Interaction Of H2O Research Articles

The Role of Sulfate in Cation Exchange Reactions: Applications to Clay–Brine Interactions on Mars

Phyllosilicates on Mars record a complex history of aqueous activity, including at Gale crater and Meridiani Planum, where stratigraphic differences in clay mineralogy have been recorded in outcrops that also contain calcium sulfate minerals. Thus, characterizing associations between phyllosilicates and calcium sulfates may provide constraints that are useful for constraining the geochemical environments that formed these outcrops. Previous studies have documented calcium sulfate precipitation as a result of clay–salt–atmospheric H2O interactions, but the compositions of brines throughout Mars’ history would have depended on the volume of water available on the Martian surface. Variations in brine composition influence the type and extent of reactions between the brines and the minerals that they come in contact with. To better understand how clay–brine interactions affected near-surface mineral assemblages on Mars, we performed two sets of experiments. The first set of experiments examined the effect of differing total brine concentrations and the second set explored variations in Na+ and SO4 2− concentrations independently. The results of this study show that gypsum readily forms due to cation exchange between montmorillonite and Na2SO4 brines of any concentration, but only near-saturated MgSO4 brines produced gypsum, and these also produced higher quantities of epsomite. Additionally, we found that the amount of gypsum produced from clay–Na2SO4 brine reactions is more strongly influenced by SO4 2− than Na+ or Cl− concentrations. Understanding how rapidly gypsum forms as a product of clay–brine interactions, as well as the influence of SO4 2− on cation exchange, will aid interpretations of sediments and environments that are observed on Mars.

Reversible aqueous aluminum metal batteries enabled by a water-in-salt electrolyte

Aluminum (Al), the most abundant metallic element on the earth crust, has been reckoned as a promising battery material for its the highest theoretical volume capacity (8046 mAh cm−3). Being rechargeable in ionic liquid electrolytes, however, the Al anode and battery case suffer from corrosion. On the other hand, Al is irreversible in aqueous electrolyte with severe hydrogen evolution reaction. Here, we demonstrate a water-in-salt aluminum ion electrolyte (WISE) based on Al and lithium salts to tackle the above challenges. In the WISE system, water molecules can be confined within the Li+ solvation structures. This diminished Al3+-H2O interaction essentially eliminates the hydrolysis effect, effectively protecting Al anode from corrosion. Therefore, long-term Al plating/stripping can be realized. Furthermore, two types of high-performance full batteries have been demonstrated using copper hexacyanoferrate (CuHCF, a Prussian Blue Analogues) and LiNi0.8Co0.1Mn0.1O2 (NCM) as cathodes. The reversibility of Al anode laid the foundation for low cost rechargeable batteries suffering for large-scale energy storage.Broader context: Al batteries are expected to become a safe and sustainable alternative to lithium batteries. For decades, chase for a feasible Al secondary battery has not been successful. The key challenge is to find suitable cathode and electrolyte materials, together with which Al anode battery can function reversibly. Currently, fatal drawbacks have impeded the practical application of Al metal batteries (AMBs), such as sustained corrosion of Al anode and battery case in ionic liquid electrolytes, irreversibility issues as well as severe hydrogen evolution reaction during cycling in aqueous electrolyte. Therefore, electrolyte and their electrochemical kinetics play a vital role in the performance and environmental operating limitations of high-energy Al metal batteries. In this work, we demonstrate a nearly neutral Al ion water-in-salt electrolyte (WISE) to tackle the above challenges. The WISE shows excellent stability in the open atmosphere. The distinct solvation-sheath structure of Al3+ in the WISE system would protect Al metal anodes from corrosion and eliminate hydrogen evolution reaction effectively, further promoting the reversibility of Al metal anodes with dendrite-free morphology. Moreover, such a WISE exhibits superior compatibility with LiNi0.3Co0.3Mn0.3O2 (NCM) and copper hexacyanoferrate (CuHCF) cathodes and long-term stabilities with high coulombic efficiency (CE) can be attained for full batteries with the WISE. The approach in this study can furnish an opportunity to develop reversible AMBs and lay the foundation for other potential multivalent-metal-based secondary batteries suffering from interface passivation and poor reversibility, which suggest the promise of multivalent metal batteries and their applications in large-scale energy storage.

