Low-temperature Reduction Research Articles

Preparation of Mn/TiO2 catalysts using recovered manganese from spent alkaline batteries for low-temperature NH3-SCR

Black mass (BM) from spent alkaline Zn-MnO2 batteries was used for the first time as a Mn source in the preparation of Mn/TiO2 catalysts for low-temperature NH3-selective catalytic reduction (SCR) of NOx. To recover Mn species and eliminate alkali and Zn species, BM powder underwent DI-water washing, followed by carbothermal reduction. The resulting slags were further dissolved in HNO3, loaded onto TiO2 particles with ball milling, and then subjected to calcination. Nearly 100% of Zn species were removed from the BM via carbothermal reduction at 950 °C for 4 h with 5.0 wt% activated carbon. The resulting catalyst, derived from the treated BM, achieved similar NOx conversion (97%) as the catalyst prepared using a reagent-grade Mn chemical at 160 °C but a higher NOx-to-N2 conversion rate at 78%. The promoted N2 selectivity was attributed to a high Mn4+/Ti ratio and the presence of impurities from BM, such as Fe3+ ions, which enhanced oxidation ability of the catalyst. Conversely, insufficient removal of Zn or carbon additives in the slags led to a decreased Mn concentration, an increased proportion of Mn2+/Mn3+ species, increased surface OH groups, and reduced oxidation ability on the surface, thus reducing NOx conversion and N2 selectivity.

Promoting effect and kinetic analysis of Fe-Co bimetallic doping on the LaMnO3 catalytic activity for methane combustion

To enhance the catalyst’s properties, a modified sol–gel method is developed in this study, and a unique perovskite catalyst, LaMnxFeyCo1-x-yO3, is successfully synthesized by doping Fe-Co into the lattice of LaMnO3. The catalytic activity of the synthesized catalysts is initially determined by applying them to methane oxidation. Then, the structural, chemical, and surface properties of these catalysts are systematically evaluated utilizing XRD, BET, O2-TPD, H2-TPR, SEM, and XPS analyses. The modified LaMn0.8Fe0.15Co0.05O3 is shown to exhibit excellent activity (T90 at 486.5 ℃) in methane catalytic combustion, comparable to several standard noble metal materials. Experimental findings indicate that such perovskite structures have a larger specific surface area, an elevated molar ratio of Mn4+, desirable low-temperature reducibility, and excellent oxygen mobility relative to the original LaMnO3. Meanwhile, more efficient electron transfer from Mn4+/Mn3+ redox cycles, as well as the emergence of oxygen defects, significantly contribute to the robust interaction between Fe-Co and LaMnO3. Further reaction kinetic analysis is conducted to determine changes in species components and identify possible catalytic pathways. Notably, Fe-Co co-doping leads to an improvement in the increase of lattice oxygen and CH4 adsorption. In addition, the MVK kinetic mechanism governs methane combustion over LaMn0.8Fe0.15Co0.05O3. This study provides new insights into enhancing energy conversion performance and efficient utilization of ventilation air methane (VAM) through the implementation of highly efficient perovskites.

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Tuning the crystallinity of the MnOx catalysts to promote toluene catalytic oxidation

ABSTRACT In this paper, the MnOx catalysts with excellent toluene oxidation performance were prepared by a simple precipitation method. The physicochemical properties of the prepared MnOx catalysts were investigated by XRD, BET, H2-TPR, O2-TPD and XPS. The obtained results revealed that the crystallinity of the prepared MnOx catalysts could be effectively regulated by changing the (NH4)2CO3/Mn(NO3)2 molar ratio, and thus affecting the oxygen vacancy concentration of the prepared MnOx catalysts. The prepared MnOx-4 catalyst with the (NH4)2CO3/Mn(NO3)2 molar ratio of 4.0 had the poor crystallinity and small grain size, which effectively promoted the oxygen defects in the MnOx catalyst to be formed. At the same time, the MnOx-4 catalyst had a large specific surface area, the highest low temperature reducibility and the largest number of oxygen vacancies and surface adsorbed oxygen species, which allowed more surface oxygen species to participate in the redox reaction, and promoted the toluene deep oxidation. Therefore, when the (NH4)2CO3/Mn(NO3)2 molar ratio was 4.0, the prepared MnOx-4 catalyst exhibited an excellent toluene catalytic oxidation performance and robust catalytic stability. What’s more, the toluene oxidation conversion on the MnOx-4 catalyst reached 99% at 230°C, and the MnOx-4 catalyst showed excellent resistance to water vapour.

