Competitive Adsorption Of Water Research Articles

Correcting implicit solvation at metal/water interfaces through the incorporation of competitive water adsorption.

Conventional continuum solvation models are ubiquitous in computational catalysis, including for describing metal/water interfaces, which are relevant to both solution-phase heterogeneous catalysis and electrocatalysis. Nonetheless, we find that such continuum models qualitatively fail to describe both the adsorption free energy and conformational preference for many organic molecules at such interfaces, largely due to the failure of continuum models to incorporate the role of competitive water adsorption. We develop a simple phenomenological model that accounts for competitive water adsorption and show that the model, when used in conjunction with continuum solvation, provides a dramatic improvement in the description of both adsorption and conformational preference. The model is also extended to additionally incorporate the influence of applied potential at the electrode surface, thus facilitating computationally efficient applications to scenarios including electrocatalysis.

Effect of water on formic acid and formaldehyde decomposition on the TiO2 (110) surface

The catalytic and photocatalytic performance of TiO2 in air pollutant degradation is significantly influenced by the adsorption of water. Here, we explore the molecular mechanism of formic acid and formaldehyde decomposition and their interaction with water on the TiO2 (110) surface, employing density functional theory (DFT) calculations and reactive molecular dynamics (RMD) simulations. RMD simulations indicate that due to the competitive adsorption of water at the surface Ti site, formic acid predominantly exists in a monodentate dissociative adsorption form on the TiO2 (110) surface. Moreover, on the TiO2 (110) surface, water molecules inhibit the adsorption and dissociation of formic acid, but they facilitate that of formaldehyde, forming methanediol (*CH2OHO) and dioxymethylene (*CH2O2). DFT calculations suggest that the formation pathway of *CH2OHO or *CH2O2 is energetically favorable, but the formation of formate is difficult. This contrasts with the adsorption of formaldehyde on the anatase surface, where formate species are formed.

Multiple effects of relative humidity on heterogeneous ozonolysis of cooking organic aerosol proxies from heated peanut oil emissions

The exposure to cooking organic aerosols (COA) is closely related to people's daily lives. Despite extensive investigations into COA's model compounds like oleic acid, the intricacies of heterogeneous ozonolysis of real COA and the effects of ambient conditions like humidity remain elusive. In this work, the ozonolysis of COA proxies from heated peanut oil emissions was investigated using diffuse reflectance infrared Fourier transform (DRIFTS) spectroscopy, and proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS). We found that humidity hinders the reaction between ozone and CC double bonds due to the competitive adsorption of water and ozone on COA. Although visible light has little influence on the ozonolysis of COA in the absence of humidity, the ozonolytic CO production is significantly promoted by visible light in the presence of humidity. It may be attributed to the formation of water-derived reactive oxygen species (ROS, mainly HO•) from the photosensitization of polycyclic aromatic hydrocarbons (PAHs) in COA. We also found that humidity can enhance the depolymerization of carboxylic acid dimers and hydrolysis of intrinsic acetals in the COA. Moreover, humidity promotes the release of VOCs during both the dark and light ozonolysis of COA. This work reveals the important roles of humidity-responsive and photo-responsive components in COA during its ozonolysis, and the change in VOC release may guide the control of human VOC exposure in indoor air.

Silica-assisted Pt1/CeO2 single-atom catalyst for enhancing the catalytic combustion performance of VOCs by inducing H2O activation

Due to the competitive adsorption of water and reactants at the active sites, especially the water toxicity of platinum-based single-atom catalysts, it is of great importance to improve the low-temperature activity and the water resistance of catalysts for the catalytic combustion of benzene. In this work, it was found that constructing a SiO2 shell layer on the catalyst not only "immobilized" the Pt single atoms, but also effectively weakened the adsorption of H2O on the Pt active sites, which resulted in excellent water resistance of the Pt single-atom catalysts. The comprehensive characterization results demonstrated that the participation of water molecules in the catalytic oxidation reaction of benzene could be effectively promoted by enhancing the strong metal-support interactions (SMSI) at the core-shell interface, which would change the electronic structure of the catalyst surface. As a result, the Pt1/CeO2@SiO2-4 catalyst with a Pt-O-Si active interface exhibits good activity (T = 190 °C) as well as excellent water resistance under the wet condition (10 vol%). This project provides a promising strategy for the design of Pt-based core-shell catalysts with excellent water resistance.

