Highly Efficient Porous FexCe1–xO2−δ with Three-Dimensional Hierarchical Nanoflower Morphology for H2S-Selective Oxidation

Nano-flower spherical NiFe LDH adsorbent for efficient removal of H2S in blast furnace gas

Removal of sulfur species from blast furnace gas is urgently needed due to the strict emission limits imposed on iron-steel industrial flue gas. Improving the sulfur capacity of H2S is a crucial challenge to reduce the operation cost. NiFe layered double hydroxide (LDH) adsorbents were synthesized using the hydrothermal method to strengthen the adsorption of H2S, achieving a high sulfur capacity of 133.6 mg/g at 50 °C. Characterization studies have revealed that the reaction pathway of H2S on the NiFe LDH surface involves adsorption, dissociation and oxidation. It has been clarified that the high sulfur capacity can be attributed to the abundant H2S dissociation sites and the excellent O2 activation sites. The dissociation sites of H2S encompass metal sites, -OH and CO32-. The interaction between O2 and the bridge site of asymmetric metal atoms significantly enhances the dissociation of O2. Strengthening the dissociation of H2S and O2 improves the sulfur capacity. The deactivation of adsorbents comes from the continuous consumption of oxygen species mainly composed of -OH and the deposition of sulfur species in the smaller mesopores ranging from 2 to 10 nm. This work provides useful insights into designing highly efficient iron-based adsorbents for the desulfurization of blast furnace gas.

Sabatier Optimal of Mn-N4 Single Atom Catalysts for Selective Oxidative Desulfurization

Understanding the relationship of competitive adsorption between reactants is the prerequisite for high activity and selectivity in heterogeneous catalysis, especially the difference between the adsorption energies (Eads) of two reactive intermediates in Langmuir-Hinshelwood (L-H) models. Using oxidative dehydrogenation of hydrogen sulfide (H2S-ODH) as a probe, we develop various metal single atoms on nitrogen-doped carbon (M-NDC) catalysts for controlling Eads-H2S, Eads-O2 and investigating the difference in activity and selectivity. Combining theoretical and experimental results, a Sabatier relationship between the catalytic performance and Eads-O2/Eads-H2S emerges. Mn-NDC as the optimal catalyst shows excellent H2S conversion (>90 %) and sulfur selectivity (>90 %) in a wide range of O2 concentrations over 100 h. Such a high-efficiency performance is attributed to appropriate Eads-H2S and Eads-O2 on Mn-N4 sites, boosting redox cycle between Mn2+ and Mn3+, as well as preferential formation of sulfur. This work provides a fundamental guidance for designing Sabatier optimal catalysts in L-H models.

Highly efficient sulfur production in hydrogen sulfide conversion over Fe3O4 with {111} crystal facets: Unveiling the promotion of oxygen vacancies and basic sites

High-performance catalysts for the selective catalytic oxidation of hydrogen sulfide (H2S-SCO) are required to achieve the conversion of hazardous H2S into harmless and valuable sulfur for environmental protection and resource utilization. Herein, three different morphologies of Fe3O4 were synthesized and used for H2S-SCO. Octahedral Fe3O4 dominated by {111} crystal facets exhibited excellent performance for H2S-SCO with an H2S conversion of ∼ 100 % and a sulfur selectivity exceeding 94.5 % in stability tests at 150 °C over 60 h. The {111} crystal facets provided weakly to moderately basic sites to promote H2S adsorption and dissociation, as well as abundant oxygen vacancies (OVs) due to lower OV formation energies on this facet, which significantly enhanced the oxidation performance of the catalyst. By revealing the promotions of OVs and basic sites, the relationship between the {111} crystal facets of Fe3O4 and the performance in the H2S-SCO was clarified. This study provides new insights into the design of efficient and stable Fe-based catalysts for the conversion of hazardous H2S from blast furnace gas into valuable sulfur.