Pseudo-Pt Monolayer for Robust Hydrogen Oxidation.

Heteroepitaxial core-shell structure is conducive to combining the advantages of the epilayer and the substrate, creating a novel multifunctionality for catalysis application. Herein, we report a pseudomorphic-Pt atomic layer (PmPt) epitaxially growing on an IrPd-core matrix (PmPt@IrPd/C) as an efficient and stable catalyst for alkaline hydrogen oxidation reaction that exhibits ∼29.2 times more mass activity enhancement than that of benchmark Pt/C. The PmPt@IrPd/C catalyst also gives rise to ∼25.0 times more enhancement than Pt/C during a 50,000-cycle accelerated stability test. This robust stability originates from the resistance to carbon corrosion owing to the stronger H2O interaction instead of carbon oxide (COx) poison species, and the modulated hydroxyl (OH*) adsorption could inhibit the OH* species from shuffling the surface Pt atoms away from the substrate. Moreover, the anion-exchange membrane fuel cells assembled by PmPt@IrPd/C with an ultralow Pt loading of 0.009 mgPt cm-2 in the anode can deliver a power density of 1.27 W cm-2.

Assembly Rules and Dehydration Mechanism of an Unconventional Hydrate: On the Complexity of the Hydrates of Creatine Phosphate Sodium

Unconventional hydrates with differently bound water molecules and related mazy intermolecular interaction networks need systematic investigation. The assembly rules, interaction analysis, and dehydration behavior can be dramatically more complicated when compared with those of common hydrates. In this work, creatine phosphate sodium (CPS) was selected as a model compound representing unconventional hydrates. The packing mode and the role of water molecules related to the dehydration mechanism were explored by the combination of experimental (diffraction, thermal, microscopy) and quantum chemistry computational (interplay visualization, binding energy calculation) methods. It was observed that in the structure of CPS heptahydrate and heminonahydrate, channel, isolated-site, and ion-associated water molecules exist simultaneously, constructing the framework via the coordination bond and hydrogen bond. The binding energy of some ion-coordinated water molecules is lower than that of hydrogen-bonded ones while that of some isolated-site water molecules is lower when compared with that of channel ones, which is counterintuitive. Moreover, the diverse types and locations of water molecules, complicated H2O···H2O interactions, and the trade-off between CPS···H2O and H2O···H2O lead to multistage, variable, and binding-energy-independent dehydration behavior. This work sheds light on the novel structure and variable dehydration mechanism of complicated hydrate systems and inspires the particularity and further investigation of unconventional hydrates.

Insight into the Molecular Structure, Interaction, and Dynamics of Aqueous Reline Deep Eutectic Solvent: A Nuclear Magnetic Resonance Investigation

Reline, which is composed of choline chloride (ChCl) and urea, is the first and most widely used deep eutectic solvent (DES) described by Abbot and co-workers. Due to the hygroscopic feature, traces of water are unavoidable, which significantly affect the physicochemical properties of reline. At present, the local structure of molecules and the impact from the presence of water are still the most significant questions in this field. Herein, reline and six aqueous dilutions with a controlled amount of water (from 3.2 to 50.0 wt %) were studied mainly by using a combination of nuclear magnetic resonance (NMR) techniques. According to 1D 35Cl NMR, 1D 15N NMR, and 2D 1H-15Cl heteronuclear Overhauser effect spectroscopy, we probed the interactions of urea···Cl- and Ch+···Cl- in pure reline, which gradually dissociated in the presence of water. Moreover, it was revealed that the dissociation rate altered when the water content reached 9.0 wt %, which is ascribed to the higher preference of hydration for Cl- ion compared to other species in the system. Furthermore, selected cross peaks in 1H-1H correlation spectroscopy spectra were analyzed. Accordingly, an enhanced correlation was observed for urea···Ch+ at a lower water fraction within 9.0 wt %. When the water content increased to 24.9 wt %, the water solvation of Ch+ and urea was also observed in COSY spectra. The interaction of H2O···Ch+ got continuously stronger when the water content increased from 24.9 to 50.0 wt %, while H2O···urea got enhanced when the water content reached 33.3 wt % and then diminished gradually from 33.3 to 50.0 wt %. 1H-1H nuclear Overhauser effect spectroscopy and 1H-1H rotating frame Overhauser effect spectroscopy experiments were also conducted for dynamics investigation. The τc value for the species in 9.0 wt % aqueous reline is very close to τccrit of 0.44 ns. For pure reline and the aqueous reline with a water fraction of less than 9.0 wt %, the τc value of the species is longer than 0.44 ns, while for the sample with water of 24.9 wt %, the τc value is much shorter than 0.44 ns. Based on our NMR study, we revealed that with the water amount increasing from 0 to 50.0 wt %, the species involved in the system behaved as the large molecules or molecules in viscous liquids transiting to the medium-sized molecules in nonviscous liquids and finally to small molecules in nonviscous liquids.

