Competitive Adsorption Of CO Research Articles

Experimental investigation of competitive co-adsorption of naproxen and diclofenac from water by an aluminum-based metal-organic framework

Commercially available Aluminum-benzenedicarboxylate (Basolite A100, MIL-53 (Al)), Metal-Organic Framework was successfully used for the adsorption and co-adsorption of Naproxen (NAP) and Diclofenac (DCF) from aqueous solutions. The adsorption experiments were carried out using single-component NAP/DCF and their binary aqueous solutions. The experimental results demonstrated the remarkable removal efficiency of the MOF (>96% for NAP and >99% for DCF). Besides, the competitive adsorption of the drugs from binary solutions showed higher selectivity toward DCF. The hydrogen bonding and π-π stacking were investigated to gain insight into the adsorption mechanism. The pH effect experiments in the range of 2 to 8 showed that as pH increased, the adsorption capacity of both drugs decreased. The fitting of the adsorption isotherm and kinetic models confirms that both contaminants conform to the Langmuir model and pseudo-second-order (PSO) models with high regression coefficient ( R 2 > 0.99). The PSO rate constant values for NAP were 0.0056 (single-component) and 0.0024 g·mg −1 ·min −1 (binary), while for DCF these values were 0.0037 (single-component) and 0.0014 g·mg −1 ·min −1 (binary). According to the isotherm model, the calculated maximum removal capacities ( q m ) values were found equal to 297 and 422 mg/g for NAP and DCF, respectively. The suitability of MIL-53(Al) for adsorption of naproxen and diclofenac in mineral water was also investigated. Finally, MIL-53(Al) was confirmed to be a promising adsorbent candidate thanks to its highly efficient removal of NAP and DCF in both single and binary solutions and then can be deployed in water treatment. • MIL-53(Al) showed great potential for water purification from pharmaceuticals. • MIL-53(Al) had better selectivity for DCF compared to NAP. • Adsorption mechanism was determined to be due to hydrogen bonding and π-π stacking. • The experimental data fitted best the Langmuir isotherm and PSO kinetic models. • The maximum adsorption capacities' values were found equal to 297 and 422 mg/g for NAP and DCF, respectively.

Synergism of Iron and Platinum Species for Low-Temperature CO Oxidation: From Two-Dimensional Surface to Nanoparticle and Single-Atom Catalysts.

CO oxidation is one of the most studied reactions in heterogeneous catalysis. It is present in air cleaning and automotive emission control. It also participates in the removal of CO from streams of hydrogen used in fuel cells. Because of the competitive adsorption of CO and O2 over active sites, the use of Pt-based catalysts for low-temperature CO oxidation remains a challenge. Recently, great progress has been made with catalysts containing Pt-Fe species because of the contribution of Fe species to O2 activation. The structure-activity relationship and reaction mechanisms have been investigated with various Pt-Fe catalysts. In this Perspective, we give a summary of the recent advances of low-temperature CO oxidation over Pt-Fe catalysts with a focus on the synergistic effect of Pt and Fe species in the CO and O2 activation of catalytic reactions. Future prospects for the preparation of highly effective Pt-Fe catalysts are also proposed.

Oxygen vacancy O-terminated surface: The most exposed surface of hexagonal WO3 (001) surface

It is known that exposed surface determines material’s performance. WO3 is widely used in gas sensing and its working surface is proposed to control its sensitivity. However, the working surface, or most exposed surface with detailed surface structure remain unclear. In this paper, DFT calculation confirmed that oxygen vacancy O-terminated surface is the most exposed hexagonal WO3 (001) surface, judging from competitive adsorption of CO and O2, working surface determination for CO sensing and comparison of oxygen vacancy formation energies on different h-WO3 (001) surfaces. It is found that DFT can be a useful alternate for exposed surface determination. Our results provide new perspectives and performance explanations for material research.

