Catalytic Oxidation Properties Research Articles

Enhancement of the redox reactions of the La0.8Sr0.2MnO3 catalyst by surface acid etching: A simple synthesis strategy to high-performance catalysts for methane combustion

Methane emission and treatment is an extremely important environmental problem, and the key and core treatment method are the application and development of catalysts in the after-treatment system. In this study, a new non-noble metal catalyst, which named OALSM, was fabricated by etching La0.8Sr0.2MnO3 with oxalic acid for the removal of methane. Related experiments and theoretical explorations by scholars had shown that acid etching of perovskite surfaces could achieve effective optimization of the catalytic oxidation properties and microscopic physical and chemical properties of the materials. And the oxalic acid reacted with high-valence state Mn to generate abundant coordination unsaturated Mn3+ sites, which could produce more active oxygen species. In addition, OALSM showed a higher methane catalysis capability than the samples that were not subjected to acid etching. Among all the as-prepared catalysts, OALSM-0.01 M demonstrated the optimal methane catalytic activity with the T50 value of 336 °C, the T90 value of 417 °C, the activation energy of 47.02 kJ·mol−1, and the favorable structural stability and toxicity resistance. This integration strategy can rationalize an innovative protocol to into the design of composite catalysts for methane oxidation, to broaden the application of acid etching in VOC oxidation.

Revisiting the Low-Index Surfaces of LaCoO3 with a Passivation Strategy

A proper modeling is essential for calculating the surface properties of complex oxides, for example, perovskite oxides. Many studies have shown that traditional selections of slab models, either symmetric or asymmetric ones, may vary the calculated results of the polar surfaces, which will finally affect the perception of surface properties. To solve this issue, we proposed a passivation method to handle the complex polar surfaces, where the pseudo-atoms with fractional charges were used to balance non-zero net charges on one side of the surfaces. Based on this method, we revisited the low-index surfaces of LaCoO3, including (11̅02), (1̅104), and (0001) surfaces, with different terminations. The results suggested that the (11̅02)-LaO, (11̅02)-CoO2, and (0001)-LaO3 terminations were stable surfaces in different O and Co chemical environments. The oxygen vacancy formation energies (EOv) of the (11̅02)-LaO and (11̅02)-CoO2 terminations were also evaluated. Different from the unpassivated cases, the EOv of the passivated LaO and CoO2 terminations converged rapidly when slab thickness increased. The upward shift trend of the EOv after passivation was more consistent with the experimental results. The electronic structure analysis indicated that the oxygen vacancy mainly changed the valence state of the surrounding Co atoms. This work provides a more accurate calculation method, which may benefit the study on catalytic properties of complex oxides.

Ferric oxide nanosheet-engineered Mg alloy for synergetic osteosarcoma photothermal/chemodynamic therapy

• Fe 3 O 4 nanosheets were prepared on Mg alloy by transforming Mg-Fe LDH. • Fe 3 O 4 nanosheets are composed of dense nanoparticles. • Fe 3 O 4 nanosheets enhanced corrosion resistance and biocompatibility of Mg alloy. • Fe 3 O 4 nanosheet-engineered Mg alloy showed PTT/CDT synergetic antitumor property. Osteosarcoma (OS) is a malignant tumor with a high rate of recurrence. Recently, biodegradable Mg-based implants have become a new therapeutic platform for bone-related diseases. However, poor biosafety and deficient intelligent tumor-killing ability of Mg-based implants are still the main challenges for the precise treatment of OS. Herein, based on the excellent catalytic and photothermal conversion properties of nanozyme ferric oxide (Fe 3 O 4 ), a novel two-step hydrothermal method for in situ preparation of Fe 3 O 4 nanosheets on the surface of plasma electrolytic oxidation (PEO)-treated Mg alloy using Mg-Fe layered double hydroxides (Mg-Fe LDH) as precursor was proposed. Compared with Mg alloy, there were no obvious corrosion cracks on the surface of Fe 3 O 4 nanosheets-coated Mg alloy (Fe 3 O 4 -NS) immersed in 0.9 wt.% NaCl for 14 days, which demonstrated the corrosion resistance of Mg alloy was significantly enhanced. Cytocompatibility experiments and hemolysis assay confirmed the great biocompatibility of Fe 3 O 4 -NS, especially, hemolysis ratio was lower than 1%. Meanwhile, Fe 3 O 4 -NS presented excellent catalytic oxidation capacity in the presence of H 2 O 2 , and its temperature can significantly increase from 27 °C to approximately 56 °C under NIR irradiation. Therefore, intelligent responsive Fe 3 O 4 nanosheets-engineered Mg-based implants demonstrated excellent antitumor properties in vivo and in vitro due to their photothermal and chemodynamic synergetic effects. This study provides a novel approach for the preparation of Fe 3 O 4 coatings on the surface of Mg alloys and a new strategy for the treatment of OS.

