Highly efficient removal of ozone by amorphous manganese oxides synthesized with a simple hydrothermal method

Amorphous manganese oxides (MnOx) were synthesized by facile hydrothermal reactions between potassium permanganate and manganese acetate. Synthesis parameters, including hydrothermal time and temperature and molar ratio of precursors, significantly affected the ozone removal performance and structure property of MnOx. Amorphous MnOx-1.5, which was prepared at the Mn2+/Mn7+ molar ratio of 1.5 under hydrothermal conditions of 120°C and 2 hr, showed the highest ozone removal rate of 93% after 480 min at the room temperature, RH (relative humidity) = 80% and WHSV (weight hourly space velocity) = 600 L/(g·hr). The morphology, composition and structure of catalysts were investigated with X-ray diffractometer (XRD), Raman spectra, N2 physisorption, field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), O2 temperature-programmed desorption (O2-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It was confirmed that high catalytic activity of amorphous MnOx for ozone removal was mainly ascribed to its abundant oxygen vacancies, high oxygen mobility and large specific surface area.

Synthetic effect of supports in Cu-Mn-doped oxide catalysts for promoting ozone decomposition under humid environment

The escalating levels of surface ozone concentration pose detrimental effects on public health and the environment. Catalytic decomposition presents an optimal solution for surface ozone removal. Nevertheless, catalyst still encounters challenges such as poisoning and deactivation in the high humidity environment. The influence of support on catalytic ozone decomposition was examined at a gas hourly space velocity of 300 L·g-1·h-1 and 85% relative humidity under ambient temperature using Cu-Mn-doped oxide catalysts synthesized via a straightforward coprecipitation method. Notably, the Cu-Mn/SiO2 catalyst exhibited remarkable performance on ozone decomposition, achieving 98% ozone conversion and stability for 10 h. Further characterization analysis indicated that the catalyst's enhanced water resistance and activity could be attributed to factors such as an increased number of active sites, a large surface area, abundant active oxygen species, and a lower Mn oxidation state. The catalytic environment created by mixed oxides can offer a clearer understanding of their synergistic effects on catalytic ozone decomposition, providing significant insights into the development of water-resistant catalysts with superior performance.

Influence of transition metal catalysts on the decomposition product distribution of PCBs and PCDD/Fs

In this study, reliable and stable polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) generation systems were used to investigate catalyst performance. The distribution characteristics of PCBs and PCDD/Fs after reaction were evaluated under different simulated flue gas conditions using NiO- and MnO₂-loaded γ-Al₂O₃ and ZSM-5 catalysts. The results showed that the active metal of the catalyst affected mainly the decomposition efficiency, the substrate type affected the distribution characteristics of PCBs, and both the active metal and substrate type jointly determined the fingerprint distribution characteristics of PCBs. Moreover, there was an apparent marginal effect of the active metal loading on the same catalyst and the decomposition efficiency of the pollutants. In the temperature range of 100-350 °C, temperature variation had little effect on the removal efficiency of PCBs, but the gas-solid phase distribution characteristics of the pollutants changed significantly, and large amounts of di- and tri-CBs were generated in the products at 200 °C. A small amount of water generated hydrogen via the water-gas shift reaction at medium temperature, which promoted the hydro-dechlorination reaction of the chlorinated organics. However, excess water in the substrate gas competes with the pollutants for adsorption sites and reduces the reaction activity of the catalyst.

Removal of diisopropyl methyl phosphonate (DIMP) from heated metal oxide surfaces

Diisopropyl methyl phosphonate (DIMP) is an organophosphorus compound used as a surrogate of sarin, a chemical weapon agent. Thermal decomposition of DIMP and similar liquids may be affected by added inorganic solids. Understanding such effects is needed to guide decontamination and environmental mitigation work. Here, liquid DIMP mixed with powders of γ-Al₂O₃ or SiO₂, was heated to 350 °C in a thermogravimetric analyzer while observing effluent gas using a mass spectrometer. For both powders, evaporation of DIMP occurred between 50 and 200 °C, followed by a second mass loss step up to 350 °C. The amount of DIMP evaporated in the first step varied; however, the size of the second, mass loss step was consistent between experiments for each solid used. For γ-alumina, 2-propanol and propene were released below the DIMP boiling point and mostly propene at higher temperatures. Calcining alumina prior to exposure to DIMP reduced the release of 2-propanol. For silica, the second mass loss step was smaller and only propene was released. Powders exposed to DIMP and recovered at different temperatures showed FTIR peaks corresponding to the individual bond vibrations of DIMP. At higher temperatures, only the P-CH ₃ stretching vibration was observed.