Interactions of H2O and O2 with char during gasification in mixed atmosphere analyzed by isotope tracer method and in-situ DRIFTS

The interactions of char with H2O and O2 were important for describing the synergistic mechanism of char gasification in H2O/O2 atmosphere. The gases produced during gasification in specific atmospheres were tracked by isotope-labeled oxygen tracing experiment. The interactions of H2O with char and O2 with char during gasification in H2O and O2 atmospheres were separately studied. This helped to explore the interactions between H2O and char and O2 and char during the gasification in mixed-gas atmosphere. It was found that H2O inhibited oxidation of char during gasification, whereas O2 promoted the char-H2O reaction in mixed atmosphere. The overall gasification reactivity in mixed-gas atmosphere was determined by superimposing the effects of O2 on char-H2O reactions and the effects of H2O on O2-char reactions. This could also explain the reason for the influence of H2O on the overall changes in reactivity, based on O2 concentration. The interactive mechanisms during char gasification with H2O and O2 atmospheres were investigated by in-situ DRIFTS experiment and molecular dynamics simulation. In the H2O/O2 atmosphere, H2O was more likely to promote the curling of char structure. The free H radicals obtained in the decomposition of H2O molecules consumed the active sites of reaction between char and O2 and decreased its reactivity. Oxygen could inhibit the curling of the char structure caused due to water and promote the formation of OH radicals. This in turn, promoted the cracking of aromatic rings, increased the number of sites for reaction between char and H2O, and improved the gasification of char in H2O. In case of mixed-gas atmosphere, the interactions between isotope decoupled single reactions could provide new understanding.

Density functional investigation of the interaction of H2O with spinel Li1-xMn2O4 surfaces: Implications for aqueous Li-ion batteries

Aqueous lithium-ion batteries are receiving a lot of attention as large-scale energy storage technology owing to their low-cost, environmentally friendly, and safe behavior in comparison to commercial organic Li-ion batteries. However, aqueous batteries suffer fast degradation due to the interaction of water with electrodes. The O loss has often been claimed to deteriorate the electrode materials and the voltage window accessible for the cathode and anode is limited by aqueous electrolyte decomposition through O2 evolution at the cathode and H2 evolution at the anode. In this work, we use density functional theory simulations to unveil the behavior of spinel Li1-xMn2O4 as cathode material for aqueous Li-ion batteries exploring the Li1-xMn2O4 electrode deterioration at the surface level. The surface stability, O vacancy formation, interaction with water, and oxygen evolution reaction have been investigated at different Li concentrations, suggesting that a partially lithiated (011) surface can produce O2 at low overpotential, and (001) termination can favor the presence of O and OOH intermediates anchored to the surface at 1.23 V, without generating O2. Our work reveals the pros and cons of this material as a cathode for aqueous electrolytes and the importance of surface termination.

