Redox Treatment Research Articles

Intermetallic Pd-In/HOPG model catalysts: Reversible tuning the surface structure by O2-induced segregation

Bimetallic Pd-In/HOPG model catalysts have been prepared and investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) techniques. The spontaneous formation of intermetallic Pd-In nanoparticles or at least partial In diffusion into Pd particles with emergence of In-Pd surface alloy already at the step of In deposition onto monometallic Pd/HOPG sample has been revealed. An additional cycle of oxidation-reduction treatment is necessary in order to form the uniform Pd-In alloy species. For a series of Pd-In/HOPG model catalysts, we demonstrate that the reversible RedOx transformation Pd-Inintermet ↔ Pd° + InOx can be efficiently used to deliberately tune the nanoparticles surface composition/structure and respective catalytic characteristics.

Redox Control of Charge Transport in Vertical Ferrocene Molecular Tunnel Junctions

Summary Controlling charge transport through molecular tunnel junctions is of crucial importance for exploring basic physical and chemical mechanisms at the molecular level and realizing the applications of molecular devices. Here, through a combined experimental and theoretical investigation, we demonstrate redox control of cross-plane charge transport in a vertical gold/self-assembled monolayer (SAM)/graphene tunnel junction composed of a ferrocene-based SAM. When an oxidant/reductant or electrochemical control is applied to the outside surface of the neutral single-layer graphene top electrode, reversible redox reactions of ferrocene groups take place with charges crossing the graphene layer. This leads to counter anions on the outer surface of graphene, which balance the charges of ferrocene cations in the oxidized state. Correspondingly, the junctions switch between a high-conductance, neutral state with asymmetrical characteristics and a low-conductance, oxidized state with symmetrical characteristics, yielding a large on/off ratio (>100).

Regeneration behavior of reforming catalysts based on perovskite oxides LaM0.95Rh0.05O3 (M: Cr, Co, Fe) by redox treatment

Perovskite-based catalysts with a self-regeneration property, named intelligent catalysts, were developed for CH4 partial oxidation, and the effect of redox treatment on regeneration behavior of the catalytic activity was investigated. Rh-substituted catalysts such as LaM0.95Rh0.05O3 (M: Cr, Co, Fe) were prepared by the Pechini method. Among the catalysts, LaCr0.95Rh0.05O3 exhibited the highest and the most stable catalytic activity for partial oxidation of methane before and after redox treatment. The precipitation and dissolution of Rh species were confirmed by X-ray photoelectron microscopy and transmission electron microscopy, indicating that the catalyst regenerated itself via the redox process.

Introduce oxygen vacancies into CeO2 catalyst for enhanced coke resistance during photothermocatalytic oxidation of typical VOCs

Carbon deposit during the catalytic oxidation of volatile organic compounds (VOCs) is a key factor to restrict long-term stability of catalysts. Herein, a modified ordered porous catalyst with high coke-resistance performance was developed by introducing oxygen vacancies (OVs) into CeO2 through simple redox and steam treatment (ARCeO2), and applied in efficiently photothermocatalytic degradation of VOCs. Abundant OVs in ARCeO2 leads to enhanced light absorption, improved charge separation and increased reactive oxygen generation, and then promote its photothermocatalytic performance. Moreover, no obvious decrease was observed in the photothermocatalytic activity of ARCeO2 at 200 °C for 25 h reaction. Its superior photothermocatalytic stability can be attributed to the less intermediates and limited coke accumulation onto ARCeO2. This work provides a facile and cost-effective strategy for the design and fabrication of CeO2 catalyst with strong coke-resistance potential and highlights the significance of OVs engineering for improving the photothermocatalytic performance of VOCs degradation.

Wetting Behavior of Zn-Al Liquid on Si-Containing Steel After Surface Oxidation and Reduction Treatment

In the hot-dip galvanization of steel products, surface oxidation–reduction treatment has been proposed recently to improve the wettability of liquid Zn-Al alloy on Si, Mn-containing high-strength steel. During surface oxidation–reduction treatment, an iron-oxide layer with a nanoscale thickness is formed on the steel surface, which is reduced to a metallic iron layer. Although elemental Si and Mn in steel react with oxygen in the atmosphere to form oxide phases, these oxides are expected to be trapped under a reduced iron layer. However, optimum oxidation–reduction conditions have been explored to achieve a good wettability of the liquid Zn-Al alloy on the steel surface. In this study, the dynamic wetting behavior of liquid Zn-Al alloy on the surface of the Si-containing steel after oxidation–reduction treatment was observed by the sessile drop method. It was found that the wettability of the liquid Zn-Al alloy on Si-containing steel depends significantly on the oxidation–reduction condition of steel, despite the Si content in steel being fixed. A porous structure formed in the reduced iron layer accelerates liquid Zn-Al alloy wetting through a capillary force, whereas oxide phases exposed to the steel surface prevent liquid alloy wetting.