Surface hydrophobicity and catalytic performance of cerium incorporated HZSM-5 zeolite for conversion of bio-ethanol

Cerium incorporated HZSM-5 (CeHZSM-5) catalyst prepared by impregnation method was tested for aqueous ethanol conversion at 200–400 °C. The CeHZSM-5 catalyst was found to be very active (21.02 %Conversion), compared to the parent HZSM-5 catalyst (9.39 %Conversion), especially at low reaction temperatures (200 °C) and when fed with high water content (80 wt% ethanol). FTIR, FT-Raman, DR-UV, NH3-TPD, IPA-TPD, DSC and contact angle techniques reveal that the incorporation of cerium species into zeolites results in the acidity and hydrophilic/hydrophobic nature. Cerium species are thought to tend to migrate into ZSM-5 channels and associate with the zeolite framework. As a result, the net electrostatic charge decreases due to the presence of tetrahedral cerium atoms. Therefore, the CeHZSM-5 exhibits a hydrophobic character, compared to the parent one. The decrease in competitive adsorption of water versus ethanol feed at the Brønsted acid site may lead to an increase in CeHZSM-5 catalyst activity.

Tailoring Hydrophobicity and Pore Environment in Physisorbents for Improved Carbon Dioxide Capture under High Humidity.

CALF-20, a Zn-triazolate-based metal-organic framework (MOF), is one of the most promising adsorbent materials for CO2 capture. However, competitive adsorption of water severely limits its performance when the relative humidity (RH) exceeds 40%, limiting the potential implementation of CALF-20 in practical settings where CO2 is saturated with moisture, such as postcombustion flue gas. In this work, three newly designed MOFs related to CALF-20, denoted as NU-220, CALF-20M-w, and CALF-20M-e that feature hydrophobic methyltriazolate linkers, are presented. Inclusion of methyl groups in the linker is proposed as a strategy to improve the uptake of CO2 in the presence of water. Notably, both CALF-20M-w and CALF-20M-e retain over 20% of their initial CO2 capture efficiency at 70% RH─a threshold at which CALF-20 shows negligible CO2 uptake. Grand canonical Monte Carlo simulations reveal that the methyl group hinders water network formation in the pores of CALF-20M-w and CALF-20M-e and enhances their CO2 selectivity over N2 in the presence of a high moisture content. Moreover, calculated radial distribution functions indicate that introducing the methyl group into the triazolate linker increases the distance between water molecules and Zn coordination bonds, offering insights into the origin of the enhanced moisture stability observed for CALF-20M-w and CALF-20M-e relative to CALF-20. Overall, this straightforward design strategy has afforded more robust sorbents that can potentially meet the challenge of effectively capturing CO2 in practical industrial applications.

The effects of water, substrate, and intermediate adsorption on the photocatalytic decomposition of air pollutants over nano-TiO2 photocatalysts.

The photocatalytic performance of nano-TiO2 photocatalysts in air pollutant degradation greatly depends on the adsorption of water, substrates, and intermediates. Especially under excessive humidity, substrate concentration, and intermediate concentration, the competitive adsorption of water, substrates, and intermediates can seriously inhibit the photocatalytic performance. In the past few years, extensive studies have been performed to investigate the influence of humidity, substrate concentration, and intermediates on the photocatalytic performance of TiO2, and significant advances have been made in the area. However, to the best of our knowledge, there is no review focusing on the effects of water, substrate, and intermediate adsorption to date. A comprehensive understanding of their mechanisms is key to overcoming the limited application of nano-TiO2 photocatalysts in the photocatalytic decomposition of air pollutants. In this review, the progress in experimental and theoretical fields, including a recent combination of photocatalytic experiments and adsorption and photocatalytic simulations by density functional theory (DFT), to explore the impact of adsorption of various reaction components on nano-TiO2 photocatalysts is comprehensively summarized. Additionally, the mechanism and broad perspective of the impact of their adsorption on the photocatalytic activity of TiO2 in air treatment are also critically discussed. Finally, several solutions are proposed to resolve the current problems related to environmental factors. In general, this review contributes a comprehensive perspective of water, substrate, and intermediate adsorption toward boosting the photocatalytic application of TiO2 nanomaterials.

