Competitive Adsorption Of CO Research Articles

Unlocking Superior Hydrogen Oxidation and CO Poisoning Resistance on Pt Enabled by Tungsten Nitride-Mediated Electronic Modulation.

Enhancing the activity and CO poisoning resistance of Pt-based catalysts for the anodic hydrogen oxidation reaction (HOR) poses a significant challenge in the development of proton exchange membrane fuel cells. Herein, we leverage theoretical calculations to demonstrate that tungsten nitride (WN) can intricately modulate the electronic structure of Pt. This modulation optimizes the hydrogen adsorption, significantly boosting HOR activity, and simultaneously weakens the CO adsorption, markedly improving resistance to CO poisoning. Through prescreening with rational design, we synthesized an efficient catalyst comprising a minimal Pt content (only 1.4 wt %) supported on the small-sized WN/reduced graphite oxide (Pt@WN/rGO). As anticipated, this catalyst showcases a remarkable acidic HOR mass activity of 3060 A gPt-1, which is approximately 11.8 times greater than that of the commercial 20 wt % Pt/C catalyst. Impressively, it maintains high activity with 98.2% retention even in the presence of 1000 ppm of CO, indicating exceptional poison resistance. Operando synchrotron radiation analyses reveal that WN harmonizes the electron state of Pt during electrochemical reactions, optimizing hydrogen adsorption/desorption dynamics. This leads to a lower peak potential of CO stripping on Pt@WN/rGO compared to that on Pt/rGO, suggesting that WN mitigates competitive CO adsorption and enhances the availability of hydrogen adsorption sites on Pt. The synergistic effect significantly accelerates HOR activity and increases antipoisoning efficacy. The assembled PEMFC demonstrates substantial tolerance to CO concentration from 10 to 1000 ppm in the H2/CO mixture.

Simultaneously activating molecular oxygen and surface lattice oxygen on Pt/TiO2 for low-temperature CO oxidation

Developing high-performance Pt-based catalysts with low Pt loading is crucial but challenging for CO oxidation at temperatures below 100 °C. Herein, we report a Pt-based catalyst with only a 0.15 wt% Pt loading, which consists of Pt–Ti intermetallic single-atom alloy (ISAA) and Pt nanoparticles (NP) co-supported on a defective TiO2 support, achieving a record high turnover frequency of 11.59 s–1 at 80 °C and complete conversion of CO at 120 °C. This is because the coexistence of Pt–Ti ISAA and Pt NP significantly alleviates the competitive adsorption of CO and O2, enhancing the activation of O2. Furthermore, Pt single atom sites are stabilized by Pt–Ti ISAA, resulting in distortion of the TiO2 lattice within Pt–Ti ISAA. This distortion activates the neighboring surface lattice oxygen, allowing for the simultaneous occurrence of the Mars-van Krevelen and Langmuir–Hinshelwood reaction paths at low temperatures.

Dynamics of oil–CO2–water three-phase under the nanopore confinement effect: Implications for CO2 enhanced shale oil recovery and carbon storage

The widespread nanopores, diverse minerals, and varying water saturation in shale reservoirs complicate the mechanism analysis and performance prediction of CO2 enhanced oil recovery (CO2-EOR) and CO2 storage (CS) in hydrated nanopores. Therefore, molecular dynamics methods were used to simulate the process of CO2 replacing shale oil in hydrated nanopores of inorganic, organic and composite minerals. Importantly, the effects of mineral type, temperature, pressure and water content on CO2-EOR and CS performances in hydrated nanopores were analyzed, and the CO2-EOR mechanisms of dissolution, extraction, viscosity reduction, miscibility and competitive adsorption were revealed. The results show that water in illite, kerogen, and composite nanopores are distributed in the forms of water films, water clusters (films), and water columns, respectively. The replacement efficiency of shale oil in three types of nanopores is improved with increased water content but reduced in kerogen nanopores under high water content. Water is not conducive to the diffusion and viscosity reduction of oil in nanopores, but the miscibility and competitive adsorption of CO2 and oil are improved. The replacement efficiency is positively correlated with temperature and pressure. The increasing temperature promotes diffusion and viscosity reduction of oil and competitive adsorption between CO2 and oil in hydrated nanopores, and increasing pressure promotes miscibility and competitive adsorption. Water columns in kerogen and composite nanopores reduce the CS performance, while thin water films in illite nanopores improve it. Moreover, an excellent CS rate can be achieved at high temperatures and pressures, but the high temperature is not conducive to CS stability. This study provides a theoretical basis for CO2 injection to improve oil production and carbon storage performance in hydrated shale reservoirs and contributes to the optimization of CO2 injection schemes.