Stability of van der Waals FePX3 materials (X: S, Se) for water-splitting applications

The interaction of high-quality transition metal trichalcogenides (TMTs) single crystals FePX3 (X: S, Se) with water molecules is studied using near-edge x-ray absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS) in a wide range of temperature and partial pressure of H2O. The physisorption nature of interaction between H2O and FePX3 is found at low temperatures and relatively small concentrations of water molecules, that is supported by the DFT results. When temperature of the FePX3 samples and partial pressure of H2O are increased, the interaction at the interface is defined by two competing processes—adsorption of molecules at high partial pressure of H2O and desorption of molecules due to the increased surface mobility and physisorption nature of interaction. Our intensive XPS/NEXAFS experiments accompanied by DFT calculations bring new understanding on the interaction of H2O with surface of a new class of 2D materials, TMTs, pointing to their stability and reactivity, that is important for further applications in different areas, like sensing and catalysis.

Physicochemical and acoustic characterization of binary mixtures of tetraalkylammonium bromide: PEG based DES and water

In modern green chemistry, Deep eutectic solvents (DESs) have gain appreciable recognition as an analogues of ionic liquids (ILs) due to inexpensive and easy to handle preparation method. DESs exhibit similar physiochemical properties to ILs and considered as a suitable alternative to volatile organic solvents. In present study, DESs were formulated by complexing HBA: Tetraethylammonium bromide and Tetrapropylammonium bromide and HBD: Polyethylene glycol of average molecular weight (200/400/600) in 1:2 M ratio. The densities (ρ), speeds of sound (u) of pure DESs and their binary mixtures with H2O were collected as a function of DES concentration and temperature. The excess molar properties: VmE and Ks,mE were calculated using these data and fitted to the Redlich-Kister equation to estimate standard deviation between the experimental and calculated values of excess molar properties. The trends of variation in calculated values of VmE and Ks,mE were interpreted in light of temperature and DES: H2O interactions occurring within the binary mixtures. The PFPT (Prigogine-Flory-Patterson Theory) and ERAS (Extended Real Associated Solution Model) were applied to evaluate the validity of theories to predict VmE for presently studied binary mixtures.

Nonlinear response and charge microtransfer between 1D/2D/3D-Ag nanodimers and H2O interactions with external fields

The properties of nano-plasmon materials are closely related to problems involving nanoscale systems. Benefitting from their spatial profile, surface plasmons (SPs) can dramatically enhance various external field–matter interactions. Here, we construct three different dimensions of silver atom dimers (1D-Ag6-Ag6, 2D-Ag6-Ag6 and 3D-Ag6-Ag6), bound to a water molecule (H2O) as the research system, using interacting external fields to interact. The results reveal that the nonlinear optics of Ag6-Ag6 are modulated (broken) by H2O, an effect directly related to the spatial dimension of the Ag6-Ag6 system. The charge micro-transfer process we analyzed at the atomic level provides a reasonable explanation for this phenomenon. Surprisingly, the 3D-Ag6-Ag6 system has application prospects as a photo-hydrolysis material, due to the outstanding SPs. We discuss nonlinear phenomena, microprocess and practical applications, with the goal to deliver guidelines for designing future highly adjustable plasmonic devices and technologies.

N-doped carbon-modified palladium catalysts with superior water resistant performance for the oxidative removal of toxic aromatics

The supported palladium catalysts perform well in the oxidative removal of hazardous aromatic hydrocarbons. However, water vapor can seriously deactivate the catalysts especially in the low-temperature regime. Hence, improving moisture resistance of the Pd-based catalysts is full of challenge in the removal of aromatics. Herein, we report a new type of Pd@NC/BN catalysts featured with nitrogen-doped carbon layers modified Pd supported on hexagonal boron nitride (h-BN), and the relationship between structure and water resistance of the catalysts. The results show that in the presence of 10 vol% H2O in the feedstock, the Pd@NC/BN catalyst could effectively oxidize o-xylene (with an almost 87% removal efficiency), whereas o-xylene conversion declined from 69% to 20% over the conventional Pd/Al2O3 at a reaction temperature of 210 °C and a space velocity of 40,000 mL/(g h). The adsorption of H2O was significantly inhibited on the nitrogen-doped carbon layers due to the hydrophobic nature. Meanwhile, the oxygen species active for o-xylene oxidation were not only from the adsorbed gas-phase oxygen but also from the new active oxygen (*OOH and *OH) species that were generated via the interaction of O2 and H2O in the presence of water in the feedstock. It is concluded that the reactive oxygen species that accelerated the activation and cleavage of C−H bonds significantly facilitated the conversion of key intermediate species (from benzaldehyde to benzoic acid), thus playing a decisive role in o-xylene oxidation. The present work provides a direction for developing the superior water resistance catalysts with hydrophobic nature and good water activation ability in the oxidative removal of volatile organic compounds.

