Increasing Reduction Temperature Research Articles

The Effect of Reduction Pretreatments on the Size of Supported Pt and Pd Nanoparticles Prepared by Strong Electrostatic Adsorption

AbstractSupported catalyst synthesis involves pretreatment (drying, reduction) of metal complexes to form metal nanoparticles. This study has been undertaken to explore the effect of reduction temperature, heating rate, and water partial pressure on final particle size of Pt and Pd supported on a total of four carbon and oxide supports. Supported nanoparticles were synthesized by strong electrostatic adsorption (SEA) and dry impregnation (DI); the former method was hypothesized to yield greater nanoparticle stability in thermochemical reducing environments stemming from the strong interaction of the precursor with the support during impregnation. Reduced samples were characterized by in-situ and ex-situ XRD and STEM. The DI-derived samples generally showed an expected increase of particle size with increased reduction temperature, and severe particle coalescence in humid hydrogen, while the SEA-derived samples did not sinter at the elevated reduction temperatures (up to 500 °C) and were remarkably stable in the humid reducing environment. Graphical Abstract

Oxygen vacancies tuning over Co3O4 nanosheet preferentially growing (2 2 0) facet for efficient Hg0 removal from flue gas

Oxygen vacancy is very important for the Hg0 oxidation process due to it can capture and activate gaseous oxygen forming surface chemisorbed oxygen to oxidize Hg0 to HgO. Precise control of oxygen vacancies amount is a big challenge in this field. For Co3O4, oxygen vacancy can be generated by Co3+ reduction to Co2+ and Co3+ mainly exist in (220) facet. Thus, in the present work, Co3O4 nanosheets preferentially growing (220) facet with more Co3+ were synthesized and CO was used as reduction agent to reduce Co3O4 at different reduction condition. After that, Co3O4 nanosheets with different amount of oxygen vacancies were obtained. XPS, Raman and PL results show that, the amount of oxygen vacancies increase firstly and then decrease with the increase of reduction temperature and time. CO can reduce Co3+ to Co2+ forming oxygen vacancies. However, when the reduction temperature and time are at a high level, Co3O4 will be over reduced to CoO leading to a decrease of oxygen vacancies. DFT confirm that, when Co3O4 is over reduced, O2 will hard to adsorb on Co3O4 surface and lattice oxygen will be formed even after O2 adsorption. Co3O4-Te300Ti2 has an optimal reduction degree leading to higher oxygen vacancy concentration and better O2 adsorption and activation ability. Therefore, Co3O4-Te300Ti2 has a high Hg0 oxidation efficiency which is over 96 % in a wide temperature range of 150–300 °C at a high GHSV of 180,000 h−1.

Sticking Behavior of Burdens During Reduction Process in Gas‐Based Shaft Furnaces

Gas‐based shaft furnaces (SFs) have garnered considerable attention because of their low CO2 emissions. The sticking behavior of their burden material influences the smooth operation of SFs. In this study, the effects of the reduction degree, temperature, and atmosphere on the sticking behavior of pellets are studied thoroughly under typical reduction conditions. The results demonstrate that the pellets will stick with each other as the reduction degree increases, the main phase of pellets at the maximum sticking index (SI) is iron, and the interconnection between iron whiskers results in the bonding phenomenon of pellets. The pellets exhibit a low SI at a relatively low reduction temperature. As the reduction temperature increases, the pellets stick, which is caused by thermal expansion and the large number of iron whiskers. With an increase in the proportion of H2 in the reducing gas, the iron particles become smaller, and the contact area between the particles decreases, effectively reducing the SI of the pellets. In general, choosing a reasonable reduction temperature and increasing the proportion of H2 in the reducing gas are helpful in controlling pellet sticking.