Pre-pilot scale study of hydrogen production from biomass syngas via water-gas shift in Pd–Ag catalytic membrane reactor and dedicated hydrogen permeation unit

The water-gas shift reaction (WGS) was evaluated in two Pd–Ag membrane reactors operating in parallel and capable of processing 0.25 Nm3·h−1 of syngas. Various configurations, syngas compositions, and steam flow rates were explored within the temperature range of 300–350 °C and pressure range of 4–8bar. The performances were evaluated in a coupled configuration, consisting of a permeator and a membrane reactor operating in series, and single configuration of membrane reactor. Two syngas mixtures were fed and treated under different combinations of temperature, pressure, and steam/CO ratio. The syngas composition used was, in one case that typically produced by updraft gasifiers operated with air and having a content of H2 19.1 vol% and, in the second case, having content of 36.8 vol%, typically achievable by oxy-steam gasification. Carbon monoxide conversion, hydrogen permeation, and hydrogen permeability of membranes were determined. The use of these membranes effectively enhances the WGS reaction, overcoming the performances of a Gibbs reactor, and produces streams of ultrapure hydrogen. Competitive strong adsorption of CO was suggested from the permeability analysis and comparison with existing literature.

Competitive adsorption of CO2/CH4 on coal: Insights from thermodynamics

The main reason for CO2 enhanced coalbed methane recovery is the competitive adsorption of CO2 and CH4 on coal. Therefore, it is necessary to study the equilibrium adsorption of CO2, CH4 and their mixed gases on coal over a wide range of pressures. This work investigates the mechanism adsorption of CO2/CH4 on coal by thermodynamics. The findings indicate that CO2 demonstrates a greater increase in Gibbs free energy and a larger decrease in entropy loss related to CH4, indicating that the adsorption process of CO2 is more to occur spontaneously. In CO2/CH4 mixed gas adsorption system, the amount of gas adsorbed for different gas ratios (yCO2:yCH4 = 1:3; yCO2:yCH4 = 2:2; yCO2:yCH4 = 3:1) falls between the amounts adsorbed for pure CO2 and CH4 components. As CO2 concentration rises, the amount of mixed gases adsorbed similarly increases. Additionally, the amount of CH4 adsorbed in any combination is lower than that of CO2, suggesting that CO2 has a predominant influence regarding the adsorption process. Furthermore, isosteric heat of adsorption for CO2 in the mixed gases exceeds that of CH4, suggesting a stronger connection between CO2 and the surface of the coal matrix during the competitive adsorption stage.

Competitive adsorption of CO2, N2, and CH4 in coal-derived asphaltenes, a computational study

Greenhouse gases are major contributors to global warming, and their concentration is increasing due to the widespread use of fossil fuels. Coal bed methane (CBM) offers a potential solution to this issue. However, the gas adsorption mechanisms of CBM, particularly in the context of coal-derived asphaltenes, are not fully understood. This study provides a comprehensive theoretical investigation of the competitive adsorption of carbon dioxide (CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}), methane (CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}), and nitrogen (N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}) in the processes of CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}- and N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}-enhanced coalbed methane recovery, with a focus on coal-derived asphaltenes functionalized with CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}, NH, O, and S groups. Using the Grand Canonical Monte Carlo (GCMC) simulation method and performing Molecular Dynamics (MD) simulations, we studied the adsorption process. To investigate the electronic effects and nature of the interactions, we performed density functional theory (DFT) calculations. The adsorption energy values and non-covalent interactions (NCI) for the adsorption of gases signify the physical adsorption (van der Waals interaction), with CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} exhibiting the highest (absolute) adsorption energy. The Monte Carlo results indicated that elevated temperatures led to a reduction in adsorption capacity. Coal-derived asphaltenes demonstrated greater selectivity for CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} compared to CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} and N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} in competitive adsorption, especially at elevated temperatures. Our findings highlight the significant potential of our asphaltene model, not only in mitigating CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} greenhouse gas emissions but also in recovering CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}, which is a valuable resource.

