Increasing Reduction Temperature Research Articles

Microstructure and magnetic properties of Fe-Al2O3 nanocomposites prepared by a versatile facile combustion-based route

Fe-Al2O3 nanocomposites with Al2O3 nanoparticles uniformly dispersed have been successfully prepared via a versatile facile and scalable combustion-based route with two steps. Firstly, the homogenous mixed oxide precursor composed with α-Fe2O3, γ-Fe2O3 and Al2O3 was prepared by solution combustion synthesis. Subsequently, Fe-Al2O3 nanocomposites with Al2O3 nanoparticles evenly dispersed were prepared by hydrogen reduction of the mixed oxide precursor. The effects of the various reduction temperatures on the phase composition, morphology, grain size and magnetic properties of the Fe-Al2O3 nanocomposites were investigated in details. The results show that the Fe-Al2O3 nanocomposites prepared at as low as 400 °C present a connected network structure with an average grain size of about 17 nm, which have a saturation magnetization of 125.3 emu/g, and a coercivity of 721.2 Oe. With the increase of reduction temperature, the average grain size, and saturation magnetization of the Fe-Al2O3 nanocomposites increase gradually, while the coercivity decrease. When the reduction temperature is increased to 500 °C and 600 °C, the grain size increases to about 27 nm and 37 nm, the saturation magnetization increases to 153.6 emu/g and 177.1 emu/g, and the coercivity decreases to 634.6 Oe and 467.8 Oe, respectively.

Tandem Upgrading of Bio-Furans to Benzene, Toluene, and p-xylene by Pt1Sn1 Intermetallic Coupling Ordered Mesoporous SnO2 Catalyst.

Benzene, toluene, and p-xylene (BTpX) are among the most important commodity chemicals, but their productions still heavily rely on fossil resources and thus pose serious environmental burdens and energy crisis. Herein, the tandem upgrading of bio-furans is reported to high-yield BTpX by rationally constructing a versatile Pt1Sn1 intermetallic coupling ordered-mesoporous SnO2 (OM-SnO2) catalyst. It is shown that with increasing reduction temperature from 200 to 350°C, Pt nanoparticles (NPs) are first formed on OM-SnO2, then converted to Pt3Sn1 intermetallic nanoparticles (iNPs), and finally to Pt1Sn1 iNPs with a gradually-thickened SnO2 overlayer. Impressively, the Pt1Sn1 iNPs and defect-rich OM-SnO2 in the optimized Pt@OM-SnO2 can serve as the highly-active species for the hydrogenolysis of 5-hydroxymethylfuran to 2,5-dimethylfuran and the aromatization of 2,5-dimethylfuran with acrylic acid to p-xylene, affording the highest yields of 99.1% and 96.1%, respectively. More importantly, it can perfectly realize the tandem upgrading of furan, furfural and 5-hydroxymethylfuran to benzene, toluene and p-xylene with high yields of 94.6%, 94.2% and 95.2%, respectively, representing a new tandem catalytic system to realize the high-yield BTpX productions from their corresponding bio-furans. This catalyst also shows good recyclability and excellent scalability, which together with its superior activity/selectivity suggest a high potential for sustainable BTpX productions.

Kinetic modelling of carbothermal reduction of nickel oxide (NiO): Design of Experiments (DOE) approach

ABSTRACT This study presents a mathematical model to evaluate the kinetics of the carbothermal reduction of NiO using graphite. Based on the shrinking core theory, the model was validated against experimental data obtained under both isothermal and non-isothermal conditions. The shrinking core model for isothermal and non-isothermal conditions was created using MATLAB software for the kinetic modelling of the reduction process to determine the extent of reduction and the reaction rate. The kinetics were mathematically modelled from independently measured physical and thermodynamic properties of the reaction system and experimentally measured properties. The carbothermal reduction method was effective in producing Ni metal from NiO and was considered an established basis for evaluating the modelling aspect of the solid–gas system. The experimental investigation of carbothermal reduction was conducted using a statistical design of experiments (DOE), employing a two-level factorial design (23). The experiments were performed for a range of different factors, namely reduction temperature (800-1000°C), reduction time (1-2 h), and the molar ratio of graphite to NiO (0.5-1.5) on the extent of reduction. The extent of reduction increases with increasing reduction temperature, reduction time, and molar ratio of C to NiO. The highest extent of reduction (77.9%) was achieved at a reduction temperature of 1000°C, 2 h of reduction time, and the molar ratio of C to NiO as 1.5. The X-ray diffraction (XRD) studies confirmed the formation of Ni at a lower reduction time, but the intensity of the Ni phase was higher for a longer duration of reduction. SEM-EDS analysis of the reduced products confirmed the formation of Ni in the form of elongated and larger grains, along with traces of residual or unreacted carbon. The predicted extent of reduction is then compared with the experimentally measured results. The kinetic modelling results proved that both isothermal and non-isothermal shrinking core models showed similarity and significant closeness to the experimental data. The deviation between the experimental and model results could be due to the varying geometry and porosity of the reactants and intermediate products.

Interaction between three key species in the sea ice-reduced Arctic Barents Sea system.

Population dynamics depend on trophic interactions that are affected by climate change. The rise in sea temperature is associated with the disappearance of sea ice in the Arctic. In the Arctic part of the Barents Sea, Atlantic cod, capelin and polar cod are three fish populations that interact and are confronted with climate-induced sea ice reductions. The first is a major predator in the system, while the last two are key species in Arctic and sub-Arctic ecosystems, respectively. There are still many unknowns regarding how predicted environmental change may influence the joint dynamics of these populations. Using time series from a 32 year long survey, we developed a state-space model that jointly modelled the dynamics of cod, capelin and polar cod. Using a hindcast scenario approach, we projected the effect of reduced sea ice on these populations. We show that the impact of sea ice reduction and concomitant sea temperature increase may lead to a decrease of polar cod abundance at the benefit of capelin but not of cod which may decrease, resulting in strong changes in the food web. Our analyses show that climate change in the Arcto-boreal system can generate different species assemblages and new trophic interactions, which is the knowledge needed for effective management measures.

Activity of bimetallic PdIn/CeO2 catalysts tuned by thermal reduction for improving methanol synthesis via CO2 hydrogenation

AbstractSynergistic Pd–In2O3 catalysts are promising candidates for producing methanol via CO2 hydrogenation, and the metal phases in them can be tuned by thermal reduction treatment affecting the catalytic activity significantly. This work presents a comprehensive investigation to gain an insight into the effect of thermal reduction temperature on the variation and interaction of Pd and In2O3 phases supported on CeO2 (viz., PdIn/CeO2) and their correlations with CO2 hydrogenation toward methanol synthesis. The findings show that Pd/In‐rich PdIn alloys and In2O3 with relatively strong interaction are key phases (by reducing the PdIn/CeO2 at 300°C) for promoting methanol formation, leading to a high selectivity to methanol at 78.9% and space–time yield (STY) of 3.6 gCH3OH gPdIn−1 h−1. A further increase in reduction temperature (from 300 to 500°C) promoted the formation of homogenized PdIn intermetallic alloys with significantly poor ability for H2 dissociation and CO2 activation, and hence poor methanol yield.

Hydrogen reduction and baking process of Pb-silicate microchannel plate and their performance studies

Microchannel plate (MCP) are honeycomb structures consisting of numerous parallel, hollow micro glass fiber channels renowned for their exceptional secondary electron multiplication. This paper investigates changes in MCP properties under hydrogen reduction temperatures ranging from 300 °C to 500 °C. The findings reveal that higher temperatures reduce surface metal oxides, which then accumulate within and darken the microchannels, affecting electron transport. Bulk resistance decreases before increasing, while gain increases and then decreases. At 350 °C, lead oxide begins to reduce to its conductive state, enhancing electron multiplication. However, increased temperatures cause clustering and roughening of the inner channel walls, which diminishes the efficiency of secondary electron release. These alterations are associated with the reduction dynamics of lead ions and temperature-induced microstructural changes. As the hydrogen reduction temperature increases, internal stresses shift outward, and the uniformity of gain varies, reaching its peak at 400 °C. Additionally, an aluminum oxide film enhances resistance to baking and ensures consistent bulk resistance. This study elucidates the relationship between MCP performance and reduction temperature, providing valuable insights for design improvement.

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

Supported 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

Reduction of natrojarosite and laterite nickel ore leaching residue composite using palm kernel shell reducing agents at temperatures of 1300-1450℃

Lateritic nickel ore processing through hydrometallurgical route generates a significant amount of residue from the leaching stage. Two examples of hydrometallurgical process residues, namely natrojarosite and leaching residue can potentially be used as secondary raw materials for the iron and steel industry. A relatively high sulfur content of up to 12% is a severe issue because the sulfur threshold value for steel raw materials is 1%. Therefore, it is necessary to reduce the sulfur content in natrojarosite and leaching residue to meet the standards as a secondary raw material for the iron and steel industry. In this research, reduction of natrojarosite, laterite nickel ore leaching residue, and palm kernel shell reducing agents composite was conducted in varying amounts of palm kernel shell reductant of 25-100% using a non-isothermal method at an initial temperature of 1000°C with a final temperature of 1300-1450°C and an isothermal method of 1000°C, 1300°C, and 1450°C for 2 hours. The results showed that an excessive amount of reductant (≥25%) would inhibit the formation of iron metal at macrosize (above 0.35 mm). Reduction, both by non-isothermal and isothermal methods, results in decreasing sulfur content in the metal phase as the reduction temperature increases, but a sulfur-rich matte phase is still observed in all experimental conditions. The proportion of the metal phase produced is getting higher and more separated from the slag phase as the temperature increases. The optimum condition was obtained at a non-isothermal reduction of 1450°C using a 25% reducing agent which resulted in iron and sulfur content in the metal phase of 88.53% and 0.49%, respectively, with a metal-matte phase proportion of 65.56%. In this case, slag was dominated by liquid phase with a FeO content of 7.64% and a viscosity of 7.313 PaS.

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.