Catalysis in VOC Abatement

Development of a CFD model indicating the quantitative relationship among reactor dimension, bed flow unevenness, and performance for VOCs biofilters

This study presents a Computational Fluid Dynamics (CFD) based biofiltration model to investigate the airflow distribution and the impact of bed flow unevenness (BFU) on the removal of Volatile Organic Compounds (VOCs) in biofilters. The biofiltration model consists of a gas flow sub-model and a VOCs removal sub-model, which were validated by pilot-scale experiments. The model was used to examine the quantitative relationship among reactor dimensions, including the width to height ratio of the filter bed and empty bed residence time (EBRT), BFU, and performance for VOCs biofilters. Simulation results demonstrate that the flow unevenness index (FUI) of the packing layer changes from 0.06 to 0.48 m2‧s-1 with reactor dimension changes. With an increase in the width to height ratio at a constant EBRT, FUI increases, BFU changes, and flow velocity fluctuation on the cross-section becomes larger, leading to a reduction of about 10% in VOCs removal efficiency. Concentration distribution of VOCs becomes uneven in the horizontal direction. At a constant width to height ratio of the filter bed, an increase in EBRT causes an increase in FUI, leading to a decrease in VOCs removal efficiency. When the width to height ratio is 0.5, velocity fluctuation of filter bed cross-section is small, the concentration of VOCs decreases evenly across the filter bed layer, and FUI is at a low level (0.06-0.11 m2‧s-1).Implication: In this manuscript, a biofiltration model of VOCs biofilter based on CFD has constructed and validated. And the manuscript gave the quantitative relationship among reactor dimension, bed flow unevenness and performance for VOCs biofilters for the first time. This study can lead to enhanced VOCs removal efficiency and improved overall performance of biofilters in practical engineering applications.

Highly active Ru/TiO2 nanostructures for total catalytic oxidation of propane

Ruthenium is a robust catalyst for a variety of applications in environmental heterogeneous catalysis. The catalytic performance of Ru/TiO2 materials, synthesized by using the deposition precipitation with urea method, was assessed in the catalytic oxidation of C3H8, varying the ruthenium loading. The highest catalytic reactivity was obtained for a Ru loading of 2 wt. % in comparison with the 1, 1.5, 3, and 4 wt. % Ru catalysts. The physicochemical properties of the synthesized materials were investigated by XRD, N2 adsorption, TEM, FT-IR pyridine, H2-TPR, and XPS. The size of ruthenium particles was found to be greatly dependent on the pretreatment gas (air or hydrogen) and the catalytic activity was enhanced by the small-size ruthenium metal nanoparticles, leading to changes in the reduction degree of ruthenium, which also increased the Brönsted and Lewis acidity. Metal to support charge transfer enhanced the reactant adsorption sites while oxygen vacancies on the interface enabled the dissociation of O2 molecules as revealed through DFT calculations. The outstanding catalytic activity of the 2Ru/TiO2 catalysts allowed to convert C3H8 into CO2 at reaction temperatures of about 100 °C. This high activity may be attributed to the metal/support interaction between Ru and TiO2, which promoted the reducibility of Ti4+/Ti3+ and Ru4+/Ru0 species, and to the fast migration of TiO2 lattice oxygen in the catalyst. Furthermore, the Ru/TiO2 catalyst exhibited high stability and reusability for 30 h under reaction conditions, using a GHSV of 45,000 h-1. The underlying alkane-metal interactions were explored theoretically in order to explain the C-H bond activation in propane by the catalyst.

Investigation on removal of multi-component volatile organic compounds in a two-stage plasma catalytic oxidation system - Comparison of X (X=Cu, Fe, Ce and La) doped Mn2O3 catalysts

Mn₂O₃-X catalysts (X = Cu, Fe, Ce and La) were prepared based on γ-Al₂O₃ for the mixture degradation of muti-component volatile organic compounds (VOCs) composed of toluene, acetone, and ethyl acetate. The catalysts were characterized, and the density functional theory (DFT) simulation of ozone adsorption on Mn₂O₃-X were carried out to investigate the influence of adsorption energy on catalytic performance. The results showed that the removal efficiency (RE) of each VOC component was similarly improved by Mn₂O₃-X catalysts, and the greatest increase in VOCs' removal efficiency was obtained (7.8% for toluene, 86.2% for acetone, and 82.5% for ethyl acetate) at a special input energy (SIE) of 700 J L^-1 with Mn₂O₃-La catalyst. Characterization results demonstrated that Mn₂O₃-La catalyst had the highest content of low valence Mn elements and the greatest O_ads/O_latt ratio, as well as the lowest reduction temperature. Mn₂O₃-La catalyst also presented superior catalytic effect in improving carbon balance (CB) and CO₂ selectivity ( [Formula: see text] ). The CB and [Formula: see text] were increased by 47.7% and 12.61% respectively with Mn₂O₃-La at a SIE of 400 J L^-1 compared with that when only γ-Al₂O₃ was applied. The DFT simulation results of ozone adsorption on Mn₂O₃-X catalysts indicated that the adsorption energy of catalyst crystal was related to the catalytic performance of the catalyst. The Mn₂O₃-La/γ-Al₂O₃ catalyst, which had the highest absolute value of adsorption energy, presented the best performance in improving VOCs' RE.

