Competitive Adsorption Behavior Research Articles

Gas Adsorption Mechanism on 2D Materials: The Hyperpolarizability Evolution Analyzed by Nonlinear Optics

AbstractWhile understanding the competitive adsorption behavior of gas sensor is important, it is yet to be unraveled. Especially for the influence of water molecules to the gas adsorbed on 2D materials. This study explores the potential of layered 2D materials as a candidate material for gas sensing, employing non‐destructive measurement, and second harmonic generation (SHG). The investigation focuses on analyzing oxygen, ammonia, and water vapor adsorbed on a WS2 surface by studying the evolutions in electric dipole and electric field. Leveraging the simplified bond hyperpolarizability model (SBHM), a foundation is established for gas sensors utilizing high‐quality 2D materials. This approach facilitates the detection of material modifications in response to environmental influences, including the inevitable water molecules. The obtained hyperpolarizability from SBHM exhibits remarkable consistency with Langmuir's adsorption model, confirming the physical adsorption in the system. In addition, the competitive effects between gases are explored by comparing experimental results with theoretical predictions based on Boltzmann distribution and density functional theory (DFT) calculations. This highlights the effectiveness of SHG and SBHM in studying gas adsorption on layered van der Waals materials.

Molecular simulation of competitive adsorption of CO2/N2/O2 gas in bituminous coal

The main cause of coal spontaneous combustion is the oxidation and temperature rise of coal. Injecting composite inert gas for fire prevention and extinguishing is one of the important methods to prevent coal spontaneous combustion. A large number of studies have macroscopically investigated the fire prevention and extinguishing effects of CO2/N2 and their synergistic actions. However, there is currently a lack of research at the molecular level on the competitive adsorption mechanism between mixed inert gases (CO2, N2) and O2 molecules in coal. Therefore, this study conducted adsorption experiments using Qian Yingzi(QYZ) bituminous coal and compared them with the simulation data of the Wiser coal model to verify the reliability of the Wiser model. Subsequently, employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods, the competitive adsorption behavior of different proportions of binary mixed component gases (CO2/O2, CO2/N2, O2/N2) at a temperature of 303.15 K was investigated from five perspectives: adsorption capacity, adsorption selectivity coefficient, potential energy distribution, competitive adsorption heat, and interaction energy. The results indicate that among the competitive component gases, CO2 exhibits the strongest adsorption effect on the entire system, which is closely correlated with the distribution range of adsorption energy sites. The adsorption heat and adsorption amount of CO2 consistently exhibit a negative correlation, whereas the relationship between the adsorption heat of N2 and O2 and the adsorption amount shows a positive correlation. Their adsorption capacities depend on the pressure and the proportion of the two gases. Based on the isothermal adsorption curve of CO2/N2, it is recommended that the gas pressure during actual inert gas injection be less than 2.5 MPa. Under this pressure, the competitive adsorption effect is no longer significant, providing a certain theoretical basis for high-pressure injection. Moreover, the preliminary determination of the optimal injection ratio range is from 4:6–3:7. Furthermore, a systematic logical framework for selecting underground inert gas composition is proposed, and an underground mobile inert gas infusion process is adopted. The actual gas composition for infusion is determined based on cost factors in practical engineering. The research results can provide guidance for the selection of gas injection parameters for mixed inert gas fire prevention and extinguishing in goaf.

Bridging Atom Engineering for Low-Temperature Oxygen Activation in a Robust Metal-Organic Framework.

Achieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy-efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein we show an example that tailoring the local environment of cobalt sites in a robust metal-organic framework through substituting the bridging atom from -Cl to -OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low-temperature CO oxidation performance was achieved with T25(Temperature for 25% conversion) = 35°C and T100 (Temperature for 100% conversion) = 150°C, which stands out from existing MOF-based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

Bridging Atom Engineering for Low‐Temperature Oxygen Activation in a Robust Metal‐Organic Framework

Achieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy‐efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein we show an example that tailoring the local environment of cobalt sites in a robust metal‐organic framework through substituting the bridging atom from ‐Cl to ‐OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low‐temperature CO oxidation performance was achieved with T25(Temperature for 25% conversion) = 35°C and T100 (Temperature for 100% conversion) = 150°C, which stands out from existing MOF‐based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

