Decomposition Of Gaseous Ozone Research Articles

A novel γ-like MnO2 catalyst for ozone decomposition in high humidity conditions

MnO2 catalysts have been widely studied for catalytic gaseous ozone decomposition. However, their poor moisture resistance often leads to undesirable catalytic effects in the presence of high humidity. In this study, a novel catalyst with γ-like MnO2 was synthesized using the selective dissolution method on LaMnO3 perovskites. The as-prepared catalyst exhibited quite stable ozone conversion of ~90% within 12 h under 75% relative humidity (400–800 ppm of ozone, 30 °C, 150 000 mL·g−1·h−1 of WHSV). In contrast, traditional γ-MnO2 catalyst showed deficient resistance to H2O and sensitivity to space velocity. Detailed characterizations showed that the larger number of oxygen vacancies induced by structure reconstruction of the γ-like MnO2 and residual La3+ cations facilitated ozone decomposition in humid atmosphere. Finally, the reaction rate of ozone decomposition was proposed by a kinetic study, which further proved that the amount and hydrophilicity of oxygen vacancies are the determinants of the first-order reaction rate constant.

High performance cobalt nanoparticle catalysts supported by carbon for ozone decomposition: the effects of the cobalt particle size and hydrophobic carbon support

Catalytic gaseous ozone decomposition under high humidity is not only an urgent need but also a significant challenge because of the low stability over the available catalysts.

Regulating oxygen vacancies in ultrathin δ-MnO2 nanosheets with superior activity for gaseous ozone decomposition

For ozone decomposition, ultrathin δ-MnO2 nanosheets were synthesized and the properties of oxygen vacancies were regulated. The as-synthesized catalyst exhibited superior activity.

Catalytic Decomposition of Gaseous Ozone at Room Temperature

Catalytic Decomposition of Gaseous Ozone at Room Temperature

Novel CeMnaOx catalyst for highly efficient catalytic decomposition of ozone

Novel CeMnaOx (a is the molar ratio of Mn to Ce) catalysts for catalytic decomposition of ozone (O3) under high GHSV conditions were successfully synthesized by a facile homogeneous precipitation method. CeMn10Ox showed ozone conversion of 96 % for 40 ppm O3 under relative humidity (RH) of 65 % and space velocity of 840 L·g−1 ·h-1 after 6 h at room temperature, which is far superior to the performance of the α-Mn2O3 (38 %). The ozone decomposition activity of α-Mn2O3 increased by a factor of 2.5 with the addition of Ce. XRD, XPS, H2-TPR, O2-TPD, EXAFS and DFT calculations data confirmed that cerium-manganese complex oxides with enhanced surface area were formed, which played a key role in the decomposition of ozone. This study provides important insights for developing improved catalysts for gaseous ozone decomposition that can be prepared by a simple method, and promoting the performance of manganese oxides for practical ozone elimination.

High‐Performance Co‐MnOx Composite Oxide Catalyst Structured onto Al‐Fiber Felt for High‐Throughput O3 Decomposition

AbstractA highly active and efficient thin‐felt Al‐fiber‐structured Co‐MnOx composite oxide catalyst (named Co‐MnOx‐Al) with unique form factor and high permeability is developed for high‐throughput catalytic decomposition of gaseous ozone (O3). Thin‐sheet Al‐fiber felt (60 μm diameter; 90 vol % voidage) chips underwent a steam‐only oxidation and calcination for endogenously growing a 0.7‐μm‐thick mesoporous layer of γ‐Al2O3 nanosheets along with the Al‐fiber. Cobalt and manganese were placed onto the ns‐γ‐Al2O3/Al‐fiber chips by incipient wetness co‐impregnation method. The best catalyst is the one with a Co/Mn molar ratio of 0.36 and Co‐Mn loading of 5 wt % after calcining at 500 °C (named Co‐MnOx(0.36)‐Al), being able to achieve full O3 conversion at 25 °C for a feed gas containing 1000±30 ppm O3, using a high gas hourly space velocity of 48000 mL gcat.−1 h−1; full O3 conversion is retained in the absence of moisture till the testing end after 720 min; in case with a relative humidity of 50 %, O3 conversion slides from 88 % of the initial value to a flat of ∼66 % within 90 min. CoOx modification is paramount for improved formation of Mn2+ species while leading to the highest fraction of (Mn2++Mn3+) in total (Mn2++Mn3++Mn4+) and more oxygen vacancies on Co‐MnOx(0.36)‐Al catalyst surface.