Oxidation of Methanol and Dichloromethane on TiO2-CeO2-CuO, TiO2-CeO2 and TiO2-CuO@VUKOPOR®A Ceramic Foams

The application-attractive form of TiO₂, CeO₂ and CuO-based open-cell foam supported catalysts was designed to investigate their catalytic performance in oxidation of two model volatile organic compounds-methanol and dichloromethane. TiO₂-CeO₂, TiO₂-CuO and TiO₂-CeO₂-CuO catalysts as thin films were deposited on VUKOPOR^®A ceramic foam using a reverse micelles-controlled sol-gel method, dip-coating and calcination. Three prepared catalytic foams were investigated via light-off tests in methanol and dichloromethane oxidation in the temperature range of 45-400 °C and 100-500 °C, respectively, at GHSV of 11, 600 h^-1, which fits to semi-pilot/industrial conditions. TiO₂-CuO@VUKOPOR^®A foam showed the best catalytic activity and CO₂ yield in methanol oxidation due to its low weak Lewis acidity, high weak basicity and easily reducible CuO species and proved good catalytic stability within 20 h test. TiO₂-CeO₂-CuO@VUKOPOR^®A foam was the best in dichloromethane oxidation. Despite of its lower catalytic activity compared to TiO₂-CeO₂@VUKOPOR^®A foam, its highly-reducible -O-Cu-Ce-O- active surface sites led to the highest CO₂ yield and the highest weak Lewis acidity contributed to the highest HCl yield. This foam also showed the lowest amount of chlorine deposits.

Production of Activated Biochar Derived from Residual Biomass for Adsorption of Volatile Organic Compounds

Volatile organic compounds (VOCs) released in air represent a major potential for environmental pollution. Capture methods based on activated biochar have attracted attention because of their low cost and for the high removal capacity of the material due to its physical and chemical properties. In this paper, activated biochars were developed and their adsorption performance for VOC capture was evaluated. In the first step, biochars derived from rapeseed cake (RSC) and walnut shells (WSC) were obtained through a carbonization process and then were activated using basic/acid agents (KOH/H₂SO₄) to increase their performance as adsorbents. Acetone and toluene were used as the VOC templates. The adsorption capacities of toluene and acetone for non-activated biochars were reduced (26.65 mg/g), while that of activated biochars increased quite significantly, up to 166.72 mg/g, and the biochars activated with H₂SO₄ presented a higher adsorption capacity of VOCs than the biochars activated with KOH. The higher adsorption capacity of biochars activated with H₂SO₄ can be attributed to their large surface area, and also to their larger pore volume. This activated biochar adsorbent could be used with good results to equip air purification filters to capture and remove VOCs.

Non-thermal plasma-enhanced catalytic activation of Mn-Zr-La/Al2O3 catalyst for meta-xylene degradation: Synergetic effects and degradation mechanism

The LaMnO₃ catalysts doped with transition metal (Zr, Co, Fe) were prepared. The influencing factors (the catalyst type, the initial concentration, the gas flow, and oxygen content) on the degradation efficiency by the non-thermal plasma synergistic the LaMnO₃ catalysts doped with Zr, Co and Fe were investigated systematically. The degradation mechanism of the meta-xylene degradation by the non-thermal plasma synergistic Mn-Zr-La/Al₂O₃ was researched. The results showed that the Mn-Zr-La/Al₂O₃ catalyst in the four catalysts had the best degradation efficiency for meta-xylene, which was 99.6% at the applied voltage of 44 kV. The by-product ozone concentration was low, and the NO_x was not detected. Meanwhile, the XPS characterization analysis study revealed that the proportion of Mn⁴⁺ element and the proportion of O_sur in the Zr-doped Mn-Zr-La/Al₂O₃ catalyst were both the highest. The degradation efficiency decreased with the increasing of the initial concentration and gas flow, but first increased and then decreased with the increasing of oxygen content. The fresh and used Mn-Zr-La/Al₂O₃ were characterized by SEM, XRD, BET, FT-IR, O₂-TPD, and the tail gas was treated by GC-MS. Then synergistic degradation mechanism for the meta-xylene by the non-thermal plasma over the Mn-Zr-La/Al₂O₃ catalyst are proposed.