Study on CO2 and CH4 Competitive Adsorption in Shale Organic and Clay Porous Media from Molecular- to Pore-Scale Simulation

Summary The elucidation of the competitive adsorption behaviors between CO2 and CH4 holds great importance in the context of improving natural gas recovery in shale reservoirs. Shale rock, as a complex porous medium, exhibits a highly interconnected multiscale pore network with pore size spanning from several to tens of nanometers. Nevertheless, accurately capturing the adsorption effects and studying the CO2/CH4 competitive adsorption within a large-scale, realistic, 3D nanoporous matrix remains a significant challenge. In this paper, we proposed a novel lattice Boltzmann method (LBM) coupled molecular simulation to investigate CO2/CH4 competitive adsorption in 3D shale nanoporous media. The initial step involves conducting Grand Canonical Monte Carlo (GCMC) simulations to simulate the competitive adsorption behaviors of CO2 and CH4 in kerogen and illite slit pores, with the aim of obtaining the atomic density distribution. Subsequently, a Shan-Chen-based lattice Boltzmann (LB) simulation is used under identical conditions. By coupling the molecular simulation results, the fluid-solid interaction parameters are determined. Finally, LB simulations are performed in designed 3D porous media, utilizing the fluid-solid interaction parameters. The effects of mineral type, CO2 concentration, and pore structure on competitive adsorption behaviors are discussed carefully. Our research offers significant contributions to the improvement of gas recovery and carbon geological sequestration through the examination of CO2/CH4 competitive adsorption in nanoporous media. Additionally, it serves as a link between molecular and pore-scale phenomena by leveraging the benefits of both molecular simulations and pore-scale simulations.

A novel porous layered K2Ti8O17 for capturing MB and Cu(Ⅱ) in wastewater

Appropriate structural design engineering is an effective method to achieve high adsorption performance, and optimizing the architecture to meet the desired properties remains challenging for adsorbents. Herein, a novel porous layered K2Ti8O17 (PLKTO) formed by interweaved nanowires has been successfully synthesized using MAX phase Ti2AlN and g-C3N4 as the precursors. The K2Ti8O17 nanowires consisted of numerous interconnected pores in a network-like distribution configuration, with a diameter of approximately 20 nm and a length exceeding one μm. Attractively, the PLKTO exhibited fast kinetics, large adsorption capacity, and excellent reusability toward methylene blue (MB) and Cu2+ adsorption. The maximum equilibrium adsorption capacity of MB and Cu2+ was 95.00 mg/g and 330.75 mg/g, with equilibrium times of ∼18 min and ∼25 min, respectively. The adsorption mechanism unveiled that the elimination of MB and Cu2+ was dominated by the pore-filling effect, electrostatic interaction, hydrogen bond, and surface complexation. Additionally, the PLKTO enjoyed highly selective for Cu2+ while investigating competitive adsorption behaviors in binary systems and real-world applications in various water matrices. These results indicated that the PLKTO revealed appealing application prospects for treating wastewater and pollutants and provided methodological guidance for design engineering in fabricating porous and layered structures.

Study on the adsorption performance of Cu2+ in wastewater by red mud

The treatment of copper-nickel wastewater has consistently posed a challenging problem in the field of environmental protection. In this experimental study, the adsorbent used was prepared from Bayer's method-derived red mud (RM). The adsorption characteristics of RM adsorbent on Cu2+ in copper-nickel wastewater, as well as the impact of Ni2+ on the removal effectcy of Cu2+, were investigated. The adsorption performance of Cu2+ in copper-nickel wastewater by adsorbent dosage, adsorption time and pH were investigated, and the adsorption mechanism was discussed. The adsorption process conformed to the pseudo-second-order kinetic model (R2 =0.986) and the Langmuir model (R2 =0.989), indicating that it was a monolayer chemical adsorption process. The raw materials were characterized using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray fluorescence (XRF). The results indicated that the adsorption process of Cu2+ and Ni2+ on RM was primarily influenced by surface chemical groups such as O-H, C-O-C, Si-C, and Si-O, among others. The adsorption rate of Cu2+ by RM could achieve 100% when the concentration of Cu2+ solution was 100 mg/L, with an optimal dosage of adsorbent at 0.20 mg/L and the best adsorption effect observed after 240 min. The adsorption of Cu2+ and Ni2+ by RM exhibits unidirectional competitive adsorption behavior. Furthermore,in competitive adsorption experiments, RM exhibits good selectivity towards Cu2+, with Ni2+ exhibiting minimal inhibitory effect on Cu2+ when the two elements coexist. Therefore, this paper offers potential research value for the large-scale application of RM in copper-nickel wastewater treatment processes.