Influence of functionalization, surface area and charge distribution of SBA15-based adsorbents on CO (II) and NI (II) removal from aqueous solutions

Amino functionalized solids were obtained by anchoring ethoxysilane and ethylenediaminetetraacetic groups onto the surface of a mesostructured silica SBA-15. The materials were characterized by nitrogen adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), and potentiometric titration. The samples SBA-15, SBA-15 -NH2 and SBA-15-EDTA were tested in the simple and competitive adsorption of Co (II) and Ni (II) ions from aqueous solutions. The equilibrium data were analyzed using the Langmuir isotherm by nonlinear regression analysis. The influence of textural and chemical characteristics of the three different silicas on Co (II) and Ni (II) removal was also studied. A complementary study based on density functional theory was performed. Adsorption isotherms of Ni and Co fitted well with Langmuir model, exhibiting high adsorption capacity of 47.7 and 27.4 mg of metal/g of SBA-15, 62.9 and 59.7 mg of metal/g of SBA-15-NH2 and 74 and 67.7 mg of metal/g of SBA-15-EDTA, respectively, in simple adsorption tests. In the case of adsorption from binary solutions, both cations compete for the same active sites, a preferential Ni adsorption being shown. A detailed data analysis demonstrated that EDTA functionalization allows the best retention efficiency of both heavy metals from their corresponding aqueous solution.

Optimisation of Cu+ impregnation of MOF-74 to improve CO/N2 and CO/CO2 separations.

Carbon monoxide (CO) purification from syngas impurities is a highly energy and cost intensive process. Adsorption separation using metal–organic frameworks (MOFs) is being explored as an alternative technology for CO/nitrogen (N2) and CO/carbon dioxide (CO2) separation. Currently, MOFs' uptake and selectivity levels do not justify displacement of the current commercially available technologies. Herein, we have impregnated a leading MOF candidate for CO purification, i.e. M-MOF-74 (M = Co or Ni), with Cu+ sites. Cu+ allows strong π-complexation from the 3d electrons with CO, potentially enhancing the separation performance. We have optimised the Cu loading procedure and confirmed the presence of the Cu+ sites using X-ray absorption fine structure analysis (XAFS). In situ XAFS and diffuse reflectance infrared Fourier Transform spectroscopy analyses have demonstrated Cu+–CO binding. The dynamic breakthrough measurements showed an improvement in CO/N2 and CO/CO2 separations upon Cu impregnation. This is because Cu sites do not block the MOF metal sites but rather increase the number of sites available for interactions with CO, and decrease the surface area/porosity available for adsorption of the lighter component.

Coadsorption of CO and H2 on an Iron Surface and Its Implication on the Hydrogen Embrittlement of Iron

We investigated the competitive coadsorption of carbon monoxide and hydrogen gas on an iron surface with a 110 facet using density functional theory. Our study discusses the hydrogen dissociation r...

Promotive effect of H2O on low-temperature NO reduction by CO over Pd/La0.9Ba0.1AlO3-

Abstract For future removal of NOx by catalysts, low-temperature NO reduction is desired. Results confirmed that a drastic improvement of catalytic activity by H2O on NO–CO–O2 reaction over Pd/La0.9Ba0.1AlO3-δ catalyst at the low temperature of 473 K or below. In a humidified condition, NO reaction with CO on Pd/La0.9Ba0.1AlO3-δ proceeded without being affected by competitive adsorption of NO and CO, whereas that on Pd/Al2O3 was inhibited by strong adsorption of CO on a Pd surface. From in-situ DRIFTS measurements, results showed that nitrite species on the support react with CO adsorbed onto Pd at the periphery of Pd particles and that carbonate species accumulated on Pd/La0.9Ba0.1AlO3-δ are removed rapidly in a humidified condition. Although NO reduction proceeds dominantly on the Pd surface in a dry condition, supplied steam promotes desorption of the surface carbonate to advance the reaction of nitrite with CO for de-NOx in a humidified condition. This mechanism occurs specifically on Pd/La0.9Ba0.1AlO3-δ by virtue of the lattice oxygen and oxygen vacancy on La0.9Ba0.1AlO3-δ.