Study on Direct Reduction in Carbon-Bearing Pellets Using Biochar

As a renewable, carbon-neutral raw material, the application of biomass in steel production is conducive to reducing greenhouse gas emissions and achieving green and sustainable development in the steel industry. The heating and reduction process of a rotary hearth furnace was simulated under laboratory conditions to roast and reduce biochar carbon-bearing pellets with coke powder and anthracite carbon-bearing pellets as a comparison. This was conducted to investigate the impact of biochar as a reducing agent on the direct reduction in carbon-bearing pellets. Under various reduction temperatures, carbon/oxygen ratios, and reduction times, tests were conducted on the compressive strength and metallization rate of carbon-bearing pellets made using typical binder bentonite. Results show that with the increase in reduction temperature, the metallization rate of pellets increases, while the compressive strength initially decreases and then increases, reaching the lowest point at 900 °C and 1000 °C. When the ratio of carbon to oxygen is between 0.7 and 0.9 and the reduction time is between 15 and 25 min, carbon-bearing pellets meet the requirements of both the metallization rate and the strength, with the metallization rate above 80%. However, severe volume swelling and low strength were observed in biochar carbon-bearing pellets at 900 °C and 1000 °C, which negatively impacted multi-layered charging and heat transfer efficiency in the blast furnace. Therefore, a novel laboratory-prepared binder was introduced in the preparation process of biochar carbon-bearing pellets at an appropriate addition ratio of 5–8%. Without producing any swelling concerns, the inclusion of this binder considerably improved the compression strength and metallization rate of the pellets, enabling them to fulfill the standards for raw materials in the blast furnace.

Investigation on the pre-reduction of ilmenite pellet using H2/CO atmospheres

ABSTRACT In this study, ilmenite and bentonite were uniformly mixed, pelletised, and baked at temperatures up to 1200°C. The reduction of ilmenite pellet by H2/CO mixtures and H2 pure gas was studied in the temperature range of 760–890°C. Reduced pellet microstructures and phases analysed by, Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray Analysis (EDX) Mapping. Experimental works shown that between 760°C, 880°C, and 890°C, the H2 amount and reduction temperature have a considerable influence on the degree of metallisation. The obtain results demonstrate the degree of metallisation increased with increase of reduction temperature and reaction time. The degree of metallisation could reach 93.64% when the sample was reduced to 890°C for 360 min in pure H2 atmosphere. In microstructural analysis, metallic iron particles became smaller and more uniformly distributed as hydrogen content of the reducing gas increased.

Wet reduction-based fabrication and characterization of a Cu-Pb(MgNb)ZrTiO3 multilayer actuator

Cu–(0.7Pb(Mg0.67Nb0.33)TiO3–0.3Pb(Zr0.48Ti0.52)O3)(PMNZT) multilayer actuators were prepared using a sequence of ceramic layer tape-casting, on-ceramic electrode printing, lamination, co-firing in air, and soaking in aqueous N2H4 at 25–100 °C. The employed wet reduction protocol converted the Cu2O produced in the electrode layers upon co-firing to Cu, while keeping the composition and structure of the PMNZT ceramic layers unaffected. Nano-pores were converted into macro-pores with increasing reduction temperature and time. This reduction process was controlled by the kinetics, which is attributed to the open structure of the electrode resulting from the presence of a sacrificial polymer (polyvinylidene difluoride, PVDF) particles. This resulted in a short path of hydrogen diffusion in the inner electrode layers. The pore size and population affected the electrical conductivity of the electrode and the performance of the PMNZT ceramics. To address this issue, the sample was immersed in aqueous HSO4 at 60 °C to fill the pores in the electrode layers, thereby mitigating their effect on electrical conductivity. The samples prepared using wet reduction and filling processes exhibited the same piezoelectric properties as the bulk PMNZT sample.

Electrocatalytic hydrodechlorination of 2,4-dichlorophenol on Pd catalysts supported on N-doped mesoporous carbons: Impact of electronic effects

The Pd catalysts supported on activated carbon (AC), ordered mesoporous carbon (CMK3) and N-doped mesoporous carbon (NCMK3) were prepared, and electrocatalytic hydrodechlorination (EHDC) of 2,4-dichlorophenol (2,4-DCP) was studied on the catalysts. The electronic properties of Pd particles in Pd/NCMK3 were modulated using varied reduction temperature. Increasing reduction temperature from 200 to 300 °C leads to the decrease of Pdn+/Pd0 in Pd/NCMK3 from 1.56 to 0.83. As a result, Pd/NCMK3 reduced at 200 °C exhibits substantially enhanced EHDC activity for 2,4-DCP with a peak mass activity of 3.37 min−1 mgPd−1, which is much better than previously reported catalysts. The DFT calculation shows that highly effective activation of C-Cl bonds can be achieved on cationic Pd species. Furthermore, the Pd/NCMK3 catalyst shows excellent electrocatalytic stability for EHDC of 2,4-DCP, demonstrating its great potential in the long-term application in the electrocatalytic removal of chlorinated pollutants.