Investigating the Effects of H2O Interaction with Rainscreen Façade ACMs During Fire Exposure

Preliminary investigations into adverse reactions between aluminum alloy sheets, used as facings for aluminum composite material rainscreen panels, and water vapor (2Al + 3H2O −> Al2O3 + 3H2) contributing to high-rise façade fire events are reported. Panels containing a PE blend (70% polyethylene 30% calcium carbonate) core were characterised and subsequently exposed to a surface irradiance of 50 kW/m2 using a cone calorimeter, in modified ISO 5660:1/ASTM 1354 procedures, involving water spray. Inverse modeling techniques were applied to determine the effects of water spray on the samples’ combustion parameters. From the current study, evidence for the liberation of diatomic hydrogen (H2) contributing to peak heat release rate during combustion was not found. Observed thermal shock and subsequent degradation led to a greater surface area exposure of combustible inner core material, contributing to an increase for both peak heat release rate (from 393 kW/m2 to 1040 kW/m2) and total energy release (97 MJ/m2 to 117 MJ/m2). Findings suggest no significant increase in the combustibility of aluminum composite panels arises through reduction–oxidation reactions between aluminum-water at 50 kW/m2 irradiance. However, thermomechanical processes, brought upon by environmental conditions and external intervention, may affect the dynamic combustion behavior of aluminum composite panels.

Kinetic and Thermodynamic Factors Influencing Palladium Nanoparticle Redispersion into Mononuclear Pd(II) Cations in Zeolite Supports

Palladium cations and nanoparticles supported on oxides and zeolites are used as catalysts and adsorbents for a wide range of chemical reactions of practical importance, with various and distinct active site requirements. Consequently, sintering and redispersion processes that interconvert site-isolated Pd cations and agglomerated nanoparticles underpin catalyst activation and deactivation phenomena, yet the influence of Pd nanoparticle size distribution and gas conditions on the thermodynamic and kinetic factors influencing such interconversion is imprecisely understood. Here, we prepare Pd nanoparticles of different particle size and distribution (normal, log–normal) supported on high-symmetry crystalline zeolites to access well-defined materials whose Pd site distributions can be quantitatively characterized by experiments and modeled accurately by theory. Ab initio thermodynamic modeling and isothermal (593–973 K) wet and dry air treatments of Pd-zeolites reveal that the widely observed deactivation in low-temperature hydrous environments reflects site interconversion thermodynamics that favor the agglomeration of isolated Pd cations into nanoparticles. Under high-temperature anhydrous conditions, experimental kinetic measurements and kinetic Monte Carlo simulations evince the preeminence of kinetic factors on Pd nanoparticle redispersion into cations, which proceeds at rates that are strongly influenced by the initial Pd particle size distribution and via a substrate diffusion-mediated Ostwald ripening process whereby Pd monomers are captured in an atom trapping process at anionic exchange sites (framework Al) in the zeolite support. These findings resolve longstanding questions regarding the roles of H2O and support interactions in Pd redispersion processes and identify strategies to enhance or suppress Pd site interconversion by modifying oxide supports and gas conditions.