Selective detection of VOCs using microfluidic gas sensor with embedded cylindrical microfeatures coated with graphene oxide

Volatile organic compounds (VOCs) are major environmental pollutants. Exposure to VOCs has been associated with adverse health outcomes. The monitoring of hazardous VOCs is a vital step towards identifying their presence and preventing the risk of acute or chronic exposure and polluting the environment. One of the challenges associated with monitoring VOCs is selectivity of the sensor. Microfluidic gas sensors offer selective and sensitive detection capabilities that have been recently applied for detection of VOCs. In this study, we achieve improved selectivity for detection of a range of VOCs by adding micro- and nanofeatures to the microchannel of microfluidic gas sensors. First, microfeatures are embedded into the microchannel and their geometries are optimized using Taguchi design of experiment method. In the next step the microfeatures embedded microchannel is coated with graphene oxide, to increase the surface to volume ratio by introducing nanofeatures to the surfaces. The nano- and microfeatures are characterized by SEM, XPS, and water contact angle measurement. Finally, the changes in the sensor response are compared to plain microfluidic gas sensor, the results show an average of 64.4% and 120.9% improvement in the selectivity of the sensor with microfeatures and both nano- and microfeatures, respectively.

The Efficiency of Pd Addition and Sr Substitution on La1−xSrxMnO3 to Remove Ventilation Air Methane in a Catalytic Flow Reversal Reactor

Ventilation air methane (VAM) is the main cause of greenhouse gas emissions in coal mining. Catalytic flow reverse reactor (CFRR) is widely used in VAM to mitigate methane emissions. In this study, palladium (Pd) and La1−xSrxMnO3 were used as catalysts in a CFRR. Different types of catalysts were prepared by loading La0.8Sr0.2MnO3, La0.9Sr0.1MnO3, and 0.1%Pd-La0.9Sr0.1MnO3 on a cordierite honeycomb reactor coated with γ-Al2O3 to compare their performances. In addition, this study compared the performance of the three catalysts in an 800 °C reactor based on different methane inlet concentrations, inlet speeds, and conversion times. The results showed: (1) 0.1% addition of Pd increased methane conversion. (2) La0.8Sr0.2MnO3 had higher efficiency at lower methane inlet concentrations, whereas La0.9Sr0.1MnO3 was more efficient at higher methane concentrations. This study demonstrates that a higher Sr loading is worth implementing only when the methane concentration of VAM is lower than 0.6%. (3) To achieve a higher methane conversion efficiency, the inlet velocity of methane should also be considered.

Techniques of Preparation of Thin Films: Catalytic Combustion

Over the past several decades, an increasing amount of attention has been given to catalytic combustion as an environmentally friendly process. However, major impediments to large-scale application still arise on the materials side. Here, we review catalytic combustion on thin film catalysts in view of highlighting some interesting features. Catalytic films open the way for new designs of structured catalysts and the construction of catalysts for catalytic combustion. A special place is occupied by materials in the form of very thin films that reveal catalytic activity for various chemical reactions. In this review, we demonstrate the high catalytic activity of thin film catalysts in these oxidation reactions.

Update on volatile organic compound (VOC) source profiles and ozone formation potential in synthetic resins industry in China

The synthetic resin industry plays an important role in Volatile organic compounds (VOCs) emissions from industrial sources. However, owing to various products and their different emission characteristics, it is extremely difficult to study the source profiles of synthetic resins. In this study, the product-based pollution characteristics of VOCs from eight synthetic resin enterprises were investigated in Shanghai, China. Up to 133 VOCs were identified, including 106 based on the Photochemical Assessment Monitoring Stations (PAMS) and the Toxic Organics (TO-15) methods, and the remaining 27 were identified based on the new mass spectrometry analysis method. Aromatics (39.7%) and oxygenated VOCs (29.9%) accounted for a relatively high proportion in the synthetic resin industry. The product-based source profiles of each process unit are compiled. Generally, 1,4-dioxane, methyl isobutyl ketone, toluene, benzene, styrene, propane, and dichloromethane are the most abundant species in synthetic resin. Furthermore, the product-based ozone formation potentials (OFPs) and sources reactivity (SR) were calculated, the synthetic resin industry SR range from 0.3 g g^-1 to 4.6 g g^-1. Results suggest that toluene, benzene, styrene, propylene, ethylene, and oxygenated VOCs (including 1,4-dioxane, methyl isobutyl ketone, and aldehyde) should be preferentially controlled to reduce the OFPs. A three-level classification was established to evaluate the degree of photochemical pollution in different industries. Emission factors were calculated and ranked for eight synthetic resins. A VOC emission inventory of Chinese synthetic resin from 2005 to 2018 was compiled. It is estimated that the Chinese synthetic resin emitted 23.96 Gg of VOCs in 2018. In this study, a product-based VOC source profile and emission inventory of the synthetic resin industry were established for the first time. Finally, combined with product types, processes, and processing equipment, feasible recommendations for reducing VOC emissions in the synthetic resin industry are proposed.

