Precursor Impregnation Research Articles

Preparation and performance of C/Ta4HfC5-SiC composite fabricated by PIP combined with RMI process

Based on self-made Ta4HfC5 precursor, C/Ta4HfC5-SiC composite material were prepared by precursor impregnation and pyrolysis (PIP) combined with reactive melting infiltration (RMI) process. The density and open porosity of C/Ta4HfC5-SiC composite material are 2.71 ± 0.73 g/cm3 and 7.07 ± 1.29 %, respectively. Pores are distributed at multiple levels, including primarily nanopores below 40 nm, micropores between 0.04 and 8.5 μm, and a small number of macropores between 10 and 285 μm. The Ta4HfC5 phase exists in two forms: dispersed particles in the matrix and a "layered interface" on the surface of fibers within the bundle. The average bending strength, elastic modulus and fracture toughness of C/Ta4HfC5-SiC composite are 84.24 ± 8.71 MPa, 16.13 ± 5.42 GPa and 3.62 ± 0.63 MPa m1/2, respectively, showing a clear brittle fracture mode during the test. The line ablation rate and mass ablation rate of 60 s assessed by the oxyacetylene flame were 7.20 ± 0.35 μm/s and 10.84 ± 0.84 mg/s, respectively. The oxidation products such as Ta2O5, HfO2, Ta(Hf)CxOy formed by Ta4HfC5 phase during ablation present as thicker oxide layers, forming the main anti-ablation components.

Impacting the Surface Chemistry of NiAu by Immobilizing on MgO/N-Rich Nanoporous Carbon Heterostructures for Boosting Catalytic Activities.

Tuning the physical and chemical interaction between metal-metal' (M-M') and metal-support is an ideal way to realize enhanced catalytic activity of metal nanoparticles (NPs). As a proof of concept, herein we report the fabrication of nickel-gold (Ni-Au) alloy nanoparticles attached to N-doped nanoporous carbon (NPC) intervened with MgO (Ni73Au27@MgO-NPC), achieved through the impregnation of metal precursors into Schiff-base network polymer (SNP) framework along with Mg(OH)2 and pyrolysis at 800 °C in N2 atmosphere. With high stability and heterogeneity, the nickel rich Ni73Au27@MgO-NPC exhibited higher catalytic activities with turnover frequencies of 29,272 h-1 (hydrogenation of p-nitrophenol), 93,843 h-1 (degradation of methyl orange), and 2,218 h-1 (epoxidation of stilbene), compared to commercial 10 wt % Pd/C. Enhanced catalytic activity is correlated to the synchronized electron density enhancement in Au, by Ni and MgO/N-rich nanoporous carbon heterostructures, as evident from detailed X-ray photoelectron spectroscopic studies.

Mechanical properties and microstructure of quartz fiber-reinforced silica matrix composite with a single layer pyrocarbon interphase

Silica matrix composites (SiO2f/SiO2), reinforced with pyrolytic carbon (PyC) interfacial layers, were synthesized using the precursor impregnation and pyrolysis (PIP) method, mechanical properties and microstructure of these composites were thoroughly investigated. The flexural strength of SiO2f/PyC/SiO2 composites exceeded 55 MPa after treatment at 450°C. Notably, at medium and high temperatures, strength of SiO2f/SiO2 composites was significantly enhanced compared to that of uncoated PyC composites. The experimental resulted indicate that PyC temporary interfacial layer effectively mitigated the strong interfacial reaction between quartz fibers and matrix. Furthermore, fiber pull-out phenomenon observed at the fracture of SiO2f/PyC/SiO2 composites suggested that interfacial bonding was weak, which contributed to the high mechanical strength of these composites.