Hydroxyl adsorption derived reactive oxygen species from carbon paper-supported Cu2O for enhanced electrochemical glucose sensing

Engineered sensitive copper nanostructured superelectrode systems have become an important part of electrochemical sensing of glucose because of their high sensitivity, specificity, abundant natural reserves, and environmental friendliness. However, the factors affecting the electrochemical catalytic activity of glucose remain a challenging issue, which largely limits the overall electrochemical sensing performance of glucose. This paper reports the design of a carbon fiber loaded cuprous oxide nanoparticle (Cu2O NPs) electrochemical sensor with electrochemical catalytic properties for glucose oxidation. The copper grown on carbon nanofibers was subjected to cyclic redox treatment to obtain Cu2ONPs with good glucose detection ability. The detection range of the prepared Cu2ONPs was 0.05 mM − 3 mM with a sensitivity of 3 mA mM−1 cm−2. The differences in the properties of copper and cuprous oxide are analyzed in depth and the reasons for the variability are explored. By observing the electrocatalytic behavior and oxygen evolution reaction behavior of the glucose oxidation process, we hypothesized that the difference in the oxygen source provided by hydroxyl adsorption would lead to the difference in the properties of cuprous oxide and copper. Our proposed differences in the oxygen source generated by hydroxyl adsorption affecting the performance of glucose detection will provide new ideas for the design of glucose electrochemical microelectrodes.

Catalytic oxidation properties of an acid-resistant cross-bridged cyclen Fe(II) complex. Influence of the rigid donor backbone and protonation on the reactivity.

The catalytic properties of an iron complex bearing a pentadentate cross-bridged ligand backbone are reported. With H2O2 as an oxidant, it displays moderate conversions in epoxidation and alkane hydroxylation and satisfactory ones in aromatic hydroxylation. Upon addition of an acid to the reaction medium, a significant enhancement in aromatic and alkene oxidation is observed. Spectroscopic analyses showed that accumulation of the expected FeIII(OOH) intermediate is limited under these conditions, unless an acid is added to the mixture. This is ascribed to the inertness induced by the cross-bridged ligand backbone, which is partly reduced under acidic conditions.

Synthesis and catalytic properties of praseodymium oxide (Pr6O11) nanorods for diesel soot oxidation

In this study, a series of praseodymium oxides (Pr6O11) was developed by CTAB-assisted coprecipitation method. The praseodymium oxides were deeply characterized by XRD, N2 adsorption, SEM, HR-TEM, H2-TPR, soot-TPR, NO-TPO and in situ DRIFTS, and tested for soot combustion in absence/presence of NO atmospheres under tight/loose contact conditions. As a non-noble metal and single element oxide, the Pr6O11 catalysts exhibited excellent catalytic performances for both soot oxidation (T10 = 341 ℃, T50 = 395 ℃) in O2 and NOx adsorption (NAC, 906 μmol/g) at low temperature. It was believed that the relatively large surface area, strong NO oxidation ability and high intrinsic activity contributed to the superior performances. A promoting effect on soot oxidation was found when NO introduced, which was ascribed to the NOx-assisted mechanism. The in situ DRIFTS was used to explore the possible mechanism in the soot oxidation reaction process. The carboxyl was detected over Pr6O11 and was speculated as carbon-oxygen intermediate in soot oxidation.