Modification of Cobalt Oxide Electrochemically Deposited on Stainless Steel Meshes with Co-Mn Thin Films Prepared by Magnetron Sputtering: Effect of Preparation Method and Application to Ethanol Oxidation

Magnetron sputtering is an advantageous method for preparing catalysts supported on stainless steel meshes. Such catalysts are particularly suitable for processes carried out at high space velocities. One of these is the catalytic total oxidation of volatile organic compounds (VOC), economically feasible and environmentally friendly method of VOC abatement. The reactive radio frequency (RF) magnetron sputtering of Mn and Co + Mn mixtures in an oxidation Ar + O2 atmosphere was applied to form additional thin oxide coatings on cobalt oxide layers prepared by electrochemical deposition and heating on stainless steel meshes. Time of the RF magnetron sputtering was changed to obtain MnOx and CoMnOx coatings of various thickness (0.1–0.3 µm). The properties of the supported CoOx-MnOx and CoOx-CoMnOx catalysts were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), Fourier-transform infrared (FTIR) and Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The catalytic activity was investigated in the deep oxidation of ethanol, which was employed as a model VOC. According to the specific activities (amount of ethanol converted per unit mass of metal oxides per hour), the performance of CoOx-MnOx catalysts was higher than that of CoOx-CoMnOx ones. The catalysts with the smallest layer thickness (0.1 µm) showed the highest catalytic activity. Compared to the commercial pelletized Co-Mn-Al mixed oxide catalyst, the sputtered catalysts exhibited considerably higher (23–87 times) catalytic activity despite the more than 360–570 times lower content of the Co and Mn active components in the catalytic bed.

Boosting the surface oxygen activity for high performance Iron-based perovskite oxide

Surface oxygen activities always play an important role in various heterogeneous reaction processes. In this study, the surface oxygen activity of studied perovskite oxides is greatly enhanced after the composition and morphology are tuned. It is worth noting that the surface oxygen activity is enhanced correspondingly, accompanied by higher surface area, better reducibility, and superior low-temperature reactivity of studied catalysts. The sample introduced with nickel atom and nanorods structure possesses higher surface oxygen activity and vacancies with superior performance including T₁₀ at 221 °C and T₉₀ at 243 °C, nearly 90 °C elevations. Double perovskite oxides, especially with nanorods structure are verified to be composed of more surface active oxygen, which could be related to low-temperature redox ability and superior oxygen vacancies. Based on the DFT calculation, introducing nickel element is confirmed to be able to efficiently boost the generation of oxygen vacancies and adsorption of oxygen molecular, in accord with the analysis of characterization. To sum up, the strategy of introducing the nickel atom and nanorods structure could effectively tune the surface oxygen activity and generate more oxygen vacancies, which would be beneficial to the catalytic performance of toluene catalytic oxidation correspondingly.

Catalytic Ozonation of Toluene over Acidic Surface Transformed Natural Zeolite: A Dual-Site Reaction Mechanism and Kinetic Approach

Volatile organic compounds (VOCs) are responsible for damage to health due to their carcinogenic effects. Catalytic ozonation using zeolite appears as a valuable process to eliminate VOCs from industrial emissions at room temperature. For full-scale application of this new abatement technology, an intrinsic reaction rate equation is needed for an effective process design and scale-up. Results obtained here provide a mechanistic approach during the initial stage of catalytic ozonation of toluene using an acidic surface transformed natural zeolite. In particular, the contribution of Lewis and Brønsted acid sites on the surface reaction mechanism and overall kinetic rate are identified through experimental data. The least-squares non-linear regression method allows the rate-determining step to be established, following a Langmuir–Hinshelwood surface reaction approximation. Experimental evidence suggest that ozone is adsorbed and decomposed at Lewis acid sites, forming active atomic oxygen that leads to the oxidation of adsorbed toluene at Brønsted acid sites.

Effect of palladium on the black mass-based catalyst prepared from spent Zn/Mn alkaline batteries for catalytic combustion of volatile organic compounds

