Oxidation Of Volatile Organic Compounds Research Articles

Supported nano-sized precious metal catalysts for oxidation of catalytic volatile organic compounds.

Volatile organic compounds (VOCs) are common contaminants found as indoor as well as outdoor pollutants, which can induce acute or chronic health hazards to the human physiological system. The catalytic oxidation method is widely considered as one of the effective methods for removing VOCs, and the development of highly effective catalysts is highly urgent for booming this interesting field. This review focuses on the recent progress of VOC oxidation catalyzed by supported nano-sized precious metal catalysts, and discusses the effects of metal composition, supports, size, and morphology on the catalytic activity. In addition, the roles played by both nano-sized precious metals and supports in enhancing the performance of catalytic VOCs are also systematically discussed, which will guide the further development of more advanced VOC catalysts.

Performance and Reaction Mechanisms of Catalytic Combustion of Toluene and Ethyl Acetate Over Fe‐Mn Oxides

AbstractIn this paper, Fe−Mn oxide catalysts were prepared by the co‐precipitation method. (Fe2O3)‐(Mn3O4)‐3 : 1 showed the best catalytic activity in the degradation of toluene and ethyl acetate, with the removal rate reaching 90 % at 166 °C and 156 °C respectively. The XRD, SEM, TEM, and XPS characterizations revealed that the interaction between Fe and Mn and the higher surface adsorption of oxygen in the (Fe2O3)‐(Mn3O4)‐3 : 1 catalyst may be the main factors promoting the catalytic oxidation. (Fe2O3)‐(Mn3O4)‐3 : 1 exhibited a better removal rate in ethyl acetate than toluene at different space velocities, concentrations and water contents. Under the same conditions, the degradation rate of (Fe2O3)‐(Mn3O4)‐3 : 1 in ethyl acetate was also greater than that in xylene and butyl acetate, which was related to their oxidation processes. FT‐IR and GC‐MS characterizations of fresh and used (Fe2O3)‐(Mn3O4)‐3 : 1 catalysts revealed intermediates in the oxidation of volatile organic compounds, and the reaction mechanisms were analyzed: Firstly, VOCs molecules were adsorbed on the catalyst surface, then decomposed into organic intermediates and oxidized to CO2 and H2O finally.

Development of a multiphase chemical mechanism to improve secondary organic aerosol formation in CAABA/MECCA (version 4.7.0)

Abstract. During the last few decades, the impact of multiphase chemistry on secondary organic aerosols (SOAs) has been demonstrated to be the key to explaining laboratory experiments and field measurements. However, global atmospheric models still show large biases when simulating atmospheric observations of organic aerosols (OAs). Major reasons for the model errors are the use of simplified chemistry schemes of the gas-phase oxidation of vapours and the parameterization of heterogeneous surface reactions. The photochemical oxidation of anthropogenic and biogenic volatile organic compounds (VOCs) leads to products that either produce new SOA or are taken up by existing aqueous media like cloud droplets and deliquescent aerosols. After partitioning, aqueous-phase processing results in polyols, organosulfates, and other products with a high molar mass and oxygen content. In this work, we introduce the formation of new low-volatility organic compounds (LVOCs) to the multiphase chemistry box model CAABA/MECCA. Most notable are the additions of the SOA precursors, limonene and n-alkanes (5 to 8 C atoms), and a semi-explicit chemical mechanism for the formation of LVOCs from isoprene oxidation in the gas and aqueous phases. Moreover, Henry's law solubility constants and their temperature dependences are estimated for the partitioning of organic molecules to the aqueous phase. Box model simulations indicate that the new chemical scheme predicts the enhanced formation of LVOCs, which are known for being precursor species to SOAs. As expected, the model predicts that LVOCs are positively correlated to temperature but negatively correlated to NOx levels. However, the aqueous-phase processing of isoprene epoxydiols (IEPOX) displays a more complex dependence on these two key variables. Semi-quantitative comparison with observations from the SOAS campaign suggests that the model may overestimate methylbutane-1,2,3,4-tetrol (MeBuTETROL) from IEPOX. Further application of the mechanism in the modelling of two chamber experiments, one in which limonene is consumed by ozone and one in which isoprene is consumed by NO3 shows a sufficient agreement with experimental results within model limitations. The extensions in CAABA/MECCA are transferred to the 3D atmospheric model MESSy for a comprehensive evaluation of the impact of aqueous- and/or aerosol-phase chemistry on SOA at a global scale in a follow-up study.

