Catalysts For Ozone Decomposition Research Articles

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.

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.

Ozone decomposition by mesoporous LnOx/MnOx catalysts derived from Mn-BTC under humid conditions

Mesoporous MnOx-Y and LnOx/MnOx ozone decomposition catalysts were prepared by calcination of Mn-BTC (BTC = 1,3,5-benzentricarboxylate) and doping of lanthanide elements (Ln = La, Ce, Sm, Eu, Er). Compared to MnOx-Y catalysts, the LnOx/MnOx catalysts showed higher ozone catalytic activity, the mutual conversion between Lnn+ and Mnn+ was helpful to improve ozone decomposition. The CeOx/MnOx catalyst showed the highest catalytic that showed 93% conversion of 40 ppm O3 in the relative humidity (RH) = 65% after 360 min, which was attributed to the largest specific surface area, more oxygen vacancies, Mn3+ and Oads. In addition, the CeOx/MnOx catalyst was loaded into the non-woven fabric to obtain CeOx/MnOx-NWF catalyst, which showed a highly efficient and stable ozone conversion under the RH range from less than 5-85%. This work will promote the practical application of Mn-BTC derived catalysts.

Templated Synthesis of Cu2S Hollow Structures for Highly Active Ozone Decomposition

Nowadays, it is highly desired to develop highly active and humidity-resistive ozone decomposition catalysts to eliminate the ozone contaminant, one of the primary pollutants in the air. In this work, a series of Cu2S hollow structured materials were rapidly synthesized using different structured Cu2O templates. The Cu2S from porous Cu2O showed the highest ozone catalytic decomposition efficiency of >95% to 400 ppm ozone with a weight hourly space velocity of 480,000 cm3·g−1·h−1 in dry air. Importantly, the conversion remained >85% in a high relative humidity of 90%. The mechanism was explored by diffusive reflectance infrared spectroscopy which showed the decomposition intermediate of O22−, and X-ray photoelectron spectroscopy revealed the dual active site of both Cu and S. The EPR and UPS characterization results also explained the superiority of porous Cu2S catalysts from the material itself. All these results show the effective decomposition of ozone by Cu2S, especially in harsh environments, promising for active ozone elimination.

Cordierite-Supported Transition-Metal-Oxide-Based Catalysts for Ozone Decomposition

Cordierite-based supported noble-metal-free catalysts for ozone decomposition are elaborated. The cordierite ceramic surface is pretreated with oxalic acid and NaOH, and Mn-Cu-Ni oxide catalysts are prepared by the impregnation method. The mass ratio of the supported oxides in the resulting catalysts is MnO2:CuO:NiO = 3:2:1, and their loadings are from 1.8 to 7.0 wt.%. The pretreated supports and catalysts are characterized by low-temperature N2 adsorption, scanning electron microscopy (SEM), powder X-ray diffraction analysis (XRD), and temperature-programmed reduction with H2 (TPR-H2). The catalysts are tested in ozone decomposition with high airflow rates (20 and 50 L/min) and with initial ozone concentrations of 1 and 2 ppm at temperatures in the range of 25–120 °C. It is shown that a combined treatment of cordierite with oxalic acid and NaOH leads to a developed porous structure and stabilization of supported Mn-Cu-Ni oxides in a highly dispersed state. The high activity of catalysts in ozone decomposition at room temperature and high airflow is demonstrated. The developed catalysts can be recommended for application in purification of air from the ozone because of their high catalytic activity, high mechanical stability, and relatively low weight and cost.

Metal doped nanocages (Sc-C82 and Sc-Si82) as effective catalysts for ozone (O3) decomposition

Metal doped nanocages (Sc-C82 and Sc-Si82) as effective catalysts for ozone (O3) decomposition

A cobalt-vacant Co3O4 as a stable catalyst for room-temperature decomposition of ozone in humid air

