Catalytic oxidation of toluene on Ce–Co and La–Co mixed oxides synthesized by exotemplating and evaporation methods

A new attempt to remove toluene using nickel-iron bimetallic particle electrode reactor

A new attempt of removing toluene waste gas using a three-dimensional electrode reaction device with nickel-iron bimetallic particle electrode is presented in this paper. The particle electrode was prepared by a simple liquid phase reduction method. Through bimetal modification, the particle electrode mass transfer rate is increased to 1.29 times, and the degradation efficiency of the reactor is increased by nearly 40%, which makes it possible to remove toluene waste gas by other electrochemical methods in addition to plasma method. The removal efficiency of the particle electrode can be stabilized at more than 80% after 5 cycles (50 h). At the same time, the relationship between independent working parameters and dependent variables is analyzed using the central composite design, and the operating parameters are optimized. Based on this study, the removal mechanism and possible degradation pathway of toluene were investigated. This study provides a supplement to the possibility and theoretical basis of new technology application for electrocatalytic oxidation removal of VOCs.

Cooperative and Bifunctional Adsorbent-Catalyst Materials for In-situ VOCs Capture-Conversion

Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed-metal oxides, polymers, activated carbons, zeolites, metal-organic frameworks (MOFs) and mixed-matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent-catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent-catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long-term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.

Unveiling the Role of In Situ Sulfidation and H2O Excess onH2S Decomposition to Carbon-Free H2 over Cobalt/Ceria Catalysts

The emerging energy and environmental concerns nowadays are highlighting the need to turn to clean fuels, such as hydrogen. In this regard, hydrogen sulfide (H2S), an abundant chemical compound found in several natural sources and industrial streams, can be considered a potential carbon-free H2 source through its decomposition. In the present work, the H2S decomposition performance of Co3O4/CeO2 mixed oxide catalysts toward hydrogen production is investigated under excess H2O conditions (1 v/v% H2S, 90 v/v% H2O, Ar as diluent), simulating the concentrated H2S-H2O inflow by the Black Sea deep waters. The effect of key operational parameters such as feed composition, temperature (550–850 °C), and cobalt loading (0–100 wt.%) on the catalytic performance of Co3O4/CeO2 catalysts was systematically explored. In order to gain insight into potential structure-performance relationships, various characterization studies involving BET, XRD, SEM/EDX, and sulfur elemental analysis were performed over the fresh and spent samples. The experimental results showed that the 30 wt.% Co/CeO2 catalyst demonstrated the optimum catalytic performance over the entire temperature range with a H2 production rate of ca. 2.1 μmol H2∙g−1·s−1 at 850 °C and a stable behavior after 10 h on stream, ascribed mainly to the in-situ formation of highly active and stable cobalt sulfided phases.

Degradation of gaseous volatile organic compounds (VOCs) by a novel UV-ozone technology

In this study, a UV-assisted ozonation (UV/O₃) process for the degradation of VOCs emissions with a final scrubbing phase was implemented to evaluate the removal efficiency of toluene and to prevent the release of polluting intermediates of the single-step process. Inlet toluene concentration and applied voltage were varied in order to investigate several operating conditions. The results highlighted that at higher inlet concentration the abatement of toluene was lower, while increase in ozone concentration led to an increase of the degradation efficiencies. The additional water scrubbing step enhanced the abatement of UV/O₃ up to 98.5%, due to the solubilisation of ozone and by-products in the process water and, thus, the further oxidation of the contaminants within this phase. A maximum Elimination Capacity (EC_max) of 22.6 g m⁻³ h⁻¹ was achieved with the UV/O₃ + Scrubbing. The combined system boosted higher performance and stability compared to the stand-alone (UV/O₃) process along with a more economical and environmental sustainability.

Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

Decomposition of nitrous oxide in hydrated cobalt(I) clusters: a theoretical insight into the mechanistic roles of ligand-binding modes

Hydrated cobalt(i) cluster ions, [Co(H2O)n]+, can decompose the inert nitrous oxide molecule, N2O. Density functional theory suggests that N2O can anchor to Co+ of [Co(N2O)(H2O)n]+ through either O end-on (η1-OL) or N end-on (η1-NL) coordinate mode. The latter is thermodynamically more favorable resulting from a subtle π backdonation from Co+ to N2O. N2O decomposition involves two major processes: (1) redox reaction and (2) N-O bond dissociation. The initial activation of N2O through an electron transfer from Co+ to N2O yields anionic N2O-, which binds to the metal center of [Co2+(N2O-)(H2O)n] also through either O end-on (η1-O) or N end-on (η1-N) mode and is stabilized by water molecules through hydrogen bonding. From η1-O, subsequent N-O bond dissociation to liberate N2, producing [CoO(H2O)n]+, is straightforward via a mechanism that is commonplace for typical metal-catalyzed N2O decompositions. Unexpectedly, the N-O bond dissociation directly from η1-N is also possible and eliminates both N2 and OH, explaining the formation of [CoOH(H2O)n]+ as observed in a previous experimental study. Interestingly, formation of [CoO(H2O)n]+ is kinetically controlled by the initial redox process between Co+ and the O-bound N2O, the activation barriers of which in large water clusters (n ≥ 14) are higher than that of the unexpected N-O bond dissociation from the N-bound structure forming [CoOH(H2O)n]+. This theoretical discovery implies that in the present of water molecules, the metal-catalyzed N2O decomposition starting from an O-bound metal complex is not mandatory.

Rational Design of Non-Precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes

Catalysis is an indispensable part of our society, involved in numerous energy and environmental applications, such as the production of value-added chemicals/fuels, hydrocarbons processing, fuel cells applications, abatement of hazardous pollutants, among others [...]

The improved activity of Co3O4 nanorods using silver in the catalytic oxidation of toluene

Co₃O₄ nanorods with diameters of ~0.15 μm and lengths of ~1 μm were prepared using a hydrothermal method via the assembly of microcrystals and tested in the catalytic oxidation of toluene. The catalytic performance of Co₃O₄ nanorods was improved by the addition of Ag at various concentrations, and the 7% Ag/Co₃O₄ catalyst achieves a toluene conversion of 90% at 256 °C with a space velocity of 78,000 mL g^-1 h^-1, which is much lower than that of the pristine Co₃O₄ (269 °C). The addition of Ag promoted the activation of the surface oxygen species and the formation of more oxygen vacancies, improving the relative low-temperature reducibility of Co₃O₄, which is favorable for toluene oxidation. Moreover, the 7% Ag/Co₃O₄ catalyst showed an excellent stability for toluene oxidation at 250 and 260 °C for 50 h under the same conditions.

First-Principles Evaluation of Volatile Organic Compounds Degradation in Z-Scheme Photocatalytic Systems: MXene and Graphitic-CN Heterostructures

It is a formidable challenge to use the traditional trial-and-error method to identify suitable catalysts for the photocatalytic degradation of volatile organic compounds (VOCs). In this work, by performing density functional theory calculations, we designed three Z-scheme g-CN/M₂CO₂ (M = Hf, Zr, and Sc) heterostructures, which not only exhibit favorable structure stability but also show promising ability for photocatalytic degradation of VOCs. The enhancement of the photocatalytic activity of these three Z-scheme systems can be ascribed to the low recombination rate of electron-hole pairs because photoelectrons migrated from the g-CN layer to the M₂CO₂ layer as well as the internal electric fields in the Z-scheme heterojunction. Among the three heterostructures, only g-CN/Zr₂CO₂ presents favorable spectra utilization under photoirradiation as well as the direct band gap. As a result, in the Z-scheme g-CN/Zr₂CO₂ heterostructure, the electrons in the conduction band of g-CN migrate to the holes in the valence band of the Zr₂CO₂ layer, which improves extraction and utilization of photogenerated electrons in the g-CN sheet. Moreover, the Z-scheme g-CN/Zr₂CO₂ system shows superior performance for photocatalytic VOC degradation in comparison with individual g-CN and Zr₂CO₂, which can be attributed to the enhanced VOC adsorption capacity as well as excellent ability to photoactivate O₂ and H₂O into ^•O₂^- and ^•OH radicals. Our findings pave a new promising way to facilitate the application of MXene-based materials for VOC photocatalytic degradation.