Metal Droplet Migration and Gathering in Semi-molten Sludge at Low Temperature Reduction

Metal Droplet Migration and Gathering in Semi-molten Sludge at Low Temperature Reduction

Preparation of Ultrafine Co- and Ni-Coated (Ti,W,Mo,Ta)(C,N) Powders and Their Influence on the Microstructure of Ti(C,N)-Based Cermets.

The use of metal-coated ceramic powders not only effectively enhances the wettability of the metal-ceramic interface but also promotes a more uniform microstructure in Ti(C,N)-based cermets, which is advantageous for improving their mechanical properties. In this study, ultrafine Co- and Ni-coated (Ti,W,Mo,Ta)(C,N) powders were synthesized via the spray-drying-in-situ carbothermal reduction method. Subsequently, Ti(C,N)-based cermets were effectively fabricated using the as-prepared ultrafine Co- and Ni-coated (Ti,W,Mo,Ta)(C,N) powders. The impact of reaction temperature, heating rate, and isothermal time on the phase and microstructure of prepared powders was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, the microstructure of the as-sintered cermets was experimentally investigated. The findings reveal that the complete reduction of Co and Ni metal salts, pre-coated on the surface of (Ti,W,Mo,Ta)(C,N) particles, can be achieved through rapid heating (10 °C/min) in a specific temperature range (600-1000 °C) with an isothermal time of 3 h at a lower reduction temperature (1000 °C). The synthesized powders have only two phases: the (Ti,W,Mo,Ta)(C,N) phase and Co/Ni phase, and no other heterogeneous phases were observed with an oxygen content of 0.261 wt.%. Notably, the conventional core-rim structure was not dominant in the cermets obtained from the prepared Co- and Ni-coated (Ti,W,Mo,Ta)(C,N) powders. Moreover, the heterogeneous segregation effect of the Co/Ni coating on the ultrafine powder particles resulted in a finer microstructure than the traditional cermets with the same composition. However, the grain size is mainly in the range of 0.5-0.8 μm. The weaker residual stresses at the core and rim interfaces and the finer particle distributions could theoretically enhance the toughness of Ti(C,N)-based cermets, simultaneously.

Hierarchical fluoride-containing zeolite Y supported Ru for catalytic conversion of xylose to xylitol

Hierarchical fluoride-containing zeolite HY (Hie-HY(F)) is an interesting material because it tunes both a high mesoporosity and a moderate acid property, which could benefit the transformation of xylose to xylitol. Herein, we synthesized a new Hie-HY(F) by etching NH4Y with ammonium fluoride (NH4F) under ultrasonication at 60 °C for 20, 40, and 60 min. After etching with NH4F solution, the Hie-HY(F)s contained fluoride in the zeolite frameworks with high mesoporosity and moderate acid properties. The sonication time longer than 20 min caused the structure to collapse rather than the creation of mesoporosity. The Hie-HY(F)s were further used as supports for the Ru catalyst. When loaded with Ru precursor and calcined in air, RuO2 phase was formed in all catalysts. The RuO2 supported on Hie-HY(F)s had a lower reduction temperature than that on HY. Ru supported on Hie-HY(F)-20 gave the reactivity of xylose conversion to xylitol, the highest yield of 80.1 %, providing the reusability up to four cycles.

Planetary Soil Simulant Characterisation: NU-LHT-2M Study Case to Support Oxygen Extraction Lab Tests with a Low-Temperature Carbothermal Process

Since the landing on the lunar surface, the lunar regolith has begun to interact in different ways with landed elements, such as the wheels of a rover, astronaut suits, drills, and plants for extracting oxygen or manufacturing objects. Therefore, a strong effort has been required on Earth to fully characterise these kinds of interactions and regolith utilisation methods. This operation can only be performed by using regolith simulants, soils that are reproduced with the Earth’s rocks and minerals to match the real features. This article presents the main guidelines and tests for obtaining the properties of a generic simulant in terms of composition, physical and mechanical properties, solid–fluid interaction, and thermal properties. These parameters are needed for the designing and testing of payloads under development for planned lunar surface missions. The same tests can be performed on lunar, martian, or asteroid simulants/soils, both in laboratory and in situ. A case study is presented on the lunar simulant NU-LHT-2M, representative of the lunar highlands. The tests are performed in the context of an in situ resource utilisation (ISRU) process that aims to extract oxygen from the lunar regolith using a low-temperature carbothermal reduction process, highlighting the main regolith-related criticalities for an in situ demonstrator plant.