Oxygen Vacancies Induced by Transition Metal Doping in γ-MnO2 for Highly Efficient Ozone Decomposition.

Transition metal (cerium and cobalt) doped γ-MnO2 (M-γ-MnO2, where M represents Ce, Co) catalysts were successfully synthesized and characterized. Cerium-doped γ-MnO2 materials showed ozone (O3) conversion of 96% for 40 ppm of O3 under relative humidity (RH) of 65% and space velocity of 840 L g-1 h-1 after 6 h at room temperature, which is far superior to the performance of the Co-γ-MnO2 (55%) and γ-MnO2 (38%) catalysts. Under space velocity of 840 L g-1 h-1, the conversion of ozone over the Ce-γ-MnO2 catalyst under RH = 65% and dry conditions within 96 h was 60% and 100%, respectively, indicating that it is a promising material for ozone decomposition. XRD and HRTEM data suggested that Ce-γ-MnO2 formed mixed crystals consisting of α-MnO2 and γ-MnO2 with specific surface area increased from 74 m2/g to 120 m2/g compared to undoped γ-MnO2, thus more surface defects were introduced. H2-TPR, O2-TPD, XPS, Raman, and EXAFS confirmed that Ce-γ-MnO2 exhibited more surface oxygen vacancies and surface defects, which play a key role during the decomposition of ozone. This study provides important insights for developing improved catalysts for gaseous ozone decomposition and promoting the performance of manganese oxide for practical ozone elimination.

Gaseous ozone decomposition over high silica zeolitic frameworks

AbstractFor several decades, it has been known that ozone emissions are harmful to humans, plants, and animals. Heterogeneous catalytic decomposition is an efficient process for removing ozone from air. This study examines the effect of the zeolite's framework and pore width on efficiency for decomposing gaseous ozone. Four highly hydrophobic zeolites are used: a large cavity zeolite (Faujasite/H‐FAU), a medium pore zeolite with parallel channel (Mordenite/H‐MOR), and two medium pore zeolites with interconnected channels (H‐ZSM‐5/H‐MFI and Na‐ZSM‐5/Na‐MFI). Experiments were conducted in fixed‐bed flow reactors loaded with zeolite at ambient conditions (20 °C and 101 kPa). Zeolite surfaces were analyzed during the experiments in order to understand the influence of physical and chemical surface properties on the ozone decomposition mechanism. A higher amount of ozone is eliminated using H‐MOR, compared with the zeolite samples H‐FAU, H‐MFI, and Na‐MFI. Pore width and micropore framework size distribution (channel and cages) appear to be key factors. A narrow channel or cage, slightly larger than the ozone molecule size, seems to promote ozone interactions with Lewis acid sites. Fourier transform infrared spectroscopy shows that Lewis acid sites (LAS), located on the walls of zeolite pores, decompose ozone. This leads to the formation of atomic oxygen species that could react with another ozone molecule to form dioxygen. Hence, LAS are regenerated, ready to decompose another ozone molecule once more.

Removing Surface Hydroxyl Groups of Ce-Modified MnO2 To Significantly Improve Its Stability for Gaseous Ozone Decomposition

Stratospheric ozone (O3), which slips into the cabin through the air-supply system in a commercial airliner, is detrimental to human health around the world. For gaseous O3 abatement, catalytic decomposition is an effective method. However, catalyst deactivation is one of the main obstacles to its practical application. In this study, a new deactivation mechanism involving the surface hydroxyl group of catalyst is found by investigating the effects of heat treatment of cerium-modified todorokite-type manganese dioxides (Ce–MnO2) on O3 decomposition, which will contribute to the development of more active and stable O3 decomposition catalysts in the future work. The in situ DRIFT study indicates that gaseous O3 reacted with surface hydroxyl groups to form surface adsorbed water, which occupied the catalytically active sites (i.e., oxygen vacancies) leading to the catalyst deactivation. Calcination at 300 °C greatly removed surface hydroxyl groups while keeping oxygen vacancies almost unchanged at the same time; thus the as-obtained catalyst showed greatly improved stability, keeping ∼98% of removal efficiency for ∼115 ppm of O3 within 5 h under a very high space velocity of 1200 L g–1 h–1 at room temperature.