Simple strategy for the construction of oxygen vacancies on α-MnO2 catalyst to improve toluene catalytic oxidation

A strategy simple, safe and suitable for large scale production of α-MnO₂ catalyst with high activity in VOCs oxidation is crucial for its application. The catalytic reactivity of α-MnO₂ catalyst is largely related with its oxygen vacancy. Herein, we report effective construction of oxygen vacancies on α-MnO₂ through simply adjusting precipitation temperature of a redox precipitation process. The key role of surface oxygen vacancies in toluene oxidation and the formation of different amount and distribution of the oxygen vacancies over the α-MnO₂ catalysts were revealed by characterizations together with DFT calculations. The best catalyst (α-MnO₂-60) exhibited significantly improved catalytic activity of α-MnO₂ catalyst in toluene oxidation (T₉₀ = 203 ℃) and excellent water resistance. The richest surface oxygen vacancies of α-MnO₂-60 contributed to its best catalytic activity, despite of its relatively lower specific surface area. This work may provide a new perspective for the rational design of high efficient VOCs catalysts.

Facet-Dependent Reactivity of Ceria Nanoparticles Exemplified by CeO2-Based Transition Metal Catalysts: A Critical Review

The rational design and fabrication of highly-active and cost-efficient catalytic materials constitutes the main research pillar in catalysis field. In this context, the fine-tuning of size and shape at the nanometer scale can exert an intense impact not only on the inherent reactivity of catalyst’s counterparts but also on their interfacial interactions; it can also opening up new horizons for the development of highly active and robust materials. The present critical review, focusing mainly on our recent advances on the topic, aims to highlight the pivotal role of shape engineering in catalysis, exemplified by noble metal-free, CeO2-based transition metal catalysts (TMs/CeO2). The underlying mechanism of facet-dependent reactivity is initially discussed. The main implications of ceria nanoparticles’ shape engineering (rods, cubes, and polyhedra) in catalysis are next discussed, on the ground of some of the most pertinent heterogeneous reactions, such as CO2 hydrogenation, CO oxidation, and N2O decomposition. It is clearly revealed that shape functionalization can remarkably affect the intrinsic features and in turn the reactivity of ceria nanoparticles. More importantly, by combining ceria nanoparticles (CeO2 NPs) of specific architecture with various transition metals (e.g., Cu, Fe, Co, and Ni) remarkably active multifunctional composites can be obtained due mainly to the synergistic metalceria interactions. From the practical point of view, novel catalyst formulations with similar or even superior reactivity to that of noble metals can be obtained by co-adjusting the shape and composition of mixed oxides, such as Cu/ceria nanorods for CO oxidation and Ni/ceria nanorods for CO2 hydrogenation. The conclusions derived could provide the design principles of earth-abundant metal oxide catalysts for various real-life environmental and energy applications.

A novel high-performance CeO2-CuMn2O4 catalyst for toluene degradation

A series of spinel CuM₂O₄ (M = Mn, Fe, and Al) was used as the catalyst to investigate the effective degradation of toluene, and then CuMn₂O₄ with better catalytic activity was selected as the research object to study its activity at different ratios of Cu and Mn. Meanwhile, CeO₂ was introduced to modify CuMn bimetallic oxide to improve its catalytic performance. The structure, morphology, and valence states of surface elements of as-prepared catalysts were characterized by XRD, TEM, SEM, N₂ adsorption-desorption, XPS, and H₂-TPR. Using toluene as a probe molecule, the catalytic activity of the catalyst was tested and the results showed that the conversion rate of toluene catalyzed by CeO₂-CuMn₂O₄ catalyst can reach 90% at 200 °C (T₉₀) and 100% at 240 °C (T₁₀₀). The CO₂ yield can also reach 100% at 248 °C. Moreover, the possible catalytic mechanism for toluene by the CeO₂-CuMn₂O₄ was briefly explored. The catalytic oxidation of toluene over the oxide follows the Mars-van Krevelen mechanism.