Constructing rich-Zn Pt1Zn1 alloy over the BEA zeolite as a selective catalyst for propane dehydrogenation

The deactivation of Pt-based catalysts is the most critical problem in nonoxidative propane dehydrogenation reaction (PDH), usually manifested in carbon deposition and active site sintering. Zn, as another cheap metal with more abundant reserves than Sn, is also widely used as an assistant in Pt-based catalysts. However, both of them are easy to be reduced to metal valence state and lost in the reaction process. Herein, the enlarged quantities of Zn are applied in the bimetallic Pt-Zn catalyst preparation. As confirmed by the increased reduction temperature of oxidized Zn species, it effectively minimizes the influence of the active metal mobility caused by Zn loss. At the same time, the constructed bimetallic structure modulates the surface acidity of Zn species and presents benign propylene desorption ability, thus the formed highly dispersed Pt sites on the surface of Pt1Zn1 alloy are well-matched with its high propylene selectivity (∼98.6%). In addition, the rich-Zn Pt1Zn1 sites are beneficial for enhancing the capability of resisting-coke, thus retarding the deactivation of this catalyst.

Removal behavior of Zn and alkalis from blast furnace dust in pre-reduction sinter process

Abstract In this study, iron concentrate and blast furnace dust were used as raw materials, and graphite was used as a reducing agent for mixing and briquetting. The briquettes were roasted in a high-temperature tube furnace at different temperatures and held for a certain time to simulate the pre-reduction sintering process. The effects of dust content, reduction time, and reduction temperature on the removal rate of zinc, potassium, and sodium and the metallization rate of the pre-reduction sintered products were investigated. The reduced briquettes were characterized by X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and flame atomic absorption spectroscopy to further explore the mechanisms of zinc, potassium, and sodium removal. The Zn removal rate and metallization rate increased gradually with the increase in dust content, reaching 97.57% and 87.14% at 30% dust content, respectively. Both K and Na removal rates reached a maximum of 83.57% and 94.78%, respectively, at 25% dust content. With the increase in reduction time and temperature, the removal rate of the three elements and the metallization rate gradually increased. When the briquettes with 20% blast furnace (BF) dust content were reduced at 1,200℃ for 20 min, the removal rates of zinc, potassium, and sodium reached 95.66%, 79.97%, and 91.49%, respectively, and the metallization rate reached 84.77%. It shows that the pre-reduction sintering process can effectively remove Zn, K, and Na from the BF dust and meet the requirements of subsequent BF production. The research results can provide some theoretical basis for industrial production.

Reductive synthesis of Fe@Al2O3 micro powders with high permeability and low magnetic loss in the MHz range

Magnetic powders with high permeability and low loss in MHz range have gained ever-increasing attention. In this work, spherical FeCO3 particles have been firstly oxidized in air, then coated with Al(OH)3 insulation shell and finally reduced by hydrogen at different temperature. The results show that as the reduction temperature increases, reduced products would gradually be converted into Fe/Fe3O4@Al2O3 and Fe@Al2O3. Meanwhile, the increase of reduction temperature leads to a gradual increase in the content and crystal size of Fe. Owing to the protection from Al2O3 layer, spherical morphology can be well preserved in reduced products, while holes would be generated in spherical particles, due to the release of gaseous products. Further investigation on magnetic properties shows that with the increment of reduction temperature, permeability would be improved, and magnetic loss would be basically decreased in the frequency range of 1–30 MHz. It should be mentioned that reduction product at high temperature (600 °C) has larger permeability and weaker magnetic loss than that of carbonyl iron powder with similar particle size. This work may provide useful reference for the development of micro magnetic powders and high-performance soft magnetic composites.