Combination of FeII-O Species and Fe-O-Zr Bonds Empowers FeOx Nanoclusters Anchored on UiO-66 Robust H2S-Selective Catalytic Oxidation Performance

The low sulfur selectivity of Fe-based H2S-selective catalytic oxidation catalysts is still a problem, especially at a high O2 content. This is alleviated here through anchoring FeOx nanoclusters on UiO-66 via the formation of Fe-O-Zr bonds. The introduced FeOx species exist in the form of FeIII and FeII. Therein the FeIII-O species are the predominant active sites for H2S-oxidation. The formed Fe-O-Zr bonds strengthen the redox cycle of FeIII/FeII through promoting electron transfer from Fe to Zr. The FeII-O species can activate molecular oxygen to oxidize H2S into elemental S, which accelerates the formation rate of atomic S, hindering its further oxidation into SO2. The combination of these factors empowers the catalysts, enabling 100% H2S conversion and 98.2% sulfur yield. The catalyst also has satisfactory stability with the sulfur selectivity only decreasing from 98.2% to 91.3% after the reaction going on 50 h. The decreased sulfur selectivity might be caused by the deterioration of pores and the deposition of elemental S on the surface. The former hinders the diffusion of sulfur oligomers timely from pores to the gas phase, while the latter is suspected to capture electrons to promote its further reaction with molecular oxygen.

Waste to Wealth: Discarded Cigarette Butt-Derived Metal-Free N-Rich Carbon Catalysts for the Selective Catalytic Oxidation of Hydrogen Sulfide to Sulfur

The selective catalytic oxidation of toxic gas H2S to elemental sulfur (H2S-SCO) is a promising desulfurization process known for its dual benefits of recovering valuable sulfur resources and mitigating environmental pollution. Nevertheless, developing cost-effective and efficient catalysts for H2S-SCO remains a significant challenge. In this study, we synthesized a low-cost and metal-free nitrogen-rich carbon catalyst (NrCC) by copyrolyzing discarded cigarette butts (organic solid wastes that are difficult to degrade naturally) with urea for the continuous H2S-SCO process at a relatively low temperature. The NrCC exhibited exceptional catalytic performance, achieving complete H2S conversion to sulfur at 180 °C, and demonstrated excellent stability in humid (RH = 80%) and high CO2 concentration environments. The catalyst succeeded due to its developed pore structure (specific surface area as high as 2267.77 m2·g-1) and abundant pyridine-N sites. DFT calculations showed that the pyridine-N neighbor carbon sites were the active sites promoting H2S adsorption and dissociation. This study presents a novel "waste control by waste" strategy that integrates the utilization of organic solid waste resources with air pollution control measures, showcasing the potential for sustainable environmental solutions.

Inverse ceria-nickel catalyst for enhanced C-O bond hydrogenolysis of biomass and polyether

Regulating interfacial electronic structure of oxide-metal composite catalyst for the selective transformation of biomass or plastic waste into high-value chemicals through specific C-O bond scission is still challenging due to the presence of multiple reducible bonds and low catalytic activity. Herein, we find that the inverse catalyst of 4CeOx/Ni can efficiently transform various lignocellulose derivatives and polyether into the corresponding value-added hydroxyl-containing chemicals with activity enhancement (up to 36.5-fold increase in rate) compared to the conventional metal/oxide supported catalyst. In situ experiments and theoretical calculations reveal the electron-rich interfacial Ce and Ni species are responsible for the selective adsorption of C-O bond and efficient generation of Hδ- species, respectively, which synergistic facilitate cleavage of C-O bond and subsequent hydrogenation. This work advances the fundamental understanding of interfacial electronic interaction over inverse catalyst and provides a promising catalyst design strategy for efficient transformation of C-O bond.

