Environmental Catalysis Research Articles

Isolation anchoring strategy for fabricating high-loading uniformly dispersed iron-based catalysts toward selective removal of phenolic compounds

Developing uniformly dispersed iron-based catalysts with high metal loading for selective removal of the phenolic compounds was a fundamental challenge in environmental catalysis. An isolation anchoring strategy was devised to prepare the uniformly dispersed nitrogen-doped porous carbon encapsulating iron catalyst (β-Fe@NC) with the Fe loading up to 16.33 wt%, which was attributed to a dual protective effect including anchoring effect of the 8-hydroxyquinoline (8-HQ) and isolation effect of the β-cyclodextrin (β-CD), effectively anchoring the iron and inhibiting the agglomeration of the iron nanoparticles (NPs) during high temperature pyrolysis. As a demonstration, β-Fe@NC achieved almost 100% 4-CP removal in 25 min and performed an excellent kobs (0.325 min−1). Moreover, β-Fe@NC showed highly selective removal performance for phenolic compounds based on the hydrophobic interaction between catalysts and contaminants. The quenching experiments and EPR detection demonstrated that the main reactive oxygen species (ROSs) was singlet oxygen (1O2). Notably, the β-Fe@NC/PMS system exhibited an extremely low activation energy (11.54 KJ/mol) and was even competent for pollutant removal at 0 °C. This work provides a valuable insight for the design of uniformly dispersed iron-based catalysts and the activation of PMS to selectively remove phenolic compounds.

Revealing oxygen transfer between Mn3O4 and CuMn2O4 and its effect on enhanced catalytic oxidization of VOCs

Hybrid catalysts are widely utilized in various environmental catalysis, such as catalytic oxidization and reduction. However, most works usually treat a hybrid catalyst as a whole, and seldom report explores interface behavior of active species between components in the hybrid. In this work, we investigated mechanism for enhanced catalytic oxidization of toluene by a mixture of Mn3O4 and CuMn2O4. The mixture removed 99% of toluene at 240 °C, far bigger than CuMn2O4 (53%) and Mn3O4 (23%). In brief, Mn3O4 had plenty of bulk lattice oxygens, which were inactive for toluene catalytic oxidization. After forming an interface between Mn3O4 and CuMn2O4, oxygen vacancy formed on the interface during the catalysis, and transferred the bulk lattice oxygen to the interface, forming active lattice oxygen. Therefore, the number of active sites was increased, resulting in an enhanced catalytic performance. This conclusion was verified in other hybrids, including Mn3O4/CuFeOx, Mn3O4/CuCeOx, and Mn3O4/CuCoOx. The main result of this work helps to understand the catalytic mechanism of volatile organic compounds by hybrid oxides. These results are also in favor of designing and optimizing catalysts.

Supported Ce/Zr pyrochlore monolayers as a route to single cerium atom catalysts with low temperature reducibility

The combination of structural characterization at atomic resolution, chemical data, and theoretical insights has revealed the unique nanostructures which develop in ceria supported on yttria-stabilized zirconia (YSZ) after being submitted to high-temperature reducing treatments. The results show that just a small ceria loading is needed for creating a supported Zr-rich pyrochlore (111) nanostructure, resembling the structure of single cerium atom catalysts. The specific atomic arrangement of this nanostructure allows to explain the improvement of the reducibility at low temperature. The reduction mechanism can be extrapolated to ceria-zirconia mixed oxides with pyrochlore-like cationic ordering, exposing Zr-rich (111) surfaces. The results gathered here provide key information to understand the redox behavior of these types of systems, which may contribute to improving the design of new ceria-zirconia based materials, with lower content of the lanthanide element, nearly 100% cerium atom utilization, and applications in environmental catalysis.