Catalyst optimization and reduction condition of continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites.

Influence of reduction conditions on the structure-activity relationships of NaNO3-promoted Ni/MgO dual function materials for integrated CO2 capture and methanation

Integrated CO2 capture and utilization (ICCU) represents an innovative concept and technique for reducing industrial carbon emissions. Ni-MgO dual function materials (DFMs) promoted by alkali metal salt (AMS) for integrated CO2 capture and methanation (ICCU-M) is gaining increasing interest. The in-situ methanation performance depends heavily on the high-temperature NiO reduction process, while this might adversely affect CO2 adsorption due to loss of AMS. Herein, we investigated the effects of H2 concentration and reduction temperature on structure–activity relationships of AMS-promoted Ni-MgO DFMs for ICCU-M. The increase in H2 concentration and reduction temperature favors NiO reduction to metallic Ni0 and boosts oxygen vacancy concentration in the DFMs. Both CO2 uptakes and CH4 yield increase with the elevating H2 concentration, and CH4 yield also increases with the increasing reduction temperature, considering the increased metallic Ni0 content and oxygen vacancy concentration. CO2 uptakes of the DFMs decline with the increase in reduction temperature, due to the obvious loss in AMS. The bulk diffusion kinetics in CO2 adsorption stage will be improved under higher H2 concentration and reduction temperature, while the chemisorption kinetics will be weakened at elevating reduction temperature. The methanation kinetics will be enhanced when the DFMs are reduced under higher H2 concentration and temperature. The AMS-NM-100-450 DFMs reduced in 100 %H2 and 450 °C exhibit good ICCU-M performance with high CO2 adsorption capacity and CH4 yield of 6.46 mmol CO2/g and 0.85 mmol CH4/g. The results in this work enlighten that the ICCU-M performance of AMS promoted Ni-MgO DFMs can be tuned by regulating the operating parameters for catalyst reduction.

Hydrogen-controlled structural reconstruction of palladium-bismuth oxide cluster to single atom alloy for low-temperature CO oxidation

Palladium (Pd) has been widely regarded as a high-performance catalyst for various oxidative reactions, however, the actual structure of active site remains controversial due to structural evolution under operation conditions. Herein, we prepared a series of bismuth (Bi)-doped silica-supported Pd catalysts and found a hydrogen-controlled structural reconstruction mechanism of palladium-bismuth oxide cluster to single atom alloy to efficiently catalyze low-temperature CO oxidation. The formation of PdxBiyOz clusters with unique Pd−O−Bi coordination structure could enhance the sinter-resistance ability of Pd species. This structural evolution of active site is clearly uncovered by in-situ XAFS results, in which metallic Bi−Pd shell gradually generates as the increase of reduction temperature without any metallic Bi−Bi bond. More importantly, PdBi1 single atom alloy exhibits a good CO oxidation activity with a CO2 production rate of 413 μmolCO2·gPd−1·s−1 at 100 °C and excellent catalytic stability. Density function calculation (DFT) results indicate that there are geometric and electronic effects between Bi and Pd atoms, which favor total linear-CO adsorption, activate CO and O2 molecules, and reduce the barrier for the formation of OO-CO intermediates in PdBi1 single atom alloy.

Kinetics Study on the Hydrogen Reduction of Bauxite Residue-Calcite Sintered Pellets at Elevated Temperature

In this study, the isothermal reduction of bauxite residue-calcite sintered pellets by hydrogen at elevated temperatures and different gas flow rates was investigated. A thermogravimetric technique was applied to study the kinetics of the direct reduction by H2 at 500–1000 °C. It was observed that iron in sintered oxide pellets mainly exists in the form of brownmillerite, srebrodolskite and fayalite. The reduction of brownmillerite, the dominant Fe-containing phase, with hydrogen produces mayenite, calcite and metallic iron. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), BET surface area, pycnometer and mercury intrusion porosimeter analyses were adopted on reduced pellets to interpret the experimental results. The order of the reduction process changes from first-order reaction kinetics to second-order with an increasing reduction temperature. The change in reaction order may be due to sintering at higher reduction temperatures and corresponding physical and microstructural changes in pellets. The activation energy of reduction was calculated as 55.1–96.6 kJ/mol based on the experimental conditions and using different kinetic model equations. From the experimental observations, it was found that 1000 °C with 60 min is the most suitable condition for bauxite residue-CaO sintered pellets’ reduction with hydrogen.