Facile synthesis of Fe-modified manganese oxide with high content of oxygen vacancies for efficient airborne ozone destruction

Oxygen vacancy engineering is an efficient strategy to improve the catalytic performance of nanomaterials. In this work, a highly active Fe-modified manganese oxide (Fe-MnOx) was synthesized and used for airborne ozone decomposition. The addition of Fe3+ during MnO2 synthesis led to higher specific surface area, greatly increased content of oxygen vacancies, evidenced by XPS, H2-TPR analysis and lower oxygen vacancy formation energy (decreased by ∼1.2eV) based on the density functional theory calculations. The ozone conversion over Fe-MnOx kept 97% after 24h reaction, while it over MnO2 slowed down to 85% under dry condition. Remarkably, under humid condition (RH=60%), the ozone conversion over Fe-MnOx kept 73% after 6h reaction, while ozone conversion over pure MnO2 decreased to 50% within 1h under the conditions of 100ppm inlet ozone concentration and weight space velocity of 660Lg−1h−1. The intermediate peroxide species (O22−) formed on the surface oxygen vacancies of Fe-MnOx and MnO2 during ozone decomposition reaction were observed using in situ Raman spectroscopy. The concentration and depletion rate of O22− on the surface of Fe-MnOx was higher than that on MnO2, illustrating that O22− acted as the key species to boost the catalytic process. The content and dispersity of oxygen vacancies were identified to be mainly responsible for the performance difference. This provides a promising idea for designing novel nanomaterial catalyst for gaseous ozone decomposition.

Oxygen vacancies enabled enhancement of catalytic property of Al reduced anatase TiO2 in the decomposition of high concentration ozone

The catalytic decomposition of gaseous ozone (O3) is investigated using anatase TiO2 (A-TiO2) and Aluminum-reduced A-TiO2 (ARA-TiO2) at high concentration and high relative humidity (RH) without light illumination. Compared with the pristine A-TiO2, the ARA-TiO2 sample possesses a unique crystalline core-amorphous shell structure. It is proved to be an excellent solar energy “capture” for solar thermal collectors due to lots of oxygen vacancies. The results indicate that the overall decomposition efficiency of O3 without any light irradiation has been greatly improved from 4.8% on A-TiO2 to 100% on ARA-TiO2 under the RH=100% condition. The ozone conversion over T500/ARA-TiO2 catalyst is still maintained at 95% after a 72h test under the reaction condition of 18.5g/m3 ozone initial concentration, and RH=90%. The results can be explained that T500/ARA-TiO2 possesses the largest amorphous contour, the lowest crystallinity, the most surface-active Ti3+/Ti4+couples, and the most oxygen vacancies. This result opens a new door to widen the application of TiO2 in the thermal-catalytic field.

Catalytic decomposition of gaseous ozone over todorokite-type manganese dioxides at room temperature: Effects of cerium modification

Catalytic decomposition of gaseous ozone (O3) over todorokite-type manganese dioxides (T-MnO2) at room temperature and the effects of cerium modification were investigated. Catalytic activity and stability were greatly improved over Ce-modified MnO2 (Ce-MnO2), which increased with the increase of Ce/Mn atomic ratios from 0.06 to 0.28. The cerium modification made agglomerated MnO2 particles transformed into small sheets of Ce-MnO2 catalyst with Ce/Mn ratio of 0.28, accordingly increasing the specific surface area. Moreover, the crystal boundaries between MnO2 and CeO2 formed at high ratios of Ce/Mn. Larger surface area and the crystal boundaries between MnO2 and CeO2 resulted in the formation of more oxygen vacancies, which act as the active sites for O3 decomposition. Besides, we found the improved catalytic stability was associated with the desorption of oxygen species occupying the positions of oxygen vacancies.