A large amount of spent batteries is produced annually. When spente batteries are buried, their harmful components may contaminate soil and water. Therefore, recycling of spent batteries is essential for environmental reasons. We evaluated the BM (black mass) of spent Zn/Mn alkaline batteries as a catalyst substance for the catalytic combustion of volatile organic compounds (VOCs: benzene, toluene, and o-xylene). The SBM catalyst (black mass-based catalyst) was prepared by treating BM with 0.1 N of sulfuric acid solution. Major elements of the SBM catalyst were manganese, zinc, iron, aluminum, potassium, and sodium except for carbon. In addition, to find out the additive effect of palladium on the SBM catalyst, we prepared the Pd/SBM catalysts using a conventional impregnation method. We investigated the physicochemical properties of the SBM and Pd/SBM catalysts by instrumental analysis. Benzene, toluene, and o-xylene (BTX) were oxidized completely over the SBM catalyst at reaction temperatures less than 410, 340, and 410 °C, respectively (gas hourly space velocity: 40,000 h^-1). As expected, for the Pd/SBM catalysts, increasing the palladium loading on the SBM from 0.1 wt% to 1.0 wt% increased the conversions of BTX. In the 1.0 wt% Pd/SBM catalyst, the reaction temperatures for catalytic combustion of BTX were greatly reduced to 310, 260, and 250 °C, respectively (gas hourly space velocity: 40,000 h^-1). Instrumental analysis indicated that the increase in activity by adding palladium resulted from the active ingredient (palladium oxide: PdO) and better redox properties.

Gold and Ceria as Catalysts for VOC Abatement: A Review

Due to its excellent oxygen storage capacity, ceria is a well-known oxidation catalyst. However, its performance in the oxidation of volatile organic compounds can be improved by the introduction of gold. Depending on the type of VOC to be oxidized, the surface of gold nanoparticles and the gold/ceria interface may contribute to enhanced activity and/or selectivity. Choosing a proper preparation method is crucial to obtain optimal gold particle size. Deposition–precipitation was found to be more suitable than coprecipitation or impregnation. For industrial applications, monolithic catalysts are needed to minimize the pressure drop in the reactor and reduce mass and heat transfer limitations. In addition to the approach used with powder catalysts, the method employed to introduce gold in/on the washcoat has to be considered.

Influence of Alumina Precursor Properties on Cu-Fe Alumina Supported Catalysts for Total Toluene Oxidation as a Model Volatile Organic Air Pollutant

The structure–property relationship of catalytic supports for the deposition of redox-active transition metals is of great importance for improving the catalytic efficiency and reusability of the catalysts. In this work, the role of alumina support precursors of Cu-Fe/Al2O3 catalysts used for the total oxidation of toluene as a model volatile organic air pollutant is elucidated. Surface characterization of the catalysts revealed that the surface area, pore volume and acid site concentration of the alumina supports are important but not the determining factors for the catalytic activity of the studied catalysts for this type of reaction. The determining factors are the structural order of the support precursor, the homogeneous distribution of the catalytic sites and reducibility, which were elucidated by XRD, NMR, TEM and temperature programed reduction (TPR). Cu–Fe/Al2O3 prepared from bayerite and pseudoboehmite as highly ordered precursors showed better catalytic performance compared to Cu-Fe/Al2O3 derived from the amorphous alumina precursor and dawsonite. Homogeneous distribution of FexOy and CuOx with defined Cu/Fe molar ratio on the Al2O3 support is required for the efficient catalytic performance of the material. The study showed a beneficial effect of low iron concentration introduced into the alumina precursor during the alumina support synthesis procedure, which resulted in a homogeneous metal oxide distribution on the support.

Catalysis by platinum and palladium species confined in the bulk of glass fibre materials

The results of studies on the application of silicate glass fibre materials in catalysis are summarized and analyzed. Despite the very low noble metal content, catalysts based on these materials showed exceptionally high activities and selectivities in some catalytic reactions. This is due to specificity of the glassy state, which makes it possible, first, to confine highly dispersed palladium and platinum species in the bulk of glass fibres and, second, selectively absorb polar molecules, thus excluding the undesirable reactions involving non-polar molecules. The size dependences of the complete oxidation of propane and selective hydrogenation of acetylene, the nature of the structure sensitivity of these reactions and the reaction mechanisms are discussed. Ways for improving glass fibre catalyst performance are proposed and examples of the successful application of Pt/glass fibre catalysts for purification of industrial gases from volatile organic compounds are given.

The bibliography includes 175 references.

A Case Study of Waste Scrap Tyre-Derived Carbon Black Tested for Nitrogen, Carbon Dioxide, and Cyclohexane Adsorption

Waste scrap tyres were thermally decomposed at the temperature of 600 °C and heating rate of 10 °C·min^-1. Decomposition was followed by the TG analysis. The resulting pyrolytic carbon black was chemically activated by a KOH solution at 800 °C. Activated and non-activated carbon black were investigated using high pressure thermogravimetry, where adsorption isotherms of N₂, CO₂, and cyclohexane were determined. Isotherms were determined over a wide range of pressure, 0.03-4.5 MPa for N₂ and 0.03-2 MPa for CO₂. In non-activated carbon black, for the same pressure and temperature, a five times greater gas uptake of CO₂ than N₂ was determined. Contrary to non-activated carbon black, activated carbon black showed improved textural properties with a well-developed irregular mesoporous-macroporous structure with a significant amount of micropores. The sorption capacity of pyrolytic carbon black was also increased by activation. The uptake of CO₂ was three times and for cyclohexane ten times higher in activated carbon black than in the non-activated one. Specific surface areas evaluated from linearized forms of Langmuir isotherm and the BET isotherm revealed that for both methods, the values are comparable for non-activated carbon black measured by CO₂ and for activated carbon black measured by cyclohexane. It was found out that the N₂ sorption capacity of carbon black depends only on its specific surface area size, contrary to CO₂ sorption capacity, which is affected by both the size of specific surface area and the nature of carbon black.

