Mechanism Of Toluene Oxidation Research Articles

Photothermal synergistic catalytic oxidation mechanism of toluene by Ce-doped SrTiO3 via one-pot hydrothermal synthesis

Industrial volatile organic compounds (VOCs) emissions pose significant environmental and human health risks, with photothermal catalysis degradation emerging as a promising VOCs treatment technology. The light response range and catalysis degradation efficiency of photocatalysts, however, need to be improved. This study prepared Ce-doped SrTiO3 perovskite catalysts via a one-pot hydrothermal method. The synergistic photic/thermal degradation mechanism of toluene was uncovered via XPS, Uv–Vis, EPR, and in-situ DRIFTS analysis. It was found that the toluene removal rate and CO2 yield reached their maximums at 200 °C, reaching 95 % and 90 %, respectively, at a Ce doping ratio of 50 %. During the catalytic process, the prerequisite to trigger toluene oxidation, and light promote the generation of reactive oxygen species (·OH and ·O2–), which facilitates the formation of intermediates and thus accelerates the deep oxidation of toluene. The doped Ce increases surface oxygen vacancies while lowering the energy band gap of the catalyst, facilitating the separation of holes and photogenerated electrons. Furthermore, in situ DRIFTS studies demonstrated that toluene undergoes a ring-opening process, producing intermediates such as benzaldehyde and benzoic acid. This study will assist in promoting the use of photothermal synergistic catalytic degradation technology to remove VOCs from industrial sources.

The promotional mechanism of Ce substituted A-site cation over YMn2O5 for toluene oxidation

Mullite-type YMn2O5 oxides have considerable potential for the removal of VOCs due to the abundance of lattice oxygen and the stability. The present study investigated the promotional mechanism of toluene oxidation by A-site cations of YMn2O5 with Ce. Y1-xCexMn2O5 was synthetized by sol-gel method and characterized with various techniques. The results revealed that samples doping with Ce could notably enhanced the toluene oxidation performance, and the toluene conversion of Y0.97Ce0.03Mn2O5 was 32% higher than that of YMn2O5 at 300 ℃. Detailed characterizations demonstrated that the modification of Ce produced an interface between YMn2O5 and YMnO3, the strong interactions at the interface improved the content of Mn3+ and oxygen vacancies, which promoted the toluene oxidation performance. Furthermore, the intermediate of toluene oxidation on Y0.97Ce0.03Mn2O5 was performed by in-situ DRIFTS. Toluene was sequentially oxidized to benzaldehyde, benzoic acid and maleic anhydride, ultimately produced H2O and CO2. This work offered a material science basis for the development of manganese-based mullite in thermal catalytic oxidation of toluene.

Insights into catalytic oxidation mechanism of toluene by lanthanum mangan-based perovskite in wet environment based on in-situ DRIFTS

This paper investigated that the catalytic activity and CO2 selectivity of LaMnO3, La0.9Ca0.1MnO3 and 3-La0.9Ca0.1MnO3 catalysts with different oxygen vacancy concentrations were compared under wet and dry conditions. The 3-La0.9Ca0.1MnO3 catalysts had excellent water resistance. The presence of H2O had less effect on toluene conversion than on CO2 selectivity. In wet environment, the 3-La0.9Ca0.1MnO3 catalyst achieved 90 % toluene conversion at 173 °C, but less than 20 % selectivity for CO2 at this time, and reached 90 % selectivity for CO2 at 220 °C. The effect of H2O on the catalytic oxidation mechanism of toluene was analyzed by in-situ DRIFTS analysis. The presence of H2O could promote the decomposition of toluene into intermediates of benzyl alcohol, benzoic acid, benzaldehyde and maleic anhydride at low temperature (50 °C), but the intermediates were difficult to decompose into CO2 and H2O. It was suggested that surface hydroxyl group could promote the transformation of toluene to intermediate at low temperature, and suitable oxygen vacancies and surface hydroxyl group could jointly promote the transformation of toluene to ideal product. This work provided a theoretical basis for the design of water-resistant catalysts in industry.

Catalytic combustion of toluene over highly dispersed Pt NPs embedded in porous TiO2 via in situ pyrolysis of MOFs

In this work, a series of x wt% Pt@TiO2 (x = 0.18, 0.42, and 0.84) catalysts with highly dispersed Pt nanoparticles (NPs) are synthesized via pyrolysis method using Ti-based metal-organic frameworks (MOFs) as precursors. Physicochemical properties of the catalysts are characterized by a number of analytical techniques. It is shown that all samples possess mesoporous structure with surface area of 59–75.6 m2/g, thus can suppress the aggregation of Pt NPs, and enhance toluene adsorption and diffusion. The 0.84 wt% Pt@TiO2 catalyst exhibits the best catalytic performance for toluene oxidation (T90% =150 °C at space velocity = 20,000 mL/ (g h)), which is attributed to the higher surface area, abundant adsorbed oxygen and Pt0 species, and strong interaction between Pt NPs and TiO2. In addition, the possible reaction mechanism of toluene oxidation is proposed based on in situ DRIFTS technique.