Polyoxovanadate-Based Cyclomatrix Polyphosphazene Microspheres as Efficient Heterogeneous Catalysts for the Selective Oxidation and Desulfurization of Sulfides

The [V6O13]2- cluster is successfully immobilized to the polymeric framework of cyclomatrix polyphosphazene via the facile precipitation polymerization between the phenol group symmetrically modified [V6O13]2- and hexachlorocyclotriphosphazene. The structure of the as-prepared polyoxometalate-containing polyphosphazene (HCCP-V) was characterized by FT-IR, XPS, TGA, BET, as well as SEM and zeta potential. The presence of a rigid polyoxometalate cluster not only supports the porous structure of the polymeric framework but also provides an improved catalytic oxidation property. By using H2O2 as an oxidant, the as-prepared HCCP-V exhibited improved catalytic oxidation activity toward MPS, DBT, and CEES, which can achieve as high as 99% conversion. More importantly, the immobilization of POMs in the network of cyclomatrix polyphosphazene also provides better recyclability and stability of the heterogeneous catalyst.

Chitosan-Grafted Polyacrylic Acid-Doped Copper Oxide Nanoflakes Used as a Potential Dye Degrader and Antibacterial Agent: In Silico Molecular Docking Analysis.

This study examined the catalytic and bactericidal properties of polymer-doped copper oxide (CuO). For this purpose, a facile co-precipitation method was used to synthesize CuO nanostructures doped with CS-g-PAA. Various concentrations (2, 4, and 6%) of dopants were systematically incorporated into a fixed amount of CuO. The prepared samples were analyzed by different optical, structural, and morphological characterizations. Field emission scanning electron microscopy and transmission electron microscopy micrographs indicated that doping transformed CuO's agglomerated rod-like surface morphology to form nanoflakes. UV-vis spectroscopy revealed that the optical spectra of the samples exhibit a redshift after doping, leading to a decrease in band gap energy from 3.3 to 2.5 eV. The purpose of the study was to test the catalytic activity of pristine and CS-g-PAA doped CuO for the degradation of methylene blue in acidic, basic, and neutral conditions using NaBH4 as a reducing agent in an aqueous medium. Furthermore, antibacterial activity was evaluated against Gram-positive and Gram-negative bacteria, namely, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Overall, enhanced bactericidal performance was observed upon doping CS-g-PAA into CuO, i.e., 4.25-6.15 and 4.40-8.15 mm against S. aureus and 1.35-4.20 and 2.25-5.25 mm against E. coli at the lowest and highest doses, respectively. The relevant catalytic and bactericidal action mechanisms of samples are also proposed in the study. Moreover, in silico molecular docking studies illustrated the role of these prepared nanomaterials as possible inhibitors of FabH and FabI enzymes of the fatty acid biosynthetic pathway.

In Situ Characterization of Oxygen Evolution Electrocatalysis of Silver Salt Oxide on a Wireless Nanopore Electrode.

Silver salt oxide shows superior oxidation ability for the applications of superconductivity, sterilization, and catalysis. However, due to the easy decomposition, the catalytic properties of silver salt oxide are difficult to characterize by conventional methods. Herein, we used a closed-type wireless nanopore electrode (CWNE) to in situ and real-time monitor the electrocatalytic performance of Ag7NO11 in the oxygen evolution reaction. The real-time current recording revealed that the deposited Ag7NO11 on the CWNE tip greatly enhanced the oxidative capacity of the electrode, resulting in water splitting. The statistical event analysis reveals the periodic O2 bubble formation and dissolution at the Ag7NO11 interface, which ensures the characterization of the oxygen evolution electrocatalytic process at the nanoscale. The calculated kcat and Markov chain modeling suggest the anisotropy of Ag7NO11 at a low voltage may lead to multiple catalytic rates. Therefore, our results demonstrate the powerful capability of CWNE in direct and in situ characterization of gas-liquid-solid catalytic reactions for unstable catalysts.