Structured cobalt oxide catalysts for VOC abatement: the effect of preparation method

Magnetron sputtering was employed for the deposition of cobalt oxide thin films on stainless steel meshes. Catalysts prepared by sputtering in inert and oxidation atmosphere were compared with those obtained by electrochemical deposition and hydrothermal synthesis. Systematic characterization using X-ray diffraction, scanning electron microscopy, N₂ physisorption, infrared spectroscopy, Raman spectroscopy, and temperature-programmed reduction by hydrogen allowed detailed monitoring of their physicochemical properties. Ethanol gas-phase oxidation was employed as a model reaction to reveal the catalytic performance of the catalysts. It was shown that the catalyst prepared by magnetron sputtering in oxidation atmosphere exhibited the best mechanical stability among all studied catalysts. Moreover, its catalytic activity was 18 times higher than that of pelletized commercial cobalt oxide.

Continuous Monitoring of Air Purification: A Study on Volatile Organic Compounds in a Gas Cell

Air pollution is one of the major environmental issues that humanity is facing. Considering Indoor Air Quality (IAQ), Volatile Organic Compounds (VOCs) are among the most harmful gases that need to be detected, but also need to be eliminated using air purification technologies. In this work, we tackle both problems simultaneously by introducing an experimental setup enabling continuous measurement of the VOCs by online absorption spectroscopy using a MEMS-based Fourier Transform infrared (FTIR) spectrometer, while those VOCs are continuously eliminated by continuous adsorption and photocatalysis, using zinc oxide nanowires (ZnO-NWs). The proposed setup enabled a preliminary study of the mechanisms involved in the purification process of acetone and toluene, taken as two different VOCs, also typical of those that can be found in tobacco smoke. Our experiments revealed very different behaviors for those two gases. An elimination ratio of 63% in 3 h was achieved for toluene, while it was only 14% for acetone under same conditions. Adsorption to the nanowires appears as the dominant mechanism for the acetone, while photocatalysis is dominant in case of the toluene.

Sorption of volatile organic compounds on non-activated biochar

This work dealt with the determination of the suitability of sorption of Volatile Organic Compounds (VOCs) on biochars prepared from neem, sugarcane and bamboo feedstocks. Six different VOCs namely benzene, toluene, methyl chloride, xylene, chloroform and carbon tetrachloride were used in a laboratory-scale set-up on non-activated biochars prepared via slow pyrolysis (350-550 °C). Although all the chars showed considerable sorption but amongst them N3 (neem-based biochar) showed the maximum removal efficiency (65.5 mg g^-1 for toluene). Variation in pyrolysis temperature and feedstock type showed significant change in the porosity and specific surface area of the biochar, which is favorable for VOC sorption efficiency. With higher surface area and contact time, the sorption capacity of char enhanced. However, the extent of sorption capacity of biochars differed with changing VOC type. Pseudo-Second-Order model fitted well with the results obtained from VOC sorption kinetics.

Effect of a mixed precursor over monolith MnOx/La–Al2O3 catalyst for toluene oxidation

The MNMA catalyst prepared with a mixed precursor of Mn(NO₃)₂ and Mn(Ac)₂·4H₂O possesses more α-MnO₂ species and good dispersion and is more active for toluene oxidation.

S-Doped three-dimensional graphene (S-3DG): a metal-free electrocatalyst for the electrochemical synthesis of ammonia under ambient conditions

3D-graphene provide abundant space for N₂, and the carbon–sulfur bonds provides a continuous supply of electrons for N₂ reduction. A remarkably large NH₃ yield of 38.81 μg_NH3 mg_cat⁻¹ h⁻¹ and FE of 7.72% for N₂ reduction was obtained.