Engineered Fe-doped activated carbon from industry waste for peroxymonosulfate activation: Performance and mechanism

Efficient and low-cost catalysts are important for contaminant remediation in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). In this study, a solid waste, generated by the polyferric chloride coagulation of the phenol-saturated powder activated carbon from an industrial wastewater treatment plant, was used to prepare metal/carbon composites under different pyrolysis temperatures (650–950 °C). The catalyst pyrolyzed at 950 °C (FeAC-950) exhibited the highest reactive activity for PMS activation as demonstrated by a series of electrochemical techniques. Nearly complete BPA elimination can be achieved within 60 min by 0.1 g L–1 FeAC-950 and 0.5 mM PMS. The results of electron paramagnetic resonance (EPR), chemical quenching and open circuit potential (OCPT) experiments demonstrate a combined radical and non-radical oxidation mechanism in the FeAC-950/PMS process and BPA was removed dominantly through radical pathway. Various persistent organic pollutants can be efficiently eliminated in the FeAC-950/PMS system. In addition, the present system showed good tolerance to natural organic matter as well as some common anions such as chloride and nitrate. This study dedicated a simple method to prepare an efficient solid waste-based catalyst in environmental catalysis. The outcomes will not only provide a value-added reuse approach for waste management but also facilitate the FeAC-950 applications in wastewater remediation technologies.

Recent Advances in Copper-Based Materials for Sustainable Environmental Applications

In recent years, copper-based nanomaterials have gained significant attention for their practical applications due to their cost-effectiveness, thermal stability, selectivity, high activity, and wide availability. This review focuses on the synthesis and extensive applications of copper nanomaterials in environmental catalysis, addressing knowledge gaps in pollution management. It highlights recent advancements in using copper-based nanomaterials for the remediation of heavy metals, organic pollutants, pharmaceuticals, and other contaminants. Also, it will be helpful to young researchers in improving the suitability of implementing copper-based nanomaterials correctly to establish and achieve sustainable goals for environmental remediation.

Unique Cluster-Support Effect of a Co3O4/TiO2-3DHS Nanoreactor for Efficient Plasma-Catalytic Oxidation Performance.

For environmental catalysis, a central topic is the design of high-performance catalysts and advanced mechanism studies. In the case of the removal of flue gas pollutants from coal-fired power plants, highly selective nanoreactors have been widely utilized together with plasma discharge characteristics, such as the catalytic oxidation of NO. Herein, a novel reactor with a three-dimensional hollow structure of TiO2 confining Co3O4 nanoclusters (Co3O4/TiO2-3DHS) has been developed for plasma-catalytic oxidation of NO, whose performance was compared with that of the commercial TiO2 confining Co3O4 cluster (Co3O4/TiO2). Specifically, Co3O4/TiO2-3DHS presented a higher efficiency (almost 100%) within lower peak-peak voltage (VP-P). More importantly, the NO oxidation efficiency was between 91.5 and 94.5% after a long time of testing, indicating that Co3O4/TiO2-3DHS exhibits more robust sulfur and water tolerance. Density functional theory calculations revealed that such impressive performance originates from the unique cluster-support effect, which changes the distribution of the active sites on the catalyst surface, resulting in the selective adsorption of flue gas. This investigation provides a new strategy for constructing a three-dimensional hollow nanoreactor for the plasma-catalytic process.

Single-atom Mo–Co catalyst with low biotoxicity for sustainable degradation of high-ionization-potential organic pollutants

Single-atom catalysts (SACs) are a promising area in environmental catalysis. We report on a bimetallic Co-Mo SAC that shows excellent performance in activating peroxymonosulfate (PMS) for sustainable degradation of organic pollutants with high ionization potential (IP > 8.5 eV). Density Functional Theory (DFT) calculations and experimental tests demonstrate that the Mo sites in Mo-Co SACs play a critical role in conducting electrons from organic pollutants to Co sites, leading to a 19.4-fold increase in the degradation rate of phenol compared to the CoCl2-PMS group. The bimetallic SACs exhibit excellent catalytic performance even under extreme conditions and show long-term activation in 10-d experiments, efficiently degrading 600 mg/L of phenol. Moreover, the catalyst has negligible toxicity toward MDA-MB-231, Hela, and MCF-7 cells, making it an environmentally friendly option for sustainable water treatment. Our findings have important implications for the design of efficient SACs for environmental remediation and other applications in biology and medicine.

