H2O Desorption Research Articles

Surface chlorination of IrO2(110) by HCl.

The ability to controllably chlorinate metal-oxide surfaces can provide opportunities for designing selective oxidation catalysts. In the present study, we investigated the surface chlorination of IrO2(110) by HCl using temperature programmed reaction spectroscopy (TPRS), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. We find that exposing IrO2(110) to HCl, followed by heating to 650K in ultrahigh vacuum, produces nearly equal quantities of on-top and bridging Cl atoms on the surface, Clt and Clbr, where the Clbr atoms replace O-atoms that are removed from the surface by H2O formation. After HCl adsorption at 85K, only H2O desorbs at low Cl coverages during TPRS, but HCl begins to desorb in increasing yields as the Cl coverage is increased above about 0.5 monolayer (ML). The desorption of Cl2 was not observed under any conditions, in good agreement with the high barrier for this reaction predicted by DFT. A maximum Cl coverage of 1 ML, with nearly equal coverages of Clt and Clbr atoms, could be generated by reacting HCl with IrO2(110) in UHV. Our results suggest that a kinetic competition between recombinative HCl and H2O desorption under the conditions studied limits the saturation Cl coverage to a value less than the 2 ML maximum predicted by thermodynamics. XPS further shows that the partitioning of Cl between the Clt and Clbr states can be altered by subjecting partially chlorinated IrO2(110) to reductive or oxidative treatments, demonstrating that the Cl site population can change dynamically in response to the gas environment. Our results provide insights for understanding the chlorination of IrO2(110) by HCl and can enable future experimental studies to determine how Cl-modification alters the surface chemical reactivity of IrO2(110) and potentially enhances selectivity toward partial oxidation chemistry.

Atomistic Insights Into the Surface Dynamics of Ni(111) During Reverse Water gas Shift Reaction

AbstractThe conversion of CO2‐H2 mixtures on Ni‐based catalysts can proceed through either the reverse water gas shift reaction (RWGS) path to produce CO or the CO2 methanation path to produce CH4. The balance between these competing reactions depends on both the reaction conditions and catalyst structure. In this study, using surface‐sensitive infrared and ambient pressure X‐ray photoelectron spectroscopies, we investigate the effect of reaction conditions on the interaction between CO2 and H2 on a Ni(111) model catalyst. Our findings highlight the occurrence of RWGS, involving direct dissociation of CO2 to CO and atomic oxygen, followed by oxygen reacting with hydrogen to form H2O, and CO and H2O desorption. Hydrogen affects the distribution of CO between hollow and top sites by displacing oxygen from the energetically preferred hollow sites. The overall balance between oxygen production from CO2 dissociation and oxygen removal by hydrogen governs the oxygen coverage and consequently the distribution of CO between top and hollow sites. This balance is significantly influenced by the reaction temperature and the H2/CO2 partial pressures.

Regulating the electronic structure of Pt SAs-Ni2P for enhanced hydrogen evolution reaction

The single atom catalysts (SACs) show immense promise as catalytic materials. By doping the single atoms (SAs) of precious metals onto substrates, the atomic utilization of these metals can be maximized, thereby reducing catalyst costs. The electronic structure of precious metal SAs is significantly influenced by compositions of doped substrates. Therefore, optimizing the electronic structure through appropriate doping of substrates can further enhance catalytic activity. Here, Pt single atoms (Pt SAs) are doped onto transition metal sulfide substrate NiS2 (Pt SAs-NiS2) and phosphide substrate Ni2P (Pt SAs-Ni2P) to design and prepare catalysts. Compared to the Pt SAs-NiS2 catalyst, the Pt SAs-Ni2P catalyst exhibits better hydrogen evolution catalytic performance and stability. Under 1 M KOH conditions, the hydrogen evolution mass activity current density of the Pt SAs-Ni2P catalyst reaches 0.225 A mgPt–1 at 50 mV, which is 33 times higher than that of commercial Pt/C catalysts. It requires only 44.9 mV to achieve a current density of 10 mA cm−2. In contrast, for the Pt SAs-NiS2 catalyst, the hydrogen evolution mass activity current density is 0.178 A mgPt–1, requiring 77.8 mV to achieve a current density of 10 mA cm−2. Theoretical calculations indicate that in Pt SAs-Ni2P, the interaction between Pt SAs and the Ni2P substrate causes the Pt d-band center to shift downward, enhancing the H2O desorption and providing optimal H binding sites. Additionally, the hollow octahedral morphology of Ni2P provides a larger surface area, exposing more reactive sites and improving reaction kinetics. This study presents an effective pathway for preparing high-performance hydrogen evolution electrocatalysts by selecting appropriate doped substrates to control the electronic structure of Pt SAs.