Cobalt Oxide Catalysts in the Form of Thin Films Prepared by Magnetron Sputtering on Stainless-Steel Meshes: Performance in Ethanol Oxidation

Catalytic total oxidation is an effective procedure to minimize emissions of volatile organic compounds (VOC) emissions in industrial gases. Catalysts in the form of meshes are remarkable as they minimize the internal diffusion of reactants during the reaction as well as the need of expensive active components. In this paper, various conditions of radio frequency magnetron sputtering of cobalt on stainless-steel meshes was applied during catalyst preparation. Properties of the supported Co3O4 catalysts were characterized by SEM, XRD, temperature programmed reduction (H2-TPR), FTIR, XPS, and Raman spectroscopy. Catalytic activity was examined in deep oxidation of ethanol chosen as a model VOC. Performance of the catalysts depended on the amount of Co3O4 deposited on the supporting meshes. According to specific activities (the amounts of ethanol converted per unit weight of Co3O4), smaller Co3O4 particle size led to increased catalytic activity. The catalyst prepared by sputtering in an Ar+O2 atmosphere without calcination showed the highest catalytic activity, which decreased after calcination due to enlargement of Co3O4 particles. However, specific activity of this catalyst was more than 20 times higher than that of pelletized commercial Co3O4 catalyst used for comparison.

Emission profiles, ozone formation potential and health-risk assessment of volatile organic compounds in rubber footwear industries in China

The emission characteristics of VOCs in the rubber footwear industry (RFI) and its effect on human health are poorly understood to date. Herein, up to 68 VOCs, sorted into seven classes including alkanes, alkenes, acetylene, aromatics, halocarbons, carbon disulfide, and oxygenated VOCs, were monitored. VOCs emitted from three main processing stages of RFI, including shaping, painting and vulcanizing, were 383, 1507 and 1026 mg/m³, respectively. The top 10 VOCs contributing to the concentration and ozone formation potential were identified. Generally, alkanes were the major component emitted from three stages, contributing 48.58%-63.07% of the total VOCs. Alkenes contributed most to the OFP, accounting for 37.2%-69.1%. Based on the risk assessment, a definite cancer risk for workers in shaping workshop should be noticed. Several VOCs with a life carcinogenic risk higher than 10^-4, especially benzene, bromodichloromethane, ethylbenzene and 1,1,2-trichloroethane, should be focused on. Therefore, more attention should be taken for the extended-ranges of VOCs in subordinate RFI, except for the publicly concerned aromatics in rubber industry. A VOCs emission inventory from the production process of Chinese RFI in 2000-2016 was compiled. It is estimated that Chinese RFIs have emitted a total of 319 × 10⁴ t VOCs in those past 17 years.

Catalytic Oxidation of Dimethyl Disulfide over Bimetallic Cu–Au and Pt–Au Catalysts Supported on γ-Al2O3, CeO2, and CeO2–Al2O3

Dimethyl disulfide (DMDS, CH3SSCH3) is an odorous and harmful air pollutant (volatile organic compound (VOC)) causing nuisance in urban areas. The abatement of DMDS emissions from industrial sources can be realized through catalytic oxidation. However, the development of active and selective catalysts having good resistance toward sulfur poisoning is required. This paper describes an investigation related to improving the performance of Pt and Cu catalysts through the addition of Au to monometallic “parent” catalysts via surface redox reactions. The catalysts were characterized using ICP-OES, N2 physisorption, XRD, XPS, HR-TEM, H2-TPR, NH3-TPD, CO2-TPD, and temperature-programmed 18O2 isotopic exchange. The performance of the catalysts was evaluated in DMDS total oxidation. In addition, the stability of a Pt–Au/Ce–Al catalyst was investigated through 40 h time onstream. Cu–Au catalysts were observed to be more active than corresponding Pt–Au catalysts based on DMDS light-off experiments. However, the reaction led to a higher amount of oxygen-containing byproduct formation, and thus the Pt–Au catalysts were more selective. H2-TPR showed that the higher redox capacity of the Cu-containing catalysts may have been the reason for better DMDS conversion and lower selectivity. The lower amount of reactive oxygen on the surface of Pt-containing catalysts was beneficial for total oxidation. The improved selectivity of ceria-containing catalysts after the Au addition may have resulted from the lowered amount of reactive oxygen as well. The Au addition improved the activity of Al2O3-supported Cu and Pt. The Au addition also had a positive effect on SO2 production in a higher temperature region. A stability test of 40 h showed that the Pt–Au/Ce–Al catalyst, while otherwise promising, was not stable enough, and further development is still needed.

Facile synthesis of porous carbons from silica-rich rice husk char for volatile organic compounds (VOCs) sorption

This work reported a facile synthesis of porous carbons from the silica-rich rice husk biochar via a ball-milling-assisted KOH activation for sorption of tar compounds and volatile organic compounds (VOCs) (i.e., toluene, phenol). The textural properties of activated biochars can be greatly influenced by the mass ratio of KOH and biochar. The high-performance biochar with a large specific surface area (S_BET: 1818 m²/g) was produced as the mass ratio was 3. This activated biochar exhibited a hierarchically meso-microporous structure, which benefited for the adsorption process. Particularly, it had long breakthrough time of 2784 min and high adsorption capacity of 264 mg/g for toluene, while it had short breakthrough time of 724 min and low adsorption capacity of 6.53 mg/g for phenol. Significantly, the mixed VOCs of toluene and phenol can be effectively adsorbed. Further, thermal desorption will be an alternative route for regeneration of waste activated biochar.