Transpacific Transport of Asian Peroxyacetyl Nitrate (PAN) Observed from Satellite: Implications for Ozone.

Peroxyacetyl nitrate (PAN) is produced in the atmosphere by photochemical oxidation of non-methane volatile organic compounds in the presence of nitrogen oxides (NOx), and it can be transported over long distances at cold temperatures before decomposing thermally to release NOx in the remote troposphere. It is both a tracer and a precursor for transpacific ozone pollution transported from East Asia to North America. Here, we directly demonstrate this transport with PAN satellite observations from the infrared atmospheric sounding interferometer (IASI). We reprocess the IASI PAN retrievals by replacing the constant prior vertical profile with vertical shape factors from the GEOS-Chem model that capture the contrasting shapes observed from aircraft over South Korea (KORUS-AQ) and the North Pacific (ATom). The reprocessed IASI PAN observations show maximum transpacific transport of East Asian pollution in spring, with events over the Northeast Pacific offshore from the Western US associated in GEOS-Chem with elevated ozone in the lower free troposphere. However, these events increase surface ozone in the US by less than 1 ppbv because the East Asian pollution mainly remains offshore as it circulates the Pacific High.

In-Depth Understanding of the Oxidative Compatibility of Volatile Organic Compounds with Mn2O3 and Pt-Loaded Catalysts.

Designing suitable catalysts for efficiently degrading volatile organic compounds (VOCs) is a great challenge due to the distinct variety and nature of VOCs. Herein, the suitability of different typical VOCs (toluene and acetone) over Pt-based catalysts and Mn2O3 was investigated carefully. The activity of Mn2O3 was inferior to Pt-loaded catalysts in toluene oxidation but showed superior ability for destroying acetone, while Pt loading could boost the catalytic activity of Mn2O3 for both acetone and toluene. This suitability could be determined by the physicochemical properties of the catalysts and the structure of the VOC since toluene destruction activity is highly reliant on Pt0 in the metallic state and linearly correlated with the amount of surface reactive oxygen species (Oads), while the crucial factor that affects acetone oxidation is the mobility of lattice oxygen (Olat). The Pt/Mn2O3 catalyst shows highly active Pt-O-Mn interfacial sites, favoring the generation of Oads and promoting Mn-Olat mobility, leading to its excellent performance. Therefore, the design of abundant active sites is an effective means of developing highly adaptive catalysts for the oxidation of different VOCs.

Efficient Catalytic Elimination of Toxic Volatile Organic Compounds via Advanced Oxidation Process Wet Scrubbing with Bifunctional Cobalt Sulfide/Activated Carbon Catalysts.

Advanced oxidation process (AOP) wet scrubber is a powerful and clean technology for organic pollutant treatment but still presents great challenges in removing the highly toxic and hydrophobic volatile organic compounds (VOCs). Herein, we elaborately designed a bifunctional cobalt sulfide (CoS2)/activated carbon (AC) catalyst to activate peroxymonosulfate (PMS) for efficient toxic VOC removal in an AOP wet scrubber. By combining the excellent VOC adsorption capacity of AC with the highly efficient PMS activation activity of CoS2, CoS2/AC can rapidly capture VOCs from the gas phase to proceed with the SO4•- and HO• radical-induced oxidation reaction. More than 90% of aromatic VOCs were removed over a wide pH range (3-11) with low Co ion leaching (0.19 mg/L). The electron-rich sulfur vacancies and low-valence Co species were the main active sites for PMS activation. SO4•- was mainly responsible for the initial oxidation of VOCs, while HO• and O2 acted in the subsequent ring-opening and mineralization processes of intermediates. No gaseous intermediates from VOC oxidation were detected, and the highly toxic liquid intermediates like benzene were also greatly decreased, thus effectively reducing the health toxicity associated with byproduct emissions. This work provided a comprehensive understanding of the deep oxidation of VOCs via AOP wet scrubber, significantly accelerating its application in environmental remediation.