CFD analysis of the effect of bed geometry on H2O adsorption and desorption efficiency

CFD analysis of the effect of bed geometry on H2O adsorption and desorption efficiency

Reaction of hydrogen peroxide with amorphous Ti–O surfaces

Amorphous Ti–O thin films were synthesized by reactive magnetron sputtering and their affinity to H2O2 was studied electrochemically. They exhibit a pronounced affinity to H2O2, with TiO0.6 outperforming TiO1.5 and TiO2. Cathodic currents in the range of −211 μA/cm2 suggest that TiO0.6 is highly electroactive to H2O2. Molecular dynamics simulations based on density functional theory revealed rapid dissociation of H2O2 into OH on Ti–O surfaces, leading to diffusion of OH, facilitating both oxidation and reduction processes. These OH groups predominantly dock onto bridge and atop sites, oxidizing the surfaces. Notably, stronger interactions observed for lower oxidation states give rise to higher cathodic currents. Additionally, the ability of amorphous Ti–O thin films to generate free H atoms implies a possible reduction mechanism, likely leading to the desorption of H2O. Hence, amorphous TiO0.6 is more suitable for detection and monitoring of H2O2 than higher oxidation states in their crystalline forms, e.g., rutile TiO2, known as a benchmark for such applications.

Spatial geometric effect driven by the different [MnO6] octahedra entity stacking configurations to facilitate the catalytic decomposition of H2O2 in wastewater

Achieving rapid decomposition of H2O2 is crucial for broadening its applications across various fields, as improper disposal or leakage can lead to serious water pollution. In this work, we explore how the octahedral coordination entity [MnO6] stacking configurations in different MnO2 polymorphs (α-, β-, γ- and δ-) affect their catalytic performance towards H2O2 decomposition. Combining experiments and theoretical simulations, we find that the catalytic activity for H2O2 decomposition strongly depends on the [MnO6] stacking configurations, following the order of δ- < α- < γ- < β-MnO2. δ-MnO2 displays edge-sharing octahedral stacking in a layered structure and thus exhibits the highest catalytic activity, efficiently decomposing H2O2 (0.5 M) in just 2 min at 25 °C without excessive energy consumption. Theoretical calculations further show that the superior active sites are located at the edge Mn-site of its 2D layered structure, with the rate-determining step of H2O desorption (0.55 eV). This study provides crucial insights into the impact of coordination entity stacking configurations on the catalytic activity differences.

Dual‐Site Trigger Electronic Communication Effects to Accelerate H2O2 Activation for Colorimetric Sensing of Uranyl Ions in Seawater

AbstractEfficient activation of hydrogen peroxide (H2O2) through biomimetic catalysis still faces a major challenge. In this work, inspired by the catalytic pocket of natural peroxidase, Cu single atom (CuSA) and AuCu nanoparticles (AuCuNPs) anchored on nitrogen‐doped carbon skeleton (CuSA‐AuCuNPs/NC) serve as dual active sites that significantly accelerate the charge transfer process and thus achieve efficient H2O2 activation. Meanwhile, the experimental and theoretical calculations show that the well‐established electronic communication effect between CuSA and AuCuNPs results in moderate electronic modifications to CuSA, which promotes the heterolysis of H2O2 and the timely desorption of H2O. As a proof of concept, CuSA‐AuCuNPs/NC show remarkable performance in detecting uranyl ions in seawater. This work provides new insights into the H2O2 activation for colorimetric sensing.

