Benzene Abatement Research Articles

The enhancement of benzene total oxidation over RuxCeO2 catalysts at low temperature: The significance of Ru incorporation

Catalytic oxidation is considered to be the most efficient technology for eliminating benzene from waste gas. The challenge is the reduction of the catalytic reaction temperature for the deep oxidation of benzene. Here, highly efficient RuxCeO2 catalysts were utilized to turn the number of surface oxygen vacancies and Ce–O–Ru bonds via a one-step hydrothermal method, resulting in a preferable low-temperature reducibility for the total oxidation of benzene. The T50 of the Ru0.2CeO2 catalyst for benzene oxidation was 135 °C, which was better than that of pristine CeO2 (239 °C) and 0.2Ru/CeO2 (190 °C). The superior performance of Ru0.2CeO2 was attributed to its large surface area (approximately 114.23 m2·g−1), abundant surface oxygen vacancies, and Ce–O–Ru bonds. The incorporation of Ru into the CeO2 lattice could effectively facilitate the destruction of the CeO bond and the facile release of lattice oxygen, inducing the generation of surface oxygen vacancies. Meanwhile, the bridging action of Ce–O–Ru bonds accelerated electron transfer and lattice oxygen transportation, which had a synergistic effect with surface oxygen vacancies to reduce the reaction temperature. The Ru0.2CeO2 catalyst also exhibited high catalytic stability, water tolerance, and impact resistance in terms of benzene abatement. Using in situ infrared spectroscopy, it was demonstrated that the Ru0.2CeO2 catalyst can effectively enhance the accumulation of maleate species, which are key intermediates for benzene ring opening, thereby enhancing the deep oxidation of benzene.

Benzene abatement catalyzed by Ceria-Supported platinum nanoparticles and single atoms

Heterogeneous catalysis is one promising technology to abate benzene at relatively low temperatures, but it remains challenging to develop efficient catalysts owing to the difficulties in activating inert benzene molecules and cleaving the strong double bonds of O2. We present the importance of frontier band orbitals in catalyst design for benzene oxidation by correlating electronic structures with catalytic activities over ceria-supported platinum nanoparticles (Ptn/CeO2) or single atoms (Pt1/CeO2). Catalytic tests demonstrate that Ptn/CeO2 shows much higher catalytic activity and lower activation energy than Pt1/CeO2 under identical conditions. By combining the experimental results and theoretical calculations, we reveal that the high activity of Ptn/CeO2 mainly originates from the energy level of the frontier band orbitals, where the lowest unoccupied and the highest occupied band orbitals are energetically favorable for activating benzene and O2, respectively, thus rendering the temperatures required for complete oxidation of benzene significantly lower. Similar trends in activity are found in high-temperature combustion of CH4 and low-temperature oxidation of CO, implicating the universal importance of the energy levels of frontier band orbitals in catalytic oxidation. This work provides a strategy to rationally design high-performance catalysts that can efficiently abate pollutants for environmental protection.

New Insights into the Capture of Low-level Gaseous Pollutants in Indoor Environment by Carbonaceous Materials: Effects of Functional Groups, Pore Size, and Presence of Moist

Abating the common indoor pollutants by adsorption is profoundly governed by the properties of adsorbent and the presence of water. We carried out Monte Carlo simulations of adsorption of five common indoor pollutants (benzene, hydrogen sulfide, sulfur dioxide, formaldehyde and ammonia) on functionalized graphitic pores at 298 K with and without the presence of water to investigate the effects of concentration and type of functional groups (FGs) and pore size. The simulation results for the isotherm, the isosteric heat at zero loading, and the spatial distribution of water and pollutant were analyzed to evaluate the effectiveness of remediation of these pollutants. It is found that adsorption of the pollutants at typical indoor concentrations (sub-ppm) occurs in the Henry's law region where the interaction between pollutant and adsorbent dominates the intermolecular interaction of pollutant. Regardless of the pollutants water is always strongly attracted to the FGs in forms of clusters, and the abatement of the pollutant rests on its electrostatic interactions with water molecules in the clusters and van der Waals interactions with the graphitic surface. The relative interplay of these interactions depends on the properties of the pollutant, and this gives rise to two distinct phenomena: competition and cooperation. For ammonia and formaldehyde whose electrostatic interactions with water (in the cluster on the FGs) are strong, their capture is enhanced. On the other hand, the abatement of benzene and hydrogen sulfide is negatively affected because of their weaker interactions with water. Given the inevitable occupation over the FGs by water, more attention should be paid on the interactions between adsorbed water and the pollutants.

Biogenic MnxOy as an efficient catalyst in the catalytic abatement of benzene: From kinetic to mathematical modeling

Abstract Experimental work on benzene oxidation over C, N doped-MnxOy species showed that the oscillation formation and utilization of sub-surface O2 species from the catalyst was the rate-determining factor for activity. The MnxOy species were synthesized using the biosynthesis method. Characterizations from XRD, XPS, H2-TPR, and In-situ DRIFT were employed to study their catalytic properties. The MnxOy@300 catalyst with low activation energy (Ea = 62 kJ/mol) and TOF of 0.035 h−1 showed the best performance. The kinetic and mathematical model was proposed based on the current results, and those from previous works. The Ea, heat of vaporization, and temperature included in the kinetic model, increased its efficiency. The parameters of the kinetic study were regressed and verified by experimental data and the oxidation route was simulated. The kinetic model was extended into a mathematical model to predict which parameters had the most effect on the C6H6 oxidation process.

The chemistry of gaseous benzene degradation using non-thermal plasma.

In this study, the abatement of benzene in a dielectric barrier discharge (DBD) reactor was studied. The efficiency was investigated in terms of benzene conversion and product formation. The composition of gas-liquid-solid three-phase product produced during degradation was observed by GC-MS. Under the optimal SED, the solid-phase product was analyzed by FT-IR, SEM, and EDS. The results suggested that the product were mainly benzonitriles, benzenedicarbonitrile, phenols, esters, and amides. The wt% of C in product decreased as SED increased, demonstrating that the high discharge voltage facilitated the conversion of VOCs to gaseous intermediate product and CO2. Possible degradation mechanism and pathways of benzene destruction in the DBD reactor were proposed.

UV–Vis–Infrared Light-Driven Photothermocatalytic Synergetic Effect Leading to Efficient Benzene Abatement by Pt Supported on Anatase TiO2 with {001} Facets

Pt supported on anatase TiO2 with {001} facets was prepared by the anatase TiO2 with {001} facets dipped in a Pt(NO3)2 solution and reduced by a NaBH4 solution. The Pt/TiO2 sample was characterized...

Effective low‐temperature catalytic abatement of benzene over porous Mn‐Ni composite oxides synthesized via the oxalate route

AbstractBACKGROUNDBenzene (C6H6) is a typical kind of volatile organic compound (VOC) which can exert great harm to both human health and the environment, and, thus, which needs to be eliminated before its emission. In this work, porous manganese–nickel (Mn‐Ni) composite oxide catalysts were synthesized through the oxalate route and applied to thermal catalytic oxidation of C6H6. By means of activity tests and relative physico‐chemical characterizations, the factors affecting the activity of those Mn‐Ni composite oxides were explored.RESULTSNitrogen (N2)‐adsorption/desorption and X‐ray photoelectron spectroscopy (XPS) measurements indicated that the Brunauer–Elmett–Teller (BET) surface area and the content of surface‐adsorbed oxygen species were increased due to the addition of Ni into Mn oxide (MnOx). Meanwhile, the oxygen mobility and reducibility also were improved in the Mn‐Ni composite oxides. Accordingly, compared with MnOx, the Mn‐Ni catalysts showed higher activity for thermal catalytic oxidation of C6H6. Moreover, porous Mn‐Ni composite oxides with a Mn:Ni molar ratio of 4:1 (Mn4Ni1) displayed the best catalytic activity. Further investigation indicated that the excellent catalytic performance of Mn4Ni1 composite oxides could be ascribed mainly to the larger BET surface area and the richer content of surface‐adsorbed oxygen species, as well as stronger oxygen mobility and better reducibility compared with other Mn‐Ni catalysts.CONCLUSIONSThe Mn4Ni1 composite oxides showed a lowest T90 value of 172 °C (C6H6 concentration 200 ppm, WHSV 60 000 mL g−1 h−1) among all of the obtained Mn‐Ni composite oxides. Moreover, it also exhibited favourable catalytic stability at 210 °C in the presence or absence of moisture. © 2019 Society of Chemical Industry

