Effect Of Reduction Treatment Research Articles

Estimation of the effect of redox treatment on microstructure and tendency to brittle fracture of anode materials of YSZ–NiO(Ni) system

The effect of reduction treatment in a high-temperature (600 °C) hydrogen-containing environment on the microstructure and tendency to brittle fracture of YSZ–NiO(Ni) materials for solid oxide fuel cell anodes has been studied. To assess the crack growth resistance of the ceramics, the Vickers indentation technique was adapted, which allowed estimating the microhardness and fracture toughness of the material in the complex.The requirements for high porosity of the anodes to ensure functional properties show that the strength may be an insufficient characteristic of the bearing capacity of the anode. More structurally sensitive characteristics are needed to assess its crack growth resistance.The average levels of microhardness of YSZ–NiO ceramics in the as-sintered state and YSZ–NiO(Ni) cermets (2.0 GPa and 0.8 GPa, respectively) and their fracture toughness (3.75 MPa·m1/2 and 2.9 MPa·m1/2, respectively) were experimentally determined.It was found that the microstructure of YSZ–NiO(Ni) cermet after redox treatment is formed by a YSZ ceramic skeleton with refined Ni-phase grains combined in a network, which provides increased electrical conductivity. Along with higher porosity of the cermet, its fracture toughness is not lower than that of the one-time reduced cermet due to the implementation of the bridging toughening mechanism of fracture.The proposed treatment method allowed forming the microstructure of the anode material, resistant to crack propagation under mechanical load. The propensity of the anode material to brittle fracture on the basis of evaluation of its crack growth resistance and analysis of the microstructure and fracture micromechanism was substantiated. This result is interesting from a theoretical point of view. From a practical point of view, the developed technique allows determining the conditions of redox treatment in the technology of manufacturing fuel cell anodes

Pt/Ni0.17Zn0.83O hybrids with enhanced photocatalytic performance: Effect of reduction treatments

Noble metal/semiconductor hybrids are potential photocatalysts due to their unique properties. Herein, Pt nanoparticles (NPs) were deposited on Ni0.17Zn0.83O support via chemical reduction (using two different reducing agents, NaBH4 and ascorbic acid (AA)) and photo-deposition. The result analysis proved that the valences state (metallic Pt0, Pt2+ and Pt4+) and particle size of Pt were closely related to the reduction treatments. The photocatalytic properties of all samples were evaluated by degradation of Methyl orange (MO), and the photo-deposited Pt/Ni0.17Zn0.83O showed the best performance that the degradation rate reached 95% in 1.5 h and remained at 89% after 5 cycles. This study will give a deeper insight for the impact of reduction treatments and provides a new idea for future research.

Effect of reduction treatments (H2 vs. CO) on the NO adsorption ability and the physicochemical properties of Pd/SSZ-13 passive NOx adsorber for cold start application

Pd/SSZ-13, which has ability to adsorb NO at low temperature, is potentially used as a passive NOx adsorber for cold start application. We investigate the changes in the physicochemical properties and low temperature NO adsorption ability of Pd/SSZ-13 resulting from the reduction treatments with H2 or CO at various temperatures. Treatment with H2 at 500 °C does not give rise to the decrease in NO adsorption ability. However, the ability begins to decrease gradually with the increasing reduction temperature from 600 to 900 °C. On the other hand, CO treatment at 500 °C induces a significant decrease in NO adsorption ability. Combined EXAFS, HAADF-STEM and H2-TPR results clearly demonstrate that CO treatment induced more severe sintering of Pd species than H2 one at the same reduction temperature. After re-oxidation at 500 °C, H2-treated sample generated Pd ion species, which are the active site for NO adsorption at low temperature, more abundantly than CO-treated one, well corresponding to the higher NO adsorption ability over the former sample. Such phenomenon is attributed to the facile sintering behavior due to the high mobility of Pd-carbonyl complex upon the treatment with CO. It can be concluded that the reduction treatments with H2 and CO have different effect on Pd sintering, which is regarded as the main deactivation mechanism of Pd/SSZ-13 passive NOx adsorber.