Research on CO2/CH4/N2 competitive adsorption characteristics of anthracite coal from Shanxi Sihe coal mine.

This study aims to solve the problem of unsatisfactory development and utilization of coalbed methane and CO2 storage efficiency. It is focused on the adsorption behavior of CO2, CH4, and N2 in the macromolecular structure model of Shanxi Sihe coal mine anthracite, as well as the competitive adsorption behavior of CO2/CH4 and CH4/N2 binary gas mixtures with different ratios. Experimental analysis such as elemental analysis, solid 13C nuclear magnetic resonance (13C NMR), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis were used to construct the Shanxi Sihe coal mine model of the macromolecular structure of anthracite coal. The Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods were used to study the adsorption capacity and heat characteristics of CO2, CH4, and N2 at different temperatures using a molecular model of anthracite coal from Shanxi Sihe coal mine, as well as the competitive adsorption characteristics of CO2/CH4 and CH4/N2 binary mixtures. The mechanism of the influence of temperature and gas properties on the adsorption capacity and heat of adsorption was revealed from a microscopic perspective. The results indicated that the aromatic carbon content of anthracite in the Sihe coal mine, Shanxi is 81.19%, and the ratio Xbp of aromatic bridgehead carbon to surrounding carbon is 0.489. The aromatic structure is mainly composed of pyrene and anthracene. The molecular formula of the macromolecular structure model of anthracite in Shanxi Sihe coal mine is C233H157O13N2. The adsorption capacity and equivalent adsorption heat of the macromolecular model for adsorbing single-component gas CO2/CH4/N2 decrease with the increase in temperature. The temperature has the greatest impact on CO2 adsorption capacity and adsorption heat, followed by CH4 and N2. Under the competitive adsorption conditions of CO2/CH4 and CH4/N2 binary mixtures, the higher the partial pressure of a single-component gas in the mixture, the greater the adsorption capacity of the gas. The difference in the adsorption heat of CH4 and N2 is smaller than that of CH4 and CO2. The conclusions obtained from the study can provide technical and theoretical support for formulating reasonable drainage methods for coalbed methane wells.

Robust prediction for CH4/CO2 competitive adsorption by genetic algorithm pruned neural network

Capturing the competitive adsorption behavior of CH4/CO2 in shale reservoirs is essential for estimating the original gas-in-place and enhancing the shale gas recovery. This study leverages the neural network with sparsity, trained on a comprehensive dataset that includes crucial parameters such as clay, total organic carbon, specific surface area, pressure, and initial composition. Sparsity diverges from Dropout by selectively pruning unnecessary connections to enhance the model's robustness. Specifically, previous attempts suffer from over-optimistic performance due to unsuitable random dataset sampling. Hierarchical clustering and permutation importance algorithm indicate that petrophysical properties including clay, total organic carbon and specific surface area. By optimizing the sparsity through a genetic algorithm and connection pruning strategy, an accuracy improvement from 0.90 to 0.95 in terms of R-squared compared to conventional fully connected networks is witnessed. Additionally, the results show that removing up to 40% of the connections without compromising accuracy. Therefore, a heterogeneous configuration of activation functions within the neural network further amplifies its predictive capability. In addition, compared to the Dropout strategy, sparsity is more advantageous for generalizability in scenarios with limited datasets.

Competitive adsorption behaviors and mechanisms of Cd, Ni, and Cu by biochar when coexisting with microplastics under single, binary, and ternary systems

