Exceptional Ozone Decomposition over δ-MnO2/AC under an Entire Humidity Environment

Applying TiO2-x -Based Electrocatalysis and Photoelectrocatalysis Induced I-/IO3 - Recycling for Green and Continuous Ozone Removal

Solution absorption is a straightforward and efficient method for ozone treatment, but waste from inactive absorption solutions poses a risk of secondary pollution and raises the operating cost. Therefore, developing a sustainable recycling process for the absorption solution is essential for green ozone removal. In this study, we constructed a novel I-/IO3 - cycling system induced by electrocatalysis and photoelectrocatalysis to facilitate the reduction of KIO3 in KI/KOH ozone absorption solution, thereby enabling absorption solution recycling. The stable operation of this system relies on high-performance cathode materials. By adjusting the concentration of oxygen vacancies on TiO2, we reduced the energy barrier for IO3 - reduction, optimized IO3 - adsorption on the electrode surface, and improved the band gap structure of the electrode material, resulting in a TiO2-x cathode with good IO3 - reduction reaction (IO3RR) performance. Notably, this method achieves an ozone removal cost of $3.72 per kilogram, only one-third of the cost associated with conventional catalytic ozone decomposition. This approach provides a promising new direction for green and efficient ozone removal.

Transforming the Poison Effects of Water Vapor into Benefits Over Adjustable Dual Acid Sites for Stable Plasma-Catalysis

Developing a new strategy to address water vapor poisoning is crucial for catalysts in real-working conditions. Except for the traditional thinking of resistance enhancement, a reverse idea is proposed herein of utilizing the inevitable H2O, converting it to active ·OH to enhance the overall performance, with the help of O3 and high energy electrons (e*) in plasma. Dual active sites of Lewis acid (Y3+) and Mn on YxMnyOx+2y catalyst promote the co-adsorption of H2O and O3, and the dissociation of H2O to surface hydroxyl species (*OH). A new OH-accompanied pathway for O3 decomposition is formed and a new intermediate species (*OOH) with a lower energy barrier (0.77 eV lower than traditional *O2 2-) is detected, in which e* in plasma can further accelerate its desorption. Thereafter, abundant active ·OH are generated and work for pollutants degradation, achieving 99.78% ethyl acetate (EA) degradation and 97.36% mineralization rate on the surface of YMO (1:2) under humid environment, with excellent long-term stability. The changed activation site of C─O bond in EA, different by-products, and reaction pathways are also analyzed. This active species regulation strategy transforms the traditional poison effects of water vapor into great benefits, paving the way for broader catalyst applications free of water vapor.

Defect-based Lewis pairs on hydrophobic MnO mesocrystals for robust and efficient ozone decomposition

Catalytic ozone decomposition is a promising technique for eliminating ozone from the environment. However, developing redox-active catalysts that efficiently decompose ozone while maintaining robust performance under high humidity remains challenging. Herein, we develop a hydrophobic carbon-coated mesocrystalline MnO (Meso-MnO@C) featuring a high density of manganese vacancies (VMn)-based Lewis pairs (LPs) for catalytic ozone decomposition. The presence of VMn induces the electronic restructuring in MnO, leading to the formation of VMn-Mn acidic sites and adjacent lattice oxygen atoms as basic sites. These LPs act as electron donors and acceptors, facilitating rapid electron transfer and lowering the energy barrier for O3 conversion to O2. The hydrophobic carbon layer protects against water accumulation on Meso-MnO@C in humid conditions. As a result, the Meso-MnO@C achieves nearly 100% O3 decomposition at a high weight hourly space velocity of 1500 L⋅g-1 h-1, with rapid reaction kinetics and stable performance for 100 hours under 65% relative humidity.

Role of Metallic Ag over Ag/MnO2 Catalysts for Ozone Decomposition under Humid Conditions