Progress on hydrogen sulfide removal: From catalytic oxidation to plasma-assisted treatment

Air pollution is a long-standing environmental challenge as well an important economic subject. Hydrogen sulfide is one the major pollutants in the industrial releases. This review focuses on the thermochemical treatment of hydrogen sulfide based on the most recent works to date regarding its removal. By analyzing fundamental steps in chemical reaction engineering, some useful factors are emphasized since they are often neglected in scientific studies, catalysts design and process scale-up. From processing side, the fluid flow conditions including velocity, H2S concentration, relative humidity, temperature and pressure strongly influence the kinetic behavior and so the catalytic performance of the H2S removal reactor. From material side, the catalyst properties including nature, porosity, pore types, size, sites distribution and layer structuration largely influence the removal performance via among others the accessibility to catalytic sites, pores connection and mass transfer resistance. Plasma-assisted catalytic removal of H2S combines many novelties in comparison with a classical thermo-catalytic process. From patents review, we can see that main concerns are about electrodes mounting, reactor lifetime and modular design to solve the problems in the industrial practice. We attempt to provide for scientists, engineers and industrialists a guidance on the design of catalysts and processes for H2S removal which could be applied in laboratorial studies and industrial processes as well.

Continuous and controllable synthesis of MnO2 adsorbents for H2S removal at low temperature

H2S is an extremely noxious impurity generated from nature and chemical industrial processes. High performing H2S adsorbents are required for chemical industry and environmental engineering. Herein, α-, γ-, and δ-MnO2 adsorbents with high sulfur capacity were synthesized through a continuous-flow approach with a microreactor system, achieving much higher efficiency than hydrothermal methods. The relationship between crystal structure and synthesis conditions such as residence time, reaction temperature, concentration of K+ in solution and reactant ratio is discussed. According to the H2S breakthrough tests at 150 °C, continuously prepared α-, γ-, and δ-MnO2 exhibited sulfur capacities of 669.5, 193.8 and 607.6 mg S/g sorbent, respectively, which was at a high level among the reported adsorbents. Such enhanced performance is related to the large surface area and mesopore volume, high reducibility, and a large number of oxygen species with high reactivity and mobility. Manganese sulfide and elemental sulfur were formed after desulfurization, which indicated the reaction consisted of two steps: redox and sulfidation of the sorbents. This study provides an innovative design strategy for the construction of nanomaterials with high H2S adsorption performances.

Review of Theoretical and Computational Studies of Bulk and Single Atom Catalysts for H2 S Catalytic Conversion

Catalytic conversion of hydrogen sulfide (H2 S) plays a vital role in environmental protection and safety production. In this review, recent theoretical advances for catalytic conversion of H2 S are systemically summarized. Firstly, different mechanisms of catalytic conversion of H2 S are elucidated. Secondly, theoretical studies of catalytic conversion of H2 S on surfaces of metals, metal compounds, and single-atom catalysts (SACs) are systematically reviewed. In the meantime, various strategies which have been adopted to improve the catalytic performance of catalysts in the catalytic conversion of H2 S are also reviewed, mainly including facet morphology control, doped heteroatoms, metal deposition, and defective engineering. Finally, new directions of catalytic conversion of H2 S are proposed and potential strategies to further promote conversion of H2 S are also suggested: including SACs, double atom catalysts (DACs), single cluster catalysts (SCCs), frustrated Lewis pairs (FLPs), etc. The present comprehensive review can provide an insight for the future development of new catalysts for the catalytic conversion of H2 S.

Recent advances in nanoflowers: compositional and structural diversification for potential applications