Removal of tetracycline hydrochloride by N, P co-doped carbon encapsulated Fe2P activating PMS: A non-radical pathway dominated by singlet oxygen

Metal phosphides are effective in environmental catalysis to remove pollutants. Herein, a novel magnetic material of Fe2P nanoparticles encapsulated in N, P-doped carbon (Fe/P-NPGC) was successfully fabricated as a peroxymonosulfate (PMS) activation catalyst. Benefiting from the electron-donating ability of Fe2P, Fe/P-NPGC consistently maintains over 90% removal rate of tetracycline hydrochloride (TCH) over a wide pH range. Based on quenching experiments and characterizations, we propose that Fe2P not only activates PMS to generate reactive oxygen species but also promotes Fe (II) regeneration, thus improving the activation efficiency of PMS and generating an efficient non-radical pathway dominated by 1O2. Both Fe2P and graphitic N have excellent interfacial electron transfer efficiency, which improves the self-decomposition activation of PMS to generate 1O2. The catalyst has excellent stability and adaptability under inorganic ions interference and real water environment, indicating that it has excellent potential for practical wastewater treatment.

Controlled synthesis of bimetallic Nb-Fe composite oxides with high thermal stability for catalytic degradation of binary VOCs pollutants

A string of niobium-iron composite oxides with varying Nb/Fe ratios and calcination temperatures were produced and utilized to remove mixed contaminants (500 ppmv chlorobenzene and 500 ppmv toluene in air), and the structure/texture of catalytic materials were systematically characterized. The findings of the structure-performance study revealed that the physicochemical qualities of Nb2O5-Fe2O3 were greatly enhanced than pure metal oxide. The presence of iron oxide hindered the crystallization of niobium oxide, which aided in the uniform dispersion of niobium-iron components into each other. Forming FeNbO4 at Nb/Fe molar ratio of 1/2 effectively improved the thermal stability of catalyst, withstood short-time thermal shock below 850 °C. The formation of niobium-iron composite oxides improved the specific surface area, optimized the pore size distribution, increased surface acid centers, enhanced reduction/oxidation cycle, and promoted metal-metal interaction for the Nb-Fe-O catalysts. At 320 °C, the catalytic degradation efficiency of 1Nb2Fe-500 could approach 90% for chlorobenzene and 85% for toluene, and it could sustain this efficiency for at least 80 h without evident deactivation, with a high CO2 selectivity of 86%. Furthermore, the Nb-Fe-O catalysts met the environmentally benign and low-cost requirements for environmental catalysis.

Constructing branch architectures on fly ash surfaces to immobilize iron tetracarboxy phthalocyanine for synergistic degradation of dye contaminants

Utilization of fly ash (FA) solid wastes as the economical carrier materials to support the high active catalysts for environmental purification would contribute to the low carbon society, resource conservation and environmental improvement. For this purpose, in-depth understanding of the surface structure dependent fly ash carriers for the high efficiency immobilization of catalyst is essential. In this study, the highly active molecule catalysts of iron tetracarboxy phthalocyanine (TCFePc) complexes were successfully supported on FA for the first time. The FA particulates were successively activated to generate the dense branch crystal surfaces for immobilizing TCFePc complexes via a simple precipitation method. The TCFePc@FA composites can activate tert-butyl hydroperoxide (BuOOH) to produce hydroxyl and alkoxy radicals along with the generation of high valent iron-oxygen species to synergistically degrade high concentration organic dyes. Significantly, the TCFePc@FA-2% (2 wt% of catalyst) exhibited obviously higher catalytic efficiency than that of pure TCFePc. The immobilization mechanism and the catalytic processes of TCFePc@FA composites were discussed in detail. Our investigation provides an efficient and economical strategy for designing FA-based catalysts in the field of environmental catalysis.