A Kinetic Study of Microwave‐Assisted Desorption of Co2 from Zeolite 13x

CO2 is the main contributor of the greenhouse gas emission which considerably accelerates climate change. The capture of CO2 requires the development of sustainable adsorption‐desorption processes, which can be upscaled to satisfy the industrial demands. It is well‐known that sustainable microwave (MW) heating leads to fast desorption of CO2 compared to conventional, but there is a lack of study on how to upscale this process. Here it is investigated a concept for the upscaled multi‐mode MW heating of zeolite 13X. The proposed concept is based on the non‐isothermal kinetic study of CO2 desorption, revealing a complex multi‐step process: activation of zeolite 13X below 40 °C and CO2 desorption at T &gt; 40 °C with Eact = 0 kJ mol−1. It was found that MW‐assisted CO2 desorption happens simultaneously with H2O desorption after zeolite MW‐activation. The mechanism of MW‐assisted desorption of CO2 has been proposed. Based on this mechanism, the parameters important for optimizing CO2 desorption process at a larger scale are offered together with an upscaled concept.

Water storage capacity of closed-shell silicon oxyhydroxide cluster cations in the gas phase

Abstract Stable compositions and H2O desorption processes of SinO2n+iH2i+1⁠+ (nominally, (SiO2)n(H2O)iH+; n = 3 to 10) clusters have been studied by gas-phase thermal desorption spectrometry coupled with density functional theory (DFT) calculations. Five or six H2O molecules were found to be stored (i = 5, 6) mainly in the clusters at room temperature. The clusters sequentially released H2O molecules upon heating to form the species with i = 2 (n = 3–5, 8) and 3 (n = 6, 7, 9, 10) as the most prominent compositions at 1,000 K. The desorption energies of H2O molecules from the clusters were evaluated from the temperature dependence data for n = 3 to 5. The experimental and theoretical results suggest that (SiO2)n(H2O)iH+ clusters with higher i (e.g. i ≥ 4 for n = 3) involve H2O molecules bound with hydrogen bonds and can easily release the H2O molecules (ΔE &amp;lt; ∼0.5 eV); species with lower i (e.g. i = 2 and 3 for n = 3) form H2O molecules from two hydroxide groups, whose desorption requires higher energies (ca. 1 to 2 eV); and H2O release is hampered if the product species does not maintain the structure with tetrahedrally coordinated Si atoms.

Process-performance of solid sorbents for Direct Air Capture (DAC) of CO2 in optimized temperature-vacuum swing adsorption (TVSA) cycles

The process performance of three amine-functionalized chemisorbents (TRI-PE-MCM-41, SI-AEATPMS, APDES-NFC-FD-S) and two physisorbents (SIFSIX-18-Ni-β and NbOFFIVE-1-Ni) was evaluated for direct air capture (DAC) of CO2 in temperature-vacuum swing adsorption (TVSA) and steam-assisted temperature-vacuum swing adsorption (s-TVSA) cycles. Rigorous process optimizations were performed to evaluate the trade-off between energy consumption and productivity. Thermal energy consumption, with main contributions arising from desorption of CO2 and H2O, sensible heat of solids, is higher than electrical energy. While steam purge generally improves productivity at the cost of energy, an exception was noticed where it was also found to reduce energy. For the sorbents studied, minimum energy and maximum productivity ranged between 6.25–30.4 MJth/kgCO2, and 0.01–0.15 TPD of CO2/m3 of sorbent, respectively. For all the sorbents, while target CO2 purity (≥95%) can be achieved with moderate vacuum pressure (≈0.30 bar), low regeneration pressures (≈0.050 bar) can lower energy demand and increase productivity. A new ambient pressure temperature swing adsorption cycle is introduced. This cycle achieves target purities, albeit at higher energy consumption compared to those that use vacuum. The study showed that physisorbents, generally not studied for DAC, can be promising. Parametric studies revealed that the lack of multi-component thermodynamic and kinetic data impedes the objective evaluation of DAC processes.