In recent years, nanoscience and nanotechnology have emerged as promising fields in materials science. Spectroscopic techniques like scanning tunneling microscopy and atomic force microscopy have revolutionized the characterization, manipulation, and size control of nanomaterials, enabling the creation of diverse materials such as fullerenes, graphene, nanotubes, nanofibers, nanorods, nanowires, nanoparticles, nanocones, and nanosheets. Among these nanomaterials, there has been considerable interest in flower-shaped hierarchical 3D nanostructures, known as nanoflowers. These structures offer advantages like a higher surface-to-volume ratio compared to spherical nanoparticles, cost-effectiveness, and environmentally friendly preparation methods. Researchers have explored various applications of 3D nanostructures with unique morphologies derived from different nanoflowers. The nanoflowers are classified as organic, inorganic and hybrid, and the hybrids are a combination thereof, and most research studies of the nanoflowers have been focused on biomedical applications. Intriguingly, among them, inorganic nanoflowers have been studied extensively in various areas, such as electro, photo, and chemical catalysis, sensors, supercapacitors, and batteries, owing to their high catalytic efficiency and optical characteristics, which arise from their composition, crystal structure, and local surface plasmon resonance (LSPR). Despite the significant interest in inorganic nanoflowers, comprehensive reviews on this topic have been scarce until now. This is the first review focusing on inorganic nanoflowers for applications in electro, photo, and chemical catalysts, sensors, supercapacitors, and batteries. Since the early 2000s, more than 350 papers have been published on this topic with many ongoing research projects. This review categorizes the reported inorganic nanoflowers into four groups based on their composition and structure: metal, metal oxide, alloy, and other nanoflowers, including silica, metal-metal oxide, core-shell, doped, coated, nitride, sulfide, phosphide, selenide, and telluride nanoflowers. The review thoroughly discusses the preparation methods, conditions for morphology and size control, mechanisms, characteristics, and potential applications of these nanoflowers, aiming to facilitate future research and promote highly effective and synergistic applications in various fields.

Highly Dispersed FeAg-MCM41 Catalyst for Medium-Temperature Hydrogen Sulfide Oxidation in Coke Oven Gas

The traditional hydrolysis-cooling-adsorption process for coke oven gas (COG) desulfurization urgently needs to be improved because of its complex nature and high energy consumption. One promising alternative for replacing the last two steps is selective catalytic oxidation. However, most catalysts used in selective catalytic oxidation require a high temperature to achieve effective desulfurization. Herein, a robust 30Fe-MCM41 catalyst is developed for direct desulfurization at medium temperatures after hydrolysis. This catalyst exhibits excellent stability for over 300 h and a high breakthrough sulfur capacity (2327.6 mgS gcat-1). Introducing Ag into the 30Fe-MCM41 (30Fe5Ag-MCM41) catalyst further enhances the H2S removal efficiency and sulfur selectivity at 120 °C. Its outstanding performance can be attributed to the synergistic effect of Fe-Ag clusters. During H2S selective oxidation, Fe serves as the active site for H2S adsorption and dissociation, while Ag functions as the catalyst promoter, increasing Fe dispersion, reducing the oxidation capacity of the catalyst, improving the desorption capacity of sulfur, and facilitating the reaction between active oxygen species and [HS]. This process provides a potential route for enhancing COG desulfurization.

"Electron Transport Chain Interference" Strategy of Amplified Mild-Photothermal Therapy and Defect-Engineered Multi-Enzymatic Activities for Synergistic Tumor-Personalized Suppression

Arming activatable mild-photothermal therapy (PTT) with the property of relieving tumor thermotolerance holds great promise for overcoming traditional mild PTT limitations such as thermoresistance, insufficient therapeutic effect, and off-target heating. Herein, a mitochondria-targeting, defect-engineered AFCT nanozyme with enhanced multi-enzymatic activity was elaborately designed as a tumor microenvironment (TME)-activatable phototheranostic agent to achieve remarkable anti-tumor therapy via "electron transport chain (ETC) interference and synergistic adjuvant therapy". Density functional theory calculations revealed that the synergistic effect among multi-enzyme active centers endows the AFCT nanozymes with excellent catalytic activity. In TME, open sources of H₂O₂ can be achieved by superoxide dismutase-mimicking AFCT nanozymes. In response to the dual stimuli of H₂O₂ and mild acidity, the peroxidase-mimicking activity of AFCT nanozymes not only catalyzes the accumulation of H₂O₂ to generate ·OH but also converts the loaded 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) into its oxidized form with strong near-infrared absorption, specifically unlocking its photothermal and photoacoustic imaging properties. Intriguingly, the undesired thermoresistance of tumor cells can be greatly alleviated owing to the reduced expression of heat shock proteins enabled by NADH POD-mimicking AFCT-mediated NADH depletion and consequent restriction of ATP supply. Meanwhile, the accumulated ·OH can facilitate both apoptosis and ferroptosis in tumor cells, resulting in synergistic therapeutic outcomes in combination with TME-activated mild PTT.