Optimization Methods of Tungsten Oxide-Based Nanostructures as Electrocatalysts for Water Splitting.

Electrocatalytic water splitting, as a sustainable, pollution-free and convenient method of hydrogen production, has attracted the attention of researchers. However, due to the high reaction barrier and slow four-electron transfer process, it is necessary to develop and design efficient electrocatalysts to promote electron transfer and improve reaction kinetics. Tungsten oxide-based nanomaterials have received extensive attention due to their great potential in energy-related and environmental catalysis. To maximize the catalytic efficiency of catalysts in practical applications, it is essential to further understand the structure-property relationship of tungsten oxide-based nanomaterials by controlling the surface/interface structure. In this review, recent methods to enhance the catalytic activities of tungsten oxide-based nanomaterials are reviewed, which are classified into four strategies: morphology regulation, phase control, defect engineering, and heterostructure construction. The structure-property relationship of tungsten oxide-based nanomaterials affected by various strategies is discussed with examples. Finally, the development prospects and challenges in tungsten oxide-based nanomaterials are discussed in the conclusion. We believe that this review provides guidance for researchers to develop more promising electrocatalysts for water splitting.

Drug-Facilitated Crystallization of Spray-Dried CD-MOFs with Tunable Morphology, Porosity, And Dissolution Profile.

Metal-organic frameworks (MOFs) with versatile functionalities have applications in environmental science, sensor separation, catalysis, and drug delivery. In particular, MOFs used in drug delivery should be biodegradable and easy to control. In this study, spray-dried cyclodextrin-based MOFs (CD-MOFs) with tunable crystallinity, porosity, and dissolution properties were fabricated. The spray-drying precursor properties, such as ethanol volume ratio, incubation time, and precursor concentration, were optimized for controlled crystallization. On the basis of the morphology, X-ray diffraction peak intensity, and specific surface areas of the spray-dried CD-MOF products, they were categorized as amorphous, partially crystalline, and highly crystalline. An active pharmaceutical ingredient ketoconazole (KCZ) was introduced into the precursor to prepare KCZ-containing CD-MOFs. The surface areas of these products were greater by 3-fold (292 m2/g) than that of the plain CD-MOF (94.1 m2/g) prepared using the same parameters. The presence of KCZ in the hydrophobic cavity between the two γ-CD molecules was correlated to the CD-MOF crystal growth. Additionally, CD-MOF particles exhibited different dissolution behaviors on the basis of the position of KCZ in the MOF. These spray-dried CD-MOFs with tunable morphology, specific surface area, and dissolution could have potential applications in various fields.

Silver Ion-Exchanged Anionic Metal–Organic Frameworks for Iodine Adsorption: Silver Species Evolution from Ions to Nanoparticles

Ag clusters and nanoparticles have attracted much attention in the fields of environmental catalysis and pollutant removal. It is a common strategy to fabricate highly dispersed Ag nanoparticles in porous scaffolds via in situ growth. Here, anionic metal–organic frameworks (MOFs) have been employed to provide robust supports for Ag species. Ag nanoparticles with well-defined sizes are observed in MOFs when internal NH2Me2+ is exchanged with extrinsic Ag+ ions. The extended X-ray absorption fine structure and X-ray photoelectron spectroscopy spectra confirm that about 20% of Ag+ are reduced into Ag0, while the rest 80% are still Ag+ species. The comparison of Ag loading into anionic and neutral Cu-BTC MOFs suggests that the exchangeable cations facilitate Ag+ migration into the interior of MOFs and thus alleviate its aggregation and spontaneous reduction. Besides, the adsorption tests verify that all the Ag species in MOFs are accessible to iodine vapor to form AgI. The charge transfer from frameworks to trapped iodine and the water in the air promote the formation of iodide ions, which react with Ag+ to produce AgI. The iodine adsorption performance of MOF beads was also evaluated using the pore diffusion model. This work provides insights into the evolution of Ag species in MOFs and potential Ag-based adsorbents for radioiodine capture.