Enhanced water resistance mechanism in Ag-Hollandite for catalytic ozone decomposition

Catalytic ozone (O3) decomposition at ambient temperature is an efficient method to mitigate O3 pollution. However, practical application is hindered by the poor water resistance of catalysts. Herein, Ag-Hollandite (Ag-HMO) with varying Ag+ content was synthesized. Catalysts with more Ag+ exhibited improved efficiency and water-resistance, with the optimal one maintaining 98% O3 conversion at 70% relative humidity (RH) within 8 h. Physicochemical characterizations revealed that Ag+ had entered the tunnel of OMS-2, facilitating oxygen species removal. Notably, enhanced H2O desorption and the complete inhibition of chemisorbed water formation on Ag-HMO were the primary reasons for its high-efficiency O3 conversion across a wide humidity range. The underlying mechanism arises from the charge redistribution induced by the Ag-O interaction within the tunnel, which reduces acidity and modulates hydrophilicity. This study aims to contribute insights for designing catalysts with higher water-resistance.

Insights into the roles of superficial lattice oxygen in formaldehyde oxidation on birnessite.

K+-modified birnessite materials were constructed to remove formaldehyde (HCHO) in this work. The introduction of K+ led to weakening of the Mn-O bonds and enhanced the migration of superficial lattice oxygen, resulting in improved redox properties and catalytic activity. MnO2-3K with the largest specific surface area and greatest abundance of superficial lattice oxygen showed the best catalytic performance at 30-130 °C. The operando analyses reveal that HCHO is primarily activated to dioxymethylene (DOM) and subsequently converted to formate species (*COOH). The accumulation of formate species caused a decline in catalytic performance during extended testing at 30 °C, a challenge that could be mitigated by raising the temperature. Theoretical studies disclose that the *COOH → *H2CO3 step with the largest energy barrier is the rate limiting step for HCHO deep decomposition. Molecular oxygen could be activated at oxygen vacancies to replenish the depleted lattice oxygen after decomposition of carbonate species (*H2CO3) and CO2 and H2O desorption. The adsorbed oxygen and water did not limit the deep oxidation of HCHO. This research presents a promising approach for designing highly efficient, non-noble metal catalysts for formaldehyde degradation.

Ce-doping induces rapid electron transfer in a bimetallic phosphide heterostructure to achieve efficient hydrogen production.

Using electrochemical water splitting to generate hydrogen is considered a desirable approach, which is greatly impeded by the sluggish dissociation of H2O and adsorption and desorption of H*. Effective hydrogen production can be achieved by speeding up the chemical process with a suitable electrocatalyst. In this work, we designed and synthesized a rare earth element cerium (Ce) regulated iron-nickel bimetallic phosphide Ce-NiFeP@NF (here NiFeP represents Fe2P/NiP2) nanoarray with nanoflowers. For the hydrogen evolution reaction (HER), Ce-NiFeP@NF only needs an overpotential of 106 mV to provide a current density of 10 mA cm-2, compared to NiFeP@NF (175 mV@10 mA cm-2). This self-supported electrocatalyst Ce-NiFeP@NF with a composite morphology exhibits excellent performance in the HER. Specifically, the introduction of Ce promotes the electron transfer process at the Fe2P/NiP2 heterojunction interface and the Ce-NiFeP@NF nanocomposite structure with nanoflowers has a larger electrochemically active specific surface area, which is more conducive to improving the intrinsic catalytic activity. Also, a dual-electrode alkaline electrolytic cell (Ce-NiFeP@NF functions as both the anode and the cathode) operates with a cell voltage of only 1.56 V to achieve a current density of 10 mA cm-2. The synergistic effect of rare earth element doping and heterojunction engineering can improve the morphology of intrinsic catalysts to achieve more efficient electrochemical water splitting for hydrogen production.

Oxygen-bridged W-Pd atomic pairs enable H2O2 activation for sensitive immunoassays.