Catalytic decomposition of gaseous ozone over manganese dioxides with different crystal structures

Ozone is a ubiquitous pollutant and manganese dioxide (MnO2) has been widely used for ozone decomposition. However, the effect of MnO2 structure on ozone decomposition has never been investigated. Three tunnel-structure polymorphs, i.e., α-, β- and γ-MnO2 were prepared and characterized by BET, TEM, XRD, H2-TPR, O2-TPD, NH3-TPD, TGA-MS and XPS. The activity of three MnO2 polymorphs for ozone decomposition followed the order of α->γ->β-MnO2. The α-MnO2 owned the largest specific surface area and lowest average oxidation state of Mn. Furthermore, the adsorbed oxygen species on the surface of α-MnO2 were more easily reduced. In-situ Raman spectroscopy results showed that peroxide species formed during ozone decomposition, and over α-MnO2 they were more easily decomposed by increasing reaction temperature. It was found that the catalytic activity of MnO2 strongly depended on the density of oxygen vacancies. Accordingly, the ozone decomposition mechanism based on the involvement and recycling of oxygen vacancy (VO) is proposed. The decomposition of peroxide species is a rate-limiting step. These findings are helpful for designing more effective catalyst for ozone removal.

The effect of morphology of α-MnO2 on catalytic decomposition of gaseous ozone

The morphology effect of α-MnO2 on the catalytic decomposition of ozone was first investigated.

Enhanced photocatalytic decomposition of gaseous ozone in cold storage environments using a TiO 2/ACF film

In order to promote the efficient photocatalytic (PC) degradation of gaseous ozone in cold storage environments using activated carbon felt-supported titanium dioxide (TiO 2/ACF), two strategies were implemented in this study at a temperature of 3 ± 1 °C and relative humidity 90 ± 3%. The two strategies are as follows (i) ACF-supported TiO 2 treated with γ-ray irradiation, and (ii) ACF-supported silver-doped TiO 2 containing Ag nanoparticles prepared by reduction using γ-radiolysis. The rate constant ( k′) of the apparent pseudo first-order kinetic model was used to define the degradation efficiency of gaseous ozone in the PC process. The results showed that (1) from analysis of the X-ray photoelectron spectrum, optimum changes had occurred in the crystal structure of the TiO 2 that had been γ-ray-irradiated with a total dose of 20 KGy (TiO 2*-20), resulting in an increase of 12.6% in the k′ of TiO 2*-20/ACF compared with that of TiO 2/ACF, (2) the presence of Ag nanoparticles prepared by reduction using γ-radiolysis on the TiO 2/ACF film enhanced the photocatalytic degradation of gaseous ozone with a molar ratio of Ag/Ti below 1%. The k′ of the films is highly dependent on the Ag/Ti molar ratios. With a Ag/Ti molar ratio of 1%, a maximum of k′ value can be attained for the Ag + (TiO 2*-20)/ACF film under the experimental conditions.

Gaseous ozone decomposition using a nonthermal plasma reactor with adsorbent and dielectric pellets

For the treatment of gaseous ozone emission, this study investigated the adsorption and enrichment of ozone and the destruction of the adsorbed ozone by nonthermal plasma. A nonthermal plasma reactor with adsorbent pellets in it was operated in two sequential modes, adsorption and decomposition of ozone. First, the ozone-containing gas was flowed through the reactor for a given period, in which the ozone was adsorbed and concentrated. In the next step, the gas was switched to argon or nitrogen, bypassing the ozone-containing gas, and AC high voltage was applied to the reactor to produce nonthermal plasma for the decomposition of the adsorbed ozone. By this method, the gaseous ozone was effectively treated with reasonable electrical energy consumption. The adsorbed ozone was converted into molecular oxygen when argon was used as the ozone decomposition gas, whereas a small amount of nitrogen oxides was formed with nitrogen. The energy consumed to decompose the adsorbed ozone was found to be 540 and 795 kJ/ g-O3 decomposed with argon and nitrogen, respectively.

Effect of Cl− anions on photocatalytic decomposition of gaseous ozone over Au @ Ag/TiO2 catalyst