Effect of Zr Modification on NH3-SCR Reaction Performance of Cu-Ce/SAPO-34 Catalysts

Molecular sieve catalysts containing transition metals have been attracting attention for their potential applications in various fields, including environmental and industrial catalysis. A Cu-Ce-Zr/SAPO-34 series of molecular sieve catalysts were prepared by the impregnation method, and the effect of Zr introduction on the selective catalytic reduction of NO by Cu-Ce/SAPO-34 molecular sieve catalysts was explored. Through various characterization methods, the physical and chemical properties of the catalysts were analyzed, and the denitration mechanism of the molecular sieve catalyst was discussed. This study found that the total acid content of the acid sites on the catalyst surface decreased with the introduction of Zr, leading to a decrease in the denitration efficiency of the catalyst. At 350–400 °C, the denitration efficiency of the 4Cu-4Ce-4Zr/SAPO-34 catalyst was over 80%, and at 400–500 °C, it was over 99%. Moreover, excessive metal Zr could destroy its CHA structure and decrease the denitration efficiency of the catalyst. This study analyzed the reaction mechanism of NH3-SCR of Zr-modified polymetallic zeolites and the effect of Zr modification on the NH3-SCR reaction results. This study contributes to the understanding of the performance of molecular sieve catalysts containing transition metals. Reliable conclusions were obtained, which offer data support for future research in the field of NH3-SCR.

An exceptional amorphous nanoscale Pd/carbon cloth composite electrode for energy-saving oxalic acid electrolysis coupled with hydrogen production

In this paper, we report a carbon cloth/amorphous nanoscale Pd (CC/AN Pd) composite electrode and realizes the modifier-free composite of low-cost intractable carbon support and low-loading Pd metal by designing a mild and facile oxidation-ion exchange-reduction (OIR) route. This CC/AN Pd composite electrode presents high activity, robust, cost-effective, modifier-free, micro-nano porous and low Pd loading characteristics compared with the traditional Pd/C electrode. This composite electrode shows superior oxalic acid (OA) oxidization reaction (OOR) catalysis performance, outperforming all the as-reported OOR catalysts especially at high current density. Moreover, on the basis of catalysis performance and the cost of Pd loading amount, this CC/AN Pd composite electrode shows superior hydrogen evolution reaction (HER) catalysis performance with high cost-effective characteristic, surpassing all the as-reported HER catalytic electrodes. Importantly, this composite electrode was used as HER and OOR electrodes to assemble an oxalic acid electrolytic cell (OAEC), which drives 10 mA/cm2 and 100 mA/cm2 current density at only 1.09 V and 1.52 V voltage, respectively, and obtains up to 95.2% average faraday efficiency for 50 mA/cm2 oxalic acid electrolysis. Notable, this CC/AN Pd composite electrode-based OAEC has better energy-saving and stability advantage compared with the commercial CC/Pd–C-based OAEC especially for high current density OA electrolysis. This work opens new avenues to the design of novel composite electrode materials and enables new opportunities in green energy or environmental catalysis areas.

Manganese Oxide Nanoparticles: An Insight into Structure, Synthesis and Applications

AbstractManganese oxide nanoparticles with different crystal phases, morphologies, and structural diversity along with their exceptional properties like high specific surface area, a high fraction of surface atoms, non‐toxic nature, and excellent redox properties are drawing attention for various applications in storage science, especially in the batteries, super‐capacitors, energy conversion, and the environmental catalysis field. Precise control of particle size, morphology, surface area, Mnx+ oxidation state, etc. is the utmost important aspect to explore their application to the full potential. Here, the emphasis is on the recent trends in manganese oxide research – structure, synthesis, and applications. The structure of numerous crystalline phases of manganese oxide nanoparticles are summerized and several facile chemical synthesis processes to achieve the desired crystalline/amorphous structure are discoursed. Temperature and different synthesis conditions dependent phase transformations of β‐MnO2, α‐Mn2O3, and Mn3O4 from α‐MnO2 are discussed as well. The pragmatic approach directs that the application field is mostly controlled by the morphologies.