Cover Feature: Facile Fabrication of Amorphous Molybdenum Oxide as a Sensitive and Stable SERS Substrate under Redox Treatment (Chem. Eur. J. 12/2020)

The amorphous MoO3−x nanosheet exhibits more sensitive and stable surface-enhanced Raman spectroscopy (SERS) activity than the crystalline counterpart. The signal is stable under repeated oxygen insertion/extraction condition, which allows the recycling of the substrate through H2O2-based Fenton-like reaction. More importantly, the interference-free operando monitoring of the photocatalytic p-nitrothiophenol reduction by loaded Pt nanoclusters can be accurately attained under UV irradiation by using methanol as the hole capturer. More information can be found in the Full Paper by J. L. Zhang, L. Z. Wang, et al. on page 2653.

Facile Fabrication of Amorphous Molybdenum Oxide as a Sensitive and Stable SERS Substrate under Redox Treatment.

Amorphous MoO3-x nanosheets were fabricated by the room-temperature oxidation of molybdenum powder with H2 O2 , followed by light-irradiation reduction in methanol. When applied as a substrate for surface-enhanced Raman spectroscopy (SERS), these nanosheets exhibit higher sensitivity than the crystalline counterpart for a wide range of analytes. Moreover, the SERS activity remains stable on repeated oxygen insertion/extraction. In contrast, the performance of crystalline MoO3-x continuously deteriorates on successive redox treatments. This unique SERS activity allows the recycling of the substrate through an H2 O2 -based Fenton-like reaction. More importantly, the non-invasive SERS was unprecedentedly used for the self-diagnosis of amorphous MoO3-x as a more selective photocatalyst than its crystalline counterpart.

A highly active Pd/H-ZSM-5 catalyst in lean methane combustion prepared via a sol–gel method and treated by reduction–oxidation

The reduction–oxidation treatment can reconstruct Pd nanoparticles, strengthen metal–support interactions and enhance catalytic performance of Pd/H-ZSM-5 in methane combustion.

From highly dispersed Rh3+ to nanoclusters and nanoparticles: Probing the low-temperature NO+CO activity of Rh-doped CeO2 catalysts

For supported catalysts based on highly-priced noble metals the maximum catalytic efficiency per metal atom is highly desired. In this work, Rh-doped CeO2 systems were studied as potential catalysts for low-temperature NO reduction by CO. Thermal and redox treatments allowed varying the Rh oxidation state and the size of rhodium particles formed on CeO2 surface. By combination of surface and bulk sensitive physicochemical techniques the structure-activity correlations were established. Initial Rh-doped CeO2 catalysts contained Rh3+ species ionically dispersed in CeO2 lattice and showed activity in CO + NO reaction already at room temperature. Reduction treatment of Rh3+-CeO2 catalysts resulted in the formation of rhodium particles of ~1 nm in size on the reduced ceria surface. The catalytic characteristics of the initial and reduced samples were comparable, indicating the close nature of the active sites and their dynamic formation directly under the reaction conditions. Calcination of Rh3+-CeO2 sample at T > 800°С resulted in formation of rhodium oxide nanoparticles on the ceria surface. Such Rh2О3/CeO2 catalysts showed activity only at T > 200°С. Their activity in 100–200 °C temperature range could be substantially improved by the reduction treatment. The oxygen vacancies of СеО2 and small Rhn0 particles proved to be essential for the catalytic activity below 100 °C.