Impact of Inverse Manganese Promotion on Silica-Supported Cobalt Catalysts for Long-Chain Hydrocarbons via Fischer–Tropsch Synthesis

One of the challenges in Fischer–Tropsch synthesis (FTS) is the high reduction temperatures, which cause sintering and the formation of silicates. These lead to pore blockages and the coverage of active metals, particularly in conventional catalyst promotion. To address the challenge, this article investigates the effects of the preparation method, specifically the inverse promotion of SiO2-supported Co catalysts with manganese (Mn), and their reduction in H2 for FTS. The catalysts were prepared using stepwise incipient wetness impregnation of a cobalt nitrate precursor into a promoted silica support. The properties of the catalysts were characterized using XRD, XPS, TPR, and BET techniques. The structure–performance relationship of the inversely promoted catalysts in FTS was studied using a fixed-bed reactor to obtain the best performing catalysts for heavy hydrocarbons (C5+). XRD and XPS results indicated that Co3O4 is the dominant cobalt phase in oxidized catalysts. It was found that with increase in Mn loading, the reduction temperature increased in the following sequence 10%Co/SiO2 < 10%Co/0.25%Mn-SiO2 < 10%Co/0.5%Mn-SiO2 < 10%Co/3.0%Mn-SiO2. The catalyst with the lowest Mn loading, 10%Co/0.25%Mn-SiO2, exhibited higher C5+ selectivity, which can be attributed to less MSI and higher reducibility. This catalyst showed the lowest CH4 selectivity possibly due to lower H2 uptake and higher CO chemisorption.

Enhanced molding and mechanical properties of SiC-based ceramic lattice structures via digital light processing

Silicon carbide (SiC) ceramic lattice structures (CLSs) hold significant potential for use in structural components and optical mirrors in space exploration due to their light weight, high strength, and excellent dimensional stability. However, they face challenges such as poor curing performance and weak mechanical strength during the digital light processing (DLP) additive manufacturing process. In this study, SiC@Al2O3 powder was prepared, resulting in a 21 % reduction in absorptivity compared to bare SiC powder. The ceramic paste derived from this powder achieved a curing thickness of up to 80 μm, exhibited a reduced over-curing width, and demonstrated a 75 % improvement in stability compared to bare SiC paste. Consequently, high-quality triply periodic minimal surfaces (TMPS) structured SiC@Al2O3 CLSs green bodies were successfully fabricated. By integrating precursor impregnation pyrolysis with the reaction melting infiltration (PIP-RMI) post-treatment densification method, SiC@Al2O3/Si CLSs were produced, exhibiting superior mechanical properties with low dimensional shrinkage. At 30 % volume fraction, the specific compressive strength of the primitive-TPMS SiC@Al2O3/Si CLSs reached 24.79 MPa. This study presents an effective method for fabricating SiC-based CLSs and establishes a foundation for the optimization of SiC ceramic fabrication processes.

Pt/C and PtRu/C Catalysts Prepared by Modified Sulfite Complex Routes for Fuel Cell Applications

In-house 30 wt.% Pt and 50 wt.% Pt1Ru1 catalysts supported on high-surface area carbon (Ketjenblack, abbreviated as KB) were synthesized by the sulfite complex route. Two different procedures involving either a direct mixing of Pt-sulfite and Ru-sulfite complexes or Pt-sulfite preparation and subsequent impregnation of Ru precursor were adopted for the bimetallic species. In both cases, an impregnation of the formed metal oxides onto KB was adopted to increase the electronic conductivity of the samples. Finally, a carbothermal treatment at 600°C in He atmosphere was carried out for the reduction of the metal oxides to metallic PtRu/C compounds. The Pt1Ru1 ratio was calculated and revealed by X-ray fluorescence (XRF) analysis whereas the carbon percentage was calculated by weight loss. 50 mg of sample was treated in air at 550°C for 2 h and, after cooling, the weight corresponded to 25 mg, confirming a carbonaceous matrix percentage of 50 wt.%. In a similar way, the 30 wt.% Pt/C was determined. X-ray diffraction (XRD) revealed that the samples showed face centered cubic (fcc) structure for Pt nanoparticles. It appears that two distinct crystallographic phases of Pt and Ru nanoparticles were encountered after the synthesis conducted by Ru impregnation. In contrast, only a single fcc phase is visible when the Pt and Ru sulfite precursors were mixed, confirming the formation of an alloy. Furthermore, Scanning Transmission Electron Microscopy-Energy dispersive X-ray spectroscopy (S/TEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the differences in morphology and surface characteristics of the catalysts.For the electrochemical measurements, rotating disc electrode (RDE) technique under acid and alkaline conditions was employed to investigate the half cell reactions. The catalysts were also deposited at the anode and cathode of fuel cells to evaluate the activity, performance, and short-term durability. Acknowledgement “This research was funded by the European Union – EIT Raw Materials in the framework of the following project: LYDIA- Recycling Critical Metals from Fuel Cells (G.A. 22019)”

Reusable adsorbent of magnetite in mesoporous carbon for antibiotic removal.