Plasma-reconstructed LaMnO3 nanonetwork supported palladium catalyst for methane catalytic combustion

Tuning the metal-support interaction is an effective strategy for improved catalytic performance in catalytic combustion of methane. Herein, we prepared Pd/LaMnO3 catalysts using two types of LaMnO3, that were achieved by plasma treatment or traditional thermal treatment respectively. Contrast to the LaMnO3 (LMO-T) support, the plasma-treated LaMnO3 (LMO-P) support has large surface specific area, porosity and many surface defects. Among these catalysts, the Pd supported on plasma-treated LaMnO3 (Pd/LMO-P) shows the best catalytic activity (T90 = 471 °C) and the lowest Ea value (74 kJ/mol). It reveals that the high performance should be attributed to the large surface area, surface-rich active species and strong metal-support interaction. The XPS techniques also demonstrated that the plasma-treated could boost the electron transfer between PdOx and LaMnO3, improving the redox properties. Moreover, the plasma-treated catalyst exhibits an excellent performance under thermal and water-vapor coexistence environment. The superior performance can arouse interest for the design of advanced catalyst in environmental catalysis.

Rational design of three-dimensional porous Ir-supported TiO2–ZrO2 microspheres for low temperature methane combustion

Construction of efficient and stable catalytic combustion materials for the removal of unburnt methane (CH4) is very critical for both applied environmental catalysis and basic materials research. Herein, a facile hydrothermal approach is designed for the fabrication of Ir/UTZX (Ir/TiO2–ZrO2) catalysts. The as-synthesized Ir/UTZX catalysts possess unique sphere morphology as well as electronic structure, leading to enlarged exposure of catalytic sites and enhancement of redox properties. As a result, the representative Ir/UTZ5 catalyst achieves a CH4 conversion of nearly 100% at 425 °C. Significantly, Ir/UTZ5 displays high long-term stability, with no obvious decrease of catalytic activity in the run of 120 h, which is much higher than those of Ir/TiO2 and Ir/ZrO2 catalysts. Our findings offer insights for designing highly efficient and stable catalysts for CH4 catalytic combustion.

Solid‐Supported Catalysts for Organic Functional Group Transformations

AbstractDesign of solid‐supported metal catalysts (SSMCs) has made an increasingly important contribution to heterogeneous catalysis in terms of fundamental understanding and technological applications. For instance, industrial use of supported catalysts for oxidation, reduction, and C−C bond formation reactions is highly prevalent. The reason behind this is that such catalysts are economical, have high thermal stability, dispersion, high exposed surface area, and above all, high reusability (up to multiple subsequent cycles). Such characteristics make supported catalysts ideal for green synthesis. However, unlike homogeneous catalysis, heterogeneous catalysis is widely applied in crude oil refining, the pharmaceutical industry, water purification, natural product synthesis, and environmental catalysis. Carbon‐carbon bond formation reactions are frequently used in the organic synthesis using SSMCs. SSMCs are attractive to synthetic chemists due to their easy recovery and excellent stability compared to unsupported metal catalysts. However, the major drawback of SSMCs is related to metal sintering at elevated temperatures caused by weak interactions between the metal and solid support in SSMCs. This review highlights major advancements in SSMCs. Three commonly reported solid supports for metal catalysts, such metal oxides, carbonaceous materials, and polymeric compounds, are discussed. Moreover, a series of thermo‐ and photocatalyzed reactions, such as hydrogenation, carbon‐carbon bond formation, oxidation reactions and multicomponent reactions and the effect of variable supports towards activity and selectivity are demonstrated.

Enabling Internal Electric Fields to Enhance Energy and Environmental Catalysis (Adv. Energy Mater. 11/2023)

Internal Electric Fields In article number 2203720, Zhong-Yong Yuan, and co-workers present an encyclopedic summary of the classification, advantages, construction and identification of internal electric fields, as well as the dramatic improvements in energy and environment catalysis that result.