Oligomerization dynamics and functionality of Trypanosoma cruzi cytosolic tryparedoxin peroxidase as peroxidase and molecular chaperone

BackgroundTrypanosoma cruzi cytosolic tryparedoxin peroxidase (c-TXNPx) is a 2-Cys peroxiredoxin that plays an important role in coping with host cell oxidative response during the infection process, for which it has been described as a virulence factor. MethodsFour residues corresponding to c-TXNPx catalytic and solvent-exposed cysteines were individually mutated to serine by site-specific mutagenesis. Susceptibility to redox treatments and oligomeric dynamics were investigated by western-blot and gel filtration chromatography. Chaperone and peroxidase activities were determined. ResultsIn this study we demonstrated that c-TXNPx exists as different oligomeric forms, from decameric to high molecular mass aggregates. Moreover, c-TXNPx functions as a dual-function protein acting both as a peroxidase and as a molecular chaperone. Its chaperone function was shown to be independent of the presence of catalytic cysteines, even in the reduced and decameric forms, although it is enhanced when the protein is overoxidized leading to the formation of high molecular mass aggregates. Conclusionsc-TXNPx has chaperone activity which does not depend on the redox state. c-TXNPx does not undergo the dimer-decamer transition in the oxidized state described for other peroxiredoxins. Overoxidized c-TXNPx exists as different oligomeric forms from decamer to high molecular mass aggregates which are in a very slow dynamic equilibrium. The non-catalytic C57 residue may have a role in the maintenance of the decameric form, but seems not to have an alternative CP and CR role. General significanceThis study provides novel insights into some key aspects of the oligomerization dynamics and function of c-TXNPx.

Role of redox iron towards an increase in mortality among patients: a systemic review and meta-analysis.

An increase in biochemical concentrations of non-transferrin bound iron (NTBI) within the patients with an increase in serum iron concentration was evaluated with the following objectives: (a) Iron overloading diseases/conditions with free radicle form of ‘iron containing’ reactive oxygen species (ROS) and its imbalance mediated mortality, and (b) Intervention with iron containing drugs in context to increased redox iron concentration and treatment induced mortality. Literature search was done within Pubmed and cochrane review articles. The Redox iron levels are increased during dys-erythropoiesis and among transfusion recipient population and are responsive to iron-chelation therapy. Near expiry ‘stored blood units’ show a significant rise in the ROS level. Iron mediated ROS damage may be estimated by the serum antioxidant level, and show reduction in toxicity with high antioxidant, low pro-oxidant levels. Iron drug therapy causes a significant increase in NTBI and labile iron levels. Hospitalized patients on iron therapy however show a lower mortality rate. Serum ferritin is a mortality indicator among the high-dose iron therapy and transfusion dependent population. The cumulative difference of pre-chelation to post chelation ROS iron level was 0.97 (0.62; 1.32; N=261) among the transfusion dependent subjects and 2.89 (1.81–3.98; N=130) in the post iron therapy ‘iron ROS’ group. In conclusion, iron mediated mortality may not be mediated by redox iron among multi-transfused and iron overloaded patients.

Metal modified hexaaluminates for syngas generation and CO2 utilization via chemical looping

Chemical looping CH4CO2 reforming (CLDR) is an emerging technology for the generation of Fischer-Tropsch ready syngas and CO2 utilization, which is strongly dependent upon the improvement in the design of efficient oxygen carriers (OCs). In this present work, different metal additives (Si, Zr and Ce ions) were introduced into Fe-based hexaaluminates and used OCs for CLDR. The microstructure and reactivity of BaFe2.8M0.2Al9O19 (M = Fe, Si, Zr, and Ce) OCs were found greatly influenced by the metal additives and CH4/CO2 redox treatment. Pure Fe and Ce doped OCs showed the co-existence of both β-Al2O3 and MP hexaaluminate phases, while the introduction of Si and Zr in the hexaaluminate structure led to the phase transformation from β-Al2O3 into MP. During the CH4/CO2 redox process, large amounts of Fe species in both BaFe2.8Si0.2Al9O19 and BaFe2.8Zr0.2Al9O19 OCs were gradually stabilized in sintering FeAl2O4 with low oxygen-storage capacity, which resulted in low CH4 reactivity and weak cyclic stability. However, Ce-doped BaFe2.8Ce0.2Al9O19 OC showed good reactivity and stability during the 10 redox cycles with CH4 conversion of 93%, H2/CO ratio of ∼2, high syngas yield of 2.2 mmol/g, and high CO2 activation ability of 0.95 mmol/g, which was associated with the preservation of hexaaluminate main phase, the formation of CeFexAl1-xO3 and the abundant oxygen vacancies.

