Adsorption Of Molecular Oxygen Research Articles

Reactivity of diamanes against oxidation: A DFT study

Diamanes, ultrathin diamond films represent a very promising class of two-dimensional carbon materials that attracts attention due to broad potential applications starting from sensing and optics and finishing with mechanical applications. We investigate here the ability of diamanes with hydrogenated and fluorinated surfaces to confront oxidation by performing density functional calculations. Simulations for adsorption of atomic and molecular oxygen show greater oxidation resistance for fluorinated diamanes in comparison with hydrogenated ones making these 2D materials promising for various applications where intensive oxidation is present.

Stability and activity of PdCu clusters embedded on pyridinic N-doped graphene: a density functional theory investigation

The stability and reactivity of Pd6-nCun (n = 0−3) clusters supported on pyridinic N-doped graphene (PNG) were investigated using the auxiliary density functional theory method. First, the stability of Pd6-nCun (n = 0−3) clusters supported on PNG was analyzed using charge transfer, interaction energy, and electron density critical point calculations. Then, the reactivity of these clusters supported on PNG was computed using frontier molecular orbitals and oxygen adsorption energies. According to the calculated interaction energy, as the Cu content increased, the interaction energy between Pd6-nCun (n = 0−3) clusters and PNG increased. The charge transfer indicated that the clusters donate charge to the PNG. Based on the energy of the frontier orbitals, the Pd5Cu cluster supported on PNG exhibits the smallest HOMO–LUMO gap inferring that this system is the most reactive, whereas the less reactive system corresponds to the Pd4Cu2 cluster supported on PNG. Finally, the oxygen adsorption energies on Pd6 (−3.86 eV) and Pd5Cu (−3.87 eV) clusters supported on PNG were similar. However, the Pd5Cu cluster has a lower Pd content than the Pd6 cluster. Therefore, this work reveals that PdCu systems supported on PNG could be cheap and efficient catalysts for the oxygen reduction reaction.

Oxygen vacancies-mediated CuO@N-doped carbon nanocomposites for non-radical-dominated photothermal catalytic degradation of contaminants

Efficient molecular oxygen activation (MOA) is a critical step for most of the environmental catalysis applications for generating reactive oxygen species (ROS), which is often limited by the lack of energy to excite electrons. The emergence of photothermal catalyst provides an opportunity to make effective use of solar energy to energize electrons for boosting activation of molecular oxygen. Herein, CuO nanoparticles wrapped into nitrogen-doped carbon nanocomposites (CuO@NCs) with abundant oxygen vacancies (OVs) were prepared through a facile one-step synthesis using carboxymethyl chitosan hydrogel as a template. The as-obtained CuO@NCs exhibited excellent photothermal catalytic properties under visible-light irradiation to achieve efficient molecular oxygen activation, thus allowing the effective degradation of bisphenol F (BPF) in complex aqueous environments and actual water matrices. Density functional theory (DFT) calculations reveal that both the enhanced properties of OVs for molecular oxygen adsorption and the accelerated properties of graphitic N for electron transfer contribute significantly to the MOA and charge separation efficiency, resulting in a large amount of ROS. Molecular oxygen is converted to superoxide (·O2−) and ultimately to singlet oxygen (1O2), which is the dominant ROS responsible for contaminants degradation. Additionally, a photothermal catalytic degradation pathway of BPF was proposed based on the product detection and theoretical calculations. This study provides an effective method for the in-situ fabrication of metal@N-doped carbon nanocomposite photothermal catalysts and elucidates the mechanism of the photothermal catalytic activation of molecular oxygen for contaminants degradation, providing a promising approach for making effective use of solar energy for environmental remediation.

Study of the mechanism of nitrogen doping in carbon supports on promoting electrocatalytic oxygen reduction reaction over platinum nanoparticles

Nitrogen-doped carbons (Nano-NC) are often employed as functional supports for boosting oxygen reduction reaction (ORR) over Pt-based catalysts, however, the mechanism of N doping on the adsorption and activation of molecular oxygen on Pt active sites is still not clear. Herein, Nano-NCs as the supports were prepared by a facile NH3 antipyretic method, which allowed to tune the kinds of nitrogen species in carbon matrix and their contents by adjusting the NH3 antipyretic temperatures. With such an exquisite control, the Pt nanoparticles loaded on the as-obtained Nano-NC showed an optimal Pt particle size (2.10 nm), a higher content of Pt0, a large electrochemically active surface area, and fast electron transport ability. As a consequence, the Pt/Nano-NC-800 catalyst with the optimal N-doping showed an outstanding ORR performance with half-wave potential of 0.80 V vs. RHE, limit diffusion current of 5.37 mA/cm2 and improved methanol/CO anti-poisoning, which is superior to the commercial Pt/C catalyst (20%, JM), and most of previously reported Pt-based catalysts. This work may pave a way for the design of the advanced supports for Pt-based catalysts for the ORR applications.