Controlling the Fe2O3-SiO2 interaction: The effect on the H2S selective catalytic oxidation and catalyst deactivation

Biogas utilization is one of the most promising options for reducing the consumption of fossil fuels for energy production, but the presence of H₂S represents a serious industrial and environmental problem. In this work, two different synthesis methods (sol-gel and incipient wetness impregnation) were used to synthesize iron oxide supported on silica catalysts (Fe₂O₃/SiO₂) with metal loadings ranging from 0.5 to 10 %wt. The catalysts were tested for the selective oxidation of H₂S, changing the operating conditions like O₂/H₂S (0.5-2.5), temperature (170-250°C), and water content (0-50%). The optimum condition was O₂/H₂S = 0.5 and no water at 230 °C with the conversion of approximately 100%, the selectivity of 97%, and the deactivation of 0.6%. A detailed characterization of the fresh and spent catalysts' surface revealed the presence of four deactivation mechanisms: metal surface reduction, oxygen vacancy loss, pore plugging, and sintering. Among the observed deactivation mechanisms, the sintering showed the highest impact on catalytic activity and deactivation. The sol-gel catalysts (SG) showed the highest metal-oxide/support interaction, which reduced the metal-oxide nanoparticles sintering compared with the incipient wetness impregnation method (IWI), reporting a lower sintering, higher activity, and selectivity, lower deactivation rates and lower sensitivity to the operating conditions. A catalytic cycle representing the possible surface intermediate states of the catalyst is proposed based on the performance and characterization results obtained.

Fe3+-Derived Boosted Charge Transfer in an FeSi4P4 Anode for Ultradurable Li-Ion Batteries

Ion and electron transportation determine the electrochemical performance of anodes in metal-ion batteries. This study demonstrates the advantage of charge transfer over mass transport in ensuring ultrastable electrochemical performance. Additionally, charge transfer governs the quality, composition, and morphology of a solid-electrolyte interphase (SEI) film. We develop FeSi₄P₄-carbon nanotube (FSPC) and reduced-FeSi₄P₄-carbon nanotube (R-FSPC) heterostructures. The FSPC contains abundant Fe³⁺ cations and negligible pore contents, whereas R-FSPC predominantly comprises Fe²⁺ and an abundance of nanopores and vacancies. The copious amount of Fe³⁺ ions in FSPC significantly improves charge transfer during Li-ion battery tests and leads to the formation of a thin monotonic SEI film. This prevents the formation of detrimental LiP and crystalline-Li_3.75Si phases and the aggregation of discharging/recharging products and guarantees the reformation of FeSi₄P₄ nanocrystals during delithiation. Thus, FSPC delivers a high initial Coulombic efficiency (>90%), exceptional rate capability (616 mAh g^-1 at 15 A g^-1), and ultrastable symmetric/asymmetric cycling performance (>1000 cycles at ultrahigh current densities). This study deepens our understanding of the effects of electron transport on regulating the structural and electrochemical properties of electrode materials in high-performance batteries.

A review on sensitivity of operating parameters on biogas catalysts for selective oxidation of Hydrogen Sulfide to elemental sulfur

Hydrogen sulfide (H₂S) is a critical problem for biogas applications, such as electricity and heat generation, or the production of different chemical compounds, due to corrosion and toxic effluent gases. The selective catalytic oxidation of H₂S to S is the most promising way to eliminate H₂S from biogas due to the lack of effluents, therefore can be considered a green technology. The most extensively used catalysts for H₂S selective oxidation can be classified in two groups: metal oxide-based catalysts, including vanadium and iron oxides, and carbon-based catalysts. Numerous studies have been devoted to studying their different catalytic performances. For industrial applications, the most suitable catalysts should be less sensitive to the operating parameters like the temperature, O₂/H₂S ratio, and H₂O content. More specifically, for metal oxides and carbon-based catalysts, the temperature and O₂/H₂S ratio have a similar effect on the conversion and selectivity, but carbon-based catalysts are less sensitive to water in all operating conditions.