The beneficial effect of lauric acid addition in nucleation stage on the soot catalytic combustion performance of cerium-manganese catalyst

For cerium-manganese catalyst system, increasing the threshold of the amount of Mnx+ entering into the CeO2 lattice can generate more oxygen vacancies and adsorb more active oxygen species, thus promoting its soot catalytic combustion. However, this is difficult to achieve under the premise of fixed cerium-manganese ratio of the catalyst. Fortunately, the results of this study show that the addition of lauric acid at the nucleation stage of the cerium-manganese catalyst can effectively improve its activity and high temperature aging resistance. Combined with a series of characterization results, the addition of lauric acid can increase the threshold of Mnx+ content in CeO2 lattice, improve the structural performance of the catalyst, increase the specific surface area and pore volume of the catalyst, inhibit the secondary aggregation of catalyst particles, increase the content of surface Ce3+, increase the low temperature reduction performance and the content of surface chemical desorbed oxygen of the catalyst. In addition, it can also prevent the phase separation of cerium-manganese solid solution, the growth of grains, the increase of reduction peak temperature and the decrease of H2 consumption during high temperature aging. Moreover, the addition of lauric acid also greatly improves the release performance of active oxygen in cerium-manganese catalyst. Therefore, this study plays a positive role in promoting the commercial application of highly active cerium-manganese catalyst.

Analysis of the reaction mechanism of N/S co-doped carbon-based catalysts for low-temperature NH3-SCR reduction of NOx

In this paper a series of N/S co-doped carbon-based low-temperature denitrification catalysts were prepared using thiourea and coal-based activated carbon. Tests such as BET, NH3-TPD, XPS and DRIFTS were applied to characterize the performance of the prepared catalysts. It was found that the denitrification activity of NSAC-1.2 catalyst was 2.08 times higher than that of coal-based activated carbon. The denitrification activity of all N/S co-doped carbon-based catalysts was greater than 80 % in the temperature range of 150–260 °C. The presence of N and S functional groups creates more acidic sites and oxygen vacancies on the catalyst surface, which leads to the reduction of the reaction energy barrier, the promotion of the adsorption and activation of reactants and in turn the improvement of the denitrification activity of the catalyst. N/S co-doping for N-5 and N-6 groups as well as C-SO2-C species enhancement affect the catalyst denitrification activity improvement comprehensively. The reaction mechanism of NH3-SCR process on N/S co-doped carbon-based catalysts was investigated by in-situ DRIFTS.

A facile method for preparing the CeMnO3 catalyst with high activity and stability of toluene oxidation: The critical role of small crystal size and Mn3+-Ov-Ce4+ sites

Volatile organic compounds (VOCs) cause severe environmental pollution and are potentially toxic to humans who have no defense against exposure. Catalytic oxidation of these compounds has thus become an interesting research topic. In this study, microcrystalline CeMnO3 catalysts were prepared by a precipitant-concentration-induced strategy and evaluated for the catalytic oxidation of toluene/benzene. The effect of crystal size on catalytic performance was confirmed by XRD, TEM, N2 adsorption-desorption, XPS, Raman, H2-TPR, and TPSR. The CeMnO3 catalyst with more Mn3+-Ov-Ce4+ active sites exhibited enhanced VOCs catalytic oxidation performance, lowest active energy, and highest turnover frequency, which was attributed to its larger surface area, lower crystal size, higher low-temperature reducibility, and presence of more oxygen defects. In-situ FTIR results suggested more oxygen vacancies can profoundly promote the conversion of benzoate to maleate species, the rate-determining step of toluene oxidation. The work provides a convenient and efficient strategy to prepare single-metal or multi-metal oxide catalysts with smaller crystal sizes for VOC oxidation or other oxidation reactions.

Effective formaldehyde elimination over pyrolusite-manganite hybrid catalysts promoted by Keggin acid decoration: Tungsten doping and chemically adsorbed active oxygen

A series of pyrolusite-manganite composites with five levels of phosphotungstic acid additions (HPWxMn, x indicating the added mass of phosphotungstic acid) were applied in the catalytic oxidation of 330–350 mg/m3 formaldehyde under ambient conditions. Different techniques were used to characterize the pristine composite and the best-performed HPW0.2Mn catalyst. Compared to the effects of hydrogen (replacing a small part of structural K+ ions) and phosphorus (not detected in the HPW0.2Mn catalyst) elements in phosphotungstic acid, the doping of tungsten would prefer to occur via forming W-O-Mn species, which significantly altered the crystallite growth and induced numerous defects. As to formaldehyde degradation, the best 91% conversion and 72% CO2 yield were achieved on HPW0.2Mn. The uniqueness of tungsten doping on boosting formaldehyde oxidation was expounded from the angles of intimate elemental interaction (XPS), redox behavior and molecular O2 activation (CO-TPR, UV-Vis DRS and O2-TPD). The incorporation of tungsten led to higher surface Mn3+ concentration, higher content of surface oxygen vacancies, better low-temperature reducibility and abounding chemically adsorbed oxygen species (They were proposed to be the dominant oxidants for formaldehyde oxidation in this study), which were well correlated with the sequence of catalytic activity. Finally, possible reaction pathways were examined by coupling the characterizations of used catalysts.

Impact of varied zeolite materials on nickel catalysts in CO2 methanation

Ni catalysts supported on 4A, 5A, 13X, ZSM-5, and BEA zeolites were prepared using the vacuum-heating method for CO2 methanation. These support materials play a pivotal role in shaping the catalysts' properties and their catalytic performance. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) mappings suggest a significant concentration of Ni nanoparticles situated on the external surfaces of catalysts with low Si/Al ratios zeolites (Ni-4A, Ni-5A, and Ni-13X). These Ni nanoparticles exhibit characteristics of weaker metal-support interaction, lower metal reduction temperatures, and moderate H2 adsorption activity. Moreover, these low Si/Al ratio zeolites demonstrate robust CO2 adsorption activity. These properties endow Ni-5A and Ni-13X catalysts with heightened CO2 conversion (70.4–70.9%) and methane selectivity (92.4–96.4%). In contrast, high Si/Al ratio zeolite-based catalysts (Ni-ZSM-5 and Ni-BEA) exhibit smaller Ni particles, strong metal-support interaction and weaker CO2 adsorption activity, resulting in reduced CO2 methanation activity and decreased methane selectivity (71.2–73.4%). The normalized CO2 conversion rate presents a correlation with the average Ni particle size.

Research on the reaction behavior of pellets in typical atmospheres of shaft furnaces: Reduction swelling and carbon deposition

In this work, the volume swelling and carbon deposition behavior of pellets under shaft furnace smelting conditions were studied. The research process on swelling reduction utilized an online detection imaging method to determine the volume changes of pellets. The results suggest that an increase in temperature and a higher proportion of carbon monoxide in the reducing gas contribute to an escalation in the swelling rate during pellet reduction. Carbon deposition induced by carbon monoxide primarily occurs at 750 °C, and the powdery carbon deposition products on the surface of the pellets change over time, transitioning from carbon to a mixture of carbon and iron carbide (Fe3C) to a mixture of carbon, Fe3C, and metallic iron. This study elucidated the behavior of pellets in the low-temperature reduction section during the shaft furnace smelting process, offering a technical foundation for shaft furnace smelting technology.

Hydrothermic reduction of rutile-ilmenite mineral producing an oxyhydride η-Ti<sub>2</sub>FeO<sub>0.2</sub>H<sub>2.8</sub>: Towards in-situ hydrogen production and storage

As an alternative to the physical storage of hydrogen as compressed gas or liquid hydrogen requiring high-pressure tanks and cryogenic temperatures, the material-based storage of hydrogen in solids involves hydrogen uptake and release from the surface of adsorbents or within interstitials of hydrides. We report a hydrothermic reduction of rutile-ilmenite mineral into hydrogen-rich fibrous products, η-Ti2FeO0.2H2.8, in an ethanol-water system at 120°C for 4 hrs. As part of a project to generate hydrogen from water-ethanol system using advanced catalysts containing graphene oxide (GO) as carbon source, a system of 62.5 μg graphene oxide per g of rutile-ilmenite mineral was employed in a concentration of 50 mg/mL of ethanol-water solution. As well as in the original mineral, XRD of thermal annealed mineral between 500 and 800°C showed no hydride or phase change in rutile-ilmenite. With hydrothermal treatment of GO/rutile-ilmenite (50 mg/mL) in ethanol-water (1:1 v/v) at 120°C, a hydrogen-rich ferrotitanium hydride phase was formed, and there was a change in morphology from plate-like and granular particles into fibrous structures. Like the release of hydrogen by its ‘carriers’ (e.g., CaH2, NH4BH4, NaBH4, NH3, formic acid), it is anticipated that hydrogen was generated from the ethanol-water system in-situ, which reduced the rutile-ilmenite mineral into a hydride. EDX results showed that the reduction affected specifically the oxides of Fe and aluminosilicates in the mineral. The study demonstrated a possibility of in-situ hydrogen generation and storage via low-temperature graphene oxide hydrothermic reduction of rutile-ilmenite mineral in an ethanol-water system.