X-ray Photoelectron Spectroscopy (XPS) Analysis of Ultrafine Au Nanoparticles Supported over Reactively Sputtered TiO2 Films.

The impact of a titania (TiO2) support film surface on the catalytic activity of gold nanoparticles (Au NP) was investigated. Using the reactive dc-magnetron sputtering technique, TiO2 films with an amorphous, anatase, and nitrogen-doped anatase crystal structure were produced for a subsequent role as a support material for Au NP. Raman spectra of these TiO2 films revealed that both vacuum and NH3 annealing treatments promoted amorphous to anatase phase transformation through the presence of a peak in the 513–519 cm−1 spectral regime. Furthermore, annealing under NH3 flux had an associated blue shift and broadening of the Raman active mode at 1430 cm−1, characteristic of an increase in the oxygen vacancies (VO). For a 3 to 15 s sputter deposition time, the Au NP over TiO2 support films were in the 6.7–17.1 nm size range. From X-ray photoelectron spectroscope (XPS) analysis, the absence of any shift in the Au 4f core level peak implied that there was no change in the electronic properties of Au NP. On the other hand, spontaneous hydroxyl (–OH) group adsorption to anatase TiO2 support was instantly detected, the magnitude of which was found to be enhanced upon increasing the Au NP loading. Nitrogen-doped anatase TiO2 supporting Au NP with ~21.8 nm exhibited a greater extent of molecular oxygen adsorption. The adsorption of both –OH and O2 species is believed to take place at the perimeter sites of the Au NP interfacing with the TiO2 film. XPS analyses and discussions about the tentative roles of O2 and –OH adsorbent species toward Au/TiO2 systems corroborate very well with interpretations of density functional theory simulations.

(Invited) Investigation of Pt-Alloy and Strained Pt As Electrocatalysts

The need to replace conventional sources of energy has driven the development of fuel cell technology. The polymer electrolyte membrane fuel cells (PEMFCs) show high performance and are important power sources for hydrogen fuel cell vehicles due to the fact that the cells can operate at relatively low temperatures (50 - 90 oC) , has high energy efficiency and only emits water as a byproduct. Furthermore, the direct methanol fuel cell emerge as an important technology for the green energy transition with the use methanol fuel. The most important electrocatalyst for the fuel cells is platinum and efforts are made to enhance its performance and reduce its requirement by alloying with other metals. Therefore, novel approaches are required to develop electrocatalysts for the oxygen reduction reaction (ORR) and methanol oxidation using reduced amounts of Pt for use at PEMFC cathodes with high electrocatalytic activity.Investigation of alloying Pt with transition metals (Ni, Co, Fe) has demonstrated increased electrocatalytic activity and is attributed to changes in the Pt-Pt atomic interaction distances. The electrocatalytic activity is linked to the adsorption of molecular oxygen to the electrocatalytic sites, which is a process enhanced by creating favorable Pt-Pt distances at the electrocatalyst. It is also understood that Pt-alloys have an increased density of d-band vacancies, resulting in stronger binding of OH species to catalyst surfaces. Furthermore, the use of alloying metals causes distortions in the atomic lattice, resulting in compressive strain in the lattice, which increases orbital overlap, widens the d-band, lowers the d-band centre and affects electrocatalytic performance. In addition, enhanced methanol oxidation on strained pure Pt platinum was recently demonstrated and is associated with the preferential absorption of reactant at optimum Pt-Pt interatomic distances.Here, we show results of electrocatalytic activity for oxygen reduction reaction of Fe-Pt alloy with a range of iron content (0 to 80%), the electrocatalytic activity of highly ordered array of Pt nanotubes for methanol oxidation and the effect of strained Pt on methanol oxidation. Structural and electrochemical data of the catalysts will be presented including rotating disk electrode (RDE) voltammetry and SEM images.

Atomic structures and electronic properties of molecular oxygen adsorption on In0.19Ga0.81As(100) surface: Ab-initio study combined with XPS/UPS analysis

Due to the surface oxidation issues, the performances of InGaAs photocathodes are hindered in practical applications, so it is necessary to carry out the corresponding research from theory to experiment. Through ab-initio study based on density functional theory, molecular oxygen adsorption at different sites on the nonpolar In0.19Ga0.81As(100) β2(2 × 4) surface is investigated from the perspectives of atomic and electronic properties. By chemical absorption, molecular oxygen easily dissociates into atomic oxygen when combining with two surface atoms of the same type. The calculation results show that As oxides have the largest destructive effect, followed by Ga oxides, while the In oxides are the least destructive. In addition, the most stable adsorption is the bonding of O atom with Ga atoms, while the bonding of O atom with As atoms is relatively unstable. Combined with the surface analysis method of photoelectron spectroscopy, it is found that the unstable As oxides are the easiest to remove, followed by the In oxides, while the Ga oxides are the most difficult to remove. It is concluded that the work function of the InGaAs surface decreases with the reduction of these oxides, which is conducive to the subsequent preparation of negative-electron-affinity InGaAs photocathodes.

Roles of Oxygen Species in Low-Temperature Catalytic o-Xylene Oxidation on MOF-Derived Bouquetlike CeO2

To realize efficient low-temperature catalytic o-xylene oxidation, MOF-derived CeO2-X catalysts were prepared via the pyrolysis of MOF precursors with different ratios of cerium nitrate to trimesic acid. Among the synthesized catalysts, the bouquet like CeO2-1 exhibited the best activity with T50 and T90 of 156 and 198 °C and the lowest activation energy of 60.67 kJ·mol-1 (WHSV= 48 000 mL·g-1·h-1, o-xylene concentration = 500 ppm). o-Xylene was completely mineralized, and no change in conversion efficiency or CO2 yield was found at 5 vol % H2O for over 50 h. The rich active oxygen species (XPS: Osur/Olatt = 0.69) and abundant oxygen vacancies (Raman: ID/IF2g = 0.036) of CeO2-1 made crucial contribution to its superior catalytic activity. The O2-TPD and H2-TPR results confirmed that CeO2-1 had more surface active oxygen and better mobility of bulk oxygen. Moreover, the reaction routes under different atmospheres were probed through in situ DRIFTS, in which oxygen vacancy played a key role in promoting the adsorption and activation of molecular oxygen and facilitating the migration of the bulk lattice oxygen.

Desorption of physisorbed molecular oxygen from coronene films and graphite surfaces.

We present a study on the adsorption and desorption of molecular oxygen (O2) on highly oriented pyrolytic graphite and coronene films deposited on it. To this end, density functional theory calculations were performed and experiments were made using the FORMOLISM device, which combines ultra-high vacuum, cryogenics, atomic or molecular beams, and mass spectrometry techniques. We first studied the desorption kinetics of dioxygen (O2) on a coronene film and graphite at 15K using the thermally programed desorption technique. We observed that the desorption of O2 occurs at a lower temperature on coronene than on graphite. We deduce the binding energies that are 12.5 kJ/mol on graphite and 10.6 kJ/mol on coronene films (pre-exponential factor, 6.88 × 1014 s-1). The graphite surfaces partially covered with coronene show both adsorption energies. In combination with theoretical density function theory (DFT) calculations using graphene and coronene as surfaces, we observe that the experimental results are in good agreement with the theoretical calculations. For the adsorption of the O2 molecule, two orientations are possible: parallel or perpendicular to the surface. It seems that O2 is best bound parallel to the surface and has a preference for the internal sites of the coronene.

Efficient Oxidation of Paracetamol Triggered by Molecular-Oxygen Activation at β-Cyclodextrin-Modified Titanate Nanotubes.