Regulating the performance of peroxidase (POD)-like nanozymes is a prerequisite for achieving highly sensitive and accurate immunoassays. Inspired by natural enzyme catalysis, we design a highly active and selective nanozyme by loading atomically dispersed tungsten (W) sites on Pd metallene (W-O-Pdene) to construct an artificial three-dimensional (3D) catalytic center. The 3D asymmetric W-O-Pd atomic pairs can effectively stretch the O-O bonds in H2O2 and further promote the desorption of H2O to enhance POD-like activity. Moreover, the W-O-Pd sites with unique spatial structures demonstrate satisfactory specificity for H2O2 activation, effectively preventing the interference of dissolved oxygen. Accordingly, the highly active and specific W-O-Pdene nanozymes are utilized for sensitive and accurate prostate-specific antigen (PSA) immunoassay with a low detection limit of 1.92 pg mL-1, superior to commercial enzyme-linked immunosorbent assay.

Conformal coating of macroscopic nanoparticle compacts with ZnO via atomic layer deposition

Conformal atomic layer deposition (ALD) inside macroscopic nanoporous solids with aspect ratios greater than 103 can require ALD reactant exposures on the order of 103 Torr-s or greater. For some ALD chemistries, such large exposures raise the concern of non-self-limiting deposition. In the case of ZnO ALD from diethylzinc (DEZ) and H2O, exposures in the 10–103 Torr-s range have resulted in metallic Zn deposition at typical temperatures used for ZnO ALD on wafers (e.g., ∼180 °C). This Zn deposition can be suppressed by lowering the deposition temperature, but this slows H2O desorption and, thus, can necessitate impractically long purge times. In this work, we use static-dose ALD with DEZ and H2O exposures &amp;gt;104 Torr-s to deposit ZnO inside Al2O3 nanoparticle compacts (NPCs) with 50.5 ± 0.3% porosity, 100 nm NP diameter, 1.55 ± 0.05 mm thickness, and an aspect ratio of 7800 ± 200 (based on the half-thickness), and we explore a novel approach to the deposition temperature, T: T is cycled between 160 °C (for H2O purges) and 120 °C (for all other steps). For comparison, we also deposit ZnO with T held constant at 120 or 160 °C. Whereas the T = 160 °C process results in Zn metal deposition and nonuniform infiltration, the temperature-cycled process yields apparently self-limiting ZnO deposition at a growth per cycle (GPC) of ∼2.1 Å/cyc, forming an electrically conductive ZnO network that is uniform throughout the thickness of the NPC, with the exception of some ZnO depletion near the NPC surfaces, possibly due to the (unoptimized) long DEZ purge time. The T = 120 °C process produces similar results, although the GPC is slightly elevated, indicating diminished removal of H2O and/or OH during purges. We employ scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffractometry, electrical resistivity measurements, and ALD chamber pressure analysis in our comparison of the three ALD processes.

Adsorption of water, hydrogen and oxygen on graphene/Pt(111) surfaces: 2D graphene cover effect studied by temperature programmed desorption

Understanding the interaction between reactive gas and graphene overlayers on metal substrates is prerequisite to study the surface reactions confined at the interfaces between graphene cover and metal surfaces. Here, we report H2O, H2 and O2 adsorption on graphene overlayer covered Pt(111) surfaces by using temperature programmed desorption (TPD). H2O has weak interaction with graphene overlayers and does not intercalate under graphene overlayers under UHV adsorption conditions. Submonolayer H2O desorption on graphene is about 20 K lower directly compared to that on Pt(111) on the submonolayer graphene/Pt(111) surfaces with well-defined metal-graphene interfaces. Both H2 and O2 can intercalate on submonolayer graphene/Pt(111) but not on the graphene fully covered Pt(111) surfaces under UHV adsorption conditions. Graphene cover weakens H2 adsorption at the graphene-Pt(111) interfaces with the H2 desorption temperature lowered by about 30 K and desorption energy lowered by 8.4 ± 0.6 kJ/mol . The intercalated oxygen under graphene reacts with the graphene overlayers above 600 K with CO2 and CO as the oxidation products.