A novel Fe-Co double-atom catalyst with high low-temperature activity and strong water-resistant for O3 decomposition: A theoretical exploration

Developing catalysts with high activity, durability, and water resistance for ozone decomposition is crucial to regulate the pollution of ozone in the troposphere, especially in indoor air. To overcome the shortcomings of metal oxide catalysts with respect to their durability and water resistance, Fe-Co double-atom catalyst (DAC) is proposed as a novel catalyst for ozone decomposition. Here, through a systematic study using density functional theory (DFT) calculations and microkinetic modeling, the adsorption and catalytic decomposition of O₃ on Fe-Co DAC have been examined based on adsorption configuration, orbital hybridization, and electron transfer. Based on Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms, the mechanisms of ozone decomposition on Fe-Co DAC were explored by analyzing reaction paths and energy variations. To confirm the water-resistant of Fe-Co DAC, competitive adsorption behavior between O₃ and dominant environmental gases was discussed through ab initio molecular dynamic (AIMD) simulation. The dominant reaction mechanism of ozone decomposition is L-H and the rate-determining step is the desorption of the first oxygen molecule from the surface of Fe-Co DAC which has an energy barrier of 0.78 eV. Due to this relatively low energy barrier and high turnover frequency (TOF), the optimal operation window of catalytic O₃ decomposition on Fe-Co DAC is <500 K suggesting that catalytic decomposition of O₃ on Fe-Co DAC can occur at room temperature. This theoretical study provides new insights for designing novel catalysts for ozone decomposition and fundamental guidance for subsequent experimental research.

Effect of Bi2WO6/g-C3N4 composite on the combustion and catalytic decomposition of energetic materials: An efficient catalyst with g-C3N4 carrier

An effective strategy involving a suitable carrier is needed to improve the dispersion, combustion and catalytic performances of catalyst nanoparticles. Herein, a Bi₂WO₆/g-C₃N₄ composite employing g-C₃N₄ as the catalyst carrier was prepared by a one-step in situ hydrothermal method, which was used as the combustion catalyst of solid propellants. The catalyst's structure, morphology and its catalytic decomposition on several energetic materials were characterized by a series of analyses. The optimal ratio of g-C₃N₄ and Bi₂WO₆ was systematically determined. The results demonstrate that Bi₂WO₆/g-C₃N₄ (4:6) composite can diminish the decomposition temperatures of ammonium perchlorate (AP), cyclotrimethylenetrinitramine (RDX), dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) and cyclotrimethylenetrinitramine + nitrocellulose (RDX + NC) by 25.0, 5.2, 24.0 and 1.2 (4.9) ° C, and reduce their apparent activation energy by 59.5, 116.7, 11.6 kJ mol^-1, respectively. Moreover, the laser ignition tests indicate that Bi₂WO₆/g-C₃N₄ can effectively promote the ignition performance of RDX and RDX + NC. A possible mechanism of Bi₂WO₆/g-C₃N₄ on AP was proposed. The g-C₃N₄ catalyst carrier is superior to GO carrier due to its low cost, simple synthesis process, improved combustion and catalytic performances, as well as high N content. These make it have broad engineering application prospects in solid propulsion and other energetic materials.

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.

Cyanotoxin cylindrospermopsin producers and the catalytic decomposition process: A review

Cylindrospermopsin (CYN) is a toxic secondary metabolite produced by several freshwater species of cyanobacteria. Its high chemical stability and wide biological activity pose a series of threats for human and animal morbidity and mortality. The biggest risk of CYN exposure for human organism comes from the consumption of contaminated water, fish or seafood. Very important for effective monitoring of the occurrence of CYN in aquatic environment is accurate identification of cyanobacteria species, that are potentially able to synthesize CYN. In this review we collect data about the discovery of CYN production in cyanobacteria and present the morphological changes between all its producers. Additionally we set together the results describing the catalytic decomposition of CYN.