Ag/MnOx catalysts have great potential for practical application in ozone (O3) decomposition due to their superior activity under humid conditions. Metallic Ag nanoparticles (Agn0) have been identified as the critical active site for O3 decomposition over Ag/MnOx catalysts. However, the role of Agn0 over Ag/MnOx catalysts during the O3 decomposition remains unclear. In this study, Agn0 and oxidized Ag nanoparticles (AgOx) are constructed on the MnO2 supports. Under a relative humidity of 65% and a high space velocity of 2800 L·g-1·h-1, the conversion of 40 ppm of O3 over the 4%Ag/γ-MnO2 catalyst (91%) within 6 h is far superior to that over the 4%Ag/α-MnO2 (22%) catalyst, which is attributed to the formation of Agn0 on the 4%Ag/γ-MnO2 catalyst and AgOx on the 4%Ag/α-MnO2 catalyst. Then, the role of Agn0 and AgOx during O3 decomposition was determined by in situ Raman spectroscopy and DFT calculations. Compared with AgOx, the competitive adsorption of H2O and O3 molecules on Agn0 is weaker, and O3 molecules can be activated more rapidly on Agn0; most importantly, peroxide species are more easily desorbed on Agn0. These advantages of Agn0 are the key to the superior O3 decomposition activity of the 4%Ag/γ-MnO2 catalyst under humid gas. This study provides guidance for understanding the Ag active sites for the decomposition of O3 and the design of highly efficient Ag/MnOx catalysts.

A novel MOF-on-MOF-derived carbon-encapsulated CeO2/Co/Co3O4 humidity-resistant heterojunction with abundant oxygen vacancies for efficient ozone removal

Ground-level ozone (O3) can infiltrate indoor environments, severely impacting the environment and human health. Moisture-induced catalyst deactivation is a major challenge in catalytic ozone removal. MOF-template-derived heterojunctions supported by carbon materials can prevent chemisorption of water vapor at active sites. This paper presents a carbon-supported CeO2/Co/Co3O4 humidity-resistant heterojunction derived from a bimetallic-organic framework (Ce-BTC/Co-ZIF-67 precursor) via hydrothermal-carbonization. Instrumental characterization confirmed the successful construction of the heterojunction. The O3 removal efficiency was evaluated at the ppb level under different relative humidity conditions (RH = 0%, 50%, and 75%) at a weight hourly space velocity (WHSV) of 10,000 L g-1 h-1 and ambient temperature. The carbon-supported 20 wt% CeO2/Co/Co3O4 composite demonstrated 99 ± 0.2% O3 removal and a high reaction rate of 1.1 ± 0.06 μg.gcat-1.sec-1 for 200 ppb O3 under an RH of 50% at ambient temperature. The O3 removal rate remained at approximately 92 ± 1.2%, even in harsh environments (75% RH), indicating excellent stability and strong moisture-resistance. Oxygen vacancies and defect structures are crucial for O3 adsorption and activation processes. The optimal catalyst exhibited greater electron mobility and redox ability than the pristine materials, as confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses. Furthermore, the as-synthesized catalyst is both recyclable and stable, making it suitable for practical applications. This research offers a new strategy for the fabrication of highly moisture-resistant MOF-derived heterojunctions, which will greatly facilitate the elimination of ground-level O3 in real indoor environments.

Mechanism for airborne ozone decomposition on X-MIL-53(Fe) (X = H, NH2, NO2)

Ground-level ozone (O3) pollution poses a significant threat to both ecosystem sustainability and human health. The catalytic decomposition of O3 presents as a promising technology to address the issues of O3 pollution. This study undertook the synthesis of various functionalized metal-organic framework (MOF) catalysts (i.e., X-MIL-53(Fe) (X = H, NH2, NO3)) to delve into the influence of ligand functional groups on skeletal structure and catalytic efficacy, particularly focusing on unraveling the mechanism of O3 catalytic decomposition under humid conditions. NH2-MIL-53(Fe) catalyst achieved complete O3 decomposition under ambient temperature and high humidity conditions (RH=75 %), exhibiting a reaction rates (mol·m-2·s-1) 129 and 10.5 times greater than that of MIL-53(Fe) and NO2-MIL-53(Fe). The NH2 group promotes electron flow within the backbone towards the hydroxyl group (OH) linked to Fe atom. In humid O3, H2O molecules augment the interaction between O3 and NH2-MIL-53(Fe), and OH is converted to·O2- after deprotonation, promoting O3 decomposition. Additionally, leveraging three-dimensional (3D) printing technology, a monolithic catalyst for O3 decomposition was prepared for application. This study not only advances understanding of the mechanisms underlying O3 decomposition but also offers practical solutions for addressing O3 pollution at humid conditions.