Pt-O-Ce interaction enhanced by Al substitution to promote the acetone degradation through accelerating the breaking of C[sbnd]C bond in acetic acid intermediate

The reaction rate of volatile organic compounds (VOCs) oxidation is controlled by the rate-limiting step in the total reaction process. This study proposes a novel strategy, by which the rate-limiting step of acetone oxidation is accelerated by enhanced chemical bond interaction with more electrons transfer through Al-substituted CeO2 loaded Pt (Pt/Al-CeO2). Results indicate that the rate-limiting step in the process of acetone oxidation is the decomposition of acetic acid. Al substitution enhances the Pt-O-Ce interaction that transfers more electrons from Pt/Al-CeO2 to acetic acid, promoting the breaking of its CC bond with a lower free energy barrier. Attributing to these, the reaction rate of Pt/Al-CeO2 is 13 times as high as that of Pt/CeO2 and its TOFPt value is 11 times as high as that of Pt/CeO2 at 150 °C. Moreover, the CO2 selectivity of Pt/Al-CeO2 also increases by 22 %. This work establishes the relationship between Pt-O-Ce interaction and acetone oxidation that provides novel perspectives on the development of efficient materials for VOCs oxidation.

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Promoting intermediates transformation by boosting H2O dissociation over core-shell Pd@CoO Janus for acetone efficacious oxidation

Reactivity loss by intermediates aggregation and water vapor inhibition are two major and longstanding challenges for the noble-metal-based catalysts in oxygenated volatile organic compounds (OVOCs) oxidation. Herein, the core-shell Pd@CoO Janus sites are creatively designed and stabilized over the HSAPO-34 support. Quasi in situ XPS spectra reveal that the strong interactions in Pd@CoO Janus sites promote the charge redistribution and electron back-donation through Pd-O-Co coordination. Therefore, abundant positively charged Pd2+ sites are formed and oxygen species transformation is facilitated, which significantly promote the low-temperature efficiency of acetone oxidation. Furthermore, the Pd@CoO/HSAPO-34 catalyst facilitates H2O molecules dissociation and produce reactive OHTer and OHTri species, which considerably promotes the rapid decomposition of aldehyde intermediate via attacked CH2O* group, ensuring low-temperature oxidation of acetone. This work provides valuable guidance to develop specific catalysts with functional active sites for rationally utilizing H2O molecules to improve low-temperature performance and modulate reaction pathways during OVOCs oxidation.

Impact of HO2∕RO2 ratio on highly oxygenated α-pinene photooxidation products and secondary organic aerosol formation potential

Abstract. Highly oxygenated molecules (HOMs) from the atmospheric oxidation of biogenic volatile organic compounds are important contributors to secondary organic aerosol (SOA). Organic peroxy radicals (RO2) and hydroperoxy radicals (HO2) are key species influencing the HOM product distribution. In laboratory studies, experimental requirements often result in overemphasis on RO2 cross-reactions compared to reactions of RO2 with HO2. We analyzed the photochemical formation of HOMs from α-pinene and their potential to contribute to SOA formation under high (≈1/1) and low (≈1/100) HO2/RO2 conditions. As HO2/RO2 > 1 is prevalent in the daytime atmosphere, sufficiently high HO2/RO2 is crucial to mimic atmospheric conditions and to prevent biases by low HO2/RO2 on the HOM product distribution and thus SOA yield. Experiments were performed under steady-state conditions in the new, continuously stirred tank reactor SAPHIR-STAR at Forschungszentrum Jülich. The HO2/RO2 ratio was increased by adding CO while keeping the OH concentration constant. We determined the HOM's SOA formation potential, considering its fraction remaining in the gas phase after seeding with (NH4)2SO4 aerosol. An increase in HO2/RO2 led to a reduction in SOA formation potential, with the main driver being a ∼ 60 % reduction in HOM-accretion products. We also observed a shift in HOM-monomer functionalization from carbonyl to hydroperoxide groups. We determined a reduction of the HOM's SOA formation potential by ∼ 30 % at HO2/RO2 ≈1/1 compared to HO2/RO2 ≈ 1/100. Particle-phase observations measured a similar decrease in SOA mass and yield. Our study shows that too low HO2/RO2 ratios compared to the atmosphere can lead to an overestimation of SOA yields.

Effect of Relative Humidity on the Rate of New Particle Formation for Different VOCs

Atmospheric new particle formation (NPF) is an important source of aerosol particles and cloud condensation nuclei, which affect both climate and human health. In pristine environments, oxidation of biogenic volatile organic compounds (VOCs) is a major contributor to NPF. However, the impact of relative humidity (RH) on NPF from these precursors remains poorly understood. Herein, we report on NPF, as inferred from measurements of total particle number density with a particle diameter (dp) > 7 nm, from three VOCs (sabinene, α-terpineol, and myrtenol) subjected to dark ozonolysis. From a series of comparative experiments under humid (60% RH) and dry (~0% RH) conditions and a variety of VOC mixing ratios (ξVOC, parts per billion by volume, ppbv), we show varied behavior in NPF at elevated RH depending on the VOC and ξVOC. In general, RH-dependent enhancement of NPF at an ξVOC between <1 ppbv and 20 ppbv was observed for select VOCs. Our results suggest that gaseous water at particle genesis enhances NPF by promoting the formation of low-volatility organic compound gas-phase products (LVOCs). This is supported by measurements of the rate of NPF for α-pinene-derived SOA, where RH had a greater influence on the initial rate of NPF than did ξVOC and ξO3.