Conventionally ozone-decomposition catalysts such as MnO2 face the gradual deactivation due to occupation of reactive site, i.e., oxygen vacancy by intermediates like O22- or ubiquitous water vapor in air. Herein, we synthesized a Co2+-vacant Co3O4 (Co3−xO4) with dominant exposure of (110) facets, it maintained superior efficiency of 98% in decomposing 100 ppm ozone over 180 h under the space velocity of 1200 L/g·h at 25 ℃ and relative humidity (RH) of 50%, well beyond the performance of any reported metal oxides catalysts. Especially, it kept stable efficiency even under RH 90% and ultrahigh space velocity of 6000 L/g·h. A new ozone decomposition mechanism under humid conditions is revealed, i.e., the Co2+ vacancy significantly promotes O3 adsorption and the hydroxylation of coordination-unsaturated oxygen (CUO), and Co3+ work together with surface OH group to decompose ozone avoiding the deactivation. This study demonstrates a new way, i.e., creating metal vacancy rather than oxygen vacancy to design stable and efficient catalysts for ozone decomposition under humid conditions.

Hygroscopic La2O3 hybridized LaCoO3-based composite catalyst for efficient ozone decomposition under humidity conditions

Herein we first report the unique hygroscopic oxide hybrid LaCoO3-based composite catalyst derived from dual-metal metal organic framework (MOF) for ozone decomposition. First, dual-metal La,Co-MOF is synthesized by solvothermal method, then La,Co-MOF is calcined at high temperature, the hygroscopic oxide (La2O3) and active oxides (LaCoO3 and Co3O4) were uniformly hybridized to form porous microspheres. Benefiting from the hybrid action of the two types of oxides, this composite catalyst exhibits highly efficient O3 removal activity within 12 h over the entire humidity conditions. The outstanding humidity resistance is attributed to the preferential adsorption of water vapor on hygroscopic oxide (La2O3), preventing the adsorption of gaseous water molecules on the surface of active oxides. In-situ FTIR further indicates that this composite catalyst possesses superior humidity resistance in the ozone catalytic decomposition.

Study on the performance of hydrotalcite-based ozone decomposition catalyst

AbstractOzone in the indoor environment is seriously harmful to human health, and the catalytic decomposition method is one of the most effective ozone purification technologies. The development of ozone decomposition catalyst with superior activity and stability is the bottleneck, especially under high humidity, high space velocity, and ambient temperature. Layered double hydroxide (LDH) has a unique two-dimensional layered structure and excellent water resistance. In the paper, Ni3Fe, Ni3Co, Ni3Mn, and Co3Fe hydrotalcite-structured catalysts were prepared by the coprecipitation method. And their ozone catalytic decomposition performance was tested under 30 °C, 600000 mL/(g·h), low humidity (RH < 5%), and high humidity (RH > 90%). The results showed that Ni3Co-LDH exhibited excellent ozone decomposition performance, and the ozone conversion was 88% and 77% under low humidity and high humidity, respectively. Combined with XRD, BET, SEM, XPS, Raman, FT-IR, TG and other characterizations, the intrinsic mechanism of the excellent ozone decomposition performance of LDH catalysts was revealed. The paper provided new ideas for developing transition metal ozone decomposition catalysts.

Coordination-Controlled Catalytic Activity of Cobalt Oxides for Ozone Decomposition.

Nowadays, it is still elusive and challenging to discover the active sites of cobalt (Co) cations in different coordination structures, though Co-based oxides show their great potency in catalytic ozone elimination for air cleaning. Herein, different Co-based oxides are controllably synthesized including hexagonal wurtzite CoO-W with Co2+ in tetrahedral coordination (CoTd2+) and CoAl spinel with dominant CoTd2+, cubic rock salt CoO-R with Co2+ in octahedral coordination (CoOh2+), MgCo spinel with dominant Co3+ in octahedral coordination (CoOh3+), and Co3O4 with mixed CoTd2+ and CoOh3+. The valences are proved by X-ray photoelectron spectroscopy, and the coordinations are verified by X-ray absorption fine structure analysis. The ozone decomposition performances are CoOh3+ ∼ CoOh2+ ≫ CoTd2+, and CoOh3+ and CoOh2+ show a lower apparent activation energy of ∼42-44 kJ/mol than CoTd2+ (∼55 kJ/mol). In specific, MgCo shows the highest decomposition efficiency of 95% toward 100 ppm ozone at a high space velocity of 1,200,000 mL/gh, which still retains at 80% after a long-term running of 36 h at room temperature. The high activity is explained by the d-orbital splitting in the octahedral coordination, favoring the electron transfer in ozone decomposition reactions, which is also verified by the simulation. These results show the promising prospect of the coordination tuning of Co-based oxides for highly active ozone decomposition catalysts.