Impact of Hydrothermally Prepared Support on the Catalytic Properties of CuCe Oxide for Preferential CO Oxidation Reaction

CuCe mixed oxide is one of the most studied catalytic systems for preferential CO oxidation (CO-PrOx) for the purification of hydrogen-rich gas stream. In this study, a series of ceria supports were prepared via a citrates-hydrothermal route by altering the synthesis parameters (concentration and temperature). The resulting supports were used for the preparation of CuCe mixed-oxide catalysts via wet impregnation. Various physicochemical techniques were utilized for the characterization of the resulting materials, whereas the CuCe oxide catalysts were assessed in CO-PrOx reaction. Through the proper modification of the hydrothermal parameters, CeO2 supports with tunable properties can be formed, thus targeting the formation of highly active and selective catalysts. The nature of the reduced copper species and the optimum content in oxygen vacancies seems to be the key factors behind the remarkable catalytic performance of a CO-PrOx reaction.

Metal Oxide Laser Ionization Mass Spectrometry Imaging of Fatty Acids and Their Double Bond Positional Isomers.

We present a novel combination of a metal oxide laser ionization mass spectrometry imaging (MOLI MSI) technique with off-line lipid derivatization by ozone for the detection of fatty acids (FA) and their carbon-carbon double bond (C═C) positional isomers in biological tissues. MOLI MSI experiments were realized with CeO2 and TiO2 nanopowders using a vacuum matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometer in the negative mode. The catalytic properties of these metal oxides allow FA cleavage from phospholipids under UV laser irradiation. At the same time, fragile ozonides produced at the sites of unsaturation decomposed, yielding four diagnostic ions specific for the C═C positions. Advantageously, two MOLI MSI runs from a single tissue sprayed with the metal oxide suspension were performed. The first run prior to ozone derivatization revealed the distribution of FAs, while the second run after the reaction with ozone offered additional information about FA C═C isomers. The developed procedure was demonstrated on MSI of a normal mouse brain and human colorectal cancer tissues uncovering the differential distribution of FAs down to the isomer level. Compared to the histological analysis, MOLI MSI showed the distinct distribution of specific FAs in different functional parts of the brain and in healthy and cancer tissues pointing toward its biological relevance. The developed technique can be directly adopted by laboratories with MALDI TOF analyzers and help in the understanding of the local FA metabolism in tissues.

Effect of hydroxyl groups on the oxygen vacancy and hydrogen-sensitive properties of CeO2 in different morphologies

The “hydroxyl-oxygen vacancy model” was of great importance for the catalytic and physicochemical properties of metal oxides. Here, we proposed a simple method to construct a hydroxyl-oxygen vacancy model for one-step reduction of palladium chloride through ascorbic acid rich in hydroxyl, loaded on rod, spherical, nanoparticles and cubic CeO2, to achieve the Ce4+/Ce3+ transition and the generation of Pd NPs. The surface-loading Pd ions activated the lattice oxygen of CeO2, and promoted the overflow of reverse oxygen at the Pd–O–Ce interface. The increasing in Ce3+ occupancy altered the reduction performance, oxygen vacancy number and active Pd valence state of the catalyst, and greatly contributed to the response and recovery times. Among the obtained sensors, the 0.50 wt % Pd/CeO2–C/R sensor show a response amplitude of 190/196% to 1000 ppm H2 at 120 °C with a response/recovery time of only 1/3 s. These excellent results are mainly attributed to the chemisorbed oxygen and Ce3+ after ascorbic acid reducing Pd are found to be 4.84 and 1.57 times higher than pure CeO2. The hydroxyl-oxygen vacancy model may open up a new avenue for detecting hydrogen sensing.