Tunable reduced graphene oxide nanofiltration membrane for efficient retention and separation of dye/salt based on molecular interactions

Effective retention and separation of mixed dyes are critical to treating textile wastewater. Graphene oxide (GO) is an ideal material for treating polluted water attributed to its unique structure and abundant oxygen-containing groups. However, GO still has some limitations, such as unstable performance, poor dye retention and no selective separation performance. Here, we report a weakly reduced graphene oxide (rGO) membrane that can modulate its water permeability and dye retention by controlling the reduction temperature. The water flux (84.35 L m−2 h−1 bar−1) of rGO membranes decreased with increasing reduction temperature but the methylene blue (MB) dye rejection rate (99.09 %) increased with increasing reduction temperature. More interestingly, the rGO membrane has completely different dye rejection rates for MB and methyl orange (MO), allowing the separation of MB and MO mixtures, effectively replacing traditional column chromatography. In addition, we investigated the reasons for the different retention rates and selective separation of dyes by rGO membranes through reduction temperature, contact angle, interlayer distance, electrostatic interactions and molecular dynamics simulations. This work uses a non-expensive and low-energy method to prepare nanofiltration membranes that can be easily extended to construct other stable and efficient filtration membranes for the separation of different dyes and salts.

Mechanistic Insights into Near Ambient Pressure Activity of Intermetallic NiZn/TiO2 Catalyst for CO2 Conversion to Methanol

AbstractNi−Zn pair is predicted through descriptor‐based studies to be conducive for CO2 hydrogenation. In this study, NiZn (1 : 1) intermetallics supported on TiO2 is identified as a potential candidate for near ambient pressure activity. The effect of reduction temperature on the catalyst textural properties as well as on CO2 to methanol reduction are explored. Structural and microscopic studies provide clear evidence of phase evolution of NiZn alloy with increasing reduction temperatures, along with phase variations of Zn based oxides. Interface between NiZn intermetallics and ZnO nanoparticles observed at reduction temperature of 550 °C, seems to play a crucial role in making this system most active and selective to methanol. In addition, in‐situ IR studies provide mechanistic insights and indicates the formation of methanolic species even at ambient pressure.

Kinetic study in selective reduction of limonitic and saprolitic nickel ore

ABSTRACT Saprolite and limonite have different behaviour in the carbothermic reduction process due to the differences in their atomic structures. This work investigates the kinetic study of these two different kinds of lateritic nickel ores. Nickel ore, coal, sodium sulfate, and calcium oxide were mixed, then pelletised into 10–15 mm diameters. The pellets were reduced with a non-isothermal condition using a muffle furnace at 950–1150 °C for 5–120 min. The reduced pellets were crushed into less than 74 µm prior to the wet magnetic separation process to obtain concentrates (ferronickel) and tailings (impurities). The result showed that the reduction rate for both lateritic nickel ores increased with the increase of reduction temperature and holding time. The Ginstling-Brouhnstein model was appropriate to describe the diffusion mechanism of the reduction process of limonite and saprolite. The activation energy in the reduction of limonite was lower than in saprolite. It indicated that the iron and nickel in magnesium silicate in saprolite have lower reducibility than the oxide structure in limonite. Modifying basicity in nickel laterite with CaO addition could also reduce the activation energy.