Engineering the CuO/MnO2 interface with multivalent conversion for low-temperature and efficient CO oxidation

A novel interface of MnO2 with CuO with multivalent conversion is fabricated by the deposition-precipitation method for low-temperature and efficient CO oxidation. It is found that the temperature for CO thermal-catalytic oxidation to reach a complete conversion significantly decreases to 105 °C for the CuO/MnO2. A combination of experimental and theoretical studies demonstrates the successful formation of the CuO/MnO2 interface, inducing a pronounced effect that promotes CO oxidation. The CuO/MnO2 interface leads to the formation of Cu-O-Mn, a superior redox system with multivalent conversion (Cu+ + Mn4+ ↔ Cu2+ + Mn3+, Cu+ + Mn3+ ↔ Cu2+ + Mn2+), abundant active sites, excellent ability to activate O2, the rapid oxygen transfer, and more suitable adsorption energy for O2, CO, and CO2. These characteristics are advantageous to CuxO-MnxOy for achieving a 100 % removal of CO at a lower temperature. Furthermore, the computational study reveals that the CO oxidation process follows two mechanistic pathways (Eley-Rideal (E-R) and Mars-van Krevelen (M-K)), indicating that there is no competitive adsorption of CO and O2 on the CuO/MnO2. This study shows that the interface created between suitable metal oxides can improve the catalytic performance and provides new perspective for catalyst design and performance enhancement mechanisms.

Ni2P active site ensembles tune electrocatalytic nitrate reduction selectivity.

We demonstrate that active site ensembles on transition metal phosphides tune the selectivity of the nitrate reduction reaction. Using Ni2P nanocrystals as a case study, we report a mechanism involving competitive co-adsorption of H* and NOx* intermediates. A near 100% faradaic efficiency for nitrate reduction over hydrogen evolution is observed at -0.4 V, while NH3 selectivity is maximized at -0.2 V vs. RHE.

Characterization of Methane Extraction during ScCO2-ECBM: Consideration of Competitive Adsorption of ScCO2 and CH4.

The supercritical CO2 enhanced coalbed methane (ScCO2-ECBM) technology is still in the development stage, and many simulation experiments and theoretical studies related to ScCO2-ECBM are being improved. Previous research works have conducted many studies on the competitive adsorption of CO2 and CH4 in coal, but there is less research on the competitive adsorption of ScCO2 and CH4 and its impact on methane extraction characteristics. In this study, a permeability model considering the competitive effects of effective stress and adsorption swelling on permeability was established. Based on the assumed conditions and permeability evolution model, different injected pressure and initial methane pressure conditions were set to obtain quantitative results of the competitive adsorption of ScCO2 and CH4, permeability changes, and CH4 production. By obtaining the competitive adsorption relationship between ScCO2 and CH4, we analyzed the evolution law of permeability and its impact on CH4 production. It was found that ScCO2 has a stronger competitive adsorption capacity, and the competitive adsorption capacity of ScCO2 and CH4 is more sensitive to injected pressure. Under two different conditions, it was found that the higher the injected pressure or injected differential pressure, the higher the initial permeability. However, due to the greater sensitivity of the competitive adsorption capacity of ScCO2 and CH4 to injected pressure, the greater the injected pressure in the later stage, the greater the decrease in permeability, resulting in a situation where the permeability at an injected pressure of 10 MPa is lower than that at an injected pressure of 8 MPa. A simple comparison was made between gaseous CO2 and ScCO2, and it was found that although injecting ScCO2 has a stronger adsorption swelling capacity that affects permeability changes, its stronger adsorption capacity can effectively displace methane and higher injected pressure, injected temperature, and advantages such as fracturing and extraction that are not yet reflected in the model. This study provides some guidance for numerical simulation of the ScCO2-ECBM process and the enhancement of coalbed methane extraction.