Efficiently Integrated Desulfurization from Natural Gas over Zn-ZIF-Derived Hierarchical Lamellar Carbon Frameworks

Selective removal of carbonyl sulfide (COS) and hydrogen sulfide (H₂S) is the key step for natural gas desulfurization due to the highly toxic and corrosive features of these gaseous sulfides, and efficient and stable desulfurizers are urgently needed in the industry. Herein, we report a class of nitrogen-functionalized, hierarchically lamellar carbon frameworks (N-HLCF-xs), which are obtained from the structural transformation of Zn zeolitic imidazolate frameworks via controllable carbonization. The N-HLCF-xs possess the desirable characteristics of large Brunauer-Emmett-Teller surface areas (645-923 m²/g), combined primary three-dimensional microporosity and secondary two-dimensional lamellar microstructure, and high density of nitrogen base sites with enhanced pyridine ratio (17.52 wt %, 59.91%). The anchored nitrogen base sites in N-HLCF-xs show improved accessibility, which boosts their interaction with acidic COS and H₂S. As expected, N-HLCF-xs can be employed as multifunctional and efficient desulfurizers for selective removal of COS and H₂S from natural gas. COS was first transformed into H₂S via catalytic hydrolysis, and the produced H₂S was then captured and separated and catalyzed oxidation into elemental sulfur. The above continuous processes can be achieved with solo N-HLCF-xs, giving extremely high efficiencies and reusability. Their integrated desulfurization performance was better than many desulfurizers used in the area, such as activated carbon, β zeolite, MIL-101(Fe), K₂CO₃/γ-Al₂O₃, and FeO_x/TiO₂.

Oxygen Vacancy-Mediated Selective H2S Oxidation over Co-Doped LaFexCo1−xO3 Perovskite

Compared to the Claus process, selective H2S catalytic oxidation to sulfur is a promising reaction, as it is not subject to thermodynamic limitations and could theoretically achieve ~100% H2S conversion to sulfur. In this study, we investigated the effects of Co and Fe co-doping in ABO3 perovskite on H2S selective catalytic oxidation. A series of LaFexCo1−xO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) perovskites were synthesized by the sol-gel method. Compared to LaFeO3 and LaCoO3, co-doped LaFexCo1−xO3 significantly improved the H2S conversion and sulfur selectivity at a lower reaction temperature. Nearly 100% sulfur yield was achieved on LaFe0.4Co0.6O3 under 220 °C with exceptional catalyst stability (above 95% sulfur yield after 77 h). The catalysts were characterized by XRD, BET, FTIR, XPS, and H2-TPR. The characterization results showed that the structure of LaFexCo1−xO3 changed from the rhombic phase of LaCoO3 to the cubic phase of LaFeO3 with Fe substitution. Doping with appropriate iron (x = 0.4) facilitates the reduction of Co ions in the catalyst, thereby promoting the H2S selective oxidation. This study demonstrates a promising approach for low-temperature H2S combustion with ~100% sulfur yield.

Engineering Multidefects on Cex Si1- x O2- δ Nanocomposites for the Catalytic Ozonation Reaction

Herein, it is shown that by engineering defects on Ce_x Si_{1- x} O_{2- δ} nanocomposites synthesized via flame spray pyrolysis, oxygen vacancies can be created with an increased density of trapped electrons, enhancing the formation of reactive oxygen species (ROSs) and hydroxyl radicals in an ozone-filled environment. Spectroscopic analysis and density functional theory calculations indicate that two-electron oxygen vacancies (O_V ⁰ ) or peroxide species, and their degree of clustering, play a critical role in forming reactive radicals. It is also found that a higher Si content in the binary oxide imposes a high O_V ⁰ ratio and, consequently, higher catalytic activity. Si inclusion in the nanocomposite appears to stabilize the surface oxygen vacancies as well as increase the reactive electron density at these sites. A mechanistic study on effective ROSs generated during catalytic ozonation reveals that the hydroxyl radical is the most effective ROS for organic degradation and is formed primarily through H₂ O₂ generation in the presence of the O_V ⁰ . Examining the binary oxides offers insights on the contribution of oxygen vacancies and their state of charge to catalytic reactions, in this instance for the catalytic ozonation of organic compounds.

Facilitating Catalytic Purification of Auto-Exhaust Carbon Particles via the Fe2O3{113} Facet-dependent Effect in Pt/Fe2O3 Catalysts

The purification efficiency of auto-exhaust carbon particles in the catalytic aftertreatment system of vehicle exhaust is strongly dependent on the interface nanostructure between the noble metal component and oxide supports. Herein, we have elaborately synthesized the catalysts (Pt/Fe₂O₃-R) of Pt nanoparticles decorated on the hexagonal bipyramid α-Fe₂O₃ nanocrystals with co-exposed twelve {113} and six {104} facets. The area ratios (R) of co-exposed {113} to {104} facets in α-Fe₂O₃ nanocrystals were adjusted by the fluoride ion concentration in the hydrothermal method. The strong Pt-Fe₂O₃{113} facet interaction boosts the formation of coordination unsaturated ferric sites for enhancing adsorption/activation of O₂ and NO. Pt/Fe₂O₃-R catalysts exhibited the Fe₂O₃{113} facet-dependent performance during catalytic purification of soot particles in the presence of H₂O. Among the catalysts, the Pt/Fe₂O₃-19 catalyst exhibits the highest catalytic activities (T₅₀ = 365 °C, TOF = 0.13 h^-1), the lowest apparent activation energy (69 kJ mol^-1), and excellent catalytic stability during soot purification. Combined with the results of characterizations and density functional theory calculations, the catalytic mechanism is proposed: the active sites located at the Pt-Fe₂O₃{113} interface can boost the key step of NO oxidation to NO₂. The crystal facet engineering is an effective strategy to obtain efficient catalysts for soot purification in practical applications.

Engineering of crystal phase over porous MnO2 with 3D morphology for highly efficient elimination of H2S

In the present work, we report a facile oxalate-derived hydrothermal method to fabricate α-, β- and δ-MnO₂ catalysts with hierarchically porous structure and study the phase-dependent behavior for selective oxidation of H₂S over MnO₂ catalysts. It was disclosed that the oxygen vacancy, reducibility and acid property of MnO₂ are essentially determined by the crystalline phase. Systematic experiments demonstrate that δ-MnO₂ is superior in active oxygen species, activation energy and H₂S adsorption capacity among the prepared catalysts. As a consequence, δ-MnO₂ nanosphere with a hierarchically porous structure shows high activity and stability with almost 100% H₂S conversion and sulfur selectivity at 210 °C, better than majority of reported Mn-based materials. Meanwhile, hierarchically porous structure of δ-MnO₂ nanosphere alleviates the generation of by-product SO₂ and sulfate, promoting the adoptability of Mn-based catalysts in industrial applications.

Solvothermal Synthesis Routes to Substituted Cerium Dioxide Materials

We review the solution-based synthesis routes to cerium oxide materials where one or more elements are included in place of a proportion of the cerium, i.e., substitution of cerium is performed. The focus is on the solvothermal method, where reagents are heated above the boiling point of the solvent to induce crystallisation directly from the solution. This yields unusual compositions with crystal morphology often on the nanoscale. Chemical elements from all parts of the periodic table are considered, from transition metals to main group elements and the rare earths, including isovalent and aliovalent cations, and surveyed using the literature published in the past ten years. We illustrate the versatility of this synthesis method to allow the formation of functional materials with applications in contemporary applications such as heterogeneous catalysis, electrodes for solid oxide fuel cells, photocatalysis, luminescence and biomedicine. We pick out emerging trends towards control of crystal habit by use of non-aqueous solvents and solution additives and identify challenges still remaining, including in detailed structural characterisation, the understanding of crystallisation mechanisms and the scale-up of synthesis.