First-Principles Study on the Interaction of H2O and Interface Defects in A-SiO2/Si(100)

The defects contained in amorphous SiO2/Si (a-SiO2/Si) interface have a considerable impact on the efficiency and stability of the device. Since the device is exposed to the atmospheric environmental conditions chronically, its performance will be limited by water diffusion and penetration. Here, we simulated the interaction of H2O and interface defects in a-SiO2/Si(100) by using the first-principles method. Our results suggest that H2O penetrated into Pb0 defect is more inclined to interact with the network in the form of silanol (Si-OH) group, while H2O incorporated into Pb1 defect is more likely to remain intact, which can be attributed to the location of Pb1 defect closer to the interface than that of Pb0 defect. Our research provides a powerful theoretical guidance for the interaction of H2O and interface defects in a-SiO2/Si(100).

A Database of Solution Additives Promoting Mg2+ Dehydration and the Onset of MgCO3 Nucleation.

Formed via aqueous carbonation of Mg2+ ions, the crystallization of magnesite (MgCO3) is a promising route to carbon capture and reuse, albeit limited by the slow precipitation of MgCO3. Although magnesite is naturally abundant, forming at low temperature conditions, its industrial production is an energy-intensive process due to the temperatures required to prevent the formation of hydrated phases. The principal difficulty in aqueous conditions arises from the very strong Mg2+···H2O interaction, with high barriers to Mg2+ dehydration. Using atomistic simulations, we have investigated the influence of 30 additive anions (Xn–, n = 1–3), ranging from simple halides to more complex molecules, on the first two steps of MgCO3 aggregation from solution, as follows: Mg2+ dehydration and subsequent prenucleative Mg2+···CO32– pairing. We have computed the thermodynamic stabilities of solvent shared ion pairs (Mg2+···H2O···Xn–) and contact ion pairs (Mg2+···Xn–) to reveal the propensity of solution additives to inhibit or promote Mg2+···CO32– formation. We have determined the stabilization of undercoordinated hydrated Mg2+ states with a vacant coordination site to which CO32– can bind, subsequently initiating MgCO3 nucleation or Mg2+ incorporation into the crystal lattice. Extensive molecular dynamics simulations of electrolyte solutions containing Na2CO3 with different sources of Mg2+ (i.e., MgCl2, MgSO4, and Mg(CH3COO)2) further show that the degree of dehydration of Mg2+ and the structure of prenucleation MgCO3 clusters change depending on the counterion identity. Through a fundamental understanding of the role of solution additives in the mechanism of Mg2+ dehydration, our results help to rationalize previously reported experimental observation of the effect of solvation environments on the growth of magnesite. This understanding may contribute to identifying the solution composition and conditions that could promote the low-temperature CO2 conversion into MgCO3 at industrially relevant scales.

Exploring Mechanisms of Hydration and Carbonation of MgO and Mg(OH)2 in Reactive Magnesium Oxide-Based Cements.

Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in carbon capture processes. However, knowledge on the driving forces that control the degree of carbonation and hydration and rate of reactions in this system remains limited. In this work, density functional theory-based simulations are used to investigate the physical nature of the reactions taking place during the fabrication of RMCs under ambient conditions. Parametric indicators such as adsorption energies, charge transfer, electron localization function, adsorption/dissociation energy barriers, and the mechanisms of interaction of H2O and CO2 molecules with MgO and brucite (Mg(OH)2) clusters are considered. The following hydration and carbonation interactions relevant to RMCs are evaluated: (i) carbonation of MgO, (ii) hydration of MgO, carbonation of hydrated MgO, (iii) carbonation of Mg(OH)2, (iv) hydration of Mg(OH)2, and (v) hydration of carbonated Mg(OH)2. A comparison of the energy barriers and reaction pathways of these mechanisms shows that the carbonation of MgO is hindered by the presence of H2O molecules, while the carbonation of Mg(OH)2 is hindered by the formation of initial carbonate and hydrate layers as well as presence of excessed H2O molecules. To compare these finding to bulk mineral surfaces, the interactions of the CO2 and H2O molecules with the MgO(001) and Mg(OH)2 (001) surfaces are studied. Therefore, this work presents deep insights into the physical nature of the reactions and the mechanisms involved in hydrated magnesium carbonates production that can be beneficial for its development.

