Application of spinel-type cobalt chromite as a novel catalyst for combustion of chlorinated organic pollutants

The elemental pegging effect in locally ordered nanocrystallites of high-entropy oxide enables superior lithium storage

High-entropy oxides (HEOs) can be well suited for lithium-ion battery anodes because of their multi-principal synergistic effect and good stability. The appropriate selection and combination of elements play a crucial role in designing conversion-type anode materials with outstanding electrochemical performance. In this study, we have successfully built a single-phase spinel-structured HEO material of (Mn0.23Fe0.23Co0.22Cr0.19Zn0.13)3O4 (HEO-MFCCZ). When the HEO-MFCCZ materials transform into a coexisting state of amorphous and nanocrystalline structures during the cycling process, the inert Zn element can initiate a pegging effect, causing enhanced stability. The transition also introduces many defect sites, effectively reducing the potential barrier for ion transport and accelerating ion transport. The increased electronic and ionic conductivities and pseudocapacitive contribution significantly enhance the rate performance. As a result, a unique and practical approach is provided for developing anode materials for lithium-ion batteries.

Review of Emission Characteristics and Purification Methods of Volatile Organic Compounds (VOCs) in Cooking Oil Fume

Volatile organic compounds (VOCs) in cooking oil fumes need to be efficiently removed due to the significant damage they cause to the environment and human health. This review discusses the emission characteristics, which are influenced by different cooking temperatures, cooking oils, and cuisines. Then, various cooking oil fume purification methods are mainly classified into physical capture, chemical decomposition, and combination methods. VOCs removal rate, system operability, secondary pollution, application area, and cost are compared. The catalytic combustion method was found to have the advantages of high VOC removal efficiency, environmental protection, and low cost. Therefore, the last part of this review focuses on the research progress of the catalytic combustion method and summarizes its mechanisms and catalysts. The Marse-van Krevelen (MVK), Langmuir-Hinshelwood (L-H), and Eley-Rideal (E-R) mechanisms are analyzed. Noble metal and non-noble metal catalysts are commonly used. The former showed excellent activity at low temperatures due to its strong adsorption and electron transfer abilities, but the high price limits its application. The transition metals primarily comprise the latter, including single metal and composite metal catalysts. Compared to single metal catalysts, the interaction between metals in composite metal catalysts can further enhance the catalytic performance.

The Liquid Phase Oxidation of Light Hydrocarbons for Thermo-Gas-Chemical Enhanced Oil Recovery Method

Heavy oil and natural bitumen resources in carbonate formations are huge and considered as the promising alternative energy resource to the conventional crude oils. However, the production of such resources is challenging due to the low permeability, high viscosity and significant content of resins and asphaltenes in the composition of heavy oil and natural bitumen. The combination of thermal, chemical and gas enhanced oil recoveries can be a promising method to unlock and upgrade heavy oil and natural bitumen in carbonate reservoirs. In this paper, we propose a novel in-situ liquid-phase oxidation of light hydrocarbons for a revolutionary thermo-gas-chemical enhanced oil recovery method, which can be applied in carbonate heavy oil reservoir formations. It is assumed that the oxidation process is carried out in a downhole well reactor, the products of which are a high temperature mixture of organic carboxylic acids and organic solvents. Here, we present the results of laboratory investigations of liquid-phase oxidation of n-hexane as a model compound imitating associated petroleum gases in the presence of Fe, Cr and Ni catalysts, which were introduced in the form of oil-soluble catalyst precursors. It was revealed that the oxidation process yields hydro peroxides, organic carboxylic acids (acetic, propionic and valeric acids), alcohols and ethers. The products of the oxidation process were justified by the results of FT-IR and GC-MS analysis methods. According to the results, Cr-based catalyst leads to the increase of CH3-groups in the products. The oxidation process in the presence of nickel-based catalyst is compared with a control sample. The naphthalene was detected in the oxidation products of all experiments, the formation of which is explained by polymerization of benzene rings. In its turn, benzene is obtained due to dehydrocyclization of n-hexane on the surface of nanoparticles. However, iron-based catalyst showed the best catalytic performance in low-temperature oxidation of n-hexane in autocatalysis mode as the yield of acetic acid prevailed 52%. The given approach provides prolonged thermal and acid treatment of carbonate formations, where the evolved CO2 gas will further assist in increasing the mobility of crude oil. Moreover, the produced alcohols, ethers and other hydrocarbons play the role of solvents, which dissolves polar and non-polar components of crude oil.