Recent progress on removal of indoor air pollutants by catalytic oxidation

Indoor air pollutant is a serious problem due to its wide diversity and variability. The harmful substances from construction materials and decorative materials may make the indoor air pollution become more and more serious and cause serious health problems. In this paper, the review summarizes the advanced technologies for the removal of indoor air pollutants and the development in the treatment of indoor air pollution by catalytic oxidation technologies. Meanwhile, some catalytic oxidation mechanisms of indoor air pollutants are proposed in detail, and suggestions for the indoor air pollution treatment are also presented, in order to provide some reference for subsequent research.

A strategy to construct uniform MOFs/PAN nanowire derived bead-like Co3O4 for VOC catalytic combustion

This study for the first time proposed two kinds of chemical modification approaches to promote the uniform and stable growth of MOFs on PAN nanowires. Acid hydrolysis was performed to form some carboxylic acid groups on the surface of PAN nanowires, and an ammonia process was used to enhance the coordination ability of PAN with metal ions. Through the modulation of the coordination environments, ZIF/H-PAN and ZIF/NH-PAN showed big differences in morphology and chemical properties. The bead-like dodecahedron H-Co₃O₄ catalyst derived from the bead-like ZIF/H-PAN showed excellent activity for the catalytic combustion of VOCs.

NiCo2O4 spinel for efficient toluene oxidation: The effect of crystal plane and solvent

Spinel oxides, e.g., NiCo₂O₄, is a promising catalyst for the catalytic oxidation of toluene. Understanding and designing versatile NiCo₂O₄ spinel is important for low-temperature toluene oxidation. Here, we investigated the surface-characteristic-dependent degradation activity of NiCo₂O₄ crystals through experiment and characterization. NiCo₂O₄ nanosheet using ethanol as solvent (named E--NiCo₂O₄) exposing {110} crystal planes exhibited the lowest temperature toluene oxidation. The T₉₉ of toluene conversion was 256 °C, which is much lower than that of NiCo₂O₄ nanosheet using ethylene glycol as solvent (named EG--NiCo₂O₄), NiCo₂O₄ octahedron (named O--NiCo₂O₄) and NiCo₂O₄ truncated octahedron (named TO--NiCo₂O₄). Characterization using various techniques such as XRD, TEM, BET, XPS, H₂-TPR and CO₂-TPD showed that Co³⁺ and surface adsorbed oxygen (O_sur) enriched surface, excellent redox properties and effective diffusion of the reaction product reasonably explain the enhancement in catalytic activity over the E--NiCo₂O₄. The research reveals that the effect of specific crystal planes and solvent was the key factor to govern the activity of low-temperature toluene oxidation.

Development of Pharmaceutical VOCs Elimination by Catalytic Processes in China

As a byproduct of emerging as one of the world’s key producers of pharmaceuticals, China is now challenged by the emission of harmful pharmaceutical VOCs. In this review, the catalogue and volume of VOCs emitted by the pharmaceutical industry in China was introduced. The commonly used VOC removal processes and technologies was recommended by some typical examples. The progress of catalytic combustion, photocatalytic oxidation, non-thermal plasma, and electron beam treatment were presented, especially the development of catalysts. The advantages and shortages of these technologies in recent years were discussed and analyzed. Lastly, the development of VOCs elimination technologies and the most promising technology were discussed.