Low-Temperature Benzene Abatement over Active Manganese Oxides with Abundant Catalytic Sites

Benzene is a typical volatile organic pollutant, and catalytic oxidation is promising for its abatement at low temperatures. Here, we prepared tunnel-structured hollandite-type manganese oxide (HMO) nanoparticles with abundant catalytically active sites (CASs). The HMO nanoparticles are more active than a traditional noble-metal catalyst, namely, Pt/Al2O3. The former catalyst can achieve 100% benzene conversion at 200 °C at a very high space velocity of 120 000 mL gcat–1 h–1. The results from relevant physicochemical characterizations and reaction kinetics studies demonstrate that the CASs are located at the tunnel openings of the HMO{001} surfaces. These CASs not only provide surface-active lattice oxygen species for benzene oxidation, but also efficiently activate O2 during the catalytic process. Moreover, HMO nanoparticles also have more CASs than HMO nanorods, thus leading to higher activity in benzene oxidation. This work may assist in the rational design of active transition-metal oxide catalysts fo...

Towards efficient Pd/Mn3O4 catalyst with enhanced acidic sites and low temperature reducibility for Benzene abatement

The activity of supported Pd catalyst as a result of metal oxide support (zinc, titanium, copper and manganese) is explored in the abatement of C6H6 in the gas-phase. The high-activity and cost-effective catalysts were synthesized utilizing impregnation assisted biosynthesis (IB) method. NH3-TPD, XRD, H2-TPR, TEM, XPS, O2 and Benzene-TPD, SEM and in situ DRIFT were done to probe their physicochemical characteristics and predict the plausible oxidation mechanism. Pd particle size and dispersion, and support active acid sites were the determining factors for activity. These factors markedly affected the catalyst ability to generate surface active O2 species from the metal oxides lattice station and controlled the benzene absorption/desorption rates. The as-synthesized Pd/Mn3O4-O with small crystallite size, good Pd dispersion, improved acid sites, and low activation energy (Ea = 45.3 kJ/mol) showed commendable O2 transportability and activity as low as 140 °C, GHSV of 120,000 mLg−1 h−1. Its T100 at 240 °C was similar to Pd supported on TiO2 but was 20, 40 and 60 °C better than Pd/Mn3O4-C, Pd/ZnO and Pd/CuO. In situ DRIFT studies showed that the main intermediate species benzoquinone are oxidized to CO2 and H2O through the alkoxide and acid sites. Moreover, it was stable and highly resistant to H2O vapor.

Enhanced removal of benzene in non-thermal plasma with ozonation, flow recycling, and flow recirculation

A double stage AC/DC sequential high voltage reactor has been developed to study the decomposition of benzene in the air stream at atmospheric pressure. The removal efficiency was measured as a function of ozonation, flow recycling, and flow recirculation. Ozonation in the inlet, and recycling of the exhaust stream increased the removal of benzene, also with increasing of specific input energy (J l−1) the effect of inlet flow ozonation on benzene decomposition was enhanced. The highest removal efficiency was obtained up to >99% in recirculation six times, while CO2 selectivity reached 99.9% and energy efficiency was 0.59 g kWh−1. O3 production/decomposition > production of OH radicals > electronic and ionic collisions were indicated as the main mechanisms influencing benzene abatement in this research.

Unique mesoporous amorphous manganese iron oxide with excellent catalytic performance for benzene abatement under UV-vis-IR and IR irradiation

Mesoporous amorphous manganese iron oxide exhibits excellent catalytic activity with UV-vis-IR and IR irradiation due to light-driven thermocatalysis and novel photoactivation.

Co3O4/TiO2 Nanocomposite Formation Leads to Improvement in Ultraviolet–Visible-Infrared-Driven Thermocatalytic Activity Due to Photoactivation and Photocatalysis–Thermocatalysis Synergetic Effect