Effect of different defects on the competitive adsorption of formaldehyde and water on the surface of carbon materials: Density functional theory study

The adsorption of formaldehyde by carbon materials is extremely limited and is also greatly influenced by the competitive adsorption of water. Therefore, it is of great significance to investigate the effect of different defects on the competitive adsorption of formaldehyde and water on the surface of carbon materials, and consequently the targeted modification of carbon materials to promote the adsorption of formaldehyde in air. In this study, multi-scale simulations were conducted to explore the problem of competitive adsorption of water and formaldehyde on the surface of carbon materials by quantum chemistry and molecular dynamics. IGMH, QTAIM, energy decomposition, electron transfer, and so on were used to conduct a comprehensive analysis of the problem of competitive adsorption of water and formaldehyde on the surface of carbon materials. The reasons for the formation of competitive adsorption between water and formaldehyde were firstly clarified, and then the adsorption interactions of different oxygen-containing functional groups on formaldehyde and water were investigated separately, which were found that the competitive adsorption of water and formaldehyde molecules by different types of oxygen-containing functional groups caused different results. And the introduction of intrinsic defects can promote the adsorption of formaldehyde in the presence of water competition for adsorption, which can well compensate the inhibitory effect of water on the adsorption of formaldehyde with strong polar functional groups. Finally, the results obtained from simulations were used to guide the modification experiments, and the experimental results were in accord with the simulation results. This study provides a new idea for the preparation of materials for efficient formaldehyde adsorption under certain humidity.

Tandem c-cl cleavage and oxidation over Pt/ZSM-5 catalysts for CH2Cl2 deep oxidation: Acidity – Redox synergy, rate – Limiting step, and catalyst stability

A Pt/ZSM-5-18 catalyst with a Si/Al molar ratio of 18 in the support was highly active for the oxidation of CH2Cl2, exhibiting high selectivity towards CO2 formation. The excellent performance can be attributed to its abundant surface acidity, which facilitates the C-Cl cleavage of CH2Cl2, as well as the strong oxidation ability of the Pt species that promotes the sequential oxidation of intermediates such as CH3Cl and CO. Quantitative analysis of the turnover frequencies (TOFs) further revealed that the C-Cl cleavage of CH2Cl2 is the rate-limiting step, while the oxidation of CH3Cl and CO on the Pt surface is more facile, with TOFs of 10-fold and 50-fold higher than that of the C-Cl cleavage, respectively. However, the rate-limiting step in CH3Cl oxidation is related to the oxidation step, suggesting a reactant-dependent kinetic relevance. The partial deactivation of the catalyst can be attributed to either coke deposition under dry conditions or competitive adsorption of water under wet conditions. Nonetheless, the catalyst’s stability is hardly influenced by Pt aggregation through the migration of framework Al sites in the support.

The Competitive Adsorption of Water and Methanol on a Hybrid Silica Stationary Phase in Supercritical Fluid Chromatography

This study investigates the adsorption of methanol, water, and their mixture in a hybrid silica stationary phase with supercritical carbon dioxide as a mobile phase in supercritical fluid chromatography (SFC). The adsorption isotherms of methanol and water were determined by two dynamic methods: the elution by characteristic point (ECP) method and the inverse method (IM). Both the single-component and competitive bi-Langmuir models were pre-selected for the inverse method. The initial parameters of the single-component isotherm for both methanol and water were estimated with the ECP method by fitting the experimental data to the bi-Langmuir isotherm model. Then, using the inverse method, we refined the single-component isotherm parameter values, which were then further used for determining the competitive isotherm of the methanol–water mixture. The elution profile of the (methanol–water) mixture sample was calculated by the equilibrium-dispersive (ED) model. The results indicated that there is a good agreement between the experimental band profile and the calculated band profile, which was obtained from the parameters of the competitive bi-Langmuir isotherm model, revealing a competition between methanol and water to reach the adsorption sites. Furthermore, the saturation capacity of the adsorption sites in the stationary phase decreased in the case of the mixture sample compared to those for the single-component sample.