Morphology effect of cerium dioxide on the catalytic performance of Ru/CeO2 catalyst for the oxidation of different CVOCs

CeO2 with different morphology of rod-shape (R-CeO2), cube-shape (C-CeO2) and octahedra-shape (O-CeO2) were synthesized as supports and impregnated with Ru to obtain Ru/CeO2 catalysts, and the performance of which in catalytic oxidation of different chlorine-containing volatile organic compounds (CVOCs) (1,2-dichloroethylene (DCE) and vinyl chloride (VC)) were investigated. Due to the stronger interaction between Ru and R-CeO2, Ru was highly dispersed on R-CeO2 and more Ru entered support lattice to form Ru-O-Ce structure, thus Ru/R-CeO2 catalyst exhibited better redox property. Ru addition enhanced the acidity of Ru/R-CeO2 and Ru/C-CeO2, while that of Ru/O-CeO2 decreased instead. The acidity mainly affected DCE catalytic activity when catalyst had sufficient redox property and chlorine resistance. Run+ content was the main factor affecting VC catalytic activity. Ru/R-CeO2 catalyst exhibited the best catalytic activity in both DCE and VC catalytic oxidation with T50 of 285 °C and 207 °C, respectively, due to its excellent redox property, acidity, and sufficient Run+. In situ DRIFTS suggested that DCE was first dissociated to VC and then oxidized to carboxylates, and the addition of Ru led to the oxidation of carboxylates to carbonyl and ultimately to complete oxidation to CO2 and H2O. Run+ was important for the oxidation of carboxylate intermediates.

Highly efficient catalytic oxidation of toluene by amorphous/microcrystalline mixed-phase MnO2

Amorphous transition metal oxides exhibit considerable potential in the catalytic oxidation of volatile organic compounds (VOCs) owing to their distinctive surface properties. In this study, we achieved the modulation of the crystalline structure of manganese oxides by employing various C3 alcohols (alcohols with three carbons) with distinct hydroxyl types during the reduction process with potassium permanganate. Subsequently, a series of characterization techniques were employed to assess the catalytic performance of the prepared MnO2 in the oxidation of toluene. Notably, the MnO2-G obtained from glycerol presented excellent catalytic activity (T90 = 219 °C), stability, and water resistance. The unique amorphous/microcrystalline state of MnO2-G exposed more phase boundaries, and the unsaturated coordination structure facilitated the generation of additional defective sites, favoring the adsorption and activation of oxygen. Furthermore, the mixed-crystalline state induced the elevated Mn3+ content on the surface of MnO2-G, leading to elongation of the Mn-O bond due to the pronounced Jahn-Teller effect of Mn3+. Consequently, the synergistic effects of the mixed crystalline state contributed to the efficient catalytic oxidation of toluene at relatively low temperatures. Additionally, the conversion pathway of toluene on MnO2-G was further revealed by in situ DRIFTS.

Ambient volatile organic compounds in the Seoul metropolitan area of South Korea: Chemical reactivity, risks and source apportionment

The chemical reactivity, contribution of emission sources, and risk assessment of volatile organic compounds (VOCs) in the atmosphere of the Seoul metropolitan area (SMA) were analyzed. Datasets collected from 6 photochemical assessment monitoring stations (PAMS) of SMA from 2018 to 2021 were used. Alkenes and aromatics contributed significantly to ozone formation relative to the emission concentrations, and aromatics accounted for most of the secondary organic aerosols (SOA) formation in the SMA. The contributions of ozone and SOA formation were found to be notably higher at measurement stations in residential areas such as Guwol (GW) and Sosabon (SS) compared to other measurement stations. From the results of an emission source analysis, it was confirmed that anthropogenic sources such as combustion sources, vehicle exhaust, fuel evaporation, and solvent use had a significant effect at all measurement stations. Assessing the health risk, non-carcinogenic compounds were at acceptable level at all measurement stations. On the other hand, carcinogenic compounds were approaching risk level (10−4), thereby demanding immediate attention. The level of exposure to carcinogenic compounds increased by age group, and male was more vulnerable than female. It was found that SS had the highest level of exposure to carcinogens in the atmosphere of the population ages 60 or older. The health threat of the SMA population is expected due to direct exposure from inhalation of ambient toxic compounds and indirect exposure from ozone and PM2.5 formations through oxidation of VOCs. This study emphasizes the importance of addressing specific emission sources within the metropolitan area and developing comprehensive regional strategies to mitigate VOCs.