Application of a co-adsorption model for the design of CIL/CIP circuits

ABSTRACTOne of the main problems in the design of carbon adsorption circuits for the processing of high silver gold ores is that the commonly used gold adsorption models are unable to replicate the frequently observed displacement of silver on carbon by gold in the first contactors of carbon-in-pulp/carbon-in-leach (CIP/CIL) trains operating with high metal loadings on carbon and high silver gold ratios.A model has been developed by Curtin University’s Gold Technology Group to simulate the competitive co-adsorption of gold and silver by activated carbon. The model utilises multi-component equilibrium isotherms and film-diffusion rate equations to describe the adsorption of gold and silver onto activated carbon. The model has been validated using laboratory and plant data.Case studies are presented to demonstrate the application of the model for the design of a greenfield project processing a gold/silver ore.

Competitive adsorption of CO and H<sub>2</sub> on strained Fe(110) surface

In this work, the competitive adsorption behavior of H<sub>2</sub> and CO on strained Fe(110) are investigated by the first-principles method based on the spin-polarized density functional theory to study the hydrogen embrittlement of steels. The results show that the most stable adsorption site for CO is top site, and the orbital of CO molecule hybridizing with Fe 3p and 4s states illustrates a strong electronic interaction between them. The adsorption energy values of CO at the four calculated adsorption sites are more negative than those of H<sub>2</sub>, which favors the binding with Fe(110) surface. The potential energy variations for CO and H<sub>2</sub> molecules close to the surface are calculated. The attractive force of the Fe(110) surface acting on CO in 1.5–3 Å is greater than that acting on H<sub>2</sub>. The pre-adsorbed CO increases the dissociation energy barrier of H<sub>2</sub> from 0.08 eV to 0.13 eV but reduces the force between H<sub>2</sub> and surface. The surface tensile strain enhances the interaction between hydrogen and Fe(110), which, however, is reduced by the compressive strain. The opposite tendency is found in the adsorption of CO. The binding strength of CO is stronger than that of H<sub>2</sub> on the strained Fe(110) surface. The difference in adsorption energy between CO and H<sub>2</sub> decreases with tensile strain increasing. The effect of surface strain and partial pressure of CO gas phase on the surface coverage ratio of H atom are also calculated quantitatively based on thermodynamics at 298 K, with the partial pressure of H<sub>2</sub> set to be 10 MPa. The surface ratio of the H atom decreases with partial pressure of CO increasing. The hydrogen coverage drops nearly to zero when the partial pressure of CO reaches a certain value. This result reveals that CO can inhibit hydrogen adsorption on Fe surface. In the case where the surface ratio of hydrogen decreases to 1%, the corresponding CO partial pressures are 105 Pa, 1.1 × 10<sup>3</sup> Pa, 2.4 × 10<sup>5</sup> Pa on –2%, 0, 2% strained Fe(110) surface, respectively. High CO partial pressure is needed to suppress the hydrogen adsorption since the binding strength of CO is close to that of H<sub>2</sub> on the expanded surface.

Novel Mn–Cu-Containing CeO2 Nanopolyhedra for the Oxidation of CO and Diesel Soot (Part II): Effect of Oxygen Concentration on the Catalytic Activity

In this work, ceria-based nanocatalysts mixed with copper and manganese were studied. All the catalysts were synthesized via the hydrothermal procedure. Four samples were prepared here denoted through the atomic ratios of the metals in the mixed oxide: Ce0.95Mn0.05, Ce0.95Cu0.05, Ce0.95Mn0.025Cu0.025 and CeO2. The samples were tested for the CO and soot oxidation reactions with different gas-phase oxygen concentrations (10, 1.0, 0.5 and 0.02 vol% O2). As a whole, the most promising catalysts for the CO oxidation reaction are the Ce0.95Cu0.05 and Ce0.95Mn0.025Cu0.025 samples. Indeed, the presence of Cu species in the solid enhances the surface redox mechanism for the CO oxidation. High vol% O2 values lead to competitive CO and O2 adsorption on the catalyst surface thus reducing the catalytic performances for binary and ternary oxides. On the other hand, the CO oxidation reaction over the CeO2 catalyst appears favored with 10 vol% O2. For the soot oxidation reaction, the most active catalyst (in terms of soot conversion %) is the CeO2 sample likely due to the unique feature of presenting well-defined and highly reactive nanocubic structures. Moreover, the presence of 10 vol% O2 in the mixture appears to be the best condition to oxidize the soot particles.

Kinetic modeling of the direct synthesis of dimethyl ether over a CuO‑ZnO‑MnO/SAPO‑18 catalyst and assessment of the CO2 conversion

A kinetic model has been established for the direct synthesis of dimethyl ether (DME) from syngas and CO2 feeds. The kinetic parameters have been determined fitting the experimental results obtained using a CuO‑ZnO‑MnO/SAPO‑18 (CZMn/S) bifunctional catalyst in a fixed‑bed isothermal reactor, under a wide range of operating conditions: 250–350 °C; 10–40 bar; CO2/CO molar ratio in the feed, between 0 and 1; H2/COX molar ratio in the feed, 3/1 and 4/1; space time, from 1.25 gcath(molC)−1, up to 20 gcath(molC)−1; time on stream, up to 30 h. The model considers the kinetic equations of the individual reactions of methanol synthesis from CO and CO2, the dehydration of methanol to DME, the water gas shift reaction (WGS) and the formation of paraffins, along with the deactivation kinetics. The attenuation of the reaction rates of methanol and paraffins synthesis has been considered by the competitive adsorption of CO2 and H2O in the metallic sites with respect to the adsorption of CO (more reactive than CO2 in the synthesis of methanol). The deactivation by coke has been quantified by a kinetic equation dependent on the concentrations of methanol and DME, and the attenuation of the deactivation by the competitive adsorption of CO2 and H2O has also been considered in this equation. The kinetic model allows predicting satisfactorily the evolution with time on stream of the concentration of the components in the reaction medium (methanol, DME, unreacted CO and CO2, and paraffins formed as by‑products). In addition, the model has been used to simulate the reactor, determining the effect of the reaction conditions on the conversion of CO2. This conversion, in contrast to the yield of DME, increases with increasing CO2 concentration in the reactor feed.

Porosity at the interface of organic matter and mineral components contribute significantly to gas adsorption on shales

Using CO2 as a shale fracturing fluid was proposed recently as an alternative to H2O fracturing, one of its advantages is enhanced recovery of CH4, which is based on the competitive adsorption of CO2 and CH4 on shales. Therefore, investigations on gas adsorption in shales are of great importance. Recent researches evidenced that organic matter (OM) in shale is the major control on its adsorption behavior, but in some cases, mineral components (MC) may also play a role. Herein, we focus on the alteration of porosity due to the presence of OM-MC interface and their influence on gas adsorption, these cannot be simply attributed to either OM or MC as frequently reported in the previous publications. In this context, OM from a shale sample was purified following reported methodology, while a universal procedure for extraction of MC was established. Further studies on the porosity and adsorption behavior were carried out on OM, MC, and shale, which were then compared with a hypothetic mixture (HM) from OM and MC bearing the same composition of shale. For the first time, we demonstrate experimentally the profound effect of porosity at the OM-MC interface on gas adsorption of shales particularly at temperatures more relevant to reservoir conditions. The current work deepened the understanding on gas adsorption of shale, and thus shed meaningful lights on related areas such as gas-in-place (GIP) estimation, CO2 sequestration in shales, and particularly the utilization of CO2 for enhanced shale gas recovery.

Experimental Study on Selective Adsorption/Desorption of CO2 and CH4 Behaviors on Shale under a High-Pressure Condition

The mechanisms of CO2 enhancing coal bed methane are investigated by many works. The competitive adsorption of CO2 and methane on coal is believed to be the dominant effect. However, whether CO2 in...