Novel Electrolytic Regeneration Method for Cyclic Regeneration of Ozone Decomposition MnOx Catalysts

The deactivation of ozone decomposition catalysts has been a bottleneck in their industrial application. As an efficient catalyst regeneration method, the liquid-phase method has attracted wide attention due to its operability and universality. However, the amount of waste liquid generated by the used regeneration liquid is a major drawback of its application. Therefore, we propose an electrolytic regeneration method for cyclic regeneration of MnOx ozone decomposition catalysts by combining the advantages of the electrolytic process. In this method, NaNO2 solution is used to react with O22- to efficiently regenerate the inactivated MnOx catalysts, while NO2- is oxidized to NO3-, and then the oxidized NO3- can be efficiently reduced to NO2- through the electrolysis process at the cathode with an 88% Faraday efficiency, ultimately realizing the recycling of the NO2-/NO3- regeneration solution. By this method, the regeneration of inactivated MnOx ozone catalysts can be realized only using electricity.

Optimization of Carbon-Defect Engineering to Boost Catalytic Ozonation Efficiency of Single Fe─N4 Coordination Motif

Carbon-defect engineering in single-atom metal-nitrogen-carbon (M─N─C) catalysts by straightforward and robust strategy, enhancing their catalytic activity for volatile organic compounds, and uncovering the carbon vacancy-catalytic activity relationship are meaningful but challenging. In this study, an iron-nitrogen-carbon (Fe─N─C) catalyst is intentionally designed through a carbon-thermal-diffusion strategy, exposing extensively the carbon-defective Fe─N4 sites within a micro-mesoporous carbon matrix. The optimization of Fe─N4 sites results in exceptional catalytic ozonation efficiency, surpassing that of intact Fe─N4 sites and commercial MnO2 by 10 and 312 times, respectively. Theoretical calculations and experimental data demonstrated that carbon-defect engineering induces selective cleavage of C─N bond neighboring the Fe─N4 motif. This induces an increase in non-uniform charges and Fermi density, leading to elevated energy levels at the center of Fe d-band. Compared to the intact atomic configuration, carbon-defective Fe─N4 site is more activated to strengthen the interaction with O3 and weaken the O─O bond, thereby reducing the barriers for highly active surface atomic oxygen (*O/*OO), ultimately achieving efficient oxidation of CH3SH and its intermediates. This research not only offers a viable approach to enhance the catalytic ozonation activity of M─N─C but also advances the fundamental comprehension of how periphery carbon environment influences the characteristics and efficacy of M─N4 sites.

Graphitized Carbon-Supported Co@Co3O4 for Ozone Decomposition over the Entire Humidity Range

Ground-level ozone (O3) pollution has emerged as a significant concern due to its detrimental effects on human health and the ecosystem. Catalytic removal of O3 has proven to be the most efficient and cost-effective method. However, its practical application faces substantial challenges, particularly in relation to its effectiveness across the entire humidity range. Herein, we proposed a novel strategy termed "dual active sites" by employing graphitized carbon-loaded core-shell cobalt catalysts (Co@Co3O4-C). Co@Co3O4-C was synthesized via the pyrolysis of a Co-organic ligand as the precursor. By utilizing this approach, we achieved a nearly constant 100% working efficiency of the Co@Co3O4-C catalyst for catalyzing O3 decomposition across the entire humidity range. Physicochemical characterization coupled with density functional theory calculations elucidates that the presence of encapsulated metallic Co nanoparticles enhances the reactivity of the cobalt oxide capping layer. Additionally, the interface carbon atom, strongly influenced by adjacent metallic Co nuclei, functions as a secondary active site for the decomposition of O3 decomposition. The utilization of dual active sites effectively mitigates the competitive adsorption of H2O molecules, thus isolating them for adsorption in the cobalt oxide capping layer. This optimized configuration allows for the decomposition of O3 without interference from moisture. Furthermore, O3 decomposition monolithic catalysts were synthesized using a material extrusion-based three-dimensional (3D) printing technology, which demonstrated a low pressure drop and exceptional mechanical strength. This work provides a "dual active site" strategy for the O3 decomposition reaction, realizing O3 catalytic decomposition over the entire humidity range.