Co3O4/TiO2 nanocomposites with different Co/Ti molar ratios were prepared by hydrolysis of cobalt acetate with urea in the presence of TiO2, and then calcined at 260 °C. Compared to pure TiO2, the Co3O4/TiO2 nanocomposite with the optimum Co/Ti molar ratio of 0.30 demonstrates significantly enhanced catalytic activity as well as excellent catalytic durability for abatement of refractory poisonous benzene (a typical air pollutant) with ultraviolet–visible-infrared (UV–vis-IR) irradiation. It also exhibits effective catalytic activity for benzene abatement even with λ > 830 nm IR irradiation. Its very high catalytic activity derives from light-driven thermocatalytic benzene oxidation on nano Co3O4 in the Co3O4/TiO2 nanocomposite. A novel synergetic effect among light-driven thermocatalysis on Co3O4 and UV photocatalysis on TiO2 in the Co3O4/TiO2 nanocomposite is discovered to remarkably promote catalytic activity and improve catalytic durability by inhibiting the formation of refractory carbonaceous interme...

UV–Vis–IR driven thermocatalytic activity of OMS-2/SnO2 nanocomposite significantly enhanced by novel photoactivation and synergetic photocatalysis-thermocatalysis

The OMS-2/SnO2 nanocomposite (OMS-2/SnO2) was synthesized with a facile redox reaction among SnSO4 and KMnO4 at 90 °C. OMS-2/SnO2 demonstrates very good photothermocatalytic activity as well as excellent photothermocatalytic stability for abatement of benzene (a typical refractory poisonous organic pollutant) under UV–Vis–IR illumination. It is found that the OMS-2/SnO2 nanocomposite formation causes a tremendous increase in the catalytic activity of SnO2. Compared to pure SnO2, the initial CO2 production rate of OMS-2/SnO2 for the photothermocatalytic benzene abatement is enhanced by 37.2 times. Under λ > 420, 480, and 690 nm Vis–IR illumination, OMS-2/SnO2 also shows good photothermocatalytic activity. The very good catalytic activity of OMS-2/SnO2 under the UV–Vis–IR illumination ascribes from the effective light-driven thermocatalytic benzene oxidation. It is discovered that the light-driven thermocatalytic activity is significantly promoted by a novel photoactivation on OMS-2 in OMS-2/SnO2: the lattice oxygen activity or reducibility of OMS-2 is promoted by Vis–IR illumination, thus its catalytic activity is significantly promoted. A novel synergetic effect among light-driven thermocatalysis on OMS-2 and UV photocatalysis on SnO2 is discovered to further promote the catalytic activity of OMS-2/SnO2.

Adsorption of Benzene by “Green” functionalization of Montmorillonite

The capacity of organically modified Montmorillonite (MMT) clay to adsorb nonpolar organic compound (benzene) in an aqueous solution, was investigated under the batch process. MMT was pretreated (centrifuged) and then functionalized with green intercalating agent i.e. 1-hexyl-3-methyl imadazolium chloride [HMim][Cl]. The characterization through Fourir Transoform Infrared Spectroscopy (FTIR), Differential Scanning Calorimeter (DSC) and Field Emission Scanning Electron Microscope (FE-SEM) confirmed the presence of the oxygen containing functional groups, changes in melting point and variation in the morphological properties. The governing parameters for the sorption of benzene such as the effect of contact time, pH, adsorbent dose and rotation were studied. The kinetic data conformed to pseuodo 2ndorder kinetic model and the isotherm experimental data were a better fit to Langmuir model with maximum adsorption capacity of 588.23mg/g under experimental conditions. Overall, MMT intercalated with 1-hexyl-3-methyl imadazolium chloride is a promising environmental friendly adsorbent for the abatement of benzene in an aqueous solution.

UV–Vis-infrared light-driven thermocatalytic abatement of benzene on Fe doped OMS-2 nanorods enhanced by a novel photoactivation