Thermodynamic stability of niobium-doped ceria surfaces

Ceria (CeO2) displays a profound catalytic capacity even when utilized as a stand-alone material. Catalyzed reactions by ceria could be enhanced when it is decorated with a trace content of d or f-metals. This study addresses the stability and properties of niobium incorporated ceria surfaces. Doping a trace amount of metals often alter catalytic properties of the host metal oxide. Herein, we investigate mixed Ce-Nb-O oxides with a prime focus on the surface free energy, lattice constant, as well as atomic charges and density of states. It was found that the most stable Ce-Nb-O configuration is obtained when Nb atoms supersede top-layer O atoms at highest niobium occupancy where the surface energy decreases by 0.3 eV/Å2 compared to neat ceria surface. It was also shown that the changes in lattice constants in this configuration is in accord with data obtained from X-Ray Diffraction patterns. Results from this study could be useful in fine-tuning catalytic attributes of ceria-based materials.

Redispersion of Pt nanoparticles encapsulated within ZSM-5 in oxygen and catalytic properties in partial oxidation of methane

Redispersion of Pt nanoparticles encapsulated within ZSM-5 in oxygen and catalytic properties in partial oxidation of methane

Chemical and electrochemical water oxidation catalyzed by heteroleptic Ru(III) complexes of anionic 2,6 pyridine dicarboxylate ligand: Experimental and theoretical study

Herein we report two new mononuclear heteroleptic Ruthenium complexes, 1 and 2 with anionic N, O donor pyridine dicarboxylate (pdc2-) ligand along with neutral bipyridine moieties. The general formula of the complexes are [RuIII(pdc2-)(L1)Cl](1), [RuIII(pdc2-)(L2)Cl](2) (Where L1 = bipyridine, L2 = 4,4′-dimethylbipyridine). Synthesis, characterization and water oxidation catalytic properties of both complexes were investigated. A combined theoretical (DFT) and experimental study were carried out to investigate the catalytic (in presence of CAN) and electrocatalytic activity of 1 and 2 for water oxidation in aqueous solution at pH ∼ 1. During electrocatalysis, the catalytic activity wave has been detected in acetonitrile/water 1:9 (v/v) solution in the range 1.39–1.41 V vs SCE. pH based electrochemistry reveals that, water oxidation (at pH = 1) takes place via sequential proton-electron transfer process to form a RuV = O moiety, which oxidises water through I2M pathway. For water oxidation by CAN, both the molecules show appreciably high TOF values 3.47971 x10-4 s−1 and 1.183 × 10–3 s−1 for 1 and 2 respectively in comparison to similar molecules [1,2].

Atomically Dispersed Platinum in Surface and Subsurface Sites on MgO Have Contrasting Catalytic Properties for CO Oxidation.

Atomically dispersed metals on metal oxide supports are a rapidly growing class of catalysts. Developing an understanding of where and how the metals are bonded to the supports is challenging because support surfaces are heterogeneous, and most reports lack a detailed consideration of these points. Herein, we report two atomically dispersed CO oxidation catalysts having markedly different metal-support interactions: platinum in the first layer of crystalline MgO powder and platinum in the second layer of this support. Structural models have been determined on the basis of data and computations, including those determined by extended X-ray absorption fine structure and X-ray absorption near edge structure spectroscopies, infrared spectroscopy of adsorbed CO, and scanning transmission electron microscopy. The data demonstrate the transformation of surface to subsurface platinum as the temperature of sample calcination increased. Catalyst performance data demonstrate the lower activity but greater stability of the subsurface platinum than of the surface platinum.

Hydrothermal Synthesis of Co3O4 Urchin-Like and their Catalytic Properties in Co Oxidation

Hydrothermal Synthesis of Co3O4 Urchin-Like and their Catalytic Properties in Co Oxidation

Oxidation Catalysis over Solid-State Keggin-Type Phosphomolybdic Acid with Oxygen Defects.