This study aims to evaluate the feasibility of an innovative reusable adsorbent through adsorption-degradation sequence for antibiotic removal from water. The magnetite/mesoporous carbon adsorbent was prepared using a two-step method of (i) in situ impregnation of magnetite precursor during resorcinol formaldehyde polymerization and (ii) pyrolysis at elevated temperature (800 °C). XRD spectra confirmed that magnetite (Fe3O4) was the only iron oxide species present in the adsorbent, and thermogravimetric analysis revealed that its content was 10 wt%. Nitrogen sorption analysis showed that Fe3O4/carbon features a high fraction of mesopores (> 80 vol.%) and a remarkable specific surface area value (246 m2g-1), outstanding properties for water treatment. The performance of the adsorbent was examined in the uptake of three relevant antibiotics. The maximum adsorption uptakes were ca. 76mgg-1, ca. 70mgg-1, and ca. 44mgg-1 for metronidazole, sulfamethoxazole, and ciprofloxacin, respectively. All adsorption curves were successfully fitted with Langmuir equilibrium model. The regeneration of adsorbent was carried out using Fenton oxidation under ambient conditions. After three consecutive runs of adsorption-regeneration, Fe3O4/carbon maintained its performance almost unchanged (up to 95% of its adsorption capacity), which highlights the high reusability of the adsorbent.

Silicon carbide ceramics formed by binder jetting: A study focusing on the printing layer thickness and the PIP densification process

Binder jetting (BJ) additive manufacturing has the advantages of high precision, fast forming speed, and no need for supporting structure, which is especially suitable for the forming of metallic and ceramic components with complex structures. In this paper, SiC ceramic parts were obtained by BJ additive manufacturing and precursor impregnation pyrolysis (PIP) cycles. It has been observed that the thickness of the printing layer significantly affects the strength of the SiC green body. The SiC green body exhibited the highest bending strength (3.1 ± 0.2 MPa) and lower dimensional deviation (0.47–1.64 %) when printed with a layer thickness of 50 μm. However, the bending strength of the SiC ceramics (after densification) had little variations when different printing layer thicknesses were utilized. In the subsequent densification process, the density, hardness, and bending strength of SiC ceramics increase as the number of PIP cycles increases obviously, and the flexural strength reached 228.7 ± 14.2 MPa after 9 PIP cycles, while the shrinkage rates in the X, Y, and Z direction were 1.9 %, 2.8 %, and 1.2 %, respectively. In addition, the influence mechanism of printing parameters on the strengths of the green bodies and SiC ceramics was also discussed. Specifically, it was found that with the layer thickness increase, the strengths of SiC ceramics also increase.

Synthesize and Characterization of Pt-supported Co-ZIF for Catalytic Hydrocracking and Hydroisomerization of n-Hexadecane

Zeolitic Imidazole Frameworks (ZIFs) are prospective porous materials as catalyst support due to their relatively large surface area, and tunability in size, structure, and porosity. Recent studies have also shown that ZIF is the best candidate for various catalytic redox reactions such as the oxidation of benzyl aromatic hydrocarbons. In this study, the synthesized Pt catalyst supported on Co-ZIF was varied by the organic ligands: imidazole, benzimidazole, and 1-(3-aminopropyl) imidazole, then followed by impregnation of Pt precursor. The catalysts were characterized its physical and chemicals properties such as Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Brunauer Emmet Teller (BET), Temperature-Programmed Desorption (NH3-TPD and CO2-TPD). The prepared catalysts were evaluated for catalytic hydrocracking and hydroisomerization of n-hexadecane in a 100 ml-batch reactor. GC-MS analysis presented that the Pt/ZIF catalyst with imidazole ligands has better performance than others. Hence, the optimization of n-Hexadecane conversion was carried out by the Pt/ZIF-imidazole catalyst varying the amount of metal loading, time and temperature reaction. The results showed that the reaction temperature of 350 ºC using 20 bar H2 for 4 h and the addition of 15 wt% Pt successfully achieved 90.77% conversion and produced the highest yield of isomers and alkanes, 4.04% and 35.75%, respectively. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Comparative Ablation Behaviors of 2D Needled C/SiC and C/SiC-ZrC Composites

To investigate the effect of ZrC on the ablative properties of C/SiC composites in a high-temperature environment, the oxidative ablation of C/SiC and C/SiC-ZrC composites at high-temperatures was examined through ablation tests. In this study, two ceramic matrix composites, C/SiC and C/SiC-ZrC, were prepared by chemical vapor deposition and precursor impregnation pyrolysis. The ablation properties of the materials were tested and analyzed using an oxyacetylene flame to simulate a high-temperature environment. The results revealed that the line ablation rate of C/SiC-ZrC was 8.48% and 20.81% lower than that of C/SiC at 30 s and 60 s, respectively. At the same ablation time, the depth of the crater resulting from erosion of the C/SiC material by the high-temperature airflow was deeper than that of C/SiC-ZrC. The traces of the fibers subjected to erosion were more prominent. In a longitudinal comparison, the mass ablation rate of C/SiC-ZrC material decreased with the increase in time, while the line ablation rate initially increased rapidly and then decreased. From 30 s to 90 s of ablation, the line ablation rate and mass ablation rate decreased by 55.62% and 89.5%, respectively. The overall trend for both rates was a decrease with the increase in time. Under the same ablation time, the ablation rate of C/SiC-ZrC was generally lower than that of C/SiC. This is because the generated molten ZrO2 was more viscous and denser than SiO2, effectively blocking oxidizing gases from penetrating the interior of the material. The molten ZrO2 provided better protection for the substrate in the high-temperature environment.

Investigation of long-term anti-sulfur and deactivation mechanism of monolithic Mn-Fe-Ce/Al2O3 catalysts for NH3-SCR: Changes in physicochemical and adsorption properties

Owing to the different reaction properties and deactivation mechanisms caused by the structural discrepancy of monolithic catalysts, abundant scientific results of powder or granular NH3-SCR catalysts have still not sufficiently robustly applied in recent years. Furthermore, minimal research has been focused on monolithic catalysts. As a result, this work prepared monolithic Mn-Fe-Ce/Al2O3 catalysts by active component impregnation (ACI-Mn-Fe-Ce/Al2O3) and precursor impregnation methods (PI-Mn-Fe-Ce/Al2O3) and investigates the long-term SO2 and H2O resistance of the catalysts. Compared with the PI-Mn-Fe-Ce/Al2O3 catalyst, the monolithic ACI-Mn-Fe-Ce/Al2O3 catalyst showed better performance. The catalytic activity follows a bell-shaped curve with an optimal performance at a drug loading of 5 %. The ACI-Mn-Fe-Ce/Al2O3 catalyst exhibits long-term resistance to SO2 and H2O and can still convert more than 70 % NOx after 168 h of SO2 and H2O resistance test. Characterization of the ACI-Mn-Fe-Ce/Al2O3 catalysts before and after the reaction showed that the reducibility decreased after the reaction, and more Mn4+ was transformed into Mn2+ to weaken the catalytic activity. However, more Fe2+ and Ce3+ were generated during the reaction, increasing the number of oxygen vacancies, oxygen defects, and hydroxyl-like groups, all of which would contribute to a certain extent to counteract the passivation effect of SO2 on the catalysts. In situ DRIFTs analysis shows that the formation of surface sulfates has a minimal effect on the adsorption of NO, but it does affect the adsorption of coordinated NH3 on Lewis acid sites. This work elucidates the deactivation details of Mn-Fe-Ce/Al2O3 catalysts from the perspective of physicochemical properties, which provides a reference for the development of better low-temperature SO2-resistance catalysts for industrial applications.

3D printing of high-purity complex SiC structures based on stereolithography

Complex Silicon carbide (SiC) structures are hardly achievable via traditional manufacturing methods, while stereolithography 3D printing technology effectively shapes sophisticated structures with high precision. However, it is a huge challenge to prepare SiC slurry for stereolithography 3D printing with excellent curing ability due to the increased light absorption of SiC powder. Therefore, a novel approach to fabricating high-purity SiC structures is proposed in this study based on the stereolithography 3D printing process, where SiO2 powder is used as an additive to increase the curing thickness from 27.8 μm to 53.0 μm. Moreover, phenolic epoxy resin (PEA) is introduced as a carbon source to transform SiO2 to SiC during sintering. As a result, there is almost no SiO2 phase or SiOC remaining in the final parts when the addition of PEA reaches 50 wt% related to the resin weight after sintering at 1600 °C for 4 h. Based on the SiC/SiO2/PEA slurry systems prepared, high-purity silicon carbide with complex structures can be successfully fabricated in one step without any pre-oxidation or precursor impregnation processes. This approach provides valuable insights into additive manufacturing of high-purity complex SiC structures.

Spherical Binderless 4A/5A Zeolite Assemblies: Synthesis, Characterization, and Adsorbent Applications.

Zeolite microspheres have been successfully applied in commercial-scale separators such as oxygen concentrators. However, further enhancement of their applications is hampered by the post-synthetic shaping process that formulates the zeolite powder into packing-sized spherical bodies with various binders leading to active site blockage and suboptimal performance. Herein, binderless zeolite microspheres with a tunable broad size range from 2 µm to 500 µm have been developed with high crystallinity, sphericity over 92%, monodispersity with a coefficient of variation (CV) less than 5%, and hierarchical pore architecture. Combining precursor impregnation and steam-assisted crystallization (SAC), mesoporous silica microspheres with a wide size range could be successfully transformed into zeolite. For preserved size and spherical morphology, a judicious selection of the synthesis conditions is crucial to ensure a pure phase, high crystallinity, and hierarchical architecture. For the sub-2-µm zeolite microsphere, low-temperature prolonged aging was important so as to suppress external zeolization that led to a large, single macroporous crystal. For the large 500 µm sphere, ultrasound pretreatment and vacuum impregnation were crucial and facilitated spatially uniform gel matrix dispersion and homogenous crystallization. The obtained zeolite 5A microspheres exhibited excellent air separation performance, while the 4A microspheres displayed ammonium removal capabilities. This work provides a general strategy to overcome the existing limitations in fabricating binder-free technical bodies of zeolites for various applications.

Rapid removal of ofloxacin with peroxymonosulfate activation process mediated by Co3O4/Sludge-derived biochar composite: Unveiling the enhancement of biochar

In this study, sludge-derived biochar loaded Co3O4 composite (Co3O4@SDBC) were successfully synthesized through cobalt impregnation and secondary calcination of sludge-derived biochar precursors. The experimental results demonstrated that the Co3O4@SDBC catalyst performed exceptionally well for peroxymonosulfate (PMS) activation, with a high degradation efficiency (>99 %) of ofloxacin (OFL) within 10 min under the optimal conditions (a catalyst dose of 0.10 g•L−1, a PMS dose of 0.975 mM and an initial pH = 6.4), and showed good adaptability across a broad pH spectrum, under the interference of the anions and humic acid (HA), as well as in various water matrices. The results of quenching experiments revealed that the non-radical pathway (especially 1O2 and electron transfer) was the dominated reactive ingredients in the PMS activation process induced by Co3O4@SDBC. Notably, the online electrochemical tests and density functional theory (DFT) results indicated the presence of biochar carrier not only effectively lowered the escape of Co ions, while enhanced the steadiness of Co3O4@SDBC, but also accelerated the electron transfer, promoted the adsorption and cleavage of PMS, facilitated the redox cycle between Co(II) and Co(III), reduced the reaction energy barriers simultaneously, thereby making it more favourable for the generation of 1O2. Furthermore, the toxicity assessment suggested that the cumulative toxicity of OFL decreased throughout degradation. Overall, this work mechanistically revealed the enhancement of biochar on the Co3O4@SDBC catalyst, offering a viable method to activate PMS for antibiotic removal and achieving a mutually beneficial strategy for sludge waste resource utilization and environmental remediation.

Layered composites made of polymer derived SiOC/ZrB2 reinforced by ZrO2/SiO2 fibers with simultaneous microwave absorption and thermal insulation

To simultaneously improve the microwave absorption and thermal insulation properties of the ceramic materials for stealth high-speed vehicles, layered composites made of polymer-derived SiOC/ZrB2 reinforced by ZrO2/SiO2 fibers were reported in this work. The composites possess a continuous multilayer structure, which was fabricated via the precursor impregnation assisted by hot press curing and pyrolysis using the transparent ZrO2/SiO2 fibers and polymer-derived SiOC and nano ZrB2. The layered composites show an effective absorption band (EAB) of 4.2 GHz at a thickness of 2.9 mm and a minimum reflection loss of –59.34 dB. The exceptional electromagnetic (EM) wave attenuation capability is ascribed to the impedance matching as well as massive EM wave loss caused by the multilayers in which the nano ZrB2 provides interfacial polarization and electrical conduction loss. With a design of the multi-curvature arch structure, a remarkable reduction of radar cross section can be achieved. Besides, the layered composites exhibit good oxidation resistance and thermal insulation when exposed to the dynamic heating environment, demonstrating the potential application in harsh environments used for multifunctional electromagnetic absorbing materials.

Removal of metronidazole from simulated wastewater using Fe/C catalyst with a combination of heterogenous Fenton and ozonation

This study examined roles of iron oxide/porous carbon material (Fe/C) for removing metronidazole in simulated wastewater by adsorption and then followed by a degradation using advanced oxidation process (H2O2, O3 and combination of H2O2/O3). Fe/C was produced by an impregnation of iron oxide precursors during resorcinol-formaldehyde synthesis followed by pyrolysis at 800 °C. For comparison, blank carbon (without iron loading) was also synthesized. The properties of porous carbon were investigated by SEM-EDX and N2-sorption analyzer. Blank carbon and Fe/C featured the specific surface area of 755 m2g-1 and 394 m2g-1, respectively. The loading of iron oxide altered the pore structures of material. The adsorption isotherm data were followed by the Langmuir isotherm model with metronidazole uptake up to 46.07 mg g-1 and 39.97 mg g-1 at 30oC by Fe/C and blank carbon. The degradation study was then carried out with catalyst dosage of 0.1 g/100 mL solution and 120 min reaction time at 30 oC. It is noticeably that, the degradation of metronidazole was better when a combination of H2O2/O3 was employed, compared with an individual of H2O2 or O3. Regarding the stability, Fe/C maintained its high activity upon four consecutive runs.

Cf/SiC Ceramic Matrix Composites with Extraordinary Thermomechanical Properties up to 2000 °C.

The thermomechanical properties of carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC CMCs) were studied up to 2000 °C using high-temperature in situ flexural testing in argon. The CMC specimens were fabricated using an ultrahigh concentration (66 vol%) aqueous slurry containing nano-sized silicon carbide powder. The SiC powder compacts were obtained by drying the slurry and were densified using the precursor impregnation and pyrolysis (PIP) method with field assisted sintering technology/spark plasma sintering (FAST/SPS). The high relative density of the SiC green body (77.6%) enabled densification within 2.5 days using four PIP cycles. In contrast, conventional PIP processes take over 7 days. The in situ flexural strength of the Cf/SiC CMC was 434 MPa at 1750 °C, which was 84% higher than the room temperature value. The value further increased to 542 MPa at 2000 °C. Possible mechanisms to explain the excellent strength of the CMC at elevated temperatures are discussed.

Enhanced Low-Temperature Activity and Hydrothermal Stability of Ce-Mn Oxide-Modified Cu-SSZ-39 Catalysts for NH3-SCR of NOx

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NOx removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NOx emissions during the cold-start period, impeding its practical application. In this study, Ce-Mn oxide-modified Cu-SSZ-39 catalysts (CeMnOx/Cu-SSZ-39) and references (CeO2/Cu-SSZ-39 and MnOx/Cu-SSZ-39) were prepared by the ion-exchange of Cu ions followed by impregnation of the oxide precursors, with the aim of enhancing the NH3-SCR performance at low temperatures. The modified catalysts exhibited improved low-temperature activity and hydrothermal stability compared to the unmodified counterpart. In particular, CeMnOx/Cu-SSZ-39 showed the highest activity among the three catalysts and achieved NOx conversions above 90% within the temperature range of 180 °C to 600 °C, even after undergoing hydrothermal aging at 800 °C. Experimental results indicated that the synergistic effect between Ce and Mn in CeMnOx improves the redox properties and acidity of the catalyst due to the presence of Ce3+, Mn4+, and abundant adsorbed oxygen species, which facilitate low-temperature SCR reactions. Furthermore, the interaction of CeMnOx with Cu-SSZ-39 stabilizes the zeolite framework and hinders the agglomeration of Cu species during the hydrothermal aging process, contributing to its exceptional hydrothermal stability. The kinetics and NO oxidation experiments demonstrated that CeMnOx provides access to fast SCR reaction pathways by oxidizing NO to NO2, resulting in a significant increase in low-temperature activity. This study provides novel guidelines for the design and preparation of Cu-SSZ-39 zeolite with outstanding SCR performance over a wide temperature range.

Conductivity and adsorbability synergistically improved electrode for high-performance viologen based aqueous organic flow batteries

In this paper, a series of heteroatom doping graphite felt electrodes are prepared by simple precursor impregnation and heat treatment, their application properties as electrode materials for viologen based aqueous organic redox flow batteries (AORFBs) are studied systematically. Elaborate physical, electrochemical characterization and density functional theory (DFT) calculation results indicate that the P-doped GF (P-GF) electrode with higher adsorption energy for viologen molecules, better conductivity and larger electrochemical reactive surface area exhibits better electrochemical performance towards viologen. The charge and discharge performance of the AORFBs with BTMAP-vi as anolyte and Nme-TEMPO as catholyte are investigated to verify the practical application performance of the P-GF electrode material. The AORFB with P-GF as electrodes shows lower polarization overpotential and higher discharge capacity at different current densities than that using pristine GF as electrodes. Specifically, the VE and EE of the BTMAP-vi/Nme-TEMPO AORFBs with P-GF as electrodes are 84.76 % and 82.85 % at the current density of 60 mA cm−2, 5.34 % and 6.18 % higher than that of the battery with GF as electrodes respectively. After 200 charge and discharge cycles, the capacity retention rate of the P-GF battery increases by more than 20 %, suggesting the better cycle stability. Besides, the peak power density of the P-GF battery achieves 120 mW cm−2, which is much higher than that of the GF battery (85 mW cm−2). The results of this work demonstrate that enhancing the conductivity and adsorption energy of the electrodes should be more effective to improve the performance of viologen based AORFBs, because the electrochemical reactivity of its active electrolytes has been excellent enough.

Synthesis and Characterization of High-Purity, High-Entropy Diboride Ceramic Powders by a Liquid Phase Method

A nano-dual-phase powder with ultra-fine grain size was synthesized by the liquid precursor method at 1200 °C. A series of single-phase high-entropy ceramic powders ((Ti, Zr, Hf, Nb)B2, (Ti, Zr, Hf, Nb, Ta)B2, (Ti, Zr, Hf, Nb, Mo)B2, (Ti, Zr, Hf, Nb, Ta, Mo)B2) with high purity (C content less than 0.9 wt% and O content less than 0.7 wt%) and ultrafine (average grain sizes of 340–570 nm) were successfully synthesized at 1800 °C. The sample of (TiZrHfNbTa)B2 exhibited a hexagonal close-packed (HCP) structure, and the metal elements were uniformly distributed at the nanoscale, microscale, and macroscale. This method did not apply to the preparation of all high-entropy ceramic powders and was unfavorable for the formation of single-phase high-entropy borides when the size difference factor exceeded 3.9%. The present work provides a guide for the development of ceramic-based composites through precursor impregnation pyrolysis.