The catalysts of Fe doped cryptomelanetype octahedral molecular sieve (OMS-2, KMn8O16) with different Fe/Mn molar ratio of 0.079, 0.097, and 0.122 were prepared by a hydrothermal redox method. The Fe doping considerably enhances the catalytic activity of OMS-2 for the catalytic abatement of benzene as one of typical VOCs. The Fe doped OMS-2 catalyst exhibits much higher catalytic activity than pure OMS-2 and Pt/Al2O3 (a commercial precious metal catalyst). The considerable promotion in the catalytic activity of OMS-2 is ascribed to the significant enhancement in the lattice oxygen activity of OMS-2 induced by the Fe doping. Remarkably, under the full solar spectrum (UV–Vis-IR) illumination from a Xe lamp, the Fe doped OMS-2 catalyst exhibits high catalytic activity and excellent durability for benzene abatement. Its very high initial rate of CO2 production (rCO2, 602.2µmolmin−1g−1) is 4 and 179 times higher than that of OMS-2 and TiO2(P25) (a benchmark photocatalyst), respectively. Even under the λ>690nm visible-infrared (Vis-IR) illumination, the Fe doped OMS-2 catalyst still demonstrates high catalytic activity with the rCO2 of 44.3µmolmin−1g−1. The high catalytic activity of the Fe doped OMS-2 catalyst under UV–Vis-IR illumination derives from the efficient solar-light-driven (SLD) thermocatalysis. The SLD thermocatalysis is ascribed to the high thermocatalytic activity of the Fe doped OMS-2 catalyst and its efficient photothermal conversion because of its strong UV–Vis-IR absorption. It is found that the SLD thermocatalytic activity of the Fe doped OMS-2 catalyst is further enhanced by a novel photoactivation effect, which is completely unlike the well-known photocatalysis on photocatalytic semiconductors (e.g. TiO2).

Hybrid Plasma-Catalytic Oxidation of VOCs with NiMn/Montmorillonite: Plasma and Catalyst Considerations

Bifunctional nanocatalyst of NiMn over alkali activated montmorillonite was prepared with different Mn contents. The prepared catalysts were examined in hybrid plasma-catalytic system for oxidation of volatile organic compounds. The prepared catalysts were characterized by XRD, FESEM, BET, FTIR and EDX analyses. FESEM pictures showed complete and uniform coverage of montmorillonite with metal oxide particles in nano scale. Increasing Mn content from 0 to 9 wt% decreased the BET surface area from 31 to 18 m2 g−1. FTIR spectra illustrated just peaks of montmorillonite and Ni or Mn related peaks were not observed even at high concentrations of Mn. The highest VOC abatement was related to NiMn/montmorillonite with 6 wt% of Mn. This catalyst in hybrid plasma-catalytic oxidation could remove 92% of benzene from polluted air with initial benzene concentration of 1000 ppm in plasma voltage of 20 kV and 9.8 kHz of frequency. While using plasma without catalyst could just remove 74% of benzene in similar conditions. NiMn/montmorillonite nanocatalyst with 6 wt% of Mn was tested at different plasma voltages (10–30 kV) and the highest VOC removal was observed at a voltage of 20 kV. Among 1–9 min residence time, the longest residence time of 9 min had supreme abatement of benzene. Study on mixture of benzene, toluene and xylene in plasma-catalytic system illustrated the highest removal for xylene and the lowest removal for benzene in plasma environment of 20 kV and 9.8 kHz.

Anoxic biodegradation of BTEX in a biotrickling filter

Emissions of BTEX (benzene, toluene, ethylbenzene and xylene) from the petrochemical industry are characterized by a low pollutants concentration and the absence of oxygen. Biodegradation of these pollutants using nitrate as the electron acceptor is of key interest to reuse the residual gas for inertization purposes. However, the biological mineralization of BTEX is often limited by their recalcitrant nature and the toxicity of the secondary metabolites produced. The potential of an anoxic biotrickling filter for the treatment of a model O2-free BTEX-laden emission at inlet individual concentrations of ~700mgm−3 was here evaluated. A UV oxidation step was also tested both in the recycling liquid and in the inlet gas emission prior to biofiltration. Removal efficiencies >90% were achieved for both toluene and ethylbenzene, corresponding to elimination capacities (ECs) of 1.4±0.2gm−3h−1 and 1.5±0.3gm−3h−1, respectively, while ~45% of xylene (EC=0.6±0.1g m−3h−1) was removed at a liquid recycling rate of 2mh−1. Benzene biodegradation was however limited by the accumulation of toxic metabolites in the liquid phase. The oxidation of these intermediates in the recycling liquid by UV photolysis boosted benzene abatement, achieving an average EC of 0.5±0.2gm−3h−1 and removals of ~40%. However, the implementation of UV oxidation as a pretreatment step in the inlet gas emission resulted in the deterioration of the BTEX biodegradation capacity of the biotrickling filter. Finally, a high bacterial diversity was observed throughout the entire experiment, the predominant phyla being Proteobacteria and Deinococcus-thermus.