In this study, the effects of coexistence with microplastics and co-ageing with the soil on adsorption behaviors and mechanisms of biochar for heavy metals were investigated. Adsorption experiments of Cd, Ni, and Cu by microplastics, biochar, and their combination were conducted in single, binary, and ternary systems. The results indicated that the heavy metal adsorption by microplastics was ranked as Ni > Cd > Cu, which increased with decreasing particle size, and the adsorption capacity of microplastics was enhanced after dry-wet and freeze-thaw ageing. Biochar preferentially adsorbed Cd in the single system, while the maximum adsorption of Cu was observed in the binary and ternary systems due to the minimizing impact of competition on the Cu adsorption by biochar. The heavy metal adsorption by the combination of microplastics and biochar was less than that by single biochar, and the smaller the particle size of microplastics, the greater the negative effects on heavy metal adsorption. Coexistence with microplastics reduced Cd adsorption of biochar by 0.72 %–50.35 %, Ni adsorption by 1.17 %–30.43 %, and Cu adsorption by 5.78 %–47.88 %, respectively. Moreover, coexistence with microplastics exacerbated the adverse impacts of competition on biochar adsorption for heavy metals. The contribution percentages of biochar mineral mechanisms for heavy metal adsorption were ranked as Cu > Cd > Ni. When coexisting with microplastics or after ageing, the mineral mechanisms of heavy metal adsorption by biochar significantly decreased. This study investigated the competitive adsorption behaviors and mechanisms of heavy metals by biochar when coexisting with microplastics, which highlighted that the application of biochar for the remediation of heavy metal pollution should be concerned with the impacts of microplastics.

Magnetic biochar coupled with bismuth tungstate for multiple antibiotic removal from contaminated water: Characteristics, performance, and competitive adsorption synergistic photocatalysis mechanism

In this study, a magnetic biochar-based bismuth tungstate composite photocatalyst was synthesized to investigate the competitive adsorption behaviors of multiple antibiotics, specifically ciprofloxacin (CIP) and tetracycline (TC), as target pollutants in aqueous environments. We aimed to elucidate the mechanism of adsorption-photocatalysis synergy for the removal of multiple antibiotics in water. Our results demonstrated that the composite catalyst exhibited remarkable degradation efficiencies of 92.41% for CIP and 95.34% for TC within the multi-solute system. Additionally, we found that the composite photocatalyst showed preferential adsorption selectivity toward CIP in this multi-solute system. The adsorption process followed a monolayer chemisorption mechanism on the catalyst surface, primarily driven by π–π interactions and surface complexation with functional groups. The photocatalytic reaction relied on the generation of·OH,·O2−, and h+ as the primary active species for degrading TC and CIP. Moreover, we observed that incorporating magnetic properties into the composite enhanced its recovery rate. We hope that these results provide new insights into the removal of various antibiotics from water.

Novel insight into the competitive adsorption behaviors of As(V), Sb(V), and P(V) on {1 1 0} facets of Goethite: Existing form and coordination structure affinity

Despite the geochemical prominence of As(V), Sb(V), and P(V) coexisting in an extensive array of iron-oxide environments, the comprehension of their mobility and destiny is constrained due to the differences in the surface properties and exposed crystal facets of iron oxides. Herein, goethite primarily exposing the {110} facet, was employed as the model iron mineral to investigate the competitive adsorption behavior of As(V), Sb(V), and P(V) via batch experiments leveraging EXAFS, CD-MUSIC model, and DFT calculations. Results showed that observed co-adsorption behaviors were attributed to the comprehensive action of goethite surface chemistry, ion existing forms and different coordination structures stability at the molecular scale. CD-MUSIC model indicated As(V) and P(V) competed for surface sites through a combination of bidentate and monodentate coordination, whereas Sb(V) was primarily adsorbed via bidentate coordination, which led to the surpassed competitiveness of As(V) and P(V) on {110} facet compared to that of Sb(V). The affinity of various coordination structures on {110} facets based on DFT was found to be consistent with the trends predicted by the CD-MUSIC model. Specifically, As(V) and Sb(V) exhibited a greater affinity for bidentate coordination, while P(V) tended to form monodentate coordination complexes. However, the existing forms of As(V), Sb(V), and P(V) under different pH, especially for protonated species, accelerated the more weakened competitive combination ability of Sb(V) than As(V) and P(V) with increasing pH. Furthermore, charge density difference and Bader analysis have confirmed the contribution of electron transfer from the surface Fe to O towards forming FeO bonds. This work provided a novel investigation way and facilitated a more profound understanding of the geochemical cycle of toxic metals.