Titanate nanotubes (TNTs) were coated with a cyclic oligosaccharide (carboxymethyl-β-cyclodextrin, CM-β-CD) to obtain a photocatalyst (CM-β-CD-TNT) for efficiently activating molecular oxygen and removing the target contaminant. The hydrophobic cavity and the large specific surface area of the photocatalyst provide abundant active sites for activating molecular oxygen. The free radical capture experiment and quenching experiment showed that cyclodextrin could facilitate adsorption and activation of molecular oxygen to produce O2 .- . Therefore, compared with the pristine TNT, CM-β-CD-TNT accelerated the oxidation efficiency of paracetamol (APAP) by 3.4 times. Moreover, the ring cleavage reaction induced by CM-β-CD-TNT effectively reduced the acute toxicity of wastewater containing APAP. Furthermore, 100% of bisphenol A (BPA), bisphenol S (BPS), phenol, 2,4-dichlorophen (2,4-DCP), and carbamazepine (CBZ) were degraded by CM-β-CD-TNT after 2.5 h ultraviolet (UV) light irradiation. This strategy provides a new dimension for the advanced treatment of organic wastewater by organic macrocyclic molecule-modified materials.

Constructing benzene ring modified graphitic carbon nitride with narrowed bandgap and enhanced molecular oxygen activation for efficient photocatalytic degradation of oxytetracycline

Popular graphitic carbon nitride (g-C3N4) photocatalyst always faces the problems of weak visible light absorption and fast recombination of photogenerated electron-hole pairs. Herein, a novel benzene ring modified g-C3N4 nanosheet (BCNNS) was synthesized by a simple calcination method. The degradation rate of oxytetracycline by BCNNS under visible light can reach 72% (within 60 min), significantly higher than that of the unmodified g-C3N4 nanosheet (50%). And the degradation rate constant of BCNNS is 0.025 min−1, which is 2.1 times higher than that of g-C3N4 (0.012 min−1). The improvement in the photocatalytic degradation performance can be attributed to the introduction of benzene ring, which can significantly broaden the light absorption range and intensify. In addition, the introduction of benzene ring can adjust the original electronic structure, thereby effectively suppressing the recombination of electron-hole pairs. Furthermore, density functional theory (DFT) calculations demonstrate that the introduction of benzene ring can significantly promote the surface adsorption of molecular oxygen and promote the transfer of electrons to molecular oxygen. This demonstrates that the embedded benzene ring can effectually advance the activation of molecular oxygen, which also well confirms that O2− and 1O2 are the main active species in the system of BCNNS photocatalytic degradation of oxytetracycline. This study reveals that benzene ring modified g-C3N4 has great potential in environmental purification, and provides a promising strategy for the removal of stubborn water contaminants.

One-pot synthesis of oxygen-vacancy-rich Cu-doped UiO-66 for collaborative adsorption and photocatalytic degradation of ciprofloxacin

UiO-66, as one of the most stable metal-organic frameworks (MOFs), has attracted a lot of attention in the field of adsorption and photocatalysis. However, this application of UiO-66 is still limited due to either the low accessibility of micropores or the poor electron-hole charge separation capability. This study aims to promote UiO-66 accessibility of micropores and charge separation through the construction of oxygen vacancies (OVs) and mesopore defects as well as copper incorporation. Herein, mesopore Cu doped UiO-66 with rich OVs was synthesized by a one-pot method and demonstrated high efficiency for the removal of ciprofloxacin (CIP) from the aquatic system. First of all, denatured mesopore defects were produced in Cu doped UiO-66 which possessed a 58% increase in specific surface area compared to UiO-66, facilitating the adsorption of molecular oxygen. Secondly, e− was preferentially trapped by OVs under light irradiation. Electron (e−) reacted rapidly with the surface adsorbed oxygen to generate superoxide radical (O2−). Meanwhile, copper incorporation increased the photocurrent and reduced the interfacial charge transfer resistance, thereby improving the charge separation efficiency. As a result, the adsorption efficiency and photocatalytic performance of mesopore Cu doped UiO-66 with OVs were 8.1 and 3.7 times higher than those of UiO-66, respectively. This study paved a way for the one-step synthesis of MOFs containing OVs and broadened the possibilities of practical applications for photo-induced removal of antibiotics from effluent.

Computational and experimental insights into reactive forms of oxygen species on dynamic Ag surfaces under ethylene epoxidation conditions

The partial oxidation of ethylene to ethylene oxide (EO) proceeds over supported Ag particles. Adsorption of molecular oxygen upon Ag forms the reactive oxygen species responsible for both epoxidation and combustion reactions, however, the catalyst surface structure and the molecular structure and identity of the reactive oxygen species present remain debated despite past use of appropriate forms of in situ spectroscopy. Specifically, there is no consensus for the molecular origin of widely reported Raman features that appear on contact with only O2 or in reactant mixtures of C2H4 and O2 at pressures and temperatures relevant for the industrial process, in part, due to the lack of concerted ab initio studies that compute vibrational frequencies for oxygen-containing Ag surfaces. Here, we elucidate the molecular structure of the catalyst surface and reactive oxygen species by coordinating spectral deconvolution of transient and steady-state surface-enhanced Raman spectroscopy of Ag catalysts exposed to oxygen (2 – 101 kPa O2, 523 – 673 K) and mixtures of oxygen and ethylene (2 – 101 kPa O2, 0.5 – 9.8 kPa C2H4, 523 K) with ab initio thermodynamic modeling and vibrational frequency calculations. These comparisons suggest that during EO catalysis reconstructed surface oxides form and partially or completely encase metallic Ag particles. Raman features near 600 cm−1 that persist in O2 or cofed C2H4 represent O–Ag–O structural motifs that form only on surface oxides and high oxygen-coverage reconstructed AgxOy surfaces. We assign features centered near 810 – 840 cm−1 and at higher frequencies, which are ubiquitous throughout the literature, to dioxygen complexes partially embedded within an oxide-like overlayer that forms during exposure either to O2 or during steady-state epoxidations. Taken together our results implicate the presence of a combination of monatomic and diatomic surface oxygen species, which emerge with appreciable quantities of subsurface oxygen at temperatures and O2 pressures representative of EO catalysis.

Deposition of Al2O3 coatings in Ar-O2 low-pressure discharge plasma under a high dissociation degree of O2

The deposition of Al2O3 coating with a corundum structure was done by anodic evaporation in a low-pressure arc with a self-heated hollow cathode. The conditions were created for increasing the energy of plasma electrons and a corresponding increase in the frequency of O2 dissociation by contraction of the discharge in the anode region. The discharge was maintained in a combined mode with a constant current (70 – 100 A), on which current pulses (100 μs, 1 kHz) with adjustable amplitude (up to 220 A) were superimposed. This mode ensured a change in the degree of O2 dissociation in the range of 0.3 – 0.5 at constant average discharge current and Al evaporation rate. It is shown that an increase in the degree of O2 dissociation leads to an increase in the rate of coating deposition by a factor of 1.3 and promotion of the preferred (300) orientation of crystallites. The effect is due to the features of the adsorption of molecular and atomic oxygen on the Al2O3.

Selective Oxygen and Hydrogen Functionalization of the h-BN/Rh(111) Nanomesh.

We present detailed studies on the covalent adsorption of molecular oxygen and atomic hydrogen on the hexagonal boron nitride (h-BN) nanomesh on Rh(111). The functionalization of this two-dimensional (2D) material was investigated under ultra-high vacuum conditions using synchrotron radiation-based in situ high-resolution X-ray photoelectron spectroscopy, temperature-programmed X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. We are able to provide a deep insight into the adsorption behavior and thermal stability of oxygen and hydrogen on h-BN/Rh(111). Oxygen functionalization was achieved via a supersonic molecular beam while hydrogen functionalization was realized using an atomic hydrogen source. Adsorption of the respective species was observed to occur selectively in the pores of h-BN leading to spatially defined modification of the 2D layer. The adsorption of the observed molecular oxygen species was found to be an activated process that requires high-energy oxygen molecules. Upon heating to 700 K, oxygen functionalization was observed to be almost reversible except for small amounts of boron oxides evolving due to the reaction of oxygen with the 2D material. Hydrogen functionalization of h-BN/Rh(111) was fully reversed upon heating to about 640 K.

Insights into surface alkaline-earth segregation on the surface of La0.3Me0.7Fe0.7Cr0.3O3−δ (Me = Sr, Ca) porous electrodes for oxygen reduction reaction