Systematic Search for Thermal Decomposition Pathways of Formic Acid on Anatase TiO2 (101) Surface**

AbstractIn this study, the reaction pathways for the thermal decomposition of formic acid on the anatase TiO2 (101) surface were systematically investigated. The investigation was carried out using a single‐component artificial force induced reaction method that combines density functional theory calculations. In order to uncover the overall mechanism at low surface coverage, we explored reaction path networks for three different conditions of the anatase TiO2 (101) surfaces: clean, protonated, and oxygen‐deficient surfaces. Previous temperature‐programmed desorption (TPD) experiments had shown that H2O desorption starts at a low temperature of about 300 K, while CO and formaldehyde desorption starts at high temperatures of about 500 K. The present reaction path networks are consistent with the overall trend observed in the TPD experiments. Using the reaction pathways extracted from these networks, the overall dissociation mechanism has been discussed.

Dimensionality Engineering of Single-Atom Nanozyme for Efficient Peroxidase-Mimicking.

In nature, enzymatic reactions occur in well-functioning catalytic pockets, where substrates bind and react by properly arranging the catalytic sites and amino acids in a three-dimensional (3D) space. Single-atom nanozymes (SAzymes) are a new type of nanozymes with active sites similar to those of natural metalloenzymes. However, the catalytic centers in current SAzymes are two-dimensional (2D) architectures and the lack of collaborative substrate-binding features limits their catalytic activity. Herein, we report a dimensionality engineering strategy to convert conventional 2D Fe-N-4 centers into 3D structures by integrating oxidized sulfur functionalities onto the carbon plane. Our results suggest that oxidized sulfur functionalities could serve as binding sites for assisting substrate orientation and facilitating the desorption of H2O, resulting in an outstanding specific activity of up to 119.77 U mg-1, which is 6.8 times higher than that of conventional FeN4C SAzymes. This study paves the way for the rational design of highly active single-atom nanozymes.

Synthesis of MoS2 Using Chemical Vapor Deposition and Conventional Hydrothermal Methods: Applications to Respiration Sensing

A promising alternative to methods for the conventional medical diagnosis of many disorders is respiratory monitoring. Unfortunately, current respiratory monitoring methods can be expensive and require inconvenient equipment, significantly limiting their medical applicability. In this study, we fabricated a respiration sensor that uses MoS2-based resistance measurements and analyzed the cause of the slow response time previously reported for MoS2-based sensors. Our results confirm that the crystal phase change of MoS2 affects the absorption and desorption of H2O and the use of the 2H structure results in high sensitivity, a fast response time, and a linear response to water vapor absorption during breathing. This study demonstrates the potential of two-dimensional nanomaterials for humidity and respiration sensors that can be applied in various fields.

Use of Sargassum muticum algae as binder strengthening for raw earth mortar

Raw earth construction (RE) is an interesting alternative approach for reducing the use of conventional construction materials. The aim of this study is the stabilization of RE by a new organic binder manufactured based on algae. The stabilization is performed on the mortar scale as well as evaluated by conducting mechanical and thermal tests. Samples of mortar were manufactured based on local soil and Sargassum muticum type algae. The incorporation weight rates of algae are 0 (reference sample), 2, 4, 6, and 8 wt.%. Results showed that the compressive and bending strengths of algae mortar were improved by 77 and 70%, respectively. In addition, it was noticed that samples with 0.63 mm maximum grain size algae binder provide higher strengths in comparison with 0.80 mm maximum grain size algae binder. It was found also that 2 wt.% of incorporated algae provide similar mechanical resistance to 15 wt.% of slaked lime. The thermal investigation of samples showed three peaks: two endothermic peaks at 100 and 800 °C, which can be respectively attributed to the desorption of H2O and CO2 due to the decomposition of calcite; the third exothermic peak at 500 °C is attributed to the decomposition of the macromolecules of the algae.