Breaking Surface Atomic Monogeneity of Rh2P Nanocatalysts by Defect‐Derived Phosphorus Vacancies for Efficient Alkaline Hydrogen Oxidation

AbstractBreaking atomic monogeneity of catalyst surfaces is promising for constructing synergistic active centers to cope with complex multi‐step catalytic reactions. Here, we report a defect‐derived strategy for creating surface phosphorous vacancies (P‐vacancies) on nanometric Rh2P electrocatalysts toward drastically boosted electrocatalysis for alkaline hydrogen oxidation reaction (HOR). This strategy disrupts the monogeneity and atomic regularity of the thermodynamically stable P‐terminated surfaces. Density functional theory calculations initially verify that the competitive adsorption behavior of Had and OHad on perfect P‐terminated Rh2P{200} facets (p‐Rh2P) can be bypassed on defective Rh2P{200} surfaces (d‐Rh2P). The P‐vacancies enable the exposure of sub‐surface Rh atoms to act as exclusive H adsorption sites. Therein, the Had cooperates with the OHad on the peripheral P‐sites to effectively accelerate the alkaline HOR. Defective Rh2P nanowires (d‐Rh2P NWs) and perfect Rh2P nanocubes (p‐Rh2P NCs) are then elaborately synthesized to experimentally represent the d‐Rh2P and p‐Rh2P catalytic surfaces. As expected, the P‐vacancy‐enriched d‐Rh2P NWs catalyst exhibits extremely high catalytic activity and outstanding CO tolerance for alkaline HOR electrocatalysis, attaining 5.7 and 14.3 times mass activity that of p‐Rh2P NCs and commercial Pt/C, respectively. This work sheds light on breaking the surface atomic monogeneity for the development of efficient heterogeneous catalysts.

Breaking Surface Atomic Monogeneity of Rh2 P Nanocatalysts by Defect-Derived Phosphorus Vacancies for Efficient Alkaline Hydrogen Oxidation.

Breaking atomic monogeneity of catalyst surfaces is promising for constructing synergistic active centers to cope with complex multi-step catalytic reactions. Here, we report a defect-derived strategy for creating surface phosphorous vacancies (P-vacancies) on nanometric Rh2 P electrocatalysts toward drastically boosted electrocatalysis for alkaline hydrogen oxidation reaction (HOR). This strategy disrupts the monogeneity and atomic regularity of the thermodynamically stable P-terminated surfaces. Density functional theory calculations initially verify that the competitive adsorption behavior of Had and OHad on perfect P-terminated Rh2 P{200} facets (p-Rh2 P) can be bypassed on defective Rh2 P{200} surfaces (d-Rh2 P). The P-vacancies enable the exposure of sub-surface Rh atoms to act as exclusive H adsorption sites. Therein, the Had cooperates with the OHad on the peripheral P-sites to effectively accelerate the alkaline HOR. Defective Rh2 P nanowires (d-Rh2 P NWs) and perfect Rh2 P nanocubes (p-Rh2 P NCs) are then elaborately synthesized to experimentally represent the d-Rh2 P and p-Rh2 P catalytic surfaces. As expected, the P-vacancy-enriched d-Rh2 P NWs catalyst exhibits extremely high catalytic activity and outstanding CO tolerance for alkaline HOR electrocatalysis, attaining 5.7 and 14.3 times mass activity that of p-Rh2 P NCs and commercial Pt/C, respectively. This work sheds light on breaking the surface atomic monogeneity for the development of efficient heterogeneous catalysts.

Quantitative competitive adsorption characteristics of sodium humate and dodecylamine on hematite and quartz surfaces

Competitive adsorption behavior of reagents is of great significance for efficient flotation separation of minerals. Motivated by the surface complex adsorption, surface complexation model (SCM) is an effective approach for quantitative characterization of reagents adsorption behavior. In this study, sodium humate (SH) adsorption and mixed SH and dodecylamine (DDA) competitive adsorption mechanisms onto hematite and quartz were quantitatively described and predicted using SCM. The model simulation suggested that there are two binding forms (monodentate and bidentate) between the groups on SH and the hematite sites and one (monodentate) with the quartz sites. The adsorption equilibrium constants (logK) of SH were calculated, which are 10.15, 23.34 (for hematite) and 10.41 (for quartz), respectively. In addition, the fitting results indicate that SH is adsorbed on the hematite surface mainly through the bidentate ≡Fe2-R(COO)2 site. Furthermore, the successful prediction of adsorption and surface potential at pH system were performed to verify the reliability of the model. Quantitative analysis of mixed SH and DDA interactions with mineral surfaces will elucidate and predict the reagents competitive adsorption behavior, which can also provide reliable data and parameters for surface complexation databases for surface complexation. Meanwhile, this finding provides valuable insights for the flotation of minerals, which enables their selective separation efficiency to be modulated and optimized.