Keggin-type phosphomolybdic acid (PMo12O40), treated with pyridine (Py), forms a crystalline material (PyPMo-HT) following heat treatment under an inert gas flow at ∼420 °C. Although this material is known to have attractive catalytic properties for gas-phase oxidation, the origin of this catalytic activity requires clarification. In this study, we investigated the crystal structure of PyPMo-HT. PyPMo-HT comprises a one-dimensional array of Keggin units and pyridinium cations (HPy), with an HPy/Keggin unit ratio of ∼1.0. Two oxygen atoms were removed from the Keggin unit during crystal structure transformation, which resulted in an electron being localized on the Mo atom in close contact with the adjacent Keggin unit. Upon the introduction of molecular oxygen, electron transfer from this Mo atom resulted in the formation of an electrophilic oxygen species that bridged two Keggin units. The electrophilic oxygen species acted as a catalytically active oxygen species, as confirmed by the selective oxidation of propylene. PyPMo-HT showed excellent catalytic activity for the selective oxidation of methacrolein, with the methacrylic acid yield being superior to that obtained with PMo12O40 and comparable to that obtained with an industrial Keggin-type polyoxometalate (POM) catalyst. The oxidation catalysis observed over PyPMo-HT provides a deeper understanding of POM-based industrial catalytic processes.

The catalytic oxidation properties for BH4− and electrochemical properties of the Ag-decorated AB5-type hydrogen storage alloy

Anode catalysts for direct borohydride fuel cells (DBFCs) are one of the key factors controlling the performance of such cells. Hydrogen storage alloys are efficient and inexpensive DBFC anode catalysts. However, when hydrogen storage alloys are used as DBFC anode catalysts, their catalytic oxidation capacity is weakened due to their easy passivation in alkaline electrolytes. In order to improve the catalytic oxidation ability of AB5-type hydrogen storage alloy, Ag-decorated AB5-type alloy catalysts with different Ag contents were prepared by vibration ball milling method in this study. The microstructures, catalytic properties on BH4− and electrochemical properties of pure Ag, AB5-type and Ag-decorated AB5-type alloy samples were studied in detail. The results show that the Ag-decorated AB5-type alloys are composed of a single LaNi5 phase. Some of Ag powders cover the surface of the AB5-type alloy particles. Among the Ag-decorated AB5-type alloys, the Ag-decorated AB5-type alloy with an Ag content of 2 wt.% exhibits the best electrochemical performance and catalytic performance for BH4−. Its maximum discharge time in 6 M KOH solution is 303 min, which is 43 min longer than that of the AB5-type alloy. The number of electrons transferred by the Ag-decorated AB5-type alloy with 2 wt.% is the largest, reaching 1.45. The improvement of the electrochemical and catalytic properties of the alloy is mainly attributed to the proper Ag powders coating on the surface of the AB5-type alloy particles, which protects the electrode from oxidation and corrosion, and enhances the conductivity of the alloy electrode.

Highly Sensitive Determination of Tenofovir in Pharmaceutical Formulations and Patients Urine-Comparative Electroanalytical Studies Using Different Sensing Methods.

This paper discusses the electrochemical behavior of antiviral drug Tenofovir (TFV) and its possible applicability towards electroanalytical determination with diverse detection strategies using square-wave voltammetry. Namely, oxidation processes were investigated using glassy carbon electrode with graphene oxide surface modification (GO/GCE), while the reduction processes, related to the studied analyte, were analyzed at a renewable silver amalgam electrode (Hg(Ag)FE). Scanning electron microscopy imaging confirmed the successful deposition of GO at the electrode surface. Catalytic properties of graphene oxide were exposed while being compared with those of bare GCE. The resultant modification of GCE with GO enhanced the electroactive surface area by 50% in comparison to the bare one. At both electrodes, i.e., GO/GCE and Hg(Ag)FE, the TFV response was used to examine and optimize the influence of square-wave excitation parameters, i.e., square wave frequency, step potential and amplitude, and supporting electrolyte composition and its pH. Broad selectivity studies were performed with miscellaneous interfering agents influence, including ascorbic acid, selected saccharides and aminoacids, metal ions, non-opioid analgesic metamizole, non-steroidal anti-inflammatory drug omeprazole, and several drugs used along with TFV treatment. The linear concentration range for TFV determination at GO/GCE and Hg(Ag)FE was found to be 0.3–30.0 µmol L–1 and 0.5–7.0 µmol L–1, respectively. The lowest LOD was calculated for GO/GCE and was equal to 48.6 nmol L–1. The developed procedure was used to detect TFV in pharmaceutical formulations and patient urine samples and has referenced utilization in HPLC studies.