The chemical interaction of support and active phase in sintering resistant La0.8Ca0.2FeO3 perovskite catalysts

The activity and sintering resistance of La0.8Ca0.2FeO3 perovskite (LCF) were found both improved in catalytic combustion of methane once dispersed on MgAl2O4 spinel (MgAl) support, which may attribute to the interaction of LCF and MgAl. To probe the mechanism, the LCF/nMgAl composite catalysts (n = 2.5 or 4, molar ratio of MgAl/LCF) were prepared by deposition-precipitation method and characterized. The results showed that on surface of bulk LCF, lattice FeL3+ dominated; yet after TPR/Re-oxidation treatments, a substantial portion of lattice FeL3+ transformed to free FeF3+, accompanied by a drastic drop in activity. While on LCF/nMgAl surface, the ratio of FeF3+/FeL3+ increased with n; and substitution of Ca2+ by Mg2+ occurred, even up to 100% in LCF/4MgAl. As the result, LCF/4MgAl demonstrated a nearly doubled activity and much improved stability against 1000 °C calcination with respect to bulk LCF. The thinner coverage of LCF on MgAl in LCF/4MgAl has enhanced the interaction, which resulted a smaller Ea value as 100.6 kJ·mol−1, in contrast to 123.1 kJ·mol−1 and 134 kJ·mol−1 for LCF/2.5MgAl and bulk LCF, respectively. More importantly, after subjecting to three round redox treatment, surface species of the LCF/nMgAl catalysts changed little and the activity and Ea even upraised slightly. Therefore, compositing with MgAl has modified the structure of active centers of LCF on chemical aspects, rather than by physical segregation or textual promotion, which is the main reason that improves the catalytic activity, stability and sintering resistance of LCF.

Wet-Chemistry Strong Metal–Support Interactions in Titania-Supported Au Catalysts

Classical strong metal-support interactions (SMSI), which play a crucial role in the preparation of supported metal nanoparticle catalysts, is one of the most important concepts in heterogeneous catalysis. The conventional wisdom for construction of classical SMSI involves in redox treatments at high-temperatures by molecular oxygen or hydrogen, sometimes causing sintered metal nanoparticles before SMSI formation. Herein, we report that the aforementioned issue can be effectively avoided by a wet-chemistry methodology. As a typical example, we demonstrate a new concept of wet-chemistry SMSI (wcSMSI) that can be constructed on titania-supported Au nanoparticles (Au/TiO2-wcSMSI), where the key is to employ a redox interaction between Auδ+ and Ti3+ precursors in aqueous solution. The wcSMSI is evidenced by covering Au nanoparticles with the TiO x overlayer, electronic interaction between Au and TiO2, and suppression of CO adsorption on Au nanoparticles. Owing to the wcSMSI, the Au-TiO x interface with an improved redox property is favorable for oxygen activation, accelerating CO oxidation. In addition, the oxide overlayer efficiently stabilizes the Au nanoparticles, achieving sinter-resistant Au/TiO2-wcSMSI catalyst in CO oxidation.

Ba-addition induced enhanced surface reducibility of SrTiO3: implications on catalytic aspects.

Surface reducibility engineering is one of the vital tools to enhance the catalytic activity of materials. A heavy redox treatment can be utilized to affect the structure and surface of catalytic materials. Here, we choose SrTiO3 (STO) with a cubic perovskite structure as a system to induce oxygen vacancies by using nascent hydrogen from NaBH4 leading to a heavily reduced version of SrTiO3 (RSTO). To further understand the surface reduction and its dependence on foreign-ion (Ba) incorporation into SrTiO3, Sr0.5Ba0.5TiO3 (SBTO) and BaTiO3 (BTO) are synthesized using a facile hydrothermal method. The reduced version of the pristine and mixed oxide shows distinct optical absorptions, indicating oxygen vacancy-mediated reducibility engineering. Detailed CO oxidation experiments suggest the order of activity over the as-prepared and reduced supports as STO > SBTO > BTO and RSBTO > RSTO > RBTO, respectively. The interesting observation of reversal of CO oxidation activity over STO and SBTO after reduction negates the assumption of a similar intensity of reduction on the surfaces of these oxide supports. The fundamental aspect of surface reducibility is addressed using temperature programmed reduction/oxidation (TPR/TPO) and XPS.