Efficient Ozone Elimination Over MnO2 via Double Moisture-Resistance Protection of Active Carbon and CeO2

The widespread ozone (O3) pollution is extremely hazardous to human health and ecosystems. Catalytic decomposition into O2 is the most promising method to eliminate ambient O3, while the fast deactivation of catalysts under humid conditions remains the primary challenge for their application. Herein, we elaborately developed a splendidly active and stable Mn-based catalyst with double hydrophobic protection of active carbon (AC) and CeO2 (CeMn@AC), which possessed abundant interfacial oxygen vacancies and excellent desorption of peroxide intermediates (O22-). Under extremely humid (RH = 90%) conditions and a high space velocity of 1200 L h-1 g-1, the optimized CeMn@AC achieved nearly 100% O3 conversion (140 h) at 5 ppm, showing unprecedented catalytic activity and moisture resistance toward O3 decomposition. In situ DRIFTS and theory calculations confirmed that the exceptional moisture resistance of CeMn@AC was ascribed to the double protection effect of AC and CeO2, which cooperatively prevented the competitive adsorption of H2O molecules and their accumulation on the active sites of MnO2. AC provided a hydrophobic reaction environment, and CeO2 further alleviated moisture deterioration of the MnO2 particles exposed on the catalyst surface via the moisture-resistant oxygen vacancies of MnO2-CeO2 crystal boundaries. This work offers a simple and efficient strategy for designing moisture-resistant materials and facilitates the practical application of the O3 decomposition catalysts in various environments.

Stable O3 Decomposition by Layered Double Hydroxides: The Pivotal Role of NiOOH Transformation

Because ozone (O3) is a significant air pollutant, advanced O3 elimination technologies, particularly those under high-humidity conditions, have become an essential research focus. In this study, a nickel-iron layered double hydroxide (NiFe-LDH) was modified via intercalation with octanoate to develop an effective hydrophobic catalyst (NiFe-OAa-LDH) for O3 decomposition. The NiFe-OAa-LDH catalyst sustained its O3 decomposition rate of >98% for 48 h under conditions of 90% relative humidity, 840 L/(g·h) space velocity, and 100 ppm inlet O3 concentration. Moreover, it maintained a decomposition rate of 90% even when tested at a higher airflow rate of 2500 L/(g·h). Based on the changes induced by the Ni-OII to Ni-OIII bonds in NiFe-OAa-LDH during O3 treatment, catalytic O3 decomposition was proposed to occur in two stages. The first stage involved the reaction between the hydroxyl groups and O3, leading to the breakage of the O-H bonds, formation of NiOOH, and structural changes in the catalyst. This transformation resulted in the formation of abundant and stable hydrogen vacancies. According to density functional theory calculations, O3 can be effectively decomposed at the hydrogen vacancies with a low energy barrier during the second stage. This study provides new insights into O3 decomposition.

Space-confined manganese oxides nanosheets for efficient catalytic decomposition of ozone

Ground-level ozone has long posed a substantial menace to human well-being and the ecological milieu. The widely reported manganese-based catalysts for ozone decomposition still facing the persisting issues encompass inefficiency and instability. To surmount these challenges, we developed a mesoporous silica thin films with perpendicular nanochannels (SBA(⊥)) confined Mn3O4 catalyst (Mn3O4@SBA(⊥)). Under a weight hourly space velocity (WHSV) of 500,000 mL g-1 h-1, the Mn3O4@SBA(⊥) catalyst exhibited 100% ozone decomposition efficiency in 5 h and stability across a wide humidity range, which exceed the performance of bulk Mn3O4 and Mn3O4 confine in commonly reported SBA-15. Rapidly decompose 20 ppm O3 to a safety level below 100 μg m-3 in the presence of dust in smog chamber (60 × 60 × 60 cm) was also realized. This prominent catalytic performance can be attributed to the unique confined structure engenders the highly exposed active sites, facilitate the reactant-active sites contact and impeded the water accumulation on the active sites. This work offers new insights into the design of confined structure catalysts for air purification.

Efficient ozone decomposition in high humidity environments using novel iron-doped OMS-2-loaded activated carbon material