Permeance inhibition of Pd-based membranes by competitive adsorption of CO: Membrane size effects and first principles predictions

Many studies have demonstrated an inhibition of hydrogen permeance through a Pd or Pd-alloy membrane due to competitive adsorption of CO, ammonia and other species. Several corrections to Sieverts’ law were suggested to account for these effects, based on a Langmuir isotherm, but they all suffer from certain drawbacks as detailed below. We derive a new correction, based on the kinetic balances on the adsorbed layer, and on the underlying dissolved H layer from which the diffusing H atoms originate. The new correction is physically reasonable and it predicts that the permeation inhibition declines with increasing membrane size, in agreement with several suggestions in the literature. We test the new expressions against published experimental data of inhibition due to CO co-adsorption, using energetic parameters that were either estimated by DFT studies or derived from experimental data. A fair agreement is obtained, but it depends on assumptions regarding entropy effects. We also derived an approximation and adjusted its parameters. Finally we comment on the observation of inhibition due to H2S and ammonia, which represent more complex cases.

Reversible Oxygen‐Driven Nickel Oxide Structural Transition on the Nickel(1 1 1) Surface at Near‐Ambient Pressure

AbstractNiO cluster formation with strictly controlled O2 exposure on a Ni(1 1 1) surface has been investigated extensively for decades under ultra‐high vacuum (UHV) conditions. The classical model of three‐stage Ni oxidation refers to the relationship between NiO cluster evolution and the kinetics of O2 exposure; however, this information has a critical inherent limitation because of the “pressure gap” between UHV and real reaction conditions. Here, we report reversible NiO phase transitions on the Ni(1 1 1) surface at near‐ambient pressure by using scanning tunneling microscopy at room temperature. The restricted kinetic growth of NiO cluster evolution expands unexpectedly to oxide multi‐layer formation at 100 mTorr of O2. Furthermore, metastable NiO islands can be manipulated by varying the partial CO pressure of the gas mixture. The interplay between the CO and O2 molecules on the Ni(1 1 1) is correlated definitely to either surface oxide formation or competitive CO adsorption on the defect‐laden multi‐layered NiO interface.

In Situ Observation of Competitive CO and O2 Adsorption on the Pt(111) Surface Using Near-Ambient Pressure Scanning Tunneling Microscopy

We investigated the competitive coadsorption of CO and O2 molecules on a Pt model surface using a catalytic reactor integrated with a scanning tunneling microscope at elevated pressure. CO-poisoned incommensurate atom-resolved structures are observed on the terrace sites of the Pt(111) surface under gaseous mixtures of CO and O2. However, in situ surface measurements revealed that segmented local structures were influenced by the CO/O2 partial pressures in the catalytic reactor at a total pressure of a few Torr. This could be related to the expected formation of the theoretical oxygen precursor intermediates during dissociation of O2 on the surface before the chemical reaction. These findings provide microscopic insights into the early steps of the catalytic reaction pathways on the Pt surface during CO oxidation in an industrial chemical reactor.

Molecular insights into competitive adsorption of CO2/CH4 mixture in shale nanopores.

In the present study, competitive adsorption behaviour of supercritical carbon dioxide and methane binary mixture in shale organic nanopores was investigated by using grand canonical Monte Carlo (GCMC) simulations. The model was firstly validated by comparing with experimental data and a satisfactory agreement was obtained. Then the effects of temperature (298–388 K), pressure (up to 60 MPa), pore size (1–4 nm) and moisture content (0–2.4 wt%) on competitive adsorption behaviour of the binary mixture were examined and discussed in depth. It is found that the adsorption capacity of carbon dioxide in shale organic nanopores is much higher than that of methane under various conditions. The mechanism of competitive adsorption was discussed in detail. In addition, the results show that a lower temperature is favorable to both the adsorption amount and selectivity of CO2/CH4 binary mixture in shale organic nanopores. However, an appropriate CO2 injection pressure should be considered to take into account the CO2 sequestration amount and the exploitation efficiency of shale gas. As for moisture content, different influences on CO2/CH4 adsorption selectivity have been observed at low and high moisture conditions. Therefore, different simulation technologies for shale gas production and CO2 sequestration should be applied depending on the actual moisture conditions of the shale reservoirs. It is expected that the findings in this work could be helpful to estimate and enhance shale gas resource recovery and also evaluate CO2 sequestration efficiency in shale reservoirs.