A facile method for preparing the CeMnO3 catalyst with high activity and stability of toluene oxidation: The critical role of small crystal size and Mn3+-Ov-Ce4+ sites

Volatile organic compounds (VOCs) cause severe environmental pollution and are potentially toxic to humans who have no defense against exposure. Catalytic oxidation of these compounds has thus become an interesting research topic. In this study, microcrystalline CeMnO3 catalysts were prepared by a precipitant-concentration-induced strategy and evaluated for the catalytic oxidation of toluene/benzene. The effect of crystal size on catalytic performance was confirmed by XRD, TEM, N2 adsorption-desorption, XPS, Raman, H2-TPR, and TPSR. The CeMnO3 catalyst with more Mn3+-Ov-Ce4+ active sites exhibited enhanced VOCs catalytic oxidation performance, lowest active energy, and highest turnover frequency, which was attributed to its larger surface area, lower crystal size, higher low-temperature reducibility, and presence of more oxygen defects. In-situ FTIR results suggested more oxygen vacancies can profoundly promote the conversion of benzoate to maleate species, the rate-determining step of toluene oxidation. The work provides a convenient and efficient strategy to prepare single-metal or multi-metal oxide catalysts with smaller crystal sizes for VOC oxidation or other oxidation reactions.

Research progress of molecular sieve supported catalysts in catalytic oxidation of chlorine-containing volatile organic compounds

Chlorinated Volatile Organic Compounds (CVOCs) come from a wide range of sources and are common precursors of PM2.5 and ozone pollution, which pose a serious threat to the environment and have adverse effects on human health. Catalytic degradation is one of the effective methods to solve CVOCs pollution, which has the advantages of low operating temperature, less chlorine-containing by-products and high degradation efficiency. The core of this technology is to design and develop catalyst materials with excellent stability and catalytic performance. At present, molecular sieve catalysts have attracted extensive attention because of their acidity and unique pore structure. In this paper, the current research status of catalysts supported by molecular sieve, such as noble metals, transition metal oxides and perovskites, and their activity, acidity, stability and selectivity in CVOCs catalytic reactions were summarized and analyzed, and the future development direction of CVOCs molecular sieve supported catalysts was prospected.

Leaf-Level Bidirectional Exchange of Formaldehyde on Deciduous and Evergreen Tree Saplings.

Gas-phase formaldehyde (HCHO) is formed in high yield from the oxidation of many volatile organic compounds (VOCs) and is commonly used as a constraint when testing the performance of VOC oxidation mechanisms in models. However, prior to using HCHO as a model constraint for VOC oxidation in forested regions, it is essential to have a thorough understanding of its foliar exchange. Therefore, a controlled laboratory setup was designed to measure the emission and dry deposition of HCHO at the leaf-level to red oak (Quercus rubra) and Leyland cypress (Cupressus × leylandii) tree saplings. The results show that HCHO has a compensation point (CP) that rises exponentially with temperature (22-35 °C) with a mean range of 0.3-0.9 ppbv. The HCHO CP results are also found to be independent of the studied tree species and 40-70% relative humidity. Given that HCHO mixing ratios in forests during the daytime are usually greater than 1 ppbv, the magnitude of the CP suggests that trees generally act as a net sink of HCHO. Additionally, the results show that HCHO foliar exchange is stomatally controlled and better matches a reactivity factor (f0) of 0 as opposed to 1 in conventional dry deposition parametrizations. At 30 °C, daytime HCHO dry deposition fluxes are reduced by upward of 50% when using f0 = 0 and a nonzero HCHO CP, although deposition remains the dominant canopy sink of HCHO. A reduced deposition sink also implies the increased importance of the gas-phase photolysis of HCHO as a source of HO2.