Effect of the preparation technique and the H2 reduction temperature of AHM-15.34 wt%Cu powder on the characteristics of sintered Mo-25%Cu powders compacts

Mo-25wt%Cu composite powders were obtained by high energy milling and mechanical mixing of ammonium heptamolybdate (AHM)-15.34wt%Cu powders and reduction in an H 2 atmosphere. The AHM-Cu powders were reduced at three different temperatures to study the influence of the reduction temperature on the characteristics of the Mo-Cu powders. The raw materials AHM and Cu; the mixed powders AHM-15.34wt%Cu, the composite powders Mo-25wt%Cu and the sintered bodies were characterized. The particle size of Mo-Cu powders increases with increasing reduction temperature. Good sinterability was exhibited by Mo-Cu powders obtained after milled for 20 h and reduced by H 2 at 700 °C. However, sinterability decreases with increasing reduction temperature from 700 to 800 °C. The samples were sintered at 1150 °C for 1 h under H 2 gas. Relative densities of 95.57 ± 2.49% and 83.61 ± 2.67% were achieved by compacts of milled and mixed Mo-Cu powders, respectively. A maximum electrical conductivity of 38.50 and 30.30% IACS and Vickers microhardness of 302 and 274.14 Hv were obtained by the sintered compacts prepared with milled and mixed Mo-Cu powders, respectively. • Impact of the preparation technique on the characteristics of Mo-Cu composites. • Mo-Cu composites prepared by High Energy Milling. • High energy milling improves the bond between Mo and Cu. • Mo-Cu composites with a relative density of 95.57 ± 2.49%. • Electrical conductivity of 38.50% IACS and Vickers microhardness of 302 HV.

Interaction of Hydrogen with Cu-Modified Cerium Oxide Surfaces

We investigate the interaction between molecular hydrogen and ultrathin epitaxial CeO2 films modified with a 2% concentration of Cu atoms using X-ray photoemission spectroscopy (XPS) during thermal reduction cycles in H2. The XPS measurements are combined with density functional theory calculations to obtain further insight into the observed modifications of the film surface. Our results show that the presence of Cu atoms decreases the barrier for H2 dissociation in comparison to that on pure ceria surfaces, leading to the formation of surface OH groups after exposure to H2. Moreover, surface oxygen vacancies are generated already at mild temperatures (470 K), most likely via water formation and desorption. The presence of surface oxygen vacancies and hydroxyls contributes to the observed large increase in surface Ce3+ concentration with increasing reduction temperature. In spite of these atomic scale modifications, the surface morphology observed by scanning tunneling microscopy remains substantially unchanged on the length scale of tens of nm.

Phase transformation and hydrogen reduction behavior of nanoscale W-Y2O3 powders synthesized by nano in-situ composite method

Powder plays an important role in the performance of tungsten composites. In this work, the nano-scaled W-Y2O3 powder was successfully synthesized by two-stage process of nano in-situ composite method: the calcination in air and hydrogen reduction. The phase transformation and microstructure evolution of powder were investigated and observed by the XRD, SEM, EDS and TEM technologies. Besides, the reaction and refining mechanisms for hydrogen reduction have initially proposed as well. Results showed that the phase transformation processes went through two stages of dehydration and deamination and finally forms complete tungsten oxide during the calcination stage. While, in the reduction stage, WO3 phase was mainly reduced to different WOX (1/3 ≤ x < 3) intermediate phase, especially the formation of W3O phase. The morphology of reduction of W-Y2O3 powder evolves from hollow spheres to slices, fragments and nano-irregular polygon as the reduction temperature increases. Simultaneously, the average particle size of W-Y2O3 powder decreases significantly with the increase of reduction temperature, while the reduction temperature is 800 °C, the change trend is opposite, but it's still much lower than pure tungsten. The addition of Y2O3 significantly affected the phase transition and microstructure evolution behavior of composite powders. The reduction was started from the surface region of powder, and then in the form of cracks or porous structures extend into the interior of the powder until all the nano-particles were formed, which was able to be explained by “shrinkage fissure - particle rupture” and “nucleation - evaporation - sedimentation” model. Moreover, the core-shell structure and Y2WO6 phase formed by addition of Y2O3 can hamper the chemical vapor transport (CVT) and the formation of WO2(OH)2 phase, thus significantly refining the reduced W-Y2O3 powder(115 nm).