Petroleum Hydrocarbon Removal from Wastewaters: A Review

Oil pollutants, due to their toxicity, mutagenicity, and carcinogenicity, are considered a serious threat to human health and the environment. Petroleum hydrocarbons compounds, for instance, benzene, toluene, ethylbenzene, xylene, are among the natural compounds of crude oil and petrol and are often found in surface and underground water as a result of industrial activities, especially the handling of petrochemicals, reservoir leakage or inappropriate waste disposal processes. Methods based on the conventional wastewater treatment processes are not able to effectively eliminate oil compounds, and the high concentrations of these pollutants, as well as active sludge, may affect the activities and normal efficiency of the refinery. The methods of removal should not involve the production of harmful secondary pollutants in addition to wastewater at the level allowed for discharge into the environment. The output of sewage filtration by coagulation and dissolved air flotation (DAF) flocculation can be transferred to a biological reactor for further purification. Advanced coagulation methods such as electrocoagulation and flocculation are more advanced than conventional physical and chemical methods, but the major disadvantages are the production of large quantities of dangerous sludge that is unrecoverable and often repelled. Physical separation methods can be used to isolate large quantities of petroleum compounds, and, in some cases, these compounds can be recycled with a number of processes. The great disadvantage of these methods is the high demand for energy and the high number of blockages and clogging of a number of tools and equipment used in this process. Third-party refinement can further meet the objective of water reuse using methods such as nano-filtration, reverse osmosis, and advanced oxidation. Adsorption is an emergency technology that can be applied using minerals and excellent materials using low-cost materials and adsorbents. By combining the adsorption process with one of the advanced methods, in addition to lower sludge production, the process cost can also be reduced.

Recent Advances on the Rational Design of Non-Precious Metal Oxide Catalysts Exemplified by CuOx/CeO2 Binary System: Implications of Size, Shape and Electronic Effects on Intrinsic Reactivity and Metal-Support Interactions

Catalysis is an indispensable part of our society, massively involved in numerous energy and environmental applications. Although, noble metals (NMs)-based catalysts are routinely employed in catalysis, their limited resources and high cost hinder the widespread practical application. In this regard, the development of NMs-free metal oxides (MOs) with improved catalytic activity, selectivity and durability is currently one of the main research pillars in the area of heterogeneous catalysis. The present review, involving our recent efforts in the field, aims to provide the latest advances—mainly in the last 10 years—on the rational design of MOs, i.e., the general optimization framework followed to fine-tune non-precious metal oxide sites and their surrounding environment by means of appropriate synthetic and promotional/modification routes, exemplified by CuOx/CeO2 binary system. The fine-tuning of size, shape and electronic/chemical state (e.g., through advanced synthetic routes, special pretreatment protocols, alkali promotion, chemical/structural modification by reduced graphene oxide (rGO)) can exert a profound influence not only to the reactivity of metal sites in its own right, but also to metal-support interfacial activity, offering highly active and stable materials for real-life energy and environmental applications. The main implications of size-, shape- and electronic/chemical-adjustment on the catalytic performance of CuOx/CeO2 binary system during some of the most relevant applications in heterogeneous catalysis, such as CO oxidation, N2O decomposition, preferential oxidation of CO (CO-PROX), water gas shift reaction (WGSR), and CO2 hydrogenation to value-added products, are thoroughly discussed. It is clearly revealed that the rational design and tailoring of NMs-free metal oxides can lead to extremely active composites, with comparable or even superior reactivity than that of NMs-based catalysts. The obtained conclusions could provide rationales and design principles towards the development of cost-effective, highly active NMs-free MOs, paving also the way for the decrease of noble metals content in NMs-based catalysts.

Catalytic combustion of toluene over CeO2–CoOx composite aerogels

The dispersion of active species and redox cycle of Co³⁺/Co²⁺ in cobalt based aerogels have an important influence on catalytic performance for toluene oxidation.

Selective cyclohexene oxidation with O2, H2O2 and tert-butyl hydroperoxide over spray-flame synthesized LaCo1−xFexO3 nanoparticles

A series of spray-flame made LaCo_1−xFe_xO₃ nanoparticles showed promising activity for liquid-phase cyclohexene oxidation. Various oxidizing agents, i.e., O₂, H₂O₂ and tert-butyl hydroperoxide, led to different product selectivities.

Plasma Treating Mixed Metal Oxides to Improve Oxidative Performance via Defect Generation

The generation of structural defects in metal oxide catalysts offers a potential pathway to improve performance. Herein, we investigated the effect of thermal hydrogenation and low-temperature plasma treatments on mixed SiO₂/TiO₂ materials. Hydrogenation at 500 °C resulted in the reduction of the material to produce Ti³⁺ in the bulk TiO₂. In contrast, low temperature plasma treatment for 10 or 20 min generated surface Ti³⁺ species via the removal of oxygen on both the neat and hydrogenated material. Assessing the photocatalytic activity of the materials demonstrated a 40–130% increase in the rate of formic acid oxidation after plasma treatment. A strong relationship between the Ti³⁺ content and catalyst activity was established, although a change in the Si–Ti interaction after plasma treating of the neat SiO₂/TiO₂ material was found to limit performance, and suggests that performance is not determined solely by the presence of Ti³⁺.

Study of reaction mechanism based on further promotion of low temperature degradation of toluene using nano-CeO2/Co3O4 under microwave radiation for cleaner production in spraying processing

Cleaner production in spraying processing was presented by advanced low temperature oxidation technology using combined methods of microwave radiation and nano-composites. Activities of samples for oxidation of toluene were estimated and the result exhibited that application of microwave radiation and nano-materials greatly promoted activities of catalysts. Moreover, the doping of Ce further enhanced catalytic activities. Samples of 5% Ce-Co showed optimal activity with conversion rate of 70% and CO₂ selection of 96% at 120 ℃ and 210 ℃, respectively. The lowest E_a (33.45 kJ/mol) was obtained calculating from kinetics process under microwave radiation using 5% Ce-Co indicating that the degradation of toluene might proceed more readily. Microwave absorption properties were first used tentatively to study the effect of "hot spots" induced by microwave radiation on catalytic oxidation of VOCs. Further, physicochemical properties of samples were also showed by XRD, SEM and XPS profiles to study oxidation activities of toluene. The maximum difference of toluene oxidation between no water and in water using 5% Ce-Co at 210 ℃ was only 3.06% manifesting that effects of moisture on activities were weak under microwave radiation. A possible degradation track using microwave heating was presented by the analysis of reaction byproducts using the GC-MS.

Effect of Small Molecular Organic Acids on the Structure and Catalytic Performance of Sol–Gel Prepared Cobalt Cerium Oxides towards Toluene Combustion

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and tartaric acid (TA), were selected. The effect of organic acids on the composition, structure, morphology and catalytic performance of metal oxides is discussed in details. The cobalt cerium oxides catalysts were characterized by various techniques, including TG–DSC, XRD, SEM–EDS, N2–adsorption and desorption, XPS, and H2–TPR analyses. The results show that the nature of organic acids influenced the hydrolysis, condensation and calcination processes, as well as strongly affected the textural and physicochemical properties of the metal oxides synthesized. The best catalytic activity was obtained with the CoCe–MA catalyst, and the toluene conversion reached 90% at 242 °C. This outstanding catalytic activity could be related to its textural, redox properties and unique surface compositions and oxidation states. In addition, the CoCe–MA catalyst also showed excellent stability in long–time activity test.

Investigation of synergistic effects and high performance of La-Co composite oxides for toluene catalytic oxidation at low temperature

Cobalt oxides have been considered as a kind of highly efficient catalyst for the oxidation of volatile organic compounds (VOCs). In this work, lanthanum-cobalt composite oxides were prepared by using the co-precipitation method, and toluene was used as the model compound. Diversified techniques including XRD, SEM, Raman spectra, XPS, H₂-TPR, and N₂ adsorption-desorption were applied to investigate the physicochemical properties of as-prepared materials. The composite catalysts showed different morphology including larger specific surface area and higher pore volume which would accelerate the adsorption of toluene and improve the amount of active sites on surface. Moreover, the addition of lanthanum could enhance the low-temperature reducibility, and it could be also beneficial to expose more Co³⁺ and adsorbed oxygen species on the surface of catalysts which could accelerate the oxidation of toluene and lower onset oxidation temperature. 0.05La-Co (with a molar ratio of lanthanum against cobalt is 0.05) showed the best catalytic performance. The complete conversion of toluene was achieved at 225 °C under the condition of toluene concentration = 1000 ppm and SV = 20,000 ml·g^-1·h^-1. Stability test over 0.05La-Co was conducted at 225 °C and it could maintain the 100% conversion of toluene for 720 min, indicating the excellent stability of as-prepared catalysts. Undoubtedly, lanthanum-cobalt composite oxide is a kind of promising material for the catalytic oxidation of VOCs.

Heterogeneous activation of persulfate by Co3O4-CeO2 catalyst for diclofenac removal

A series of Co₃O₄-CeO₂ mixed metal oxides were synthesized by co-precipitation method and successfully used to activate persulfate for diclofenac removal. The effects of Co:Ce mole ratio, calcination temperature and calcination time on the catalytic activities were investigated. Results showed that the activity of Co₃O₄-CeO₂ catalysts increased with Co:Ce mole ratio from 1:9 to 7:3, and decreased with the calcination temperature from 300 to 800 °C. 90% diclofenac was removed with Co₇Ce₃-300-1 catalyst (Co:Ce = 7:3, calcinated at 300 °C for 1 h) after 15 min. Moreover, short calcination time and low temperature resulted in smaller crystallite size, more structural defects, more active crystal surfaces and larger surface area of the catalyst, which led to higher removal efficiency of diclofenac. The high ratios of Co²⁺/Co³⁺, Ce³⁺/Ce⁴⁺ and O_ads/O_latt were very important to enhance the catalytic activity. Finally, a potential reaction mechanism was proposed based on characterization of the fresh and spent catalysts.

Arrangement Models of Keggin-Al30 and Keggin-Al13 in the Interlayer of Montmorillonite and the Impacts of Pillaring on Surface Acidity: A Comparative Study on Catalytic Oxidation of Toluene

Acid-base reactivity is a key factor for understanding the interfacial geochemistry of clay minerals. Numerous studies showed the significant role of surface acidity of clay minerals in the geological processes and environmentally related applications. In this work, montmorillonite (Mt) was pillared by polycations of Keggin-Al₁₃ and Keggin-Al₃₀. Arrangement models of Keggin-Al₁₃ and Keggin-Al₃₀ in the interlayer region of Mt were put forward based on the chemical composition analysis, the structural formula calculation of Mt, and the results of powder X-ray diffraction. Ammonia temperature-programmed desorption and diffuse reflectance Fourier transform infrared methods were applied to explore the impacts of pillaring by polycations (Keggin-Al₁₃ and Keggin-Al₃₀) on the surface acidic characteristics of Mt. Results demonstrated that one Keggin-Al₃₀ polycation can affect an area of 9.5 unit cells (from two layers, with 4.7-4.8 unit cells in each layer) in Mt, whereas a Keggin-Al₁₃ polycation controls an area of 7.1 unit cells (from two layers, with 3.5-3.6 unit cells in each layer). Pillaring by polycations could lead to a lot of surface acid sites (1.33 mmol NH₃/g) on Mt with the main type of Bronsted acid sites. The increase of surface acid sites on both Keggin-Al₁₃-pillared Mt (Al₁₃-PILM) and Keggin-Al₃₀-pillared Mt (Al₃₀-PILM) is attributed to the high positive charge and high content of aluminum per unit of polycation, which affects the formation of Bronsted acid sites and structural changes of Mt layers. Catalytic oxidation of toluene provided evidence for the high catalytic activity of Al₃₀-PILM under much lower temperature at 78 °C compared with that of Al₁₃-PILM and Mt at 207 and 285 °C, respectively. The basic finding in this study not only reveals the possible sources of abundant micropores and mesopores in the micro/mesoporous materials of Al₁₃-PILM and Al₃₀-PILM but also provides a reasonable mechanism for the formation of abundant Bronsted surface acid sites on these two types of pillared materials. The novel Al₃₀-PILM with an excellent micro/mesoporous structure and extremely high thermal stability also exhibits a potential ability in the application of heterogeneous acid catalysis.

Fabrication of homogeneous and highly dispersed CoMn catalysts for outstanding low temperature catalytic oxidation performance

A series of homogeneous and highly dispersed CoMnO_x bimetallic oxides with different ratios were prepared through pyrolysis of CoMn-MOF-71, which was applied to the catalytic oxidation of toluene.

Effect of Ce and La dopants in Co3O4 nanorods on the catalytic activity of CO and C3H6 oxidation

The catalytic activity is enhanced by Ce but inhibited by La dopant. The catalysts have been characterized in light of structural properties, reducibility, mobility of adsorbed oxygen and lattice oxygen, and surface reaction intermediates.