Competitive Adsorption of CO2 over N2 in Asphaltene Slit Nanopores Studied by Molecular Simulation

CO2 capture and sequestration (CCS) is recognized as one of the most promising alternatives to weaken the greenhouse effect, and nanoporous materials are regarded as the promising candidates; therefore, developing a new cost-effective sorbent to achieve CCS is crucial. In this study, asphaltene-based slit nanopores were used to simulate capturing of CO2 from flue gas. The grand canonical Monte Carlo and molecular dynamics simulation methods were employed to examine the microscopic behaviors of CO2 and N2 in asphaltene slit nanopores. The isosteric heat of CO2 and N2 molecules adsorbed in asphaltene slit nanopores, the adsorption energy of a single molecule of CO2 and N2 adsorbed on the surface of asphaltene fragments, and the self-diffusion of CO2 and N2 molecules adsorbed in asphaltene slit nanopores were examined. Strong competitive adsorption of CO2 over N2 is found in a broad range of temperatures and pressures, and it was found that the temperature plays an important role on the competitive adsorptio...

Construction of Layered Double Hydroxides/Hollow Carbon Microsphere Composites and Its Applications for Mutual Removal of Pb(II) and Humic Acid from Aqueous Solutions

Development of a highly efficient material with large specific area was scientifically and technologically important for simultaneous elimination of inorganic and organic pollutants from wastewater. In this work, layered-double-hydroxides-coated (LDHs-coated) hollow carbon microsphere composites (HCMSs; LDHs/HCMSs) were fabricated using carbon spheres as templates via a hydrothermal method and were then applied for mutual removal of Pb(II) and humic acid (HA) under various experimental conditions, i.e., pH, ionic strength, contact time, addition sequences, and coexisting ions. The results indicated that the copresence of Pb(II) and HA facilitated single target pollutant [Pb(II) or HA] adsorption at pH < 8.0. The adsorbed HA was responsible for the improvement of Pb(II) adsorption, primarily as a result of the formation of HA-Pb-LDHs/HCMSs ternary complexes. Competitive adsorption of Cu(II), Co(II), Pb(II), and Ni(II) ions on LDHs/HCMSs was also investigated, and the LDHs/HCMSs had the affinity in the orde...

(Invited) Superconformal Film Growth:Impact of Additives and Deposition on Hydrophilicity

State of the art manufacturing of semiconductor devices involves electrodeposition of copper for device wiring and more recently for through-silicon-vias (TSVs). The process depends on the use of electrolyte additives that affect the local deposition rate thereby resulting in superconformal, or bottom–up “superfilling” of trenches and vias. Quantitative descriptions based on mass balance analysis of the additives and their effect on the local deposition rate have been shown to be effective for describing Damascene feature filling (CEAC, Curvature Enhanced Coverage Mechanism) and larger scale TSV filling (S_NDR, S-shaped negative differential resistance models). Despite the success of these processes much remains to be known concerning the detailed molecular nature of the competitive co-adsorption processes involved in both the suppression and acceleration of the metal deposition reaction. Accordingly, the application of in situ surface science tools such as in situ STM and SEIRAS towards a better understanding of the additive interaction will also be detailed. These studies show that the addition of Cl- to an acidified CuSO4 electrolyte displaces co-adsorbed SO4 2--water species from the Cu surface. The rapidly formed ordered halide overlayer disrupts the adjacent solvent hydrogen bond network to create a hydrophobic interface that facilitates co-adsorption of polyethers, such as poly(ethylene glycol) (PEG), polyoxamers (EPE), polyoxamines (TET), that are known to block the Cu deposition reaction by limiting access of Cu2+ aq to the underlying metal surface. When challenged by bis-(3-sodium sulfopropyl disulfide) (SPS), or mercaptopropane sulfonate (MPS), competitive disulfide/thiol adsorption leads to disruption and displacement of the polymer suppressor. The disulfide/thiol head group tethers SPS/MPS to the surface, via Cu adatoms or defects in the Cl- covered surface, while the SO3 - terminal group makes the interface hydrophilic which accounts for its anti-suppressor action. The potential dependence of competitive SPS adsorption and its dependence on the strength of polyether adsorption were measured.