oxidation reaction conditions. The synergistic effect between PtCu alloy and CuOx species enables good CO oxidation activity through the regulation of CO adsorption and O2 dissociation. At low temperatures, CO oxidation is predominantly catalyzed by surface CuOx species via the Mars-van Krevelen mechanism, in which CuOx can provide abundant active oxygen species. As the reaction temperature increases, both surface CuOx species and PtCu alloy collaborate to activate gaseous oxygen, facilitating CO oxidation mainly through the Langmuir-Hinshelwood mechanism.

Analyzing the degradation mechanism of solid oxide fuel cell during different time periods

Improving the lifetime and robustness of solid oxide fuel cells (SOFCs) is crucial for their commercial viability. This study aims to elucidate the degradation mechanism of SOFCs during galvanostatic tests and understand the internal and external factors influencing the cell degradation. Three nominally identical cells underwent galvanostatic testing for different durations to illustrate the evolution mechanism of SOFCs degradation at different stages. The electrochemical impedance spectroscopy (EIS) measurements under the open circuit voltage (OCV) and the direct current (DC) bias at different periods were carefully analyzed. By combining distribution of relaxation times (DRT) with equivalent circuit model (ECM) fitting, the contribution of each electrode process to cell performance degradation during galvanostatic testing was quantified. The polarization impedance, primarily associated with the charge transfer reactions in the anode, exhibited continuous increase under DC bias, contributing more than 80 % to the increase overall polarization impedance. Conversely, the cathode, related to O2 dissociation and diffusion process, contributed 7.2 %. The rapid degradation in the early stage was attributed to the degeneration of the anode microstructure, resulting from the formation of numerous isolated micron Ni particles and a subsequent decrease in three phase boundary (TPB) density. The anode microstructure after galvanostatic testing was characterized, revealing a novel Ni migration evolution mechanism. This mechanism involves the rapid agglomeration of Ni crystal particles at the beginning test, subsequent diffusion as micro-particles within 25 h, and eventual coarsening into dispersive agglomerates over time. The proposed mechanism of anodic microstructure evolution offers insights for optimizing anodic structures and lays the foundation for enhancing the long-term stability of SOFCs.

Benzene Oxidation in Air by an Amine-Functionalized Metal-Organic Framework-Derived Carbon- and Nitrogen-Loaded Zirconium Dioxide-Supported Platinum Catalyst.

To learn more about the behavior of amine (NH2)-functionalized metal-organic framework (MOF)-derived noble metal catalysts in the removal of aromatic volatile organic compounds in air, benzene oxidation at low temperatures has been investigated using 0.2-, 0.8-, and 1.5%-platinum (Pt)/Universitetet i Oslo (UiO)-66-NH2. The benzene conversion (XB) of x%-Pt/UiO-66-NH2-R under dry conditions (175 °C) was 23% (x = 0.2%) < 52% (x = 0.8%) < 100% (x = 1.5%): 'R' suffix denotes reduction pretreatment using a hydrogen (10 vol %) and nitrogen mixture at 300 °C for the generation of metallic Pt (Pt0) sites and simultaneous partial MOF decomposition into carbon- and nitrogen-loaded zirconium dioxide. The prominent role of reduction pretreatment was apparent in benzene oxidation as 1.5%-Pt/UiO-66-NH2 did not exhibit catalytic activity below 175 °C (dry condition). The promotional role of moisture in benzene oxidation by 1.5%-Pt/UiO-66-NH2-R was evident with a rise in the steady-state reaction rate (r) at 110 °C (21 kPa molecular oxygen (O2)) from 1.3 × 10-3 to 5.0 × 10-3 μmol g-1 s-1 as the water (H2O) partial pressure increased from 0 to 1.88 kPa. In contrast, the activity was lowered with increasing RH due to catalyst poisoning by excess moisture (r (110 °C) of 6.6 × 10-04 μmol g-1 s-1 at 2.83 kPa H2O (21 kPa O2)). Kinetic modeling suggests that XB proceeds through the Langmuir-Hinshelwood mechanism on the Pt/UiO-66-NH2-R surface (dissociative O2 chemisorption and the involvement of two oxygen species in benzene oxidation). According to the density functional theory simulation, the carbon and nitrogen impurities are to make the first XB step (i.e., hydrogen migration from the benzene molecule to the substrate) energetically favorable. The second hydrogen atom from the benzene molecule is also extracted effectively, while the oxygen derived from O2 facilitates further XB. The Pt0 sites dissociate the O2 and H2O molecules, while the product of the latter, i.e., free hydrogen and hydroxyl, makes the subsequent XB steps energetically favorable.

First Principles Study of O2 Dissociative Adsorption on Pt-Skin Pt3Cu(111) Surface

The O2 dissociative adsorption serves as a pivotal criterion for assessing the efficacy of oxygen reduction catalysts. We conducted a systematic investigation into O2 dissociative adsorption on the Pt-skin Pt3Cu(111) surface by means of the density functional theory (DFT). The computational findings reveal that the O2 adsorption on Pt-skin Pt3Cu(111) surface exhibits comparatively lower stability when contrasted with that on the Pt(111) surface. For O2 dissociation, two paths have been identified. One progresses from the t-f-b state towards the generation of two oxygen atoms situated within nearest-neighbour hcp sites. The other commences from the t-b-t state, leading to the generation of two oxygen atoms occupying nearest-neighbour fcc sites. Moreover, the analysis of the energy barrier associated with O2 dissociation indicates that O2 on the Pt-skin Pt3Cu(111) surface is more difficult to dissociate than on the Pt(111) surface. This study can offer a valuable guide for the practical application of high-performance oxygen reduction catalysts.