Effect of Reduction Treatment on CO Oxidation with CeO2 Nanorod‐Supported CuOx Catalysts

AbstractUnderstanding the correlation of thermal treatment with catalyst activity provides mechanistic information about how the catalysts can be activated or deactivated. In this paper, we report that a comparative study was conducted on CeO2 nanorod‐supported CuOx catalysts before and after reduction treatment to gain insight on the effects of the copper oxidation state and catalyst–support interfacial interactions on CO oxidation. X‐ray diffraction, Raman spectroscopy, hydrogen temperature‐programmed reduction (H2‐TPR), and transmission electron microscopy (TEM) were used in a comprehensive way to study the effects of CuOx (0≤x≤1) composition as well as their spatial distribution on CeO2 nanorods on the H2 consumption and CO oxidation of the catalysts. These techniques were then used to gain a better understanding of the correlation between the different copper species (α, β, and γ‐type CuOx) and the multiple reduction (H2 consumption) peaks, found in the H2‐TPR data during the first run and during in situ reduction and redox cycling experiments. Also concluded from this study is that an abundance of surface defects are found on CeO2 nanorods from high‐resolution TEM, which consequently may be critical to strong CuOx(0≤x≤1)–CeO2−x(0≤x≤0.5) interactions, therefore resulting in the improved low‐temperature catalytic activity.

Enhanced photocatalytic activity of titania nanotube array films supported with highly dispersed Pt nanoparticles

Self-organized Pt–TiO2 nanotube array films were prepared on Ti sheets by anodizing in ethylene glycol solution containing a low concentration of NH4F and subsequent photoreduction process. Pt–TiO2 nanotube array films were characterized by means of X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and ultraviolet–visible light diffuse reflectance spectra. SEM images show the highly dispersed Pt nanoparticles were deposited on the surface of TiO2 nanotube array films. The effect of reduction treatment on the photocatalytic degradation activity of methyl orange for Pt–TiO2 nanotube array films was investigated. The photocatalytic results showed that an optimum calcination temperature of methyl orange photocatalytic degradation activity was at 473 K and the further increased temperature could be detrimental to the photocatalytic activity due to the decrease of surface Pt concentration.

Effect of Reduction Treatment on Structural Properties of TiO2 Supported Pt Nanoparticles and Their Catalytic Activity for Benzene Oxidation

A series of highly active Pt-TiO2 catalysts have been prepared by impregnation methods via different reduction processes and used for catalytic decomposition of benzene. The oxidized and reduced Pt-TiO2 catalysts exhibit apparent differences in physical/chemical features (e.g. particle size, chemical state, and electronic property of Pt nanoparticles, and surface oxygen) and catalytic activities for benzene oxidation. Nearly 100 % benzene conversion is achieved on Pt-TiO2 catalysts obtained by the sodium citrate (C6H5Na3O7 center dot 2H(2)O, Na(3)Ct) reduction at approximate 160 A degrees C. Metallic Pt nanoparticles have strong capacity for oxygen activation, and the negative charges and rich chemisorbed oxygen on the surface of metallic Pt nanoparticles are probably responsible for their high catalytic activities for benzene oxidation. 1 wt% Pt-TiO2 catalysts have been prepared by impregnation methods via different reduction processes and used for catalytic decomposition of benzene. The oxidized and reduced catalysts exhibit apparent differences in physical/chemical features and catalytic activities for benzene oxidation. Metallic Pt nanoparticles have strong capacity for oxygen activation, and the negative charges and rich chemisorbed oxygen on the surface of metallic Pt nanoparticles are probably responsible for their high catalytic activities for benzene oxidation.

Synthesis of Potassium Tungsten Bronze Nanosheets by Phase Transformation

Single‐crystalline potassium tungsten bronze nanosheets were prepared by reducing potassium tungsten oxide nanosheets grown on a W foil. The nanosheets showed no evident shape change before and after reduction. Morphology, structure, and composition analyses revealed that a phase transformation from orthorhombic potassium tungsten oxide to hexagonal potassium tungsten bronze occurred. Better field emission with lower turn‐on field was measured from potassium tungsten bronze nanosheet film. The effects of reduction treatment on field emission performance are discussed.