Efficient UV–vis-infrared light-driven catalytic abatement of benzene on amorphous manganese oxide supported on anatase TiO2 nanosheet with dominant {001} facets promoted by a photothermocatalytic synergetic effect

The nanocomposites of amorphous manganese oxide (MnOx) supported on anatase TiO2 nanosheet with dominant {001} facets (TNS) with different Mn/Ti molar ratio were prepared by hydrothermal redox reaction of KMnO4 and Mn(NO3)2 in the presence of TNS. The MnOx/TNS nanocomposites were characterized by XRD, SEM, TEM, ICP, XPS, BET, and diffuse reflectance UV–vis-Infrared adsorption. MnOx/TNS with the optimum Mn/Ti molar ratio of 0.40 exhibits highly efficient photothermocatalytic activity and excellent durability for the oxidation of the recalcitrant and carcinogenic benzene under the full solar spectrum irradiation from a Xe lamp. Remarkably, the CO2 production rate of MnOx/TNS enhances by 99 times as compared to TNS. Impressively, MnOx/TNS also exhibits efficient photocatalytic activity with the visible-infrared irradiation, even with the infrared irradiation. The highly efficient photothermocatalytic activity of MnOx/TNS under the full solar spectrum irradiation originates from the highly efficient solar light-driven thermocatalysis on MnOx due to its strong absorption in entire solar spectrum region and the efficient thermocatalytic activity, which is considerably promoted by a photothermocatalytic synergetic effect. We put insight into the photothermocatalytic synergetic effect by CO temperature-programmed reduction of MnOx/TNS in dark and with the solar light irradiation: the active species generated by the photocatalysis on TNS migrate to MnOx via the MnOx/TiO2 interface, and accelerate the solar light-driven thermocatalysis on MnOx in the nanocomposite.

Decomposition of Benzene Using a Pulse-Modulated DBD Plasma

To improve the energy yield (EY) of plasma volatile organic compound decomposition, a dielectric barrier discharge plasma driven by pulse-modulated AC power was used to experimentally study the abatement of benzene in atmospheric pressure air and at room temperature. The effects of the duty cycle on decomposition efficiency, EY, CO2 selectivity and the formation of ozone and NO2 were investigated. The results show that applying pulse modulation improves the EY and the CO2 selectivity and greatly reduces the wall temperature of the reaction chamber.

Novel photothermocatalytic synergetic effect leads to high catalytic activity and excellent durability of anatase TiO2 nanosheets with dominant {001} facets for benzene abatement

We studied the effect of reaction temperature on the photocatalytic activity of anatase TiO2 nanosheets with dominant {001} facets for the gas-phase photocatalytic oxidation of recalcitrant and carcinogenic benzene. It is found that the photocatalytic activity of the TiO2 nanosheets significantly enhances with increasing reaction temperature from room temperature to 240, and 290°C. Meanwhile, obvious thermocatalytic oxidation of benzene is observed on the TiO2 nanosheets in the dark when the reaction temperature increases above 240°C. The photothermocatalytic activity (CO2 production rate, rCO2-ptc) of the TiO2 nanosheets at 240 or 290°C under the irradiation of an Hg lamp is much higher than the summation of the photocatalytic activity (rCO2-pc) with the same UV light intensity at room temperature and thermocatalytic activity (rCO2-tc) at the same reaction temperature in the dark. This result indicates the presence of a photothermocatalytic synergetic effect between the photocatalysis and the thermocatalysis on the TiO2 nanosheets, thus significantly increasing the catalytic activity. The photothermocatalytic synergetic effect is further verified by in-situ FTIR spectra with CO as probe molecule: active species produced by photogenerated electrons and holes accelerate the thermocatalytic oxidation on the TiO2 nanosheets, thus significantly increasing the catalytic activity. Just by coating the sample of TiO2 nanosheets on the surface of the Hg lamp, we realized highly efficient photothermocatalytic oxidation of benzene with utilizing UV light and heating effect of infrared light from the He lamp without using additional heater. Under such photothermocatalytic condition, the photothermocatalytic activity (rCO2-ptc) of the TiO2 nanosheets increased by 42.3 times as compared to the photocatalytic activity (rCO2-pc) at room temperature with the same Hg lamp, and the TiO2 nanosheets exhibit excellent durability for benzene oxidation.