Competitive adsorption of VOCs (benzene, xylene and ethylbenzene) with Fe3O4@SiO2-NH@BENZOPHENONE magnetic nanoadsorbents

Volatile organic compounds (VOCs), which are toxic, mutagenic and carcinogenic, are considered a critical factor for air pollution and cause serious harm to the eco-environment and human health. In this study, Fe3O4, Fe3O4@SiO2-NH2, Fe3O4@SiO2-NH@BENZOFENONE were synthesized as new magnetic nanoadsorbents (MNAs) and used for the first time in the removal of gas-phase benzene, xylene and ethylbenzene. The synthesised MNAs were characterized by SEM-EDS, TEM, FTIR, XRD, VSM, TGA and BET analyses. The characterization results showed that the MNAs have mesoporous structure, type IV physioresorption and type H3 hysteresis loop character. In order to clarify the comparative and competitive adsorption behaviour, the adsorption capacity of Fe3O4@SiO2-NH@BENZOFENONE MNA was found to be in the order of xylene > ethylbenzene > benzene in both single, binary and ternary component systems. The adsorption kinetics of benzene, xylene and ethylbenzene with Fe3O4@SiO2-NH@BENZOFENONE MNA were found to be governed by multistep mechanisms. Fe3O4@SiO2-NH@BENZOFENONE MNA showed reuse efficiencies of 83.07%, 84.35% and 82.99% after 5 cycles for benzene, xylene and ethylbenzene respectively. In the framework of the results, Fe3O4@SiO2-NH@BENZOPHENONE MNA, which has a high potential in terms of both adsorption capacity and reuse efficiency, is proposed as a promising adsorbent for the efficient removal of benzene, xylene and ethylbenzene.

Boosting urea electrooxidation on oxyanion-engineered nickel sites via inhibited water oxidation

Renewable energy-based electrocatalytic oxidation of organic nucleophiles (e.g.methanol, urea, and amine) are more thermodynamically favourable and, economically attractive to replace conventional pure water electrooxidation in electrolyser to produce hydrogen. However, it is challenging due to the competitive oxygen evolution reaction under a high current density (e.g., >300 mA cm−2), which reduces the anode electrocatalyst’s activity and stability. Herein, taking lower energy cost urea electrooxidation reaction as the model reaction, we developed oxyanion-engineered Nickel catalysts to inhibit competing oxygen evolution reaction during urea oxidation reaction, achieving an ultrahigh 323.4 mA cm−2 current density at 1.65 V with 99.3 ± 0.4% selectivity of N-products. In situ spectra studies reveal that such in situ generated oxyanions not only inhibit OH− adsorption and guarantee high coverage of urea reactant on active sites to avoid oxygen evolution reaction, but also accelerate urea’s C − N bond cleavage to form CNO − intermediates for facilitating urea oxidation reaction. Accordingly, a comprehensive mechanism for competitive adsorption behaviour between OH− and urea to boost urea electrooxidation and dynamic change of Ni active sites during urea oxidation reaction was proposed. This work presents a feasible route for high-efficiency urea electrooxidation reaction and even various electrooxidation reactions in practical applications.

Competitive adsorption law of multi-component gases during CO2 displacement of CH4 in coal seams