Transient kinetic analysis of CO oxidation over a Cu-SSZ-13 catalyst proves complete conversion of ZCu2+(OH)- cations to binuclear Cu2+ species

The nuclearity of Cu2+ species active in the low-temperature Reduction Half Cycle (RHC) of NOx Selective Catalytic Reduction with NH3 over Cu-CHA catalysts is controversial. In the past, transient CO to CO2 oxidation protocols have been used to titrate binuclear Cu2+ species, and identified NH3-solvated ZCu2+(OH)- ions as their precursors. However, the prior results relied on asymptotic extrapolation due to the very slow CO oxidation kinetics. We herein present the results from a prolonged (24 h) CO titration experiment under dry conditions over an industrial Cu-SSZ-13 catalyst: the results demonstrate the conversion of all ZCu2+(OH)- ions to binuclear Cu2+ complexes and agree well with the extrapolation of a shorter (90 min) experiment, based on the assumption of the CO oxidation rate being second order in ZCu2+(OH)-. These outcomes confirm the adequacy of short CO oxidation tests to titrate ZCu2+(OH)- ions and support a Cu2+ pair mediated RHC pathway.

A novel CeO2 nanowire catalyst prepared by the freeze-drying method with significantly improved catalytic performance for toluene oxidation

A wire like CeO2 catalyst (CeO2-w) was obtained after the calcination of the precursor at 400 °C, which was prepared by the freeze-drying method for the first time. It shows good performance for catalytic oxidation of toluene with T90 of 220 °C, which is much better than the CeO2 catalysts with other structures prepared by the different methods. The good performance of CeO2-w is due to the bigger pore volume, more active oxygen species, more oxygen vacancies, better low temperature reducibility, higher surface area normalized reaction rates and lower Ea value. Additionally, the CeO2-w catalyst exhibits good water resistance and catalyst stability. In situ DRIFTS indicates the catalytic oxidation of toluene on CeO2-w undergoes the progress of toluene → benzaldehyde → benzoic acid → maleic acid → CO2 and H2O. This work affords a new idea to prepare high active CeO2 nanowire catalysts for catalytic oxidation of toluene, and open an efficient way for the construction of CeO2 based composite catalysts for VOCs degradation.

Metallurgical Properties of Vacuum Extrusion Iron‐Rich Dust Briquette and Its Effects on Blast Furnace Soft Melting Zone

The vacuum extrusion iron‐rich dust briquette (VEIDB) in this study is prepared by vacuum extrusion of iron ore fines and blast furnace dust. In this article, the metallurgical properties such as compressive strength, tumbler strength, low temperature reduction disintegration performance, reducibility, and softening melting properties of VEIDB are studied. The effect of VEIDB on the soft melting zone of blast furnace is also studied. Results show that the compressive strength of VEIDB is 5.684 kN/VEIDB, the tumbler strength is 89.87%, RDI−0.5 = 2.82%, and the metallization degree after reduction is 96.9%. However, its softening and melting properties is bad. The study on the influence of VEIDB on softening and melting properties of iron‐containing burden shows that, adding VEIDB in blast furnace burden would make the soft melting zone of blast furnace move up and expand; with the increase of the VEIDB amount, the permeability decreases first and then increases. The addition of VEIDB in blast furnace burden should be controlled within 10%.

Mn-MIL-100 non-thermally derived MnOx catalysts for toluene oxidation

Herein, a novel preparation method via non-thermal derivation by using Mn-MIL-100 as the precursor to synthesize MnOx catalysts was proposed. The synthesized catalysts were applied to toluene oxidation. Characterizations and experiments results showed that the more surface Mn3+, Oads species, large surface area, better low-temperature reducibility and higher lattice oxygen mobility of Mn-Na2CO3 prepared via Na2CO3 treatment induced its great catalytic activity for toluene oxidation.

Modulating the C and Mo Exposure of Molybdenum Carbide for Efficient Low-Temperature CO2 Reduction to CO

Modulating the C and Mo Exposure of Molybdenum Carbide for Efficient Low-Temperature CO2 Reduction to CO