Catalytic decomposition of dioxins and other unintentional POPs in flue gas from a municipal waste incinerator (MWI) in China: a pilot testing

Unintentionally produced persistent organic pollutants (UPOPs) include polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), pentachlorobenzene (PeCBz), and hexachlorobenzene (HxCBz). With the booming of municipal waste incinerators (MWIs) in China, the emission of UPOPs has generated great concern. As an alternative technology of dioxin control, catalytic decomposition has not been used in China, mainly due to the absence of national demonstration projects. Also, the simultaneous removal of various UPOPs has not been well investigated.In this study, a pilot-scale selective catalytic oxidative (SCO) system using a self-developed honeycomb catalyst was built and tested in a typical municipal waste incinerator (MWI) of China. The original concentration of PCDD/Fs in flue gas after the treatment of activated carbon injection (ACI) still exceeded the national emission standard (0.1 ng I-TEQ/Nm³), while the concentrations of PeCBz and HxCBz were one order of magnitude higher than that of PCDD/Fs. For the testing temperature varying from 300 to 200 °C, the removal efficiency of PCDD/Fs range from 39 to 95 %, followed by dl-PCBs with the range of 56-89 %. PeCBz and HxCBz were also removed, though their removal efficiencies were lower than those of PCDD/Fs and dl-PCBs. Both temperature and degree of chlorination influence the removal efficiencies.

Catalytic decomposition of PCDD/Fs on a V2O5-WO3/nano-TiO2 catalyst: effect of NaCl

The effect of NaCl addition on the properties, activity, and deactivation of a V₂O₅-WO₃/nano-TiO₂ catalyst was investigated during catalytic decomposition of gas-phase polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The extent of deactivation relates directly to the NaCl loading of the catalyst. Poisoning by sodium neutralizes acid sites, interacts strongly with active VO_x species, and reduces the redox capacity of catalysts. In addition, NaCl is also a chlorine source and may actually accelerate the synthesis of new PCDD/Fs. Washing a catalyst with dilute sulfuric acid largely restores catalytic activity, breaking the interaction of Na⁺ ions and dispersed vanadia and removing Na from the catalyst surface. Consequently, catalyst acidity and redox capacity almost recover. Furthermore, sulfate residues react with surface adsorbed water to generate Brønsted acid sites, ensuing a surge of strong acidity of the catalysts.

The catalytic destruction of antibiotic tetracycline by sulfur-doped manganese oxide (S-MgO) nanoparticles

The present study evaluates the efficacy of S-doped MgO (S-MgO) as compared with the plain MgO as a catalyst for destructive removal of tetracycline (TTC) in aqueous solutions. The S-MgO had around 6% S in its structure. Doping MgO with S caused increase in surface oxygen vacancy defects. Adding S-MgO (12 g/L) to a TTC aqueous solution (50 mg/L) caused removal of around 99% TTC at the neutral pH (ca. 5.1) and a short reaction time of 10 min. In comparison, plain MgO could remove only around 15% of TTC under similar experimental conditions. Diffusing O₂ into the TTC solution under the reaction with S-MgO resulted in a considerable improvement of TTC removal as compared to diffusing N₂. Complete removal of TTC and 86.4% removal of its TOC could be obtained using 2 g/L S-MgO nanoparticles. The removal of TTC increased with the increase in solution temperature. The presence of nitrate, sulfate and chloride did not considerably affect the removal of TTC using S-MgO while TTC removal significantly decreased at the presence of bicarbonate and phosphate. The S-MgO was a stable and reusable catalyst exhibiting much higher catalytic activity than plain MgO for the TTC destruction. Accordingly, S-MgO is an emerging and efficient catalyst for catalytic decomposition and mineralization of such pharmaceutical compounds as TTC under atmospheric temperature and pressure.

Methane Cracking over Cobalt Molybdenum Carbides

Abstract

The catalytic behaviour of Co₃Mo₃C, Co₆Mo₆C, Co₃Mo₃N and Co₆Mo₆N for methane cracking has been studied to determine the relationship between the methane cracking activity and the chemical composition. The characterisation of post-reaction samples showed a complex phase composition with the presence of Co₃Mo₃C, α-Co and β-Mo₂C as catalytic phases and the deposition of different forms of carbon during reaction.

Graphical Abstract

Electronic supplementary material

The online version of this article (10.1007/s10562-018-2378-4) contains supplementary material, which is available to authorized users.

Theoretical investigation of the selective dehydration and dehydrogenation of ethanol catalyzed by small molecules

Catalytic dehydration and dehydrogenation reactions of ethanol have been investigated systematically using the ab initio quantum chemistry methods The catalysts include water, hydrogen peroxide, formic acid, phosphoric acid, hydrogen fluoride, ammonia, and ethanol itself. Moreover, a few clusters of water and ethanol were considered to simulate the catalytic mechanisms in supercritical water and supercritical ethanol. The barriers for both dehydration and dehydrogenation can be reduced significantly in the presence of the catalysts. It is revealed that the selectivity of the catalytic dehydration and dehydrogenation depends on the acidity and basicity of the catalysts and the sizes of the clusters. The acidic catalyst prefers dehydration while the basic catalysts tend to promote dehydrogenation more effectively. The calculated water-dimer catalysis mechanism supports the experimental results of the selective oxidation of ethanol in the supercritical water. It is suggested that the solvent- and catalyst-free self-oxidation of the supercritical ethanol could be an important mechanism for the selective dehydrogenation of ethanol on the theoretical point of view.

Catalytic decomposition of gaseous PCDD/Fs over V2O5/TiO2-CNTs catalyst: Effect of NO and NH3 addition

There is a strong need for a control technology that simultaneously achieving the abatement of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) and nitrogen oxides (NOx) emissions in waste incineration industry. TiO2 and carbon nanotubes (CNTs) were used as composite carriers to support vanadium oxide as an innovative catalyst to simultaneously control PCDD/Fs and NO emissions. The removal efficiencies (RE) of PCDD/Fs by V2O5/TiO2-CNTs catalyst under a space velocity (SV) of 20,000 h(-1) reaches 99.9% at 150 °C and adsorption is supposed to be the main mechanism at this temperature. The influence of NONH3 reaction on PCDD/Fs catalytic reaction is investigated. The kinetics analysis exhibits that the addition of NO and NH3 reduces the activation energies for OCDD (octachlorodibenzo-p-dioxin) and OCDF (octachlorodibenzofuran) decomposition to 3.6 kJ/mol and 5.4 kJ/mol respectively.

Dioxin formation and control in a gasification-melting plant

We investigated dioxin formation and removal in a commercial thermal waste treatment plant employing a gasification and melting process that has become widespread in the last decade in Japan. The aim was to clarify the possibility of dioxin formation in a process operation at high temperatures and the applicability of catalytic decomposition of dioxins. Also, the possible use of dioxin surrogate compounds for plant monitoring was further evaluated. The main test parameter was the influence of changes in the amount and type of municipal solid waste (MSW) supplied to the thermal waste treatment plant which from day to day operation is a relevant parameter also from commercial perspective. Here especially, the plastic content on dioxin release was assessed. The following conclusions were reached: (1) disturbance of combustion by adding plastic waste above the capability of the system resulted in a considerable increase in dioxin content of the flue gas at the inlet of the bag house and (2) bag filter equipment incorporating a catalytic filter effectively reduced the gaseous dioxin content below the standard of 0.1 ng toxic equivalency (TEQ)/m(3) N, by decomposition and partly adsorption, as was revealed by total dioxin mass balance and an increased levels in the fly ash. Also, the possible use of organohalogen compounds as dioxin surrogate compounds for plant monitoring was further evaluated. The levels of these surrogates did not exceed values corresponding to 0.1 ng TEQ/m(3) N dioxins established from former tests. This further substantiated that surrogate measurement therefore can well reflect dioxin levels.

N₂O decomposition over K/Na-promoted Mg/Zn-Ce-cobalt mixed oxides catalysts

Three groups of cobalt mixed oxide catalysts (Mg/Zn-Co, Mg/Zn-Ce-C, K/Na-Mg/Zn-Ce-Co) were prepared by sol-gel or impregnation methods. The synergistic effects of transition metal, rare earth metal and alkali metal on cobalt mixed catalysts for nitrous oxide (N₂O) decomposing to N₂ and O₂ were investigated. The experimental results revealed that the catalytic activity for N₂O decomposition was promoted as Co²⁺ was replaced partially by Zn²⁺/Mg²⁺, moreover, the characterization analysis by XRD and XPS showed that Zn²⁺/Mg²⁺ replaced Co²⁺ successfully into the spinel structure of Co3O₄ and promoted significantly the catalytic activity. Especially, the addition of CeO₂ and K₂O/Na₂O decreased the binding energy and resulted in an increase in the density of the electron cloud around Co and an improvement of the catalytic activity. Of the investigated cobalt mixed catalysts, the best catalytic activity was shown by 2% K-Zn0.5-Ce0.05-Co catalyst.