Cu Species-Modified OMS-2 Materials for Enhancing Ozone Catalytic Decomposition under Humid Conditions.

Manganese oxide octahedral molecular sieves (OMS-2) exhibit an excellent performance in ozone catalytic decomposition in dry atmosphere conditions, which however is severely limited by deactivation in humid conditions. Herein, it was found that the OMS-2 materials modified with Cu species could obviously improve both the ozone decomposition activity and water resistance. Based on the characterization results, it was found that these CuOx/OMS-2 catalysts exhibited dispersed CuOx nanosheets attached and located at the external surface accompanied with ionic Cu species entering the MnO6 octahedral framework of OMS-2. In addition, it was demonstrated that the main reason for the promotion of ozone catalytic decomposition could be ascribed to the combined effect of different Cu species in these catalysts. On the one hand, ionic Cu entered the MnO6 octahedral framework of OMS-2 near the catalyst surface and substituted ionic Mn species, resulting in an enhanced mobility of surface oxygen species and formation of more oxygen vacancies, which act as the active sites for ozone decomposition. On the other hand, the CuOx nanosheets could serve as non-oxygen vacancy sites for H2O adsorption, which could alleviate the catalyst deactivation to some extent caused by the occupancy of H2O on surface oxygen vacancies. Finally, different reaction pathways for ozone catalytic decomposition over OMS-2 and CuOx/OMS-2 under humid conditions were proposed. The findings in this work may shed new light on the design of highly efficient catalysts for ozone decomposition with improved water resistance.

Unlocking efficient and robust ozone decomposition with CNT-confined manganese oxide via synergistic electronic modulation

Manganese oxides (MnO2)-based catalysts are prominent candidates for ozone elimination, which always bear the accumulation of the intermediate oxygen species and water, resulting in unsatisfactory catalytic efficiency. To overcome this critical defect, we propose carbon nanotubes confined MnO2 catalysts (MnO2-in-CNT) for efficient and stable ozone decomposition over a wide relative humidity range (RH, 15–90%). Strikingly, the catalyst exhibits an efficient and sustainable ozone conversion (98%) over 100 h under a gas hourly space velocity (GHSV) of 600,000 mL g−1 h−1 and RH of 15%, and durability under high RH (77% over 50 h, RH 70%), well beyond its unconfined analog and most reported works. This excellent catalytic performance can be attributed to the facilitated intermediate desorption on active sites and the confined structure alleviated the effect of water on inner MnO2. This discovery is expected to drive great progress in the applications of confined-structure catalysts for air purification.

Amorphous nanophosphates of dual-metal (Co and Ni) for the decomposition of ozone under humid conditions

Ozone has gradually become a kind of air pollutant that can not be ignored. A highly efficient and stable catalyst for ozone decomposition in humid environments is still a challenge. This paper used a series of novel phosphate catalysts in the ozone field. With the increase of Ni Content in Co(3−x)Ni(x)(PO4)2, crystal formation in Co(3−x)Ni(x)(PO4)2, but excessive Ni destroyed the lattice structure of Co(3−x)Ni(x)(PO4)2 which becomes amorphous. As a result, the specific surface area of materials has an obvious enlargement along with an increase of the surface oxygen content from crystal to amorphous, which is beneficial for improving its active sites on the catalyst. At a condition of relative humidity (RH)= 65 %, Co(3−x)Ni(x)(PO4)2 exhibited outstanding catalytic activity and stability at room temperature. Most importantly, Co1.8Ni1.2PO4 could degrade O3 against the influence of water vapor at RH of 90 %. The research shows the development prospect of phosphate in the field of efficient catalytic decomposition of ozone.