Catalytic oxidation at pilot-scale: Efficient degradation of volatile organic compounds in gas phase

Volatile organic compounds (VOCs) are responsible for environmental problems and may affect human health. Several treatment technologies minimize VOCs emissions; among those, catalytic oxidation appears as a promising alternative. In this study, a pilot-scale catalytic reactor was developed and the influence of process parameters on toluene degradation were investigated. Inlet gases were heated by electrical resistances and the catalyst employed was a honeycomb shape commercial automotive catalyst (Umicore, model AFT). Toluene degradation higher than 99% was achieved for several conditions and temperature showed to be the most important process variable for it. For all concentrations, it was observed that when increasing temperature led to a decrease on the space time. At 800 ppmv, varying from 543 K to 633 K, the space time decreased from 0.121 s to 0.08 s, respectively. At 1600 ppmv for the same temperature range, space time was reduced from 0.098 s to 0.040 s, respectively. At 2400 ppmv, varying from 543 K to 633 K, space time decreased from 0.081 s to 0.048 s. The catalytic reactor developed proved to be efficient for VOCs treatment, showing a high potential of application at industrial emission sources.

Use of a novel coupled-oxidation tubular reactor (COTR)/ NTP-DBD catalytic plasma in a synergistic electro-catalysis system for odorous mercaptans degradation

In this work, a novel coupled-oxidation tubular reactor (COTR)/non-thermal dielectric barrier discharge (NTP-DBD) catalytic plasma in a synergistic electro-catalysis system was investigated for odorous mercaptans decomposition. In order to enhance the degradation efficiency of electro-oxidation, a novel enhanced Ti/PbO₂ electro-catalytic tubular reactor prepared by using flow dynamic electrodeposition was designed and applied as pretreatment process for CH₃SNa wastewater. The results indicated that the optimal condition was 7 mA cm^-2 of current density, 10 g L^-1 of initial concentration of CH₃SNa, 9.0 of pH and 5.0 g L^-1 of electrolyte concentration. Addition of Fe²⁺ and H₂O₂ and mechanism of COTR system were first put forward. The target species CH₃SNa were removed over 90% by this process. In order to treat the CH₃SH effusion which was co-produced with CH₃SNa aqueous solution, the technology of NTP-DBD catalytic plasma reactor followed by a chemical absorption has been developed. MSH could be removed over 95% under the condition of 2 s of residence time, 15 kV of output voltage with oxygen concentration of 9%. Moreover, the synthetic Ni-doped AC catalyst had the best performance under 0.7 mmol g^-1 of nickel loading. The conclusion was the energetic electrons generated in the DBD reactor played a key role on the removal of MSH, and the major decomposition products of MSH were detected as CH₃SSCH₃, SO₂ and NO₂. Moreover, the gaseous products in the plasma exhaust could be absorbed and fixed by the subsequent aqueous NaOH solution.

The promotion effect of tungsten on monolith Pt/Ce0.65Zr0.35O2 catalysts for the catalytic oxidation of toluene

The temperature for the complete conversion of toluene on the monolith Pt-WO₃/Ce_0.65Zr_0.35O₂ catalyst decreases by about 30 °C compared to that on Pt/Ce_0.65Zr_0.35O₂.

Effect of TiO2/GAC and water vapor on chloroform decomposition in a hybrid plasma-catalytic system

This paper presents the combination of TiO₂/GAC catalyst and NTP for the decomposition of chloroform using a DBD reactor. The experiments were performed using an AC transformer as the power supply system to determine the optimal conditions of the chloroform conversion in the presence of a hydrogen-rich substance, that is, water vapor. TiO₂/GAC enhanced the removal efficiency and also CO₂ selectivity significantly, leading to an acceptable conversion rate at SIEs higher than 400 J L^-1. The adsorption property of GAC was noticed to be an effective factor for catalytic activity by increasing the residence time, although the higher retention time prevented the accurate determination of chlorine and carbon balance. Selectivity toward HCl was improved considerably from 24.3% to 64.3% over catalyst when water was fed as a hydrogen-rich compound. At the same time, the harmful chlorinated by-products such as TCBA and TCE declined significantly. A noticeable enhancement in the selectivity toward CO₂ was observed when both catalyst and water were introduced, regardless of the inlet concentration. Our findings suggest that the hybrid of NTP with TiO₂/GAC will highly be effective in the abatement of chloroform, and the addition of H₂O will successfully decline harmful chlorinated by-products.