Mechanism of attapulgite processed by calcination and grinding on hydration process and mechanical properties of cementitious materials

In this paper, the effects of attapulgite processed by two different methods, burning and grinding attapulgite (BGA) and grinding and burning attapulgite (GBA), on the macroscopic mechanical properties and microscopic hydration mechanism of cement paste were systematically studied. The application potential of these two materials in the field of cement-based materials was analyzed and evaluated. The results indicated that both BGA and GBA inhibited the hydration of cement to varying degrees at 7th day of age. Due to the competitive adsorption of water by the nanorod crystal structure of BGA and GBA, the amount of water used for cement hydration decreased, thus reducing the hydration degree of cement. The decrease of hydration product content increased the porosity and leaded to the decrease of mechanical strength. At the age of 28th days, due to the slow-release effect of the nanorod crystal structure and the pozzolanic effect, the macroscopic mechanical strength of the admixture ratio except for 20 % BGA all exceeded that of control paste. The mass generation of hydration products of the paste formed a dense micro structure and thus reduced the porosity. The structure and morphology of Calcium silicate hydrate (CSH) formed by BGA and GBA were distinctive by SEM-EDS at 28th days, because Ca/Si in CSH decreased to different degrees. In general, the performance of GBA on cement hydration kinetics and macroscopic mechanical strength was better than that of BGA at 7th and 28th day, and 20 % GBA was the optimal ratio of all mixture ratios.

Highly active alkali etching silica-modified Cu-Ce-Ti catalyst with superior water resistance for low temperature NOx reduction

In this study, Cu-Ce oxides supported on a silica modified TiO2 with post-alkali treatment (Cu-Ce/TS-am) were synthesized to enhance the catalytic activity and water resistance for low-temperature NOx reduction with ammonia. Experiment results revealed that the optimal Cu-Ce/TS-am sample possessed over 90% NOx conversion at 180–350 °C in the presence of 10 vol% water. Essentially, the formed Ti-Si strong interactions after Si addition could be responsible for that. On the one hand, the interactions increased specific surface area, total acidity and oxygen mobility, thus promoting SCR activity. On the other hand, it could enhance the hydrophobicity of the catalysts as there existed lower surface roughness, smaller particle size and enlarged mesoporous pore size after Si addition, alleviating the competitive adsorption of water with NH3. Additionally, the alkali treatment removed uncombined SiOx, which optimized the mesoporous pore structure and increased the exposure of active sites and acidic sites on the catalyst surface, further enhancing water resistance and catalytic activity. These findings could provide useful guidelines for the development of highly active SCR catalyst with well water resistance in real application.

Facile fabrication of 3D graphene hydrogel (rGH) for enhanced removal of heavy metal Cr (VI)

The reduced graphene hydrogel (rGH) was prepared by chemical reduction method, and removal performance of heavy metal Cr (VI) in static water was studied. The rGH has a three-dimensional structure and narrow pore size distribution, that the adsorption process of Cr (VI) by rGH is in accordance with Langmuir isotherm model, and the maximum adsorption capacity is 139.6 mg·g-1 .The significant adsorption capacity is mainly attributed to the fact that rGH has nano-sheet structure, and maintains the surface adsorption characteristics of graphene with rapid adsorption. The π-π action will reduce the competitive adsorption of water and increase the adsorption capacity.

Ordered mesoporous Co3O4-Al2O3 bimetal oxides for CO2 hydrogenation to synthetic natural gas: Effects of surface Al2O3 distribution

The highly ordered mesoporous structures of Co3O4-Al2O3 mixed metal oxide, prepared by using a hard template of the mesoporous KIT-6, revealed a higher catalytic activity and stability for CO2 hydrogenation to synthetic methane at an optimal surface Al content with ∼6 wt% (m-CoAl(1)). The higher CO2 conversion (42.5%) and CH4 selectivity (96.7%) were attributed to the adjusted surface hydrophobicity with optimal amount of spinel CoAl2O4 phases, where the CoAl2O4 phases mainly acted as structural stabilizing components in the ordered mesoporous Co3O4-Al2O3 matrices by suppressing the aggregations of Co3O4 nanoparticles as well as by generating more hydrophobic surfaces. At an optimal surface Al2O3 content (m-CoAl(1)), the stronger interactions of Co3O4-Al2O3 were selectively formed with the help of an optimal amount of the spinel CoAl2O4 phases, which further enhanced the surface hydrophobicity and oxygen vacant sites to effectively suppress competitive adsorption of water formed by CO2 hydrogenation.