β-Co(OH)2 Nanostructures with High Spin Co(II) in Distorted [CoO6] for Catalytic Ozone Decomposition

There is a high demand to synthesize ozone decomposition catalysts especially in high-space-velocity and high-relative-humidity (RH) environments. Herein, two polymorphs of cobalt hydroxide, α- and β-Co(OH)2, are synthesized and applied for ozone elimination. β-Co(OH)2 shows ∼90% ozone decomposition efficiency under high space velocity (weight hourly space velocity (WHSV) = 1,200,000 mL g–1 h–1, 25 °C, 40 ppm), which is far higher than that of α-Co(OH)2 (∼5%). β-Co(OH)2 has high spin Co(II) in distorted octahedral coordination caused by the Jahn-Teller effect, leading to a higher crystal field splitting energy level and thus contributing to the easier electron transfer between the ozone and catalyst. Moreover, β-Co(OH)2 still shows high performance (∼87%) even in humid conditions (RH ∼50%, 25 °C, 40 ppm, WHSV = 600,000 mL g–1 h–1), which is attributable to its abundant surface non-hydrogen-bonded hydroxyls weakening water molecule adsorption, providing an idea to develop highly efficient catalysts for ozone decomposition in humid environments.

A novel hollow microsphere composite MnOx/PAA: effective catalyst for ozone decomposition at high humidity.

Ozone air pollution poses a serious threat to human health and ecological environment. Manganese oxide (MnOx) is a popular material for ozone decomposition with excellent catalytic performance. However, the catalytic activity may be reduced under high-humidity conditions because of oxygen vacancy of MnOx from the water evaporation. In this paper, a new type of MnOx/poly(acrylic acid-co-divinylbenzene) (PAA) catalyst with MnOx supported on hollow PAA was successfully prepared, which greatly improved the ozone decomposition efficiency under high humidity. It was shown that when the acrylic acid (AA) content was more than 50%, the PAA polymer layer was hydrophilic and the ozone decomposition efficiency would keep high activity for both the low- and high-humidity conditions. The best performance of ozone decomposition was identified for the methanol reduction and AA content of 60%, in which the efficiencies reached 94.5% and 85% at 50% and 90% humidity levels, respectively. It is the synergetic effect of the hydrophilic PAA support and hollow structure that retains and improves the decomposition activity, which can absorb the water vapor molecules and increase the ozone retention time. Therefore, the hollow microsphere catalyst prepared in this paper has great potential in solving the problem of ozone air pollution.

Controllable Synthesis of a Cu/Cu2O Mott–Schottky Heterojunctioned Catalyst for Highly Efficient Ozone Decomposition

In recent years, researchers have spent much effort on the development of specific catalytic materials for ozone decomposition, yet investigation on its mechanism is still needed. In this work, a semiconductor metal oxide catalyst strengthened by the Mott–Schottky effect is prepared. In several synthesized Cu/Cu2O samples, the scale of heterojunctions is adjusted during synthesis, and its influence is investigated by varieties of characterization techniques. In the catalytic test of ozone decomposition, ozone conversion reached 92% at a high weight hourly space velocity (WHSV) of 1,920,000 cm3 g–1 h–1, and compared with the control group without a heterojunction, it has obvious performance improvement. In this work, the application feasibility of the Mott–Schottky effect in the ozone decomposition field is researched from the version of the carrier transfer mechanism. This work proves that the Cu/Cu2O heterojunctioned catalyst has great application prospects; meanwhile, it also provides a new idea for finding other suitable catalysts for ozone decomposition.

Ozone Decomposition Mechanism at Different Structural Oxygen Vacancies on Manganese Dioxide

MnO2 is a promising catalyst for ozone decomposition, and oxygen vacancy has been regarded as the determinant factor for decomposition effectiveness. MnO2 with two different oxygen vacancies, that is, [Mn3+]-V0-[Mn3+] and [Mn3+]-V0, was synthesized and characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The catalytic decomposition rate of [Mn3+]-V0-[Mn3+] was significantly greater than that of [Mn3+]-V0. MnO2 with [Mn3+]-V0-[Mn3+] showed the lowest average oxidation state of Mn and the fastest electron transfer capacity. A new pathway for ozone decomposition at [Mn3+]-V0-[Mn3+] was proposed accordingly. The reaction sequence involved (i) dissociative adsorption of ozone to form an oxygen molecule and an atomic O– at [Mn3+], (ii) reaction of O– further with another O3 molecule to form [Mn4+]-O-O-[Mn4+], and (iii) [Mn4+]-O-O-[Mn4+] decomposition to form a gas-phase oxygen molecule and [Mn3+]-V0-[Mn3+] for further ozone adsorption. This work revealed a new avenue for designing efficient catalysts for ozone elimination.