Urea electro-oxidation byproducts impact on NiO/NiOOH anode performance studied by operando electrochemical impedance spectroscopy

With significant quantities of urea (CO(NH2)2) being worldwide produced and its presence at high concentration in urine, simultaneous treatment of urea effluents and hydrogen production by paired electrolysis represents a very attractive approach in circular economy. Urea electro-oxidation on Ni-based catalysts in alkaline solution represents a promising approach, but poor stability of the Ni-based catalytic performance has been reported. In this work, the performance and stability of a nanostructured NiO/NiOOH anode for urea electro-oxidation has been evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (CA). Firstly, the thickness of the NiOOH active film formed during the electrochemical activation process on NiO NPs (< 50 nm) is estimated from EIS data at about 4 nm. Secondly, the impact on the catalyst performance of all previously identified urea electro-oxidation by-products (ammonia (NH3), carbonate (CO32−), cyanate (−OCN) and nitrite (NO2−)) has been individually addressed by operando EIS, and none of them are responsible for the NiO/NiOOH catalytic deactivation. In addition to this, more insight into the competitive adsorption of CO(NH2)2 and OH− on the catalyst surface during electrode aging was gained by the response of EIS in different potential regions.

Activation of lignin-derived biochar with mixed H2O and CO2: Characterization of reaction intermediates and investigation their potential synergistic effects

Physical activation of biomass with H2O or CO2 is an important method for producing activated carbon (AC). Activation of biomass with CO2 or H2O follows varied mechanisms and the use of mixed CO2/H2O might show potential synergistic effects for creating pores. This was investigated by activation of lignin-derived biochar with H2O, CO2 and their mixture. The results demonstrated that H2O as an activator was much more effective than CO2 for generation of pores (804.1 m2g−1 versus 516.1 m2g−1in CO2), especially mesopores (40% versus 14% in CO2). This was achieved via enhancing cracking/gasification reactions of the biochar with H2O. The synergistic effect of CO2 and H2O for activation of the lignin-derived biochar was insignificant as cracking/gasification reactions were not enhanced, leading to remarkably lower specific surface area of the AC (674.8 m2g−1) than that with H2O as an activator alone. Competitive adsorption of CO2 and H2O existed and preferable adsorption of CO2 hindered deoxygenation of the biochar with H2O. The in-situ IR characterization indicated that CO2 presence suppressed decarbonylation reactions, retaining more oxygen species in form of CO, while it was the opposite in H2O. Additionally, activation with H2O formed numerous round-shape dents on surface of activated carbon, while the activation with CO2 formed the characteristic round edges. The AC activated with H2O showed superior capability for adsorption of phenol than that activated with CO2 or mixed H2O/CO2.

Bio-engineering of carbon adsorbents to capture CO2 from industrial sources: The cement case

Pine cone leaves (PCL) and pine kernel shells (PKS), abundant by-products of the Spanish food industry, were selected as precursors for activated carbons (ACs) to adsorb CO2 selectively at industrial post-combustion capture conditions. The goal was to maximize the development of narrow microporosity in the final carbons to boost the CO2 adsorption capacity. We have designed kinetics and equilibrium of adsorption experiments with CO2/H2O/N2 on a selected AC derived from PCL in a thermogravimetric analyzer (TGA) at 50 °C and three partial pressures of CO2 to prove the suitability to capture CO2 from industrial off-gases. When humid flue gas streams were tested, competitive adsorption of CO2 and H2O occurred; however, the difference in the uptake rates favored CO2 adsorption in the early stages. The joint CO2 + H2O uptake was around 2 mmol g−1 at 50 °C in humid conditions, where CO2 reached the equilibrium uptake at the corresponding partial pressure for 15 and 32 vol% CO2 in the feed stream. Moreover, the dynamic performance was addressed by cyclic adsorption–desorption experiments representing different industrial post-combustion capture scenarios in a lab-scale fixed-bed rig. The selected AC showed a stable performance in adsorption-regeneration cycles and very remarkable CO2 capture capacity under dry conditions (up to 1.08 mmol g−1 at 50 ˚C for 30 vol% CO2). Kinetics analysis also supported the faster adsorption of CO2 under cement flue gas conditions.

Enhancing shale gas recovery by carbon dioxide injection: A method of carbon capture, utilization and storage (CCUS)

CO2 injection in shale gas reservoir can not only increase the production of shale gas, but also realize carbon dioxide capture, utilization and storage. At present, most experimental studies of CO2 injection in shale are carried out by conventional core experiments. However, it is difficult to analyze the process of CO2 replacing shale gas and adsorption in shale pores on microscopic scale. In this study, nuclear magnetic resonance (NMR) technology is used to analyze the migration and conversion of CH4 in process of CO2 injection and depressurization production. Based on above experiments, microscopic mechanism of competitive adsorption of CH4 and CO2 during CO2 injection is clarified, and the stimulation mechanism of CO2 injection to improve shale gas recovery is further proposed. The results show that CH4 preferentially exists in form of adsorption state in shale. When CH4 adsorption amount reaches a certain degree, CH4 gas in form of free state gradually appears. During depressurization stage, further depressurization failed to promote the desorption of adsorbed gas when pressure reduced to 3 MPa. Therefore, adsorbed CH4 gas still exists after depressurization production. Shale has stronger adsorption capacity for CO2 than CH4. CO2 can replace CH4 adsorbed on the pore surface, and promote the desorption of adsorbed CH4 gas to free state. CO2 has the best displacement effect on adsorbed CH4 in pores with diameter of 15.04–21.62 nm, but it fails to replace CH4 in pores with diameter less than 1.08 nm. The competitive adsorption of CO2 and CH4 can effectively promote the further desorption of residual adsorbed CH4 gas after depressurization, and significantly improve the cumulative shale gas production.

Impedance-Based Detection of NO2 Using Ni-MOF-74: Influence of Competitive Gas Adsorption.

Chemically robust, low-power sensors are needed for the direct electrical detection of toxic gases. Metal-organic frameworks (MOFs) offer exceptional chemical and structural tunability to meet this challenge, though further understanding is needed regarding how coadsorbed gases influence or interfere with the electrical response. To probe the influence of competitive gases on trace NO2 detection in a simulated flue gas stream, a combined structure-property study integrating synchrotron powder diffraction and pair distribution function analyses was undertaken, to elucidate how structural changes associated with gas binding inside Ni-MOF-74 pores correlate with the electrical response from Ni-MOF-74-based sensors. Data were evaluated for 16 gas combinations of N2, NO2, SO2, CO2, and H2O at 50 °C. Fourier difference maps from a rigid-body Rietveld analysis showed that additional electron density localized around the Ni-MOF-74 lattice correlated with large decreases in Ni-MOF-74 film resistance of up to a factor of 6 × 103, observed only when NO2 was present. These changes in resistance were significantly amplified by the presence of competing gases, except for CO2. Without NO2, H2O rapidly (<120 s) produced small (1-3×) decreases in resistance, though this effect could be differentiated from the slower adsorption of NO2 by the evaluation of the MOF's capacitance. Furthermore, samples exposed to H2O displayed a significant shift in lattice parameters toward a larger lattice and more diffuse charge density in the MOF pore. Evaluating the Ni-MOF-74 impedance in real time, NO2 adsorption was associated with two electrically distinct processes, the faster of which was inhibited by competitive adsorption of CO2. Together, this work points to the unique interaction of NO2 and other specific gases (e.g., H2O, SO2) with the MOF's surface, leading to orders of magnitude decrease in MOF resistance and enhanced NO2 detection. Understanding and leveraging these coadsorbed gases will further improve the gas detection properties of MOF materials.