Evidence of anomalous conventional and spontaneous exchange bias, high coercivity in Fe doped NiCr2O4 spinel

NiCr2-xFexO4 (x = 0 and 0.2) polycrystalline ceramics have been synthesized successfully through a simple co-precipitation technique to study the evolution of structural and magnetic properties by doping Fe. X-ray diffraction (XRD) reveals that the high-temperature cubic phase (space group Fd3[combining macron]m) observed at 320 K in bulk NiCr2O4 is stabilized at room temperature by decreasing the particle size to nanometer in x = 0 as well as after incorporating 20 at% Fe in the NiCr2O4 lattice. The cation distribution obtained from X-ray absorption fine structure (XAFS) analysis illustrates that while in x = 0, Ni2+ and Cr3+ ions occupy the tetrahedral (A) and octahedral (B) sites, respectively, x = 0.2, Fe3+ and Cr3+ ions occupy the A and B sites, respectively, and Ni2+ ions are distributed among the A and B sites. This transformation from the normal to mixed spinel structure strongly affects the magnetic properties. While the paramagnetic to long-range ferrimagnetic ordering temperature TC is enhanced from 71 to 192 K, significantly large coercive field (HC) of ∼29 kOe is observed for x = 0.2 as compared to the HC ∼13 kOe for x = 0. Moreover, unusually large conventional and spontaneous exchange bias fields of ∼26 and ∼2.6 kOe are observed for x = 0.2, which is absent for x = 0. The presence of anomalous exchange bias field is ascribed to the unidirectional exchange anisotropy between the two magnetic sublattices at A and B sites. The training effect of the exchange bias field is discussed using a phenomenological model, which considers the contribution from irreversible uncompensated spins that modify the exchange anisotropy at the interface between A and B magnetic sublattices. In addition, diffuse neutron scattering (DNS) with XYZ analysis is employed for both compositions to clearly illustrate the low-temperature peculiar magnetic phase transitions such as spin spiral transition, TS and spin lock-in transition, Tl. The DNS demonstrates that while Tl decreases from 10 K to 7 K with the incorporation of Fe in the NiCr2O4 lattice, TS significantly increases from 28 K to 50 K.

The identification of active chromium species to enhance catalytic behaviors of alumina-based catalysts for sulfur-containing VOC abatement

As to the treatment of sulfur containing VOCs (examples are compounds of CH₃SH and C₂H₅SH), finding a catalyst with high performance is necessary. In this work, Cr_(x)-Al₂O₃ (x = 1.0, 2.5, 5.0, 7.5 and 10 wt%) catalysts were synthesized, and their behaviors toward CH₃SH and C₂H₅SH abatement were investigated. The results indicated that Cr_(7.5)-Al₂O₃ exhibited higher activity than other samples and the reported catalysts, on which CH₃SH could be almost completely converted at 375 °C, while the temperature for the reported catalysts was above 450 °C. Moreover, there was no obvious deactivation during 30 h on stream over Cr_(7.5)-Al₂O₃, while only about 10 h was found on the reported CeO₂ and HZSM-5 catalysts. The improvement in the catalytic performance could be explained by the important role of the Cr⁶⁺ species, while the state of Cr³⁺ was suggested to be ineffective in the degradation process. The identification of the active Cr sites was proved by the characterization measurements, and the control experiments by using mechanical mixtures of CrO₃ or Cr₂O₃ with Al₂O₃ as well as the comparison studies between spent Al₂O₃ and spent Cr_(7.5)-Al₂O₃ catalysts.

Plasma assisted Cu-Mn mixed oxide catalysts for trichloroethylene abatement in moist air

The removal of dilute trichloroethylene (TCE) in moist air by post-plasma catalysis (PPC) using Cu-Mn mixed oxides heated at 150 °C was investigated. Cu-Mn mixed oxides were prepared by redox- and co-precipitation method. In comparison to the catalytic oxidation and non-thermal plasma (NTP) process, PPC was found to be the best process to convert TCE into CO₂, in particular when Cu-Mn oxide was synthetized by redox precipitation method. The highest TCE conversion efficiency of more than 80% was obtained at the energy density of 60 J.L^-1 using the catalyst prepared by redox-precipitation process in PPC configuration. The performance of Cu-Mn oxide prepared by redox-precipitation method did not show increase in TCE conversion with energy density which is attributed to the changes on the catalyst surface (such as reduction in S_BET, chlorine poisoning and Mn enrichment). Although, Cu-Mn oxide prepared by co-precipitation method showed a lower TCE conversion, it exhibited a better stability in the PPC process for TCE abatement.

Synthesis and characterization of some nanostructured composite oxides for low temperature catalytic combustion of dilute propane

Five nanosized perovskite and four ferrospinel powders were prepared by sol–gel self-combustion technique. The La_0.6Pb_0.2Mg_0.2MnO₃ perovskite was found to exhibit the best catalytic performance with respect to propane combustion at low temperatures.

Three-dimensionally ordered macroporous spinel-type MCr2O4 (M = Co, Ni, Zn, Mn) catalysts with highly enhanced catalytic performance for soot combustion

MCr₂O₄ catalysts with three-dimensional ordered macroporous structures displayed superior catalytic activity for soot combustion to their bulk counterparts.

Catalytic oxidation of 1,2-dichloroethane over Al2O3–CeO2 catalysts: combined effects of acid and redox properties

The lower temperature catalytic combustion of 1,2-dichloroethane (DCE) over Al₂O₃, CeO₂ and Al₂O₃–CeO₂ catalysts were studied.

Roles of Li+ and Zr4+ cations in the catalytic performances of Co(1-x)M(x)Cr(2)O(4) (M = Li, Zr; x = 0-0.2) for methane combustion

Co(1-x)M(x)Cr(2)O(4) (M = Li, Zr; x = 0-0.2) catalysts were prepared via the citric acid method and investigated for catalytic combustion of methane. Substitution at tetrahedral (A) sites with monovalent (Li) or tetravalent (Zr) metal ions led to a decrease or increase of the catalytic activity, respectively. The Co(0.95)Zr(0.05)Cr(2)O(4) catalyst proved to be the most active and its catalytic activity reached 90% of methane conversion at 448 °C, which dropped by 66 °C compared with that of the undoped CoCr(2)O(4) catalyst. XRD and Raman results indicated that lithium or zirconium substitution could modify the spinel structure and electronic properties. For lithium-doped catalysts, oxygen deficiency and a strong surface enrichment in lithium and chromium were detected. Zirconium substitution enhanced the reducibility of zirconium-doped catalysts and decreased the strength constant of both the Co-O band and the Cr-O band, which may contribute to the catalytic activity toward methane combustion. In addition, the prevalent catalytic combustion activity of the zirconium-substituted catalysts could be explained by their higher concentration of suprafacial, weakly chemisorbed oxygen.

Three-dimensionally ordered and wormhole-like mesoporous iron oxide catalysts highly active for the oxidation of acetone and methanol

Three-dimensionally (3D) ordered and wormhole-like mesoporous iron oxides (denoted as Fe-KIT6 and Fe-CA) were respectively prepared by adopting the 3D ordered mesoporous silica KIT-6-templating and modified citric acid-complexing strategies, and characterized by a number of analytical techniques. It is shown that the Fe-KIT6-400 and Fe-CA-400 catalysts derived after 400°C-calcination possessed high surface areas (113-165 m(2)/g), high surface adsorbed oxygen concentrations, and good low-temperature reducibility, giving 90% conversion below 189 and 208°C for acetone and methanol oxidation at 20,000 mL/(g h), respectively. It is believed that the good catalytic performance of Fe-CA-400 and Fe-KIT6-400 was related to factors such as higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and 3D mesoporous architecture.

Destruction of polychlorinated aromatic compounds by spinel-type complex oxides

Destruction of polychlorinated aromatic compounds was carried out over spinel-type catalysts XY2O4 (where X = Mg, Ca, Cu, Ni, Zn, and Y = Al, Fe). The catalysts were characterized by XRD, nitrogen adsorption-desorption isotherms and FTIR. The performance of these catalysts toward the decomposition of hexachlorobenzene (HCB) and octachlorodibenzo-p-dioxin (OCDD) was evaluated in a closed system. The spinel-type catalyst with mesoporous structure demonstrated high catalytic activity for the hydrodechlorination of polychlorinated aromatic compounds. Among them, the copper-aluminum spinel (CuAl2O4), specifically calcined at 600 degrees C, exhibited the best activity. More than 85% dechlorination efficiency of HCB and 99% decomposition of polychlorinated dibenzodioxin (PCDD) were achieved at 250 degrees C for 30 min over the above catalyst which was more effective than the corresponding metallic copper and copper oxide catalysts during the thermal degradation of polychlorinated aromatic compounds. The correlation of catalytic performance to structural characteristics is discussed based on the detailed characterization. The simple preparation procedure and reasonable cost of the spinel-type catalysts present a good potential for the thermal treatment of polychlorinated aromatic pollutants at lower temperatures.

Role of water and other H-rich additives in the catalytic combustion of 1,2-dichloroethane and trichloroethylene

In several practical applications gas streams containing chlorinated volatile organic compounds with variable chemical nature (namely, 1,2-dichloroethane and trichloroethylene) and a significant moisture content (15000ppm) must be addressed. In this paper the control of such emissions by catalytic oxidation over Ce/Zr mixed oxides was analysed. Results in terms of activity and selectivity were compared with those obtained when other H-rich additives (1000ppm), such as hexane or toluene, were fed. High activity was found from mixed oxides featuring a suitable combination of a large population of acid sites, easily accessible oxygen species, and hydrophobic nature attributable to cerium content. The presence of additional H-rich compounds in the feed stream (water, toluene or hexane) tended to decrease the catalytic activity due to the blockage and/or competition for actives sites. However, the increased presence of hydrogen atoms in the stream notably promoted the selectivity to hydrogen chloride instead of molecular chlorine.