Two-dimensional MXene supported single transition metal atom for HCHO catalytic oxidation: A first-principles study combined with Microkinetics

Catalytic oxidation is an efficient and environmentally friendly strategy for the removal of pollutant HCHO. Recent proof-of-concepts experiments indicate that single-atom catalysts (SACs) exhibit good activity for HCHO catalytic degradation, but a major obstacle is to look for an effective SAC. Herein, ten 3d transition metal SACs decorated on Mo2CS2 substrate were designed and constructed to catalyze HCHO using periodic density functional theory calculations. The results showed that the single atoms are inclined to locate at the Mo top site on the surface and most SACs can stay stable. Among these SCAs, Ti, V, Cr, and Mn SACs have shallow energy barriers of O2 activation and can facilitate O2 dissociation at room temperature. Therefore, two typical HCHO oxidation pathways on TM@Mo2CS2 (TM = Ti, V, Cr, and Mn) catalyst were investigated in detail. The V@Mo2CS2 has the lowest energy barrier of 1.72 eV for the rate-limiting step during HCHO oxidation via path-Ⅰ (O2 adsorption and activation, HCHO* → CHO* → CO* → CO2*). Correlation analysis verifies that the Bader charge and O2 adsorption are the appropriate descriptions for HCHO catalytic oxidation activity. Microkinetic simulations are further performed to reveal the relationship between HCHO oxidation rate and temperature.

Insight into the performance-boosting mechanism of Ag/MgAlOx for NH3 selective catalytic oxidation: Perspective from the support crystalline phase structures

Arranging an ammonia oxidation process after the selective catalytic reduction of NOx by NH3 (NH3-SCR) system is an effective way for ensuring the DeNOx efficiency and controlling the slip ammonia. To improve operability and reduce operating costs in ammonia selective catalytic oxidation (NH3-SCO), developing feasible and efficient catalysts becomes meaningful. Herein, focusing on the dilemma of Ag/Al2O3 catalysts in NH3-SCO applications, Ag/MgAlOx catalysts with different support different crystalline phase structures (5 %Ag/MgAl-LDO and 5 %Ag/MgAl2O4) were innovatively synthesized and systematically evaluated application potential in NH3-SCO. Results indicated that the introduction of Mg apparently broadened reaction temperature window and catalytic performance of 5 %Ag/MgAl2O4 was higher than 5 %Ag/MgAl-LDO, while the N2 selectivity was completely opposite. The combination of series characterization and density functional theory (DFT) calculations revealed that 5 %Ag/MgAl2O4 surface has more Ag0 species with small particle size, which is favorable for ammonia adsorption and activated dehydrogenation to further promote reaction of NOx species, resulting in a higher NH3-SCO activity. In contrast, 5 %Ag/MgAl-LDO readily induces oxidized Ag species and Ag0 is more inclined to be present in large particle sizes, which is more conducive to dissociation of O2 to produce reactive O species (O*) leading to the peroxidation of ammonia to nitrate and thus, positively affects the improvement of N2 selectivity. Model catalyst 5 %Ag/MgAl-650 (mixed-phase) was prepared by controlling the roasting conditions and exhibited excellent catalytic performance in NH3-SCO with almost 93 % of NH3 oxidized at 250 °C (N2 selectivity up to 71 %). This work could afford theoretical support for the optimization and application of catalysts with high performance at low temperatures in selective catalytic oxidation of slip ammonia.

Catalytic oxidation of SO2 in O2-aerated aqueous Solution: superior catalytic capability of KOH/urea-treated biochars and catalytic mechanism

The catalytic oxidation of SO2 (COS) by dissolved oxygen in aqueous solution allows to recycle sulfate salt/sulfuric acid from the SO2-containing flue gas, and high-performance catalysts are desired for an efficient COS process. In this study, the chestnut leaves-derived biochars treated by the co-pyrolysis process with KOH/urea exhibited a favorable capability to catalyze the oxidation of SO2 in aqueous solution. The BK-N-8 biochar catalyst was the optimal one due to its moderate nitrogen content and appropriate surface functional groups. It exhibited a fast initial conversion rate from SO2 to SO42− (6.50 μmol g−1 s−1), and an excellent cycling durability for the COS process. The material showed a catalytic activity that surpassed all the reported carbonaceous materials. The surface functionalities were revealed to be the decisive factor for the conversion rate and durability of catalytic capacity. The superiority of the BK-N-8 with pyridinic N-doped aromatic cluster (AC) was further investigated via density-functional-theory calculations. The epoxy groups from O2 dissociation at the edge sites of ACs played a pivotal role for COS process onto biochars. This study provides insightful information for an in-depth understanding of the mechanism of COS process catalyzed by carbonaceous materials.