Fluorinated metal–organic frameworks for enhanced stability and iodine adsorption selectivity under humid conditions

The selective removal of radioactive iodine from off-gases of reprocessing plants with high humidity is crucial for environmental security, and the metal–organic framework (MOF)-based porous material is considered as one of the promising adsorbents. However, MOFs usually suffer from low structural stability and the competitive adsorption of water. Herein, fluorinated groups are introduced into MOFs to improve the iodine adsorption performance under humid conditions. Two different strategies, the ligand exchange and direct synthesis, were employed to construct fluorinated Zr-based PCN-222 and UiO-66, respectively. Both the two fluorinated MOFs exhibit enhanced structural stability when interacting with iodine guests, and thus the iodine adsorption capacity is improved due to the more stable pore structure. Besides, after fluorination, the iodine adsorption selectivity is also enhanced in the presence of high humidity. Particularly, UiO-66-F exhibits an iodine adsorption capacity of 0.93 g/g under wet iodine vapor with 18% RH at 80 ℃, close to that in the dry iodine vapor. DFT calculation and XPS analysis suggest there is no F…I halogen bonding interaction between fluorinated groups and trapped iodine, and the Zr nodes transfer negative charges to iodine via O-containing groups in the Zr nodes.

Perspectives of Gas Adsorption and Storage in Kerogens and Shales

Shale gas from unconventional resources will contribute to meeting the energy demand during the transition to a net-zero carbon economy. In this minireview, the current status of understanding methane adsorption on kerogens and shales is discussed in relation to methane storage capacity. Standard subcritical adsorption studies provide characterization data (micropore volumes, total pore volumes, surface areas, and pore size distributions) for the porous structures of shales and kerogens. However, supercritical methane adsorption measurements under simulated geological conditions are necessary to assess realistic methane adsorption storage capacities. Supercritical methane adsorption on shale and shale components (kerogens and clays) under high pressure and temperature conditions that simulated geological conditions is compared. Kerogen structural characteristics are discussed in relation to supercritical methane isotherms and isobars. The contribution of adsorbed methane gas relative to “free” or compressed gas to the total gas stored in shale is considered. The importance of kerogens in both storage of the adsorbed phase and as the source of methane is highlighted, and the areas where knowledge and understanding are deficient are identified, in particular, the relationship of kerogen type and maturity with supercritical methane adsorption under simulated geological conditions. The competitive adsorption of water on methane capacity is also an area where more detailed studies are necessary. These are challenges to address gaps in the current knowledge and understanding, which require future research.

Improving the stability of La-exchanged zeolite Y catalysts in the vapor-phase isomerization of endo-tetrahydrodicyclopentadiene by co-feeding steam

• La 3+ exchanged zeolite Y is more effective than HY catalyst for isomerizing endo-THDCPD to its exo isomer in vapor phase. • LaY catalyst has more Brönsted acidity and more moderate acid sites than HY catalyst. • Deactivated LaY catalyst could be completely recovered after calcination in air. • Improved stability of LaY catalyst was observed in the presence of a small amount of steam. The activities of La-exchanged zeolite Y (LaNaY) catalysts were investigated and compared with that of HNaY catalyst for the vapor-phase isomerization of endo-tetrahydrodicyclopentadiene (endo-THDCPD) to exo-THDCPD. HNaY and LaNaY catalysts were characterized by means of X-ray diffraction (XRD), nitrogen adsorption, NH 3 -TPD, pyridine-adsorbed Fourier Transformation Infrared Spectroscopy (FTIR). The LaNaY catalysts with La loading of 2-5 wt% showed better catalytic performance than the HNaY catalyst. All catalysts deactivated gradually with number of run. The activity of the deactivated LaNaY catalyst could be completely recovered after calcination in air for 4 h at 550 °C. The effect of steam co-feeding on the stability of the LaNaY catalyst was investigated. The results show that the stability of the LaNaY catalyst was improved by co-feeding steam compared to those in the absence of steam, which was attributed to the replacement of adamantane adsorbed on the active sites of the catalyst by competitive adsorption of water. In the presence of 5 % steam, the effect of temperature on the stability of the LaNaY catalyst was also studied. A high and stable activity was observed at 185 °C.

Competitive adsorption of water and collector molecules on sulfide mineral surfaces

To study the influence of water molecules on the adsorption behavior of flotation reagents at the solid-liquid interface system, a model of the molecule interaction between sulfide minerals and flotation reagents at the solid–liquid interface system was established based on the density functional theory (DFT). The results of the calculations show that the surfaces of the galena and pyrite are hydrophobic after the adsorption of the xanthate molecules. In addition, using molecular dynamics simulation can positively explain the competitive adsorption behavior occurring between water molecules and xanthate molecules. This study provides some theoretical basis and guidance for the study of the interaction mechanism between flotation reagents and the surface of sulfide minerals under the solid–liquid interface system.

Understanding the complementarities of surface-enhanced infrared and Raman spectroscopies in CO adsorption and electrochemical reduction

In situ/operando surface enhanced infrared and Raman spectroscopies are widely employed in electrocatalysis research to extract mechanistic information and establish structure-activity relations. However, these two spectroscopic techniques are more frequently employed in isolation than in combination, owing to the assumption that they provide largely overlapping information regarding reaction intermediates. Here we show that surface enhanced infrared and Raman spectroscopies tend to probe different subpopulations of adsorbates on weakly adsorbing surfaces while providing similar information on strongly binding surfaces by conducting both techniques on the same electrode surfaces, i.e., platinum, palladium, gold and oxide-derived copper, in tandem. Complementary density functional theory computations confirm that the infrared and Raman intensities do not necessarily track each other when carbon monoxide is adsorbed on different sites, given the lack of scaling between the derivatives of the dipole moment and the polarizability. Through a comparison of adsorbed carbon monoxide and water adsorption energies, we suggest that differences in the infrared vs. Raman responses amongst metal surfaces could stem from the competitive adsorption of water on weak binding metals. We further determined that only copper sites capable of adsorbing carbon monoxide in an atop configuration visible to the surface enhanced infrared spectroscopy are active in the electrochemical carbon monoxide reduction reaction.

Reduced graphene oxide as an effective promoter to the layered manganese oxide-supported Ag catalysts for the oxidation of ethyl acetate and carbon monoxide

The layered manganese oxide (δ-MnO2)-supported reduced graphene oxide (rGO)-promoted silver catalysts (xAg− yrGO/δ-MnO2; x and y are the Ag and rGO contents (wt%), respectively) were prepared via a polyvinyl alcohol-protected reduction route. Physicochemical properties of these materials were determined using the numerous techniques, and their catalytic activities were evaluated for the oxidation of CO and ethyl acetate. It is found that the loading of rGO as an electron transfer promoter could significantly strengthen the metal−support interaction (SMSI) between Ag and δ-MnO2 and increase specific surface area of the sample, hence improving catalytic performance of the sample. Activity evaluation reveals that 1Ag− 1.0rGO/δ-MnO2 showed the best catalytic activity and the lowest apparent activation energy (Ea), giving a T90% of 140 °C and an Ea of 42.7 kJ/mol for CO oxidation, and a T90% of 160 °C and an Ea of 39.8 kJ/mol for ethyl acetate oxidation at space velocity (SV) = 60,000 mL/(g h). The good performance of 1Ag− 1.0rGO/δ-MnO2 was associated with its high Mn3+/Mn4+ or Oads/Olatt molar ratio, good low-temperature reducibility, and strong SMSI between Ag and δ-MnO2. The in situ DRIFTS characterization demonstrates that the carbonate and acetate species were the main intermediate products in CO and ethyl acetate oxidation over 1Ag− 1.0rGO/δ-MnO2, respectively. The 1Ag− 1.0rGO/δ-MnO2 sample was not significantly altered in physicochemical property after 55 h of stability test, but its activity decreased in the presence of water vapor, especially such an effect on ethyl acetate oxidation was more obvious, which was possibly due to the competitive adsorption of water and reactants on the catalyst surface.