Simultaneous catalytic oxidation of toluene and CO over Cu-V/Al-Ce catalysts: Physicochemical properties-activity relationship and simultaneous oxidation mechanism

Cu-V/Al-Ce with varying ratios of Al2O3/CeO2 were prepared to study the simultaneous catalytic oxidation of toluene and CO. Experimental results show that Cu-V/20Al-80Ce exhibits optimal simultaneous oxidation activity and good durability. This superior performance is related to Cu-Ce, V-Ce, and Al-Ce interactions, which facilitate the exposure of active centers, the creation of oxygen vacanicies, and efficient electron transfer. The mutual influence between toluene and CO during the simultaneous oxidation is then demonstrated. Toluene hinders CO oxidation through the competitive adsorption and the consumption of reactive oxygen species. CO enhances toluene oxidation, which is comprehensively explained by affecting the competition between the desorption and oxidation of benzaldehyde. Despite the mutual influence between toluene and CO, the pathways of CO and toluene oxidation are mutually independent. Toluene oxidation proceeds sequentially from toluene to benzyl alcohol, benzaldehyde, benzoate, and finally to CO2. Before being completely oxidized to CO2, CO is initially converted to carboxylic acid, hydrogen carbonate, free carbonate ion, bidentate formate, and monodentate carbonate.

Catalytic Oxidation Mechanism of Toluene on the Ce0.875Zr0.125O2 (110) Surface

Aromatic volatile organic compounds (VOCs) are toxic to public health and contribute to global air pollution; thus, it is urgent to control VOC emissions. Catalytic oxidation technology has been widely investigated to eliminate aromatic VOCs; this technology exhibits high catalytic efficiency even at low temperatures. However, the reaction mechanism of aromatic VOCs’ total oxidation over metal-oxide-based catalysts, which is of great significance in the design of catalysts, is not yet clear. In this study, we systemically calculated the catalytic oxidation mechanism of toluene over the Ce0.875Zr0.125O2 catalyst using density functional theory (DFT). The results show that toluene first loses hydrogen from the methyl group via oxy-dehydrogenation and is gradually oxidized by lattice or adsorbed oxygen to benzyl alcohol, benzaldehyde, and benzoic acid following the Mars-van Krevelen (MVK) mechanism. Afterwards, there is a decarboxylation step to produce phenyl, which is further oxidized to benzoquinone. The rate-determining step then proceeds via the ring-opening reaction, leading to the formation of small molecule intermediates, which are finally oxidized to CO2 and H2O. This work may provide atomic-scale insight into the role of lattice and adsorbed oxygen in catalytic oxidation reactions.

Modification of Fe on hydrophobic ZSM-5 zeolite: Optimization of adsorption and catalytic performance for decomposition of VOCs at low-temperature

The conjugation of high adsorption and excellent catalytic characteristics is desirable for the removal of volatile-organic-compounds (VOCs) at low-temperatures. In this study, ZSM-5 zeolites with varying Si/Al ratios (15, 30, 100, and 200) were synthesized using the hydrothermal-method to assess their adsorption capability for VOCs. Among them, the ZSM-5(30) sample exhibited a well-defined zeolite structure, exceptional hydrophobicity, a high surface area (SBET), and micropores, resulting in a higher toluene adsorption capacity of 135 mg/g compared to other adsorbents. Additionally, the ZSM-5(30) sample demonstrated excellent regenerative stability in both dry and humid environments. Consequently, ZSM-5(30), identified as the most effective adsorbent, was subjected to loading with various amounts of Fe metal for the catalytic-oxidation of toluene at low-temperatures. Due to its abundant oxygen-vacancies, adequate acid-sites, and various active oxygen-species, the Fe0.2/ZSM-5(30) catalyst (Fe/(Si + Al) = 0.2) not only exhibited a high adsorption capacity for toluene with good stability over five successive cycles but also demonstrated excellent performance in the catalytic oxidation of toluene. The complete conversion of toluene was attained at temperatures approximately 200 °C, with a gas hourly space velocity (GHSV) of 20,000 mL/(g∙h), and maintained stability for 40 h. Furthermore, in-situ diffuse-reflectance infrared-Fourier-transform-spectroscopy (DRIFTS) and gas chromatography-mass spectrometry (GC–MS) results, along with the Mars-Van-Krevelen model, were utilized to elucidate the adsorption and oxidation mechanism of toluene. The unique adsorption and oxidation capabilities of Fe0.2/ZSM-5(30) for toluene indicate its promising potential for the removal of VOCs in real industrial-environments. This study provides valuable insights for the design of high-performance bifunctional materials for the adsorption and catalytic-oxidation of VOCs.

Thermally Inducing Viscous Fluids to Generate Co-Based Perovskites Enriched with Active Species for the Removal of VOCs.

Various Co-based perovskites are synthesized through thermally driving viscous fluids. In this process, rare earth salts, cobalt salts, and citric acid do not require homogeneous mixing but only need to be heated until they melt into a molten viscous slurry. The physicochemical properties of cobalt-based perovskites were examined using techniques such as X-ray diffraction (XRD), electron paramagnetic resonance (EPR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-Mapping-EDS), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), and N2 adsorption-desorption. The results indicate that the surface-active species can be controlled by altering the A-site elements of cobalt-based perovskites. All catalysts synthesized through the thermal treatment of viscous mixtures exhibited a low activation temperature and a low apparent activation energy for the catalytic oxidation of toluene. Among all cobalt-based perovskites, LaCoO3 demonstrated the most outstanding catalytic activity, primarily attributed to its capacity to expose a larger number of surface-active sites and oxygen species, as well as its superior reducibility. Furthermore, the formation process of optimal LaCoO3 was monitored using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), and the byproducts of the low-temperature catalytic oxidation of toