Oxygen Mobility Research Articles

Low temperature atomic layer deposition of PbO2 for electrochemical applications

A low temperature atomic layer deposition (ALD) process for PbO2was developed using bis(1-dimethylamino-2-methyl-2-propanolate)lead(II), Pb(DMAMP)2, and O3as the reactants, with a high growth rate of 2.6 Å/cycle. PbO2readily reduces under low oxygen partial pressures at moderate temperatures making it challenging to deposit ALD PbO2from Pb2+precursors. However, thin films deposited with this process showed small crystalline grains of α-PbO2and β-PbO2, without signs of reduced PbOxphases. The ALD PbO2thin films show the high electrical conductivity characteristic of bulk PbO2. In situ measurements of ALD PbO2film conductivity during growth suggest a reaction mechanism by which sub-surface oxygen mobility contributes to the growth of resistive PbO or PbOxduring the Pb(DMAMP)2surface reaction step, which is only fully oxidized from Pb2+to Pb4+during the O3reaction step. These films were electrochemically reduced to PbSO4in H2SO4and then reoxidized to PbO2, demonstrating their suitability for use as an electrode material for fundamental battery research and other electrochemical applications.

Efficient low-temperature CO removal from high-humidity sintering flue gas by combination Cu and OMS-2

The non-precious metal manganese-based catalysts currently show insufficient CO catalytic oxidation performance in actual sintering flue gas conditions, with increased water vapor levels causing catalyst deactivation. This study utilized a high-performance manganese dioxide octahedral molecular sieve (OMS-2). The effect of metal doping on the catalytic CO oxidation performance was investigated in preparing OMS-2 using the co-precipitation method. The experiments showed that Cu doping increased CO conversion efficiency more than other metals (Co, Ag, Zn, and Fe), with optimal performance achieved at a 1.91 wt% doping level. Besides, Cu doping significantly enhanced water resistance of the catalyst, enabling effective CO removal in high-humidity conditions. The study observed that Cu ions infiltrated the catalyst framework by substituting some of the Mn ions, creating additional active sites in the form of oxygen vacancies and improving surface oxygen mobility, thereby enhancing the performance of CO catalytic oxidation. Furthermore, Cu doping demonstrated selective absorption of water vapor, with CuxO in the catalyst, effectively adsorbing water vapor and protecting the initial active sites, thereby mitigating water vapor-induced poisoning. Even in 15 vol% H2O at 150 °C, 1.91%Cu-OMS-2 maintained total catalytic activity. Therefore, the co-precipitation method-prepared 1.91%Cu-OMS-2 catalyst holds excellent potential for CO removal in sintering flue gas and shows promise for practical applications.

A novel homological approach for the comprehensive study of nonstoichiometric oxide with exceptional oxygen mobility

Actual work devoted to the development of a novel homological approach for describing the kinetic properties of grossly nonstoichiometric oxides ABO3-δ with perovskite structure. The approach consists in considering such oxides having different oxygen stoichiometry 3-δ as chemical homologues involved in the same oxygen exchange reaction and forming a continuous series in δ. The proposed approach is considered using the oxide with exceptional oxygen mobility Ba0·5Sr0·5Co0·8Fe0·2O3-δ (BSCF). The kinetic properties of BSCF were studied by new method of the oxygen partial pressure relaxation. The equilibrium properties of BSCF were reported earlier and obtained by original technique of the quasi-equilibrium oxygen release. The power law dependence of the kinetic parameters on the equilibrium oxygen partial pressure is considered as the consequence of linear free energy relationship similar to the Brønsted-Evans-Polanyi relation.

Comparative Study between Ultrasound Guided Quadratus Lumborum Block versus Transversus Abdominis Block in Post-Operative Pain Management after Cesarean Section

Abstract Background Cesarean section rate increased those days and postoperative pain control. The goal of postoperative pain management is provision of comfort, early mobilization and improved respiratory function without causing inadequate sedation and respiratory compromise, which can be achieved through using multimodal analgesic therapy, preference for regional techniques, avoidance of sedatives, non-invasive ventilation with supplemental oxygen and early mobilization. Aim of the Work The aim of this study was to assess the analgesic efficacy of ultrasound-guided trans- muscular QLB compared with TAP block during cesarean section surgery and in the early postoperative period regarding pain relief, provision of comfort, and improved respiratory functions. Patients and Methods After approval of anesthesiology department scientific and ethical committees in Ain Shams University Hospitals, female patients were included in the study, and were divided into two groups (n = 25; each); group QLB and group TAP. Group QLB: Patients (n = 25) of this group received bilateral ultrasound-guided QLB after induction of spinal anesthesia using (2-2.5 mg/kg of bupivacaine not to exceed 175 mg per dose and maximum 400mg/24h) without exceeding the toxic dose 3 mg/kg. Group TAP: Patients (n = 25) of this group received bilateral ultrasound-guided TAP block after induction of spinal anesthesia using (2-2.5 mg/kg of bupivacaine not to exceed 175 mg per dose and maximum 400mg/24h) without exceeding the toxic dose 3 mg/kg. Results The present study showed that the quadratus lumborum block was more efficient than the tansversus abdominis plane block. The first rescue for analgesia (pethidine), total pethidine consumption and pain scores (visual analog scale) indicated that the superiority of the QL block technique over the TAP block technique. The patients of group TAB had higher pain scores and were the first to ask for rescue analgesia; therefore, they had highest total pethidine consumption in the first 24 hours postoperatively in comparison to patients of group QLB. This is mainly due to the extension of the local anesthetic agent in QLB beyond the transverse abdominal plane to the thoracic paravertebral space, which then results in more analgesia, even somatic and visceral pain control. Conclusion Quadratus lumborum block was the most effective technique in providing analgesia after cesarean section in comparison to transversus abdominis plane block and even more time covering to rescue opioid.

Improved biohydrogen production using Ni/ZrxCeyO2 loaded on foam reactor through steam gasification of sewage sludge

The pervasive generation of sewage sludge (SES) and deficiencies in its disposal methods have resulted in several significant environmental and human health challenges. This study explored the catalytic effect of nickel (Ni)-based CeO2, ZrO2, Zr0.8Ce0.2O2, Zr0.4Ce0.6O2, and γ-Al2O3 supports in fixed beds and foam reactors in the steam gasification of SES. A comparison of the hydrogen selectivity and gas yield of the synthesized catalysts confirmed that the metal composite support, especially Zr0.8Ce0.2O2, had a positive effect on the catalytic activity and stability. This can be attributed to the enhanced oxygen vacancies and oxygen mobility, resistance to coke deposition, uniform morphology, improved dispersion, and increased number of Ni sites on the Zr0.8Ce0.2O2 support. Furthermore, foam reactors offer unique advantages in improving hydrogen production. This study provides an advanced strategy for SES valorization that fulfills the requirements of an economically and environmentally sustainable technology.

Revealing the promotional effect of Zr and phosphate Co-decorated on δ-MnO2 catalysts for highly efficient catalytic elimination of chlorinated VOCs: An experimental and theoretical study

The development of advanced catalysts for catalytic oxidation of CVOCs still presents challenges in terms of low activity, chlorination poisoning and the formation of toxic byproducts. In this study, a series of nP-MnxZry catalysts with exceptional catalytic oxidation activity were developed for the removal of CVOCs in industry. Among them, 15P‐MZ exhibited the optimal catalytic activity and stability for CB degradation, achieving a T90 of 180 ℃. Notably, the CB oxidation rate of 15P‐MZ was found to be 5.76 times higher than that of MnO2 at 155 °C. Structure and properties analysis combining with DFT calculations revealed that the dual modification strategy involved Zr doping and phosphate loading induced the formation of high concentration of oxygen vacancy over 15P‐MZ, which enhanced oxygen mobility, facilitating the breakage of the aromatic ring. Meanwhile, this strategy introduced more Brønsted acid sites, promoting the dissociation of Cl in the form of HCl, thereby inhibiting the formation of polychlorinated byproducts. Moreover, the activation effect of phosphate on the dissociation of H2O further promoted the Cl dissociation, thereby regenerating more active sites and improving catalytic activity and stability in humid environment, making it more promising for industrial applications.

In situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies (VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document}). Notwithstanding its significance, behaviors of the defective structure and VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (Ce0.88Gd0.12O2-δ) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massive VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} rearrangement are stimulated and visualized in situ with sub-Å resolution. Electron dose rate is identified as a pivotal factor in modulating the phase transition, and both the VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} concentration and the orientation of the newly formed phase can be altered via electron beam. Our results provide indispensable insights for understanding and refining the microscopic pathways of phase transition as well as defect engineering, and could be applied to other similar functional oxides.

Polaron assisted hopping mechanism in microwave processed Nd doped second layered aurivillius SrBi2Nb2O9 ceramics

The polycrystalline Sr0.8Sn0.2Bi1.75Nd0.25Nb2O9 (NdSBN) was synthesized using the green synthesis microwave sintering method, which significantly reduced the processing parameters of the NdSBN ceramics. Orthorhombic crystal structure with A21am symmetry was revealed by Rietveld refinement study, whereas the doping-induced strain and crystallite size was studied using the Williamson Hall method. Crossectional SEM micrographs confirm the plate-like structure, with an average grain size of 273.7 nm. A diffuse type of phase transition was observed at 345 °C, which usually arises due to compositional fluctuations and mobile oxygen vacancies; further, the diffusiveness of the NdSBN was studied using Uchino and Nomura function, a modified version of Curie-Weiss law (CW). The frequency and temperature-dependent dielectric study of NdSBN ceramics display a Maxwell-Wagner relaxation with a high loss in a low frequency regime, possibly due to the presence of leakage current in the solid solution. Frequency dependent AC conductivity obeys Jonscher's power law, whereas DC conductivity supports polaron assisted hopping in NdSBN composition with dual activation energies of 0.55 eV and 0.75 eV, which correspond to electrons and ions, respectively. The non-Debye type relaxation mechanism in conjunction with negative temperature coefficient of resistance (NTCR) behavior was demonstrated by temperature dependent impedance spectroscopy, while modulus spectroscopy confirmed the multiple relaxation processes in NdSBN ceramics.

Effect of A-site cation doping on the catalytic oxidation of toluene over mullite catalyst GdMn2O5

Manganese-based mullite (AMn2O5) catalysts are promising for the catalytic oxidation of VOCs, with their oxidation reaction performance being tunable by modifying the composition of the A-site elements. In this work, various manganese-based mullite catalysts (Gd0.9X0.1Mn2O5, X =Sr, Ce, or Ca) with different A-site elements doping were prepared by the citric acid sol–gel method and applied to the catalytic oxidation of toluene. The activity tests indicated that the enhancement of catalytic performance by doping elements was in the order of Sr > Ce > Ca. Notably, the T90 of the Gd0.9Sr0.1Mn2O5 catalyst was 235.6 °C, a lower 37.8 °C than that of the GdMn2O5. Comprehensive characterization and density functional theory (DFT) simulations revealed that Sr doping facilitates the reduction of Mn4+ to Mn3+, increases the electron occupancy of the eg orbitals in octahedral Mn sites, and elevates the Mn-d band center, thus facilitating the adsorption and activation of O2. Additionally, the raised O-p band center caused by Sr doping enhances lattice oxygen mobility. In situ DRIFTS analysis indicated that the introduction of Sr at the A-site optimizes the toluene reaction pathway and accelerates the reaction rate. This work reveals that a simple A-site cation doping strategy can effectively regulate manganese-based mullite catalysts’ electronic structure and surface reaction activity, providing a feasible method for the large-scale preparation of manganese-based mullite catalysts with excellent catalytic performance.

Tuning the oxygen storage capacity and oxygen release properties of CeO2-based catalysts for catalytic combustion of toluene

CeO2 with varied doping transition metal was investigated to understand the oxygen storage capacity and oxygen release property of CeO2-based catalysts for toluene combustion. The order of catalytic activity was as follows: CuCeOx ≈ CoCeOx > MnCeOx > FeCeOx > NiCeOx > ZrCeOx > CeO2. Kinetic studies showed that the reaction on CuCeOx proceed via an MvK mechanism and the oxygen of catalyst was crucial factor for the toluene combustion. H2-TPR and XPS showed the addition of transition metal to CeO2 could modify the surface lattice oxygen. Moreover, the oxygen storage capacity and oxygen release properties showed the transition metal additive not only change the amount of oxygen, but also affect the oxygen mobility. A linear relationship was observed between the catalytic activity and oxygen storage capacity. Diffuse reflectance infrared fourier transform spectroscopy showed the toluene first adsorbed on the surface of catalyst, and then reacted with oxygen of catalyst to form benzyl, benzoate and benzyl carbonate species. All these results provided a new strategy to develop high performance catalyst.

Highly efficient removal of ozone on amorphous manganese oxides modified by alkali metals

Low stability deriving from the accumulation of moisture and intermediates represents the major challenge for practical applications of manganese oxides (MnOx) for ozone elimination. Here, Li+, Na+ and K+ were successfully introduced into the channel framework of amorphous MnOx to improve its stability through a simple post-treatment method. Alkali metal modification can promote the removal of ozone by amorphous MnOx, and Na-MnOx exhibited superior catalytic activity and remarkable stability in water-resistance, cycling and long-term tests. The Na introduction facilitated the formation of oxygen vacancies, and improved low-temperature reducibility and lattice oxygen mobility. The mechanism of ozone decomposition on amorphous MnOx and Na-MnOx catalysts was deeply investigated by in situ diffuse reflectance infrared Fourier transform spectra (in-situ DRIFTS). The Na addition strengthened the hydrophobicity of oxygen vacancies, but also greatly boosted the desorption of intermediate oxygen species and the ozone decomposition cycle.

Dry reforming of toluene over Ni/pyrochlore catalysts with A-site Sr doping

Dry reforming with CO2 is one potential method for tar removal and further production of syngas in biomass gasification, but the crucial catalysts with good reaction characteristics are still being developed. In the work, Ni/pyrochlore was proposed to be utilized as catalysts in the dry reforming of tar, and thermodynamic calculation, reaction progress test, and materials characterization were conducted to reveal dry reforming characteristics over Ni/pyrochlore catalysts and the reaction mechanism behind. Results show that YS0.2C catalyst exhibits the best activity (toluene and CO2 conversion of 70.1% and 79.5%) and stability among all catalysts under the optimized conditions of 700 °C with a CO2/toluene molar ratio of 7. Analysis on physicochemical properties of the catalysts indicate Sr doping can effectively promote catalytic reforming by enhanced interaction between Ni and support, CO2 adsorption and oxygen mobility. The work offers a promising catalyst type in improving tar removal by dry reforming.

Synthesis and Physicochemical Characterization of Solid Oxide Electrolyte and Electrode Materials for Medium Temperature Fuel Cells

Finely dispersed СeO2–Nd2O3 and Gd2O3–La2O3–SrO–Ni(Co)2O3–δ mesoporous powders are synthesized by co-crystallization of the corresponding nitrates solutions with ultrasonic treatment and used to prepare nanoceramic materials with a fluorite-like, orthorhombic perovskite and tetragonal perovskite crystal structures respectively with CSR ~ 55–90 нм (1300ºC). The study of physicochemical properties of the obtained ceramic materials revealed an open porosity 7–11% for СeO2–Nd2O3 and 17–42% for Gd2O3–La2O3–SrO–Ni(Co)2O3–ä. Cerium oxide-based materials possess a predominantly ionic electrical conductivity with σ700ºС = 0.31 · 10–2 S/cm (ion transfer number ti = 0.71–0.89 in the temperature range 300–700°C) due to the formation of mobile oxygen vacancies at heterovalent substitution of Nd3+ for Се4+. Solid solutions based on lanthanum nickelate and cobaltite feature a mixed electronic-ionic conductivity with σ700°С = 0.59 ∙ 10–1 S/cm with the electron and ion transfer numbers te = 0.92–0.99 and ti = 0.08–0.01. The obtained ceramic materials are shown to be promising as solid oxide electrolyrtes and electrodes for medium temperature fuel cells.

Conversion of CO2(g) to CO(g) via reverse water–gas shift cycle on mixed cerium/praseodymium oxides at 500 °C

Reactions of cerium/praseodymium oxides under hydrogen atmospheres, and subsequently, carbon dioxide, involved in chemical looping reverse water–gas shift cycles (RWGS) at 500 °C were investigated by in-situ high-temperature X-ray powder diffraction, FTIR and thermogravimetry. The RWGS cycle is a critical chemical process for converting carbon dioxide into useful products, such as carbon monoxide, which can be used to synthesize fuels and chemicals. The mixed oxides exploit the redox properties of Ce and Pr, which can switch between oxidation states, making them suitable for oxygen incorporation and release during the RWGS process allowing them to react with H2(g), and subsequently with CO2(g), promoting their interaction and conversion into H2O(g) and CO(g). Pure cerium and praseodymium oxides showed poor CO2(g) conversion efficiency. However, we found that nanometric Ce/Pr mixed oxides exhibit enhanced oxyreduction performance suitable for this application, particularly with a composition of 75 mol% Ce and 25 mol% Pr, significantly improved performance, achieving an average CO(g) yield of 0.6 mmol/(goxide.cycle) and a maximum rate of 0.26 mmol/(goxide.min). Pr enhances oxygen mobility in CeO2, which improves the dissociation of C═O bonds in CO2(g). This is because the remaining oxygen atoms are delivered more quickly to the support sink, thereby cleaning up the vacant sites generated during the reduction step. These findings suggest that Ce/Pr mixed oxides are highly effective for CO2(g) conversion to CO(g) via RWGS cycle, offering a potentially viable option for industrial application.

Mn-Ce solid solution growth on Mn2O3 surface to form heterostructure catalysts with multiple active sites for toluene degradation

A solid solution-heterostructure catalyst with abundant active sites was successfully constructed in this study by in situ growth of Mn-Ce solid solution on the surface of Mn2O3. The solid solution structures with optimum physical and chemical properties were synthesized initially by controlling the Mn-Ce ratios. Subsequently, the reaction time was controlled to realize the orderly growth of the solid solution on the Mn2O3 surface. The catalyst (M−CeMn0.5) with solid solution-heterostructure formed by the reaction of Ce3Mn1 and Mn2O3 for 0.5 h could reach more than 90 % toluene degradation rate at 183 °C and was operated continuously for 15 h without deactivation. XRD showed that the appropriate reaction time resulted in the active components on the catalyst surface exhibiting lower crystallinity and reduced grain size. The reduction capacity (2.28 → 10.47 mmol/g) and the mobility of lattice oxygen were significantly enhanced in the M−CeMn0.5 catalyst compared to the Mn-Ce solid solution. Meanwhile, a high content of low valent metal ions (Ce3+/Ce4+ 0.33, Mn3+/Mn4+ 1.64) and reactive oxygen species (Oads/Olatt 0.53) were also present on the catalyst surface. The DFT demonstrated that the Mn atoms and Mn-O bridge sites on the solid solution surface exhibited high adsorption energy values for toluene (−0.8402/-0.8406 eV) and oxygen (−1.6546/-1.661 eV) molecules. The TEM indicated that lattice distortion and oxygen vacancies were formed at the interface between the solid solution and Mn2O3 at the interface. The synergy of multiple active sites favors the generation of reactive oxygen species and thus promotes p-methyl dehydrogenation. Meanwhile, the high mobility of lattice oxygen facilitates the breakage of benzene ring. This study provides a new strategy for the synthesis of efficient Mn-Ce-based catalysts.

Strong interaction between promoter and metal in Pd-Ba/TiO2 catalysts for formaldehyde oxidation

As our previous works found, alkali metals have a common promotion effect on supported noble metals catalysts for formaldehyde (HCHO) oxidation. As second-group elements, alkaline earth metals (AEMs) are neighbors to the first-group elements and share some properties in common. However, detailed investigations into the specific mechanisms underlying AEMs’ effects on HCHO oxidation remain limited. In this study, we found that Ba addition showed a similar promotion effect on HCHO oxidation for Pd/TiO2. Ba species stabilized Pd groups, improved the dispersion, and even caused a large number of monatomic-like Pd sites to appear, which may be attributed to the electronic interaction between promoter and metal (EIPM) between Ba and Pd. Besides, AEM loading had the important effect of increasing the electron density of metallic Pd nanoparticles, which further improved the ability for O2 activation and so enhanced the mobility of chemisorbed oxygen on the catalyst surface. For Pd/TiO2, the HCHO oxidation path is mainly HCHO→HCOOH→HCOO→H2O+CO2. By contrast, for Pd-Ba/TiO2, with more surface-active species, the formate intermediate was more likely to be directly oxidized into H2O and CO2, which is a more effective reaction pathway. The details of the EIPM between Pd and Ba were investigated by GPAW (DFT calculation module) in ASE (Atomic Simulation Environment). The AEM Ba acted as an electron donor and could interact with Pd d orbital electrons through BaO sp orbital electrons. Ba species were highly dispersed on the carrier due to the Ba-Ti interaction. Ba species dispersed over large areas stabilized the Pd particles and donated electrons to Pd. Therefore, adding an AEM is an efficacious strategy to improve the performance of the catalytic oxidation of HCHO.

Enhancing hydrogen production via dry reforming of methane: Optimization of Co and Ni on scandia-ceria-zirconia supports for catalytic efficiency and economic feasibility

The Novel “Scandia-ceria incorporated zirconia” (10ScCeZr) is a well-recognized material in ceramic and solid oxide electrolytes due to stable phases (like cubic ZrO2) and oxide conducting phases (like hexagonal Sc4Zr3O12 phases). The objective of the current study is to introduce 10ScCeZr as support for bearing a proportional ratio of active sites (Ni and Co), investigating catalytic performance in DRM and studying the economic viability with respect to other catalysts. The 10ScCeZr support is used first time where the concentration of ceria is minimal to minimize the risk of oxidation of active sites but achieve the benefit of mobile lattice oxygen along with scandia and zirconia. Upon dispersion of different proportions of Ni and Co over 10ScCeZr, the reducibility pattern, stability of active sites, stability of oxide vacancy, and type of carbon deposit are modified markedly. Upon using 3: 1 Ni and Co over 10ScCeZr, the crystallinity of the catalyst is minimal, and the total concentration of active site and stable active sites doesn’t fluctuate more than 5Ni/10ScCeZr, and active sites are majorly derived by NiO. During the DRM, less inert carbon is deposited over the catalyst (than 5Ni/10ScCeZr). These physiochemical modifications over 3.75Ni1.25Co/10ScCeZr result in the highest 45 % H2 yield at 700 °C and 79 % H2 yield at 800 °C at the end of 300 min. The significant high operational savings due to the 0.44 % increased H2-yield validate the long-term financial benefits upon industrialization of the current catalyst. Now, this catalyst is open for further investigation on promotors’ effect and process optimization for developing a high-performance catalyst with excellent savings in H2-production through DRM.

Excellent performance of Ce doped CoMn2O4/TiO2 catalyst in NH3-SCR of NOx under H2O&SO2 conditions

Mn-based catalysts have become a research hotspot for low-temperature NH3-SCR, and the improvement of anti-SO2 poisoning performance is crucial to promote their industrial application for NH3 selective catalytic reduction of NOx. In this work, the CoMn2O4/Ce-TiO2 catalyst was able to maintain 95 % NOx conversion even in the presence of 10 vol% H2O+50 ppm SO2 for 24 h at 250 °C.The excellent performance was attributed to the large mesoporous structure, specific surface area, and the enhancement of acid and redox properties associated with the catalysts. The Ce doped CoMn2O4/Ce-TiO2 catalyst maintained Mn3+, Mn4+ and Co3+ in high concentrations on the surface, which improved the lattice oxygen mobility, and the electron transfer and interaction. The presence of more Ce4+ provided higher SCR activity due to the strong oxygen storage migration and also release ability. The reaction process of NH3-SCR for NOx removal on the surface of CoMn2O4/Ce-TiO2 catalyst mainly followed the Eley-Rideal (E-R) mechanism. The NH3 adsorbed on the catalyst surface reacted mainly with NO/NO2 species, even under H2O&SO2. The E-R reaction mechanism on the surface of CoMn2O4/Ce-TiO2 catalyst was less restricted by the inhibition of H2O&SO2. This is one of the primary reasons for the superior anti-sulfur toxicity performance of the catalyst. This work opens a new avenue for the design of efficient and environmentally friendly NH3-SCR catalysts with good application prospects.

Synergistic SiC/Co3O4 composites for enhanced microwave-assisted benzene catalytic removal performance

Microwave-assisted catalysis is a promising technique for enhancing catalytic reactions through selective heating, potentially leading to improved reaction rates and energy efficiency. However, understanding the complex interactions between microwave absorption and catalytic performance in composite catalysts remains a challenge. In this study, Cobalt oxide(Co3O4)/silicon carbide(SiC) composite catalysts with varying SiC content were synthesized and characterized to investigate the relationship between their microwave absorption properties and catalytic performance. Quantitative analysis revealed that SiC and Co3O4 absorb microwave energy through relaxation polarization and magnetic loss mechanisms, respectively. Increasing SiC content enhanced the dielectric and magnetic loss capabilities of the composites, with the Co3O4/SiC composite containing 10 wt% SiC (Co3O4/SiC-10) exhibiting a dielectric loss tangent of 3.87 and a minimum reflection loss of −35dB. However, higher SiC content decreased the surface chemically adsorbed oxygen, surface oxygen mobility, and benzene adsorption capacity, weakening the catalytic activity under conventional heating. The Co3O4/SiC-10 sample achieved a significantly better balance between microwave absorption and catalytic performance, significantly outperforming the original Co3O4 sample under microwave irradiation. These founding establishes a quantitative research methodology that correlates dielectric loss tangent, reflection loss, and other crucial parameters with microwave absorption performance and further catalytic properties, providing insights for the rational design of catalysts that optimize both microwave absorption and catalytic activity.

Influence of the La/Ce ratio on La-Ce oxides promoted by Sr in the methane oxidative coupling reaction

The high methane availability and its significant role as a greenhouse gas have led the scientific community to pursue methods for its use. This paper proposes the usage of the oxidative coupling of methane (OCM) as a promising path to transform methane directly into value-added hydrocarbons, mostly ethylene, which serves as a crucial compound in the petrochemical sector. An efficient OCM catalyst should contain substantial basicity and oxygen vacancies for providing surface electrophilic oxygen species, such as superoxides and peroxides, instrumental for boosting selectivity towards C2 products. Mixed lanthanum-cerium oxide (La-Ce) catalysts have emerged as strong candidates in OCM due to their high thermal stability, oxygen mobility, and high alkalinity. In this study, they were prepared through a surfactant-assisted hydrothermal method with different La/Ce ratios for fine-tuning their basic properties and promoting oxygen mobility on the surface of the catalysts. Samples followed a volcano-shaped relationship between C2 yield and La content, with optimal performance at a La/Ce molar ratio of 2.1, attributed to the interplay between the high amount of basic sites and oxygen vacancies, increasing the presence of superoxide species over lattice oxygen. Moreover, the Sr-promoted catalyst showed high density of strong basic sites while preserving the reactive oxygen species, achieving 20 % CH4 conversion, with 57 % C2 compounds selectivity at 750 °C and GHSV of 18.000 mL.gcat−1.h−1.