Phosphorus Fractionation Responds to Dynamic Redox Conditions in a Humid Tropical Forest Soil

AbstractPhosphorus (P) is a key limiting nutrient in highly weathered soils of humid tropical forests. A large proportion of P in these soils is bound to redox‐sensitive iron (Fe) minerals; however, little is known about how Fe redox interactions affect soil P cycling. In an incubation experiment, we changed bulk soil redox regimes by varying headspace conditions (air versus N2 gas) and examined the responses of soil P and Fe species to two fluctuating treatments (4‐ or 8‐day oxic followed by 4‐day anoxic) and two static redox treatments (oxic and anoxic). A static anoxic headspace increased NaOH‐extractable inorganic P and ammonium oxalate‐extractable total P (AO‐Pt) by 10% and 38%, respectively, relative to a static oxic headspace. Persistent anoxia also increased NaHCO3‐extractable total P (NaHCO3‐Pt) toward the end of the experiment. Effects of redox fluctuation were more complex and dependent on temporal scales. Ammonium oxalate‐extractable Fe and Pt concentrations responded to redox fluctuation early in the experiment, but not thereafter, suggesting a depletion of reductant over time. Immediately following a switch from an oxic to anoxic headspace, concentrations of AO‐Pt, AO‐Fe, and HCl‐extractable Fe(II) increased (within 30 min) but fell back to initial levels by 180 min. Surprisingly, the labile P pool (NaHCO3‐Pt) decreased immediately after reduction events, potentially due to resorption and microbial uptake. Overall, our data demonstrate that P fractions can respond rapidly to changes in soil redox conditions, and in environments where redox oscillation is common, roots and microbes may benefit from these rapid P dynamics.

Mn3O4 with different morphologies tuned through one-step electrochemical method for high-performance lithium-ion batteries anode

A simple, green, efficient, and controllable electrochemical potential perturbation method has been developed to synthesize Mn3O4 nanomaterials. No toxic or explosive chemicals are used during the fabrication process. Taking pure Mn metal as the working electrode and 2 M KCl aqueous solution as the electrolyte solution, the Mn3O4 products with rod-like, spherical-like and mixed structures can be obtained through cyclic voltammetry technology under rapid scan rates of 5, 200 and 50 V s−1 within a potential range of −2.0 to 2.0 V (vs Saturated calomel electrode, SCE), respectively. Rapid and repeated redox treatment of Mn metal surface accompanying intense oxygen and hydrogen evolution will lead to the dispersion of Mn metal and the formation of the Mn3O4 nanomaterials. The lithium-ion storage behaviors of these as-fabricated Mn3O4 nanomaterials have been studied contrastively, showing that the spherical-like Mn3O4-S nanoparticles with the highest Li-ion chemical diffusion coefficient display the best cycling stability and rate capability. As a consequence, it shows an excellent specific capacity of up to 780 mAh g−1 after 250 cycles a high rate of 1000 mA g−1 and a good rate capability of 895, 798, 722, 683, 601 and 530 mAh g−1 at current densities of 200, 500, 800, 1000, 1500 and 2000 mA g−1, respectively. This work is of importance for energy storage as it provides a new and efficient electrochemical way for the fabrication of anode materials for the next-generation LIBs with outstanding electrochemical performances.

Tunable Chiroptical Properties from the Plasmonic Band to Metal–Ligand Charge Transfer Band of Cysteine‐Capped Molybdenum Oxide Nanoparticles

AbstractUnderstanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Now, chiral molybdenum oxide nanoparticles are presented in which chirality is transferred via a bio‐to‐nano approach. With facile control of the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in the plasmon region and metal–ligand charge‐transfer band. The obtained enhanced CD signals with tunable lineshapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics, and photocatalysts.

Tunable Chiroptical Properties from the Plasmonic Band to Metal-Ligand Charge Transfer Band of Cysteine-Capped Molybdenum Oxide Nanoparticles.

Understanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Now, chiral molybdenum oxide nanoparticles are presented in which chirality is transferred via a bio-to-nano approach. With facile control of the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in the plasmon region and metal-ligand charge-transfer band. The obtained enhanced CD signals with tunable lineshapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics, and photocatalysts.

OXIDIZING REACTIVATION OF COPPER CATALYST FOR METHANOL SYNTHESIS

The change in phase composition and catalytic properties of a copper-containing catalyst for methanol synthesis which was deactivated under industrial operation was studied at its redox treatment. The possibility of catalyst partial reactivation was shown. Conditions of reactivation were choosen at the increase in catalyst running time.