Surface alkaline-earth segregation is a common problem encountered for the cathodes of solid oxide fuels cells based on perovskites (ABO3) containing alkaline-earth acceptor dopants. In this work, the porous electrodes of La0.3Me0.7Fe0.7Cr0.3O3−δ (Me = Sr, Ca) were employed as the model specimens to look into the surface segregation issue. The two electrodes were cathodically polarized by continuously testing their cathodic current polarization curves. The electrocatalytic activity of the two electrodes was examined in relation with their cathodic polarization history. Moreover, the crystal and surface structures of the cathodically polarized electrodes were analyzed. An appreciable segregation of strontium onto the surface was detected for cathodically polarized La0.3Sr0.7Fe0.7Cr0.3O3−δ electrode, leading to an obvious deceleration of disassociative adsorption of molecular oxygen on the surface and thus degradation of the electrode activity. In contrast, La0.3Ca0.7Fe0.7Cr0.3O3−δ electrode displayed nearly negligible surface calcium segregation and degradation of the electrocatalytic activity after experiencing an identical cathodic polarization history. The disparity of the two electrodes was related to their A-site compositions. This work exemplifies the importance of minimizing A-site cation size mismatch in stabilizing the crystal structure of the perovskite electrodes under cathodic polarization conditions and therefore alleviating the segregation of A-site alkaline-earth cations onto the electrode surface.

Impact of oxygen adsorption on the electronic properties and contact type of a defective epitaxial graphene-SiC interface

Adsorption and dissociation of molecular oxygen on a defective graphene buffer layer (BL) grown on Si-terminated SiC(0001) are herein studied by means of periodic DFT calculations coupled with the nudged elastic band method. We considered a single vacancy (SV) and a divacancy (DV) defective BL on SiC, with or without the uppermost epitaxial monolayer graphene (EG). The adsorption energy of O2 on SV and DV surfaces, producing SV-O and DV-O oxidized systems, is between 2 and 3 times as strong as that on a defect-free BL surface and lacks an energy barrier. In addition, we demonstrate that the n-doping measured in the EG layer of SiC-BL-EG systems, which stems from the charge transfer in the SiC-BL interface, can be fully compensated by oxidizing the DV defective BL. The DV-O-EG interface forms a p-type Schottky contact with a small Schottky barrier height. Instead, a p-type Ohmic contact was measured at the SV-O-EG interface.

Recent advances in molecular oxygen activation via photocatalysis and its application in oxidation reactions

• Molecular oxygen activation via energy and charge transfer processes is summarized. • Molecular oxygen activation pathway analysis and reactive oxygen detection methods are introduced. • Application of activated molecular oxygen in oxidation reactions is reviewed. Molecular oxygen is the greenest potential oxidant, but its spin-forbidden nature limits its activation and application. The use of photocatalysis technology to activate molecular oxygen into reactive oxygen species (ROS) is a feasible strategy for initiating molecular oxygen activation performance from the activation methods of energy transfer process and charge transfer process, such as improving the efficiency of inter-system crossing, reducing non-radiative decay, and enhancing molecular oxygen adsorption and charge separation efficiency. New perspectives on the analysis of molecular oxygen activation pathways and the detection methods of ROS are introduced. In addition, the application of activated molecular oxygen in some oxidative reactions including degradation of organic pollutants, organic synthesis and photodynamic therapy of tumors are summarized. Finally, conclusions and challenges are briefly presented.

Binary molten salts mediated defect engineering on hexagonal boron nitride catalyst with long-term stability for aerobic oxidative desulfurization

Molten salts mediation is a potential strategy for the development of functional materials. Herein, a controllable defect engineering on the hexagonal boron nitride (h-BN) was approached via the binary molten salts (BMS) mediated strategy. The as-synthesized h-BN catalyst had a high crystalline structure with adequate nitrogen-terminated defects, which can work as the reactive sites for the adsorption and activation of molecular oxygen in the aerobic oxidative desulfurization of fuel. These reactive sites on the high crystalline h-BN catalyst showed outstanding stability with only a 1% loss of activity after continuous operation for 120 h. Moreover, the induced number of defects in the high-crystalline h-BN varied with the melting point of BMS, which could be simply modulated by adjusting its binary composition. Thus, via adjusting the melting temperature of BMS close to the eutectic point, a defective high-crystalline h-BN was optimized as the high-performance catalyst, achieving 96% of sulfur conversion in the aerobic oxidation of refractory aromatic sulfur compounds, and remaining active after 15 times of the recycling experiment. This work provides a new approach for the controllable synthesis of high-performance h-BN in the mediation of molten salts.

CO Oxidation Efficiency and Hysteresis Behavior over Mesoporous Pd/SiO2 Catalyst

Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO2 catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (Tig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than Tig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO2 catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at Tig to form CO2. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO2 support interaction, and PdO formation and decomposition.