Multi-component Adsorption Isotherms: Review and Modeling Studies

Adsorption is an important phenomenon widely used for the removal of contaminants. Several drinking water contaminants such as arsenic and fluoride, vanadium and chromium, nickel, cadmium and cobalt are found to coexist in nature as multi-component mixtures in water. Hence, the modeling of multi-component adsorption isotherms for designing water treatment systems has gained importance recently. However, review studies of multi-component adsorption and competitive adsorption modeling are limited. The current review paper summarizes twenty-six multi-component adsorption isotherm models. Also, case studies of several common multi-component adsorption systems and the mechanisms of multi-component adsorption are discussed. Furthermore, a modeling analysis of four multi-component isotherms models for three commonly found two-component adsorption systems, i.e., cadmium-nickel, nickel–cobalt, and cadmium-cobalt, is reported. The Extended Langmuir isotherm, Competitive Langmuir isotherm, Extended Langmuir–Freundlich isotherm and Extended Freundlich isotherm models were applied in the modeling study for the competitive adsorption of Cd, Ni, and Co. The goodness of fit parameters and adsorption isotherm constants were estimated for these models. The factors influencing competitive adsorption, mechanisms of adsorption, various single and multi-component isotherm models, their significance, and limitations are also discussed in this review article.Highlights• Twenty-six multi-component and ten single-component isotherm models are compiled• Factors affecting multi-component competitive adsorption isotherms are discussed in this review paper• The applications of four multi-component isotherm models for three binary contaminant systems are presented.Graphical

In situ single-crystal synchrotron X-ray diffraction studies of biologically active gases in metal-organic frameworks

Metal-organic frameworks (MOFs) are well known for their ability to adsorb various gases. The use of MOFs for the storage and release of biologically active gases, particularly nitric oxide (NO) and carbon monoxide (CO), has been a subject of interest. To elucidate the binding mechanisms and geometry of these gases, an in situ single crystal X-ray diffraction (scXRD) study using synchrotron radiation at Diamond Light Source has been performed on a set of MOFs that display promising gas adsorption properties. NO and CO, were introduced into activated Ni-CPO-27 and the related Co-4,6-dihydroxyisophthalate (Co-4,6-dhip). Both MOFs show strong binding affinity towards CO and NO, however CO suffers more from competitive co-adsorption of water. Additionally, we show that morphology can play an important role in the ease of dehydration for these two systems.

Discerning and modulating critical surface active sites for propane and CO oxidation over Co3O4 based catalyst

Identifyingactive sites is critical for rational catalyst design. We clarified the surface active sites for propane and CO oxidation over Co3O4-based catalysts using probe reactions of propane and CO oxidation, respectively. In comparison to Co3O4/ZSM-5, Co3O4/CeO2 has superior CO oxidation activity but inferior propane oxidation activity. CeO2 oxygen vacancies promote O2 activation,the rate-determined step (RSD) for CO oxidation, and avoid competitive adsorption of O2 and CO on Co3O4 species, resulting in superior CO oxidation activity on Co3O4/CeO2. Whereas the RSD for propane oxidation is synergistic catalysis of Co3O4 species and acid sites, Co3O4/ZSM-5 exhibits improved propane oxidation activity as a result of the abundant acid sites from ZSM-5. Due to a lack of oxygen vacancies for O2 activation, competitive adsorption of O2 with propane or CO on Co3O4 species is observed on Co3O4/ZSM-5. Furthermore, surface Co3+ species in Co3O4 are discovered to beactive sites for both CO and propane activation. As a result of the increased surface Co3+ species, the pre-reduced and post-oxidized Co3O4 catalysts (Co3O4/ZSM-5-A and Co3O4/CeO2-A) exhibit improved activity for both propane and CO oxidation.