Effect of reduction pretreatment and support materials on selective CO methanation over supported Ru catalysts

Selective CO methanation over Ru/Al 2O 3 and Ru/TiO 2 was investigated as a CO removal method from reforming gas, and the effect of reduction treatment and the support materials on the selectivity and activity was examined. CO methanation activity was degraded over both Ru catalysts by raising reduction treatment temperature, which brought about Ru particle growth except for Ru/TiO 2 reduced at 600 °C. Ru/TiO 2 showed higher CO methanation activity than Ru/Al 2O 3 due to smaller Ru particle size. A close correlation was found between CO 2 methanation rate and interfacial length of Ru particle and support, which indicates that the interface was identified as the reaction sites of CO 2 methanation in CO and CO 2 coexisting atmosphere. CO 2 methanation over Ru/TiO 2 was suppressed in spite of long length of the interface compared to Ru/Al 2O 3, stemming from the small amount of CO 2 adsorbed onto Ru/TiO 2. Ru/TiO 2 catalyst exhibited wider temperature window for selective CO methanation than Ru/Al 2O 3 catalyst.

Effect of Reduction Treatment on Copper Modified Activated Carbons on NOx Adsorption at Room Temperature

Activated carbon was impregnated with copper salt and then exposed to reductive environment using hydrazine hydrate or heat treatment under nitrogen at 925 °C. On the obtained samples, adsorption of NO(2) was carried out at dynamic conditions at ambient temperature. The adsorbents before and after exposure to nitrogen dioxide were characterized by X-ray diffraction (XRD), thermal analysis, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), N(2)-sorption at -196 °C, and potentiometric titration. Copper loading improved the adsorption capacity of NO(2) as well as the retention of NO formed in the process of NO(2) reduction on the carbon surface. That improvement is linked to the presence of copper metal and its high dispersion on the surface. Even though both reduction methods lead to the reduction of copper, different reactions with the carbon surface take place. Heat treatment results in a significant percentage of metallic copper and a reduction of oxygen functional groups of the carbon matrix, whereas hydrazine, besides reduction of copper, leads to an incorporation of nitrogen. The results suggest that NO(2) mainly is converted to copper nitrates although the possibility to its reduction to N(2) is not ruled out. A high capacity on hydrazine treated samples is linked to the high dispersion of metallic copper on the surface of this carbon.

Effect of reduction treatment on CO oxidation over Pt/SnO 2 catalyst

Carbon monoxide oxidation over the supported platinum catalysts was investigated. The catalyst of Pt/SnO 2 exhibited superior catalytic activity despite the low surface area compared to Pt/γ-Al 2O 3. It was confirmed by the temperature-programmed reduction analysis that the reduction of platinum species over Pt/SnO 2 was initiated below room temperature. The platinum species reducible at lower temperature should be responsible for the high activity for the complete oxidation of carbon monoxide. Moreover, the influence of the reduction treatments on these supported platinum catalysts was studied. In the case of Pt/γ-Al 2O 3, the catalytic activity was improved as the reduction temperature was elevated. This is because the adsorption sites of CO on platinum particles increased by the reduction at higher temperature, leading to the high catalytic activity. In contrast, the activity of Pt/SnO 2 was enhanced even by the reduction at 25 °C and the catalyst reduced at 90 °C attained the highest activity. Correlations between the amount of adsorbed CO and the catalytic activity were observed in the Pt/γ-Al 2O 3 system, which were not found in the reduced Pt/SnO 2. These results suggest that the oxygen species of the SnO 2 support activated by the reduction treatments contribute to carbon monoxide oxidation. The activity of the sample was significantly degraded by the reduction at 400 °C. This behavior was attributed to a decrease in reaction sites due to the formation of intermetallic compounds.

Effect of reduction treatment on structural properties of TiO2 supported Pt nanoparticles and their catalytic activity for formaldehyde oxidation

A series of highly active Pt/TiO2 catalysts were prepared by impregnation and deposition precipitation methods with different reduction processes. Their catalytic activities were evaluated by catalytic decomposition of formaldehyde (HCHO) at room temperature. The effects of reduction treatment on structural properties and catalytic activity were studied. Reduced Pt/TiO2 catalysts showed large differences in structural properties (such as particle size, oxidation state, surface content and electronic property of Pt nanoparticles, and surface oxygen) and catalytic activity for HCHO oxidation compared with the unreduced ones. Nearly 100% HCHO conversion was achieved on the former. Especially, sodium borohydride reduced Pt/TiO2 catalysts even with 0.1% Pt loading showed nearly complete oxidation of HCHO. Well-dispersed and negatively charged metallic Pt nanoparticles, and rich chemisorbed oxygen are probably responsible for their high catalytic activities.

Low-Temperature Complete Oxidation of Ethyl Acetate Over CeO2-Supported Precious Metal Catalysts

Catalytic combustion of ethyl acetate was investigated over various CeO2-supported precious metal catalysts prepared by impregnation method, and the effect of reduction treatment on the activity was examined. Among the catalysts tested, Ru/CeO2 achieved the highest activity for ethyl acetate combustion, and the activity was almost unchanged by the heat treatment in a hydrogen atmosphere. In the cases of Pt/CeO2, Pd/CeO2, and Rh/CeO2, the catalytic activity was enhanced by the reduction treatment at 400 °C, though the activity of the reduced catalysts was still inferior to that of Ru/CeO2. It was confirmed by temperature-programmed reduction that the reduction of the ruthenium species was initiated at the lowest temperature among the CeO2-supported precious metals. The precious metal species reducible at lower temperatures should be responsible for the high activity in the complete oxidation of ethyl acetate.

Support effect on complete oxidation of volatile organic compounds over Ru catalysts

Catalytic combustion of ethyl acetate, acetaldehyde, and toluene was investigated on various supported Ru catalysts prepared by the impregnation method, and the effect of reduction treatment on the activity was examined. Among the as-calcined catalysts tested, Ru/CeO2 showed the highest activity for all tests regardless of the pre-treatment in hydrogen atmosphere. The catalytic activity of Ru/SnO2 was significantly degraded by the reduction treatment, whereas the activity of Ru/ZrO2 and Ru/γ-Al2O3 was enhanced. To reveal these phenomena, the as-calcined and reduced catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and BET surface area. The dispersion of ruthenium on the supports was evaluated by chemisorption methods of carbon monoxide. The catalytic activity was strongly related to ruthenium species easily oxidizable and reducible at low temperatures. Such ruthenium species were loaded on CeO2 in a highly dispersed state, resulting in the highest activity.

Effects of Reduction Treatment on Fracture Properties of Cerium Oxide

The reduction treatment effects on the flexural strength and the fracture toughness of ceria were evaluated at room temperature. The results reveal that the flexural strength decreases significantly after reduction under very low oxygen partial pressures; however, in contrast, fracture toughness is increased by 30%–40% when the oxygen partial pressure was decreased to 10−20–10−22 atm range. The large microcracks and the surface tensile stresses developed upon reduction treatment and cooling process are responsible for the decreased strength. The enhancement in toughness is also discussed in terms of internal stresses, microcrack toughening, and crack deflection mechanisms.

Effect of reduction treatment on catalytic performance of Zn-based catalyst for the alcoholysis of urea to dimethyl carbonate

The catalytic activity of zinc powder was evaluated for preparation of dimethyl carbonate (DMC) through alcoholysis of urea. Then a comprehensive study was made on the loaded Zn-based catalysts to find preferable preparation conditions including reduction temperature and loaded amount of the active component. TPR was carried out to determine the preferable reduction temperature, and XPS was used to detect the change of the chemical state of the catalyst. The prepared catalysts were also characterized by means of XRD. Under the selected reaction conditions, DMC yield reached 12.7% and 8.9%, respectively, over zinc powder and loaded Zn-based catalyst. The activity of the loaded Zn-based catalyst increased for six times comparing with that of the zinc powder catalyst.

Magnetic Resonance in Pb[sub x]Nb[sub y]O[sub z] Ceramics as a System Containing Chemical Fluctuation Regions

Simulation of the chemical fluctuation regions in PMN-like relaxors through growth of the PbxNbyOz eramics was performed. Different PbxNbyOz clusters (chemically and structurally) coexist in such ceramics. Hole polaron and bipolaron (Cr3+-two polaronic-hole) paramagnetic complexes were considered for explanation of the EPR spectra in PbxNbyOz ceramics. Dynamical averaging, light-induced effects, and significant effects of reduction treatment giving the coexistence of Nb5+ and Nb3+ ions, as well as of a strong internal magnetic field, were discovered in this ceramics. The latter could be related to antiferromagnetic phase realization in PbxNbyOz clusters containing a sufficiently high concentration of magnetic Nb3+ host lattice ions. Such a situation leads to antiferromagnetic resonance on Nb3+ ions, as well as to EPR of Cr3+-related paramagnetic complexes in a Nb3+-induced internal magnetic field. Charge transfer vibronic excitons (CTVE) in free and in CTVE phase states were detected in PbxNbyOz ceramics by photoluminescence studies.