Au core Ag shell composite structure nanoparticles were prepared using a sol method. The Au core Ag shell composite nanoparticles were loaded on TiO2 nanoparticles as support using a modified powder–sol method, enabling the generation of Au @ Ag/TiO2 photocatalysts for photocatalytic decomposition and elimination of ozone. The sols were characterized by means of ultraviolet–visible light (UV–Vis) reflection spectrometry, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The activity of the Au @ Ag/TiO2 photocatalysts for photocatalytic decomposition and elimination of ozone was evaluated and the effect of Cl− anions on the photocatalytic activity of the catalysts was highlighted. Results showed that Au @ Ag/TiO2 prepared via the modified powder–sol route in the presence of an appropriate amount of NaCl solid as demulsifier had better activity in the photocatalytic decomposition and elimination of ozone. At the same time, Au @ Ag/TiO2 catalysts had better ability to resist poisonous Cl− anions than conventional Au/TiO2 catalyst. The reasons could be, first, that NaCl was capable of reducing the concentration of free Ag+ by adsorption on the surface of Ag particles forming AgCl and enhancing the formation of Au core Ag shell particles, leading to a better resistance to Cl− anions of the catalysts, and, second, AgCl took part in the photocatalytic decomposition of ozone together with Au @ Ag/TiO2 catalysts and had a synergistic effect on the latter, resulting in better photocatalytic activity of Au @ Ag/TiO2 catalysts.

PREPARATION OF Au-LOADED TiO2 BY PHOTOCHEMICAL DEPOSITION AND OZONE PHOTOCATALYTIC DECOMPOSITION

In this paper, Au -loaded TiO 2( Au/TiO 2) photocatalysts were prepared by photochemical deposition method and characterized by transmission electron microscopy, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results indicated the metallic Au nanoparticles were deposited on the surface of TiO 2 after the high-pressure mercury irradiation and regarded as an electronegative center. The photocatalytic decomposition of gaseous ozone was investigated on TiO 2 and Au -loaded TiO 2 at room temperature. Results indicated that the photocatalytic conversion of ozone can be improved by Au/TiO 2 and photocatalytic activity increased with the increase of the photodeposition time. The photocatalytic removal rate of ozone remained above 96% on the surface of 1% Au/TiO 2 with photodeposition for 120 min under black lamp irradiation for 20 h. Au cluster deposited on the surface of TiO 2 functioned not only as the electron trap center but also as the adsorption site of O 3 in photocatalytic reaction.

Characterization of Gaseous Ozone Decomposition in Soil

Laboratory scale batch experiments were performed to investigate the decomposition characteristics of gaseous ozone in porous media. The decomposition rates of gaseous ozone in several solid media were determined, and the relationship of moisture content with sorbed ozone molecules was evaluated. Ozone decomposition in control and glass beads packed columns followed second-order reaction kinetics, while ozone consumption in a sand-packed column demonstrated first-order kinetics with a rate constant of 0.0109 min−1 and half-life of 1.0 h. The presence of typical metal oxides in the soil resulted in ozone consumption rates in the following order: hematite (Fe2O3) > silica-alumina (SiO2Al2O3) > alumina (Al2O3) > silica (SiO2). Ozone decomposition was highly dependent upon soil moisture content. Over 90% of the total ozone mass decomposed in the field soil with moisture content at less than 1 wt%, whereas as low as 5–15% of the total ozone mass degraded with moisture content at more than 2 wt%. In conclusion, ozone decomposition in soils was primarily controlled not only by soil organic matter but also by reactive metal oxides on the soil surface. These two factors were shown to be highly dependent upon soil moisture content.

Reaction Kinetics of Ozone in Variably Saturated Porous Media

A kinetic model based on the mass balance principle with equilibrium partitioning of gaseous ozone into pore water was developed to delineate the reactions of ozone in variably saturated porous media contaminated with phenanthrene. Dimensionless fraction factors were used in the kinetic model to account for the reactions of ozone with soil organic matter ~SOM!, metal oxide ~MO!, and phenanthrene as a function of water saturation. The enhanced removal of phenanthrene resulting from heterogeneous catalytic reactions between ozone and soil organic matter and metal oxide was incorporated as lumped parameters in the reaction rate coefficients of gaseous and dissolved ozone with phenanthrene. Laboratory experiments employing 5 cm long mini column reactor systems were conducted to estimate the reaction constants for three porous medium types ~glass beads, baked field soil, and field soil ! at various water-saturation levels. Water saturation and SOM were found to significantly affect the decomposition of gaseous ozone in both uncontaminated and contaminated porous media. It was found that water saturation over 75% completely eliminates gas-to-solid interfacial ozone reactions with SOM and MO. The kinetic model, with the reaction parameters estimated in this study, predicted reasonably well the experimental data obtained from both the mini column reactor and 20 cm long columns packed with field soil, suggesting that the kinetic model would be suitable for describing the fate and reactions of ozone in variably saturated porous media for soil types and experimental conditions similar to those tested in this study.