Source and variability of formaldehyde in the Fenwei Plain: An integrated multi-source satellite and emission inventory study

Formaldehyde (HCHO) is a high-yield product of the oxidation of volatile organic compounds (VOCs) released by anthropogenic activities, fires, and vegetations. Hence, we examined the spatiotemporal variation trends in HCHO columns observed using the Ozone Monitoring Instrument (OMI) during 2005–2021 across the Fenwei Plain (FWP) and analysed the source and variability of HCHO using multi-source data, such as thermal anomalies. The spatial distribution of the annual mean HCHO in the FWP increased from northwest to southeast during 2005–2021, and the high-value aggregation areas contracted and gradually clustered, forming a belt-shaped distribution area from Xi'an to Baoji, north of the Qinling Mountains. The annual mean HCHO concentration generally showed a two-step increase over the 17 years. Fires showed a single-peak trend in March and a double-peak M-shaped trend in March and October, whereas urban thermal anomalies (UTAs) showed an inverted U-shaped trend over 17 years, with peaks occurring in May. The HCHO peaks are mainly caused by the alternating contributions of fires and UTAs. The fires and UTAs (predominantly industrial heat sources) played a role in controlling the background level of HCHO in the FWP. Precipitation and temperature were also important influencing variables for seasonal variations, and the influence of plant sources on HCHO concentrations had significant regional characteristics and contributions. In addition, the FWP has poor dispersion conditions and is an aggregated area for the long-range transport of air pollutants.

Co doping induced phase transition and its distinct effects on the catalytic performance of MnO2 toward toluene oxidation

Manganese oxides are very important and conventional catalysts that have demonstrated appreciable catalytic activity for the oxidation of volatile organic compounds (VOCs). Nevertheless, pure manganese oxides suffer from poor activity especially at low temperatures, making it difficult to meet industrial applications. In this work, Co species were successfully doped into the lattice of MnO2 aiming at constructing defects to boost its catalytic performance for VOCs oxidation. In combination with the results of systematic characterizations, we found that Co doping forced the catalyst to transform from α‐MnO2 to spinel phase (Co,Mn)(Co,Mn)2O4. During this process, the metal–oxygen bonds are significantly weakened, which induces the massive generation of oxygen defects, endowing the Co modified catalysts with enhanced redox property and improved ability to adsorb and activate gaseous oxygen. As a result, Co doped catalysts show much better catalytic activity compared with pristine α‐MnO2, among which Mn10Co10 exhibits the best performance showing a decrease of 41°C and 51°C in T50 and T90 compared with the raw sample, respectively. Furthermore, Mn10Co10 demonstrates excellent stability, water resistance, and reusability, illustrating a great potential for industrial applications. Moreover, path of toluene decomposition over Co10Mn10 was revealed by in situ DRIFTS experiment, which complies with the sequence of toluene → benzyl alcohol → benzaldehyde → benzoate → maleic anhydride → CO2 and H2O.

Chlorobenzene Oxidation over Phosphotungstic-Acid-Coated Cerium Oxide: Synergistic Effect of Phosphotungstic and Cerium Oxide and Inhibition Mechanism of Sulfur Dioxide

Ce–based catalysts exhibit a poor stability and activity in chlorinated volatile organic compound (Cl–VOC) oxidation due to their rapid Cl poisoning. Herein, phosphotungstic acid (HPW) was coated on CeO2 to improve its activity and stability for chlorobenzene (CB) oxidation. The HPW coating not only promoted CB adsorption onto CeO2, but also provided Brønsted acid sites to CeO2 for Cl species removal as HCl, thus avoiding Cl poisoning. Hence, a synergistic effect of CeO2 and HPW on HPW/CeO2 was observed, resulting in superior CB oxidation activity and stability. Additionally, to improve the sulfur resistance of the catalyst, the inhibition mechanism of SO2 on CB oxidation by HPW/CeO2 was explored. HPW/CeO2 was prone to sulfation due to the formation of Ce2(SO4)3 from the reaction of SO2 and CeO2. Thus, the oxidation ability of HPW/CeO2; the amount of adsorption sites for CB adsorption; and the amounts of Ce4+ bonded with O2−, lattice oxygen species, and adsorbed oxygen species were decreased by SO2. Meanwhile, SO2 competed with CB for the adsorption sites on HPW/CeO2. Therefore, CB oxidation by HPW/CeO2 was remarkably restrained by SO2. The present work promotes further work on Cl–VOC removal by Ce-based catalysts for anti-SO2 poisoning modification in the future.