The CO2 enhanced coal bed methane recovery technology provides an excellent way to mitigate the greenhouse effect and energy crisis. The features and mechanism of CO2/CH4 competitive adsorption in the coal rock matrix have a critical impact on the production of CBM. For CO2/CH4 competitive adsorption process components and pressure changes, a multi-component gases competitive adsorption experiment was carried out with CO2 and CH4 binary gases as the study objects, and a multi-component adsorption model was developed by the expanded Langmuir equation. Based on the principles of molecular dynamics and thermodynamics, important parameters such as the average free range of gas molecules and adsorption potential are introduced to explain the competitive adsorption behavior from multiple perspectives and explore the competitive adsorption law of CH4 and CO2 under multiple component conditions, so as to provide some theoretical basis and field guidance for improving the extraction effect of CH4 in coal seams. The results show that: Under two critical conditions (100%CO2 +0%CH4 and 0%CO2 +100%CH4), the Langmuir volumes of CO2 for HN 1/3 coking coal and HL weakly caking coal respectively are 2.21 and 3.01 times higher than those of CH4; the overall adsorption capacity of binary gas is in between the adsorption capacities of both critical conditions and increases with increasing CO2 concentration in the gas source ratio; using E-L equation for binary gas component partitioning, the CH4 partition curves were all below CO2, the concentration of free-phase CH4 was always higher than that in the adsorbed phase, and coal samples had stronger adsorption ability for CO2 than CH4. CO2 has a stronger adsorption potential at the surface for HL weakly caking coal. CH4 has a slightly stronger adsorption potential at the surface for HN 1/3 coking coal. The higher coalification degree of the coal sample, the stronger the adsorption ability for CH4 and the weaker the adsorption ability for CO2. The slope of the overall adsorption curve of multi-component gases is analogous to the slope of the component with a high ratio of gas or strong adsorption capacity; the capacity of one-component adsorption for dual gas is closely related to the partial pressure of the free-phase gas and the separation factor α21. When the concentration ratio of CH4/CO2 in free phase is y2/y1 =α21, the concentration of both gases in adsorption phase is 50%, and α21 correlation is weakened, then the free phase gas partial pressure is dominant and there is a threshold value makes CH4 and CO2 adsorption capacity equal; when y2/y1 <α21, the coal preferentially adsorbs CO2 in the binary gas; when y2/y1 >α21, the coal preferentially adsorbs CH4 in the binary gas.

Insight into the mechanisms of activity promotion and SO2 resistance over Fe-doped Ce-W oxide catalyst for NOx reduction

Ceria-based catalysts for the selective catalytic reduction of NOx with NH3 (NH3-SCR) are always subject to deactivation by sulfur poisoning. In this study, Fe-doped Ce-W mixed oxides, which were synthesized by the co-precipitation method, improved the SCR activity and SO2 durability at low temperatures of undoped Ce-W oxides. The improved low-temperature activity was mainly due to the enhancement of redox properties at low temperatures and more active oxygen species, together with the adsorption and activation of more abundant NOx species, facilitating the “fast SCR” reaction. In the presence of SO2, doping with Fe species effectively prevented sulfate deposition on the CeW catalyst, due to the interaction between Fe, Ce, and W species inducing electron transfer among different metal sites and altering the electron distribution. The competitive adsorption behavior between NO and SO2 was changed by Fe doping, in which the adsorption and oxidation of SO2 were restrained. Besides, the elevated NO oxidation accelerated the decomposition of ammonium bisulfate, causing the SCR reaction to not be greatly suppressed. Hence, Fe-doped Ce-W oxides catalysts showed excellent sulfur resistance. This study provides an in-depth understanding of efficient Ce-based catalysts for SO2-tolerance strategies.

Dynamic adsorption behavior of 1.1.1.2-tetrafluoroethane (R134a) on activated carbon beds under different humidity and moisture levels

1.1.1.2-Tetrafluoroethane (R134a) is developed as a tracer for mechanical leakage detection in military chemistry. Due to the weaker physical adsorption properties, water vapor competitive adsorption limits the use of tracer R134a. Thus, it is urgent to the analyze dynamic competitive adsorption behavior of R134a and water vapor on the activated carbon. In this study, R134a breakthrough curves on the fixed beds packed with activated carbons under different relative humidity and moisture content levels were systematically measured. Combining mass spectrometry, gas chromatography, and a novel fiber Bragg grating temperature sensor, the dynamic competitive adsorption processes and axial temperature of fixed beds were first reported. Interestingly, with increasing moisture content, R134a breakthrough time decreased, but dynamic adsorption capacity increased. This was attributed to the fact that the residual water vapor could increase the specific surface area and pore volume of activated carbon to enhance R134a dynamic adsorption capacity. Using the R134a as the standard, the dynamic competitive adsorption process was first revealed and could be divided into four stages including Co-adsorption, Co-breakthrough, Competitive Adsorption (“Rolling Up” and “Adsorption Platform”), and Dynamic Adsorption Equilibrium. “Rolling Up” and “Adsorption Platform” phenomena are mainly determined by the strength of intermolecular interactions, the concentration difference of adsorbate, and the thermal effect induced by water vapor adsorption/desorption.