This study effectively addresses the rapid deactivation of manganese-based catalysts in humid environments during ozone decomposition by introducing iron-doped manganese oxide octahedral molecular sieve (Fe-OMS-2) catalysts supported on activated carbon (AC). By optimizing the doping ratio of Fe-OMS-2, the Fe-OMS-20.5/AC catalyst achieves nearly 100% ozone decomposition efficiency across a wide range of relative humidity levels (0 to 60%), even at elevated air flow rates of 800 L·g-1·h-1, outperforming standalone AC, Fe-OMS-2, or a simple mixture of OMS-2 and AC. The Fe-OMS-20.5/AC catalyst features a porous surface and a mesoporous structure, providing a substantial specific surface area that facilitates the uniform distribution of the Fe-OMS-2 active phase on the AC surface. The incorporation of Fe3+ ions enhances electron transfer between valence state transitions of Mn, thereby improving the catalyst's efficiency in ozone decomposition. Additionally, the AC component protects catalytic sites and enhances the catalyst's humidity resistance. In conclusion, this research presents a novel strategy for developing highly efficient and cost-effective ozone decomposition catalysts that enhance dehumidification, significantly contributing to industrial ozone treatment technologies and advancing environmental protection.

Mn-Based Mullites for Environmental and Energy Applications

Mn-based mullite oxides AMn2O5 (A = lanthanide, Y, Bi) is a novel type of ternary catalyst in terms of their electronic and geometric structures. The coexistence of pyramid Mn3+-O and octahedral Mn4+-O makes the d-orbital selectively active toward various catalytic reactions. The alternative edge- and corner-sharing stacking configuration constructs the confined active sites and abundant active oxygen species. As a result, they tend to show superior catalytic behaviors and thus gain great attention in environmental treatment and energy conversion and storage. In environmental applications, Mn-based mullites have been demonstrated to be highly active toward low-temperature oxidization of CO, NO, volatile organic compounds (VOCs), etc. Recent research further shows that mullites decompose O3 and ozonize VOCs from -20 °C to room temperature. Moreover, mullites enhance oxygen reduction reactions (ORR) and sulfur reduction reactions (SRR), critical kinetic steps in air-battery and Li-S batteries, respectively. Their distinctive structures also facilitate applications in gas-sensitive sensing, ionic conduction, high mobility dielectrics, oxygen storage, piezoelectricity, dehydration, H2O2 decomposition, and beyond. A comprehensive review from basic physicochemical properties to application certainly not only gains a full picture of mullite oxides but also provides new insights into designing heterogeneous catalysts.

Enhancement Effect Induced by the Second Metal to Promote Ozone Catalytic Oxidation of VOCs

It is a promising research direction to develop catalysts with high stability and ozone utilization for low-temperature ozone catalytic oxidation of VOCs. While bimetallic catalysts exhibit excellent catalytic activity compared with conventional single noble metal catalysts, limited success has been achieved in the influence of the bimetallic effect on the stability and ozone utilization of metal catalysts. Herein, it is necessary to systematically study the enhancement effect in the ozone catalytic reaction induced by the second metal. With a simple continuous impregnation method, a platinum-cerium bimetallic catalyst is prepared. Also highlighted are studies from several aspects of the contribution of the second metal (Ce) to the stability and ozone utilization of the catalysts, including the "electronic effect" and "geometric effect". The synergistic removal rate of toluene and ozone is nearly 100% at 30 °C, and it still shows positive stability after high humidity and a long reaction time. More importantly, the instructive significance, which is the in-depth knowledge of enhanced catalytic mechanism of bimetallic catalysts resulting from a second metal, is provided by this work.

Precisely constructing orbital coupling-modulated iron dinuclear site for enhanced catalytic ozonation performance

The advancement of atomically precise dinuclear heterogeneous catalysts holds great potential in achieving efficient catalytic ozonation performance and contributes to the understanding of synergy mechanisms during reaction conditions. Herein, we demonstrate a "ship-in-a-bottle and pyrolysis" strategy that utilizes Fe2(CO)9 dinuclear-cluster to precisely construct Fe2 site, consisting of two Fe1-N3 units connected by Fe-Fe bonds and firmly bonded to N-doped carbon. Systematic characterizations and theoretical modeling reveal that the Fe-Fe coordination motif markedly reduced the devotion of the antibonding state in the Fe-O bond because of the strong orbital coupling interaction of dual Fe d-d orbitals. This facilitates O-O covalent bond cleavage of O3 and enhances binding strength with reaction intermediates (atomic oxygen species; *O and *OO), thus boosting catalytic ozonation performance. As a result, Fe dinuclear site catalyst exhibits 100% ozonation efficiency for CH3SH elimination, outperforming commercial MnO2 catalysts by 1,200-fold. This research provides insights into the atomic-level structure-activity relationship of ozonation catalysts and extends the use of dinuclear catalysts in catalytic ozonation and beyond.