The effect of reduction treatment on the photorefractive properties of Zn:Fe:LiNbO3 crystal

The effect of reduction treatment on the photorefractive properties of Zn:Fe:LiNbO3 crystal was studied experimentally. It was found that, after reduction treatment, the response time of the crystal is shortened, the ability of optical damage resistance is enhanced and the absorption edge is shifted towards the infrared band. Meanwhile, a self-erasing phenomenon was observed for the first time in reduced Zn:Fe:LiNbO3 crystal. The evolution of diffraction efficiency with time going on is non-monotonic, but grows gradually to its maximum and then decays a great extent during the recording process. The mechanism of the electron–hole competition was presented to explain this phenomenon.

Structural Changes of Hair Keratin by Reduction, Heat and subsequent Oxidation Treatments

A commercial method for permanent hair straightening process including three chemical reaction steps: i.e., reduction, heat treatment and subsequent oxidation has been widely used. The effects of reduction treatment on chemical, morphological and fine structural changes of hair were studied. Reduction was performed by using a thioglycolic acid (TGA) only and a bicomponent system composed of TGA and dithiodiglycolic acid (DTDG). Our approach was focussed on the effects of DTDG on hair damage. Amino acid analysis showed that in the presence of DTDG, the reduction of disulfide bonds is suppressed, while the formation of thiol groups from the mixed disulfide which is made by the reaction of cystine thiol and thioglycolic acid is enhanced. The results of high pressure DSC and the histochemical observation of cortical cells suggested that the hair straightening treatments give rise to a destruction of the α-crystallites in part and more or less degradation of either the non-keratinous components or the amorphous matrix. However, FT-IR spectral data suggested that the α-helical materials are present in the straightened hairs at the same level as detected in the untreated hair. The reducing system containing DTDG decreased chemical attack on the amorphous matrix and the structural regularity of the matrix remained to be almost unchanged.

Effects of reduction treatment on the photorefractive properties of Pb0.5Ba0.5Nb2O6

Abstract Lead barium niobate is a new photorefractive material of high interest for a variety of applications including holographic storage. Pb0.5Ba0.5Nb2O6 crystals have been grown by the Bridgman method, and the effects of heat treatments on their photorefractive properties were investigated using Ar ion laser at λ=514.5 nm. The color and absorption spectrum of the crystals varied depending on the oxygen partial pressure during heat treatment. The oxygen diffusivity was estimated to be in the order of 10−6 and 10−5 cm2/h at 425 and 550 °C, respectively. Reduction treatment at an oxygen pressure of 215 mTorr increased the effective density of photorefractive charges about three times from 8.0×1015 to 2.2×1016 cm−3 and made the charge transport more electron-dominant. As a result, the maximum gain coefficient improved from 5.5 to 13.8 cm−1. A diffraction efficiency as high as 70% was achieved in a reduced crystal.

In Situ PAC Study of InPt Exchanged Zeolites under Different Redox Conditions

The effect of reduction treatments in H2 at 500 °C in both wet and dry atmosphere on mono and bimetallic In−zeolite supported catalysts has been studied using the perturbed angular correlation technique. The relaxation in the observed hyperfine interaction has been associated with the formation of oxygen vacancies in the indium sesquioxide particles present on the external surface of the catalysts. The addition of Pt has consequences for the relaxation process. The effect of Pt atoms could be associated with the trapping of vacancies, thus slowing down their jump frequency. This particular and indirect In−Pt interaction does not seem to have any effect on the enhancement of the catalytic activity observed in the bimetallic sample. A new indium species with cubic symmetry for the In site, i.e., metallic indium and/or In2O3 nanosized crystallites, was detected in reduced In/ferrierite and InPt/ferrierite samples.