Synthesis and Characterization of Catalytically Active Au Core─Pd Shell Nanoparticles Supported on Alumina.

A two-step seeded-growth method was refined to synthesize Au@Pd core@shell nanoparticles with thin Pd shells, which were then deposited onto alumina to obtain a supported Au@Pd/Al2O3 catalyst active for prototypical CO oxidation. By the strict control of temperature and Pd/Au molar ratio and the use of l-ascorbic acid for making both Au cores and Pd shells, a 1.5 nm Pd layer is formed around the Au core, as evidenced by transmission electron microscopy and energy-dispersive spectroscopy. The core@shell structure and the Pd shell remain intact upon deposition onto alumina and after being used for CO oxidation, as revealed by additional X-ray diffraction and X-ray photoemission spectroscopy before and after the reaction. The Pd shell surface was characterized with in situ infrared (IR) spectroscopy using CO as a chemical probe during CO adsorption–desorption. The IR bands for CO ad-species on the Pd shell suggest that the shell exposes mostly low-index surfaces, likely Pd(111) as the majority facet. Generally, the IR bands are blue-shifted as compared to conventional Pd/alumina catalysts, which may be due to the different support materials for Pd, Au versus Al2O3, and/or less strain of the Pd shell. Frequencies obtained from density functional calculations suggest the latter to be significant. Further, the catalytic CO oxidation ignition-extinction processes were followed by in situ IR, which shows the common CO poisoning and kinetic behavior associated with competitive adsorption of CO and O2 that is typically observed for noble metal catalysts.

Ab Initio to Activity: Machine Learning-Assisted Optimization of High-Entropy Alloy Catalytic Activity

High-entropy alloys are slowly making their debut as a platform for catalyst discovery, but conventional methods, theoretical as well as experimental, may fall short of screening the vast composition space inhabited by this class of materials. New theoretical approaches are needed to gauge the catalytic activity of high-entropy alloys and optimize the alloy composition within a feasible time frame as a prerequisite for further experimental studies. Herein, we establish a workflow for simulations of catalysis on high-entropy alloy surfaces. For each step of the modeling we present our choice of method, however, we also acknowledge that alternative options are available. We apply the developed methodology to predict the net catalytic activity of any alloy composition, within the composition space spanned by Ag–Ir–Pd–Pt–Ru, for the oxygen reduction reaction. Based on first-principle calculations, a graph convolution neural network is used to predict adsorption energies of *OH and *O. Subsequently, taking competitive co-adsorption of reaction intermediates into account, we couple the net adsorption energy distribution of a high-entropy alloy surface to the expected current density. Lastly, this procedure is used in conjunction with a Bayesian optimization scheme to search for optimal alloy compositions, which yields several promising compositions. This result shows that an unbiased in silico pre-screening and discovery of catalyst candidates is viable and will help scale the otherwise insurmountable challenge of searching for high-entropy alloy catalysts. It is our hope that our computational framework, which is freely available on GitHub, will aid other research groups to efficiently identify promising high-entropy alloy catalysts.

2D Ising Model for Enantiomer Adsorption on Achiral Surfaces: L- and D-Aspartic Acid on Cu(111)

The 2D Ising model is well-formulated to address problems in adsorption thermodynamics. It is particularly well-suited to describing the adsorption isotherms predicting the surface enantiomeric excess, , observed during competitive co-adsorption of enantiomers onto achiral surfaces. Herein, we make the direct one-to-one correspondence between the 2D Ising model Hamiltonian and the Hamiltonian used to describe competitive enantiomer adsorption on achiral surfaces. We then demonstrate that adsorption from racemic mixtures of enantiomers and adsorption of prochiral molecules are directly analogous to the Ising model with no applied magnetic field, i.e., the enantiomeric excess on chiral surfaces can be predicted using Onsager’s solution to the 2D Ising model. The implication is that enantiomeric purity on the surface can be achieved during equilibrium exposure of prochiral compounds or racemic mixtures of enantiomers to achiral surfaces.