Defective Ultrafine MnOx Nanoparticles Confined within a Carbon Matrix for Low-Temperature Oxidation of Volatile Organic Compounds

The development of catalysts for volatile organic compound (VOC) treatment by catalytic oxidation is of great significance to improve the atmospheric environment. Size-effect and oxygen vacancy engineering are effective strategies for designing high-efficiency heterogeneous catalysts. Herein, we explored the in situ carbon-confinement-oxidation method to synthesize ultrafine MnO_x nanoparticles with adequately exposed defects. They exhibited an outstanding catalytic performance with a T₉₀ of 167 °C for acetone oxidation, which is 73 °C lower than that of bulk MnO_x (240 °C). This excellent catalytic activity was primarily ascribed to their high surface area, rich oxygen vacancies, abundant active oxygen species, and good reducibility at low temperatures. Importantly, the synthesized ultrafine MnO_x exhibited impressive stability in long-term, cycling and water-resistance tests. Moreover, the possible mechanism for acetone oxidation over MnO_x-NA was revealed. In this work, we not only prepared a promising material for removing VOCs but also provided a new strategy for the rational design of ultrafine nanoparticles with abundant defects.

N-doped honeycomb-like porous carbon derived from biomass as an efficient carbocatalyst for H2S selective oxidation

3D interconnected porous N-doped carbocatalyst derived from the waste air-laid paper plays as an efficient metal-free catalyst for H₂S removal in super-Claus reaction. The honeycomb-like porous nitrogen-doped carbons are fabricated through a facile impregnation of alkaline solution and NH₃ post-treatment method. The experiments prove that NH₃ post-treatment is an efficient way to improve the catalytic performance, which resulting in outstanding reactivity and stability with highest sulfur formation rate of 496.6 g_sulfurkg_cat.^-1 h^-1 and sulfur yield of 86.7 % in feed gas with high concentration (ca. 10,000 ppm) of H₂S for selective oxidation. Significantly, the optimized pyridinic-N content and defect degree endow the N-doped porous carbon (NPC700) with highest catalytic activity according to the Raman and XPS results. The high surface area and abundant porous structure also contribute to the high catalytic performance by increasing the exposure degree of active site and offering additional active surface. Based on the XPS, SEM, TEM and EDS mapping results, the N-doped porous carbon are proved to be stable catalysts since the morphology and surface chemical environment remain similar after the oxidative desulfurization process.

Highly Active and Sulfur-Resistant Fe-N4 Sites in Porous Carbon Nitride for the Oxidation of H2 S into Elemental Sulfur

Iron-based catalysts have been widely studied for the oxidation of H₂ S into elemental S. However, the prevention of iron sites from deactivation remains a big challenge. Herein, a facile copolymerization strategy is proposed for the construction of isolated Fe sites confined in polymeric carbon nitride (CN) (Fe-CNNχ). The as-prepared Fe-CNNχ catalysts possess unique 2D structure as well as electronic property, resulting in enlarged exposure of active sites and enhancement of redox performance. Combining systematic characterizations with density functional theory calculation, it is disclosed that the isolated Fe atoms prefer to occupy four-coordinate doping configurations (Fe-N₄ ). Such Fe-N₄ centers favor the adsorption and activation of O₂ and H₂ S. As a consequence, Fe-CNNχ exhibit excellent catalytic activity for the catalytic oxidation of H₂ S to S. More importantly, the Fe-CNNχ catalysts are resistant to water and sulfur poisoning, exhibiting outstanding catalytic stability (over 270 h of continuous operation), better than most of the reported catalysts.