The interaction of H2O, O2 and H2O + O2 molecules with g-C3N4 surface:A first-principle study

The interactions between H2O, O2, H2O + O2 and graphene carbon nitride (g-C3N4) surface were investigated by using first-principle method. The results indicated that the N atoms near the bridge sites and vacancies for g-C3N4 surface have high activity, which can promote the dissociation of water molecules and form hydrogen bonds after water and oxygen adsorption. The H2O and O2 molecules are not dissociated for only H2O or O2 molecules adsorption on g-C3N4 surface, and the hydrogen bonds are formed after H2O molecule adsorption. Two oxygen atoms of O2 molecule are bonded to carbon and nitrogen atoms of g-C3N4 surface respectively after O2 adsorption. There are two stable configurations for H2O + O2 co-adsorption on g-C3N4 surface (MA and MC), and their adsorption energies are −57.35 kJ/mol, −61.10 kJ/mol, respectively. For the MA, two oxygen atoms of O2 molecule are bonded to C and N atoms of g-C3N4 surface, respectively, and one hydrogen bond is formed between H2O and O2 molecules. As for the MC, three hydrogen bonds are formed in the interface of H2O + O2 and g-C3N4 surface. H2O molecule is dissociated, and O2 molecule turns to superoxide radical by gaining electrons. The formation of superoxide radical contributes to the degradation of organic pollutants for g-C3N4.

In situ NAP-XPS study of CO2 and H2O adsorption on cerium oxide thin films

Insights of CO2 and H2O activation on cerium oxide based catalysts are of great interest to many important catalytic processes, which are widely studied in model systems under ultrahigh vacuum conditions. Here, in situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to study CO2 and H2O adsorption on fully oxidized CeO2 and partially reduced CeO2−x surfaces. It is found that CO2 only weakly interacts with the stoichiometric CeO2 but strongly adsorbs on partially reduced CeO2−x surfaces with surface carbonate formation. H2O dissociatively adsorbs reversely on the CeO2 surface with H2O exposure pressure above 1 × 10−3 mbar, while H2O strongly dissociates on the partially reduced CeO2−x surfaces. The surface dissociated OH and H species are stable on the CeO2−x surface up to 600 K. Both CO2 and H2O adsorption cause clear reoxidation of partially reduced CeO2−x. This study provides new insights into CO2 and H2O interaction with cerium oxide surfaces at near ambient pressure conditions.

Hydroxylation of Platinum Surface Oxides Induced by Water Vapor.

With its high stability and well-tuned binding strength for adsorbates, platinum is an excellent catalyst for a wide range of reactions. In applications like car exhaust purification, the oxidation of hydrocarbons, and fuel cells, platinum is exposed to highly oxidizing conditions, which often leads to the formation of surface oxides. To reveal the structure of these surface oxides, the oxidation of Pt in O2 has been widely studied. However, in most applications, H2O is also an important or even dominant part of the reaction mixture. Here, we investigate the interaction of H2O with Pt surface oxides using near-ambient-pressure X-ray photoelectron spectroscopy. We find that reversible hydroxylation readily occurs in H2O/O2 mixtures. Using time-resolved measurements, we show that O–OH exchange occurs on a time scale of seconds.

H2O adsorption and O-H breaking on Co5M (M = Co, Y-Ag) clusters: A DFT study

Interactions of H2O and metal clusters are of fundamental interest for several catalytic reactions. The adsorption and dissociation of H2O on Co5M clusters (M = Co, Y-Ag) were investigated with the density functional theory (DFT) method. The doping of Y, Zr, Nb, and Mo atoms in Co5M clusters not only enhances the adsorption strength for H2O but also decreases the barriers of O-H bond breaking, which is in the range of 0.17–0.36 eV. Therefore, the catalysis activity of the small cobalt clusters for H2O splitting can be optimized by doping heteroatoms. Molecular electrostatic potential (MESP) and overlaps partial density of states (OPDOS), and quantum theory of atoms in molecules (QTAIM) were employed for understanding the interaction characteristics.