Exploring an electric-aid ozone decomposition mode to enhance water resistance over manganese oxide monolith catalyst under high humidity

In this work, a facile, green, and effective reaction mode of electric-aid ozone decomposition (EAOD) was developed over a manganese-based monolith catalyst for eliminating ozone under high humidity. The catalyst was prepared by directly growing α-MnO2 nanorods on Al honeycomb substrate (MnO2/Al) via a simple hydrothermal process, and the EAOD mode was performed just by connecting the MnO2/Al monolith catalyst with a DC power supply during ozone decomposition reaction. In the EAOD mode reaction, the MnO2/Al catalyst exhibited a stable ozone conversion efficiency of over 82 % and excellent stability over 720 min under a relative humidity of 90%, well beyond the performance of catalyst in the conventional ozone decomposition reaction without the help of electric aid. Here, the water evaporation by the external electric field generated from the EAOD mode hinders the competitive adsorption of water vapor on the active sites of MnO2/Al catalyst, consequently enhances its water resistance. Moreover, increasing input electric current of the DC power supply could further improve the catalytic activity and stability of the monolith catalyst for ozone decomposition in EAOD mode reaction.

Ozone Decomposition below Room Temperature Using Mn-based Mullite YMn2O5.

A super-low-temperature ozone decomposition is realized without energy consumption on a ternary oxide catalyst mullite YMn2O5 for the first time. The YMn2O5 oxide catalyzed ozone decomposition from a low temperature of -40 °C with 29% conversion (reaction rate: 1534.2 μmol g-1 h-1) and quickly reached 100% (5459.5 μmol g-1 h-1) when warmed up to -5 °C. The superior low-temperature performance over YMn2O5 could surpass that of the reported ozone decomposition catalysts. The structure and element valence characterizations confirmed that YMn2O5 remained the same after 100 h of room-temperature reaction, indicating excellent durability of the catalyst. O2-TPD (O2-temperature-programmed desorption) showed that the active sites are the Mn3+ sites bonded with singly coordinated oxygen on the surface. Combined with in situ Raman measurements and density functional theory calculations, we found that the ozone decomposition reaction on YMn2O5 showed a barrier of only 0.29 eV, following the Eley-Rideal (E-R) mechanism with a rate-limiting step of intermediate O22- desorption. The low barrier minimizes the accumulation of intermediate products and realizes the fast O3 decomposition even at super-low temperatures. Fundamentally, the moderate Mn-O bonding strength in the low-symmetry ternary oxides is crucial to produce singly coordinated active species on the surface responsible for the efficient ozone degradation at low temperatures.

Influence of water molecule on active sites of manganese oxide-based catalysts for ozone decomposition

Developing an efficient approach to decompose ground-level O3 in humidity is crucial for preventing O3 pollution in practical application scenes. In this study, MnOx, CuO, and Cu/MnOx were synthesized to investigate the influence of H2O on the variation of active sites during O3 decomposition. The structural characterizations of the as-synthetic catalysts were measured by N2 physisorption, XRD, SEM, O2-TPD, H2-TPR, TG, and FT-IR analyses. In dry conditions, the elimination rate of O3 followed the sequence of MnOx > Cu/MnOx > CuO. The introduction of Cu to MnOx enhanced the surface area and pore volume of Cu/MnOx, accordingly diminishing the amounts of surface defects and the participation of sub-surface lattice oxygen for catalytic cycle, indicating that surface defects and oxygen vacancies (VO) determined the catalytic activity for O3 decomposition. In humid conditions, the elimination rate of O3 changed to the sequence of Cu/MnOx > MnOx > CuO, with a variation rate compared to dry conditions of −62.9% for MnOx, 14.2% for CuO, and 27.7% for Cu/MnOx. The decrease of participant sub-surface lattice oxygen and the accumulation of intermediates in humidity diminished the decomposition of O3 on MnOx, while the active species such as superoxide radicals generating from the reaction of H2O and Cu/MnOx facilitated the participation of VO and the desorption of O2 from the occupied active sites, accelerating the catalytic cycle on Cu/MnOx. This work developed a deeper understanding of the influence of H2O on catalytic activity, promoting the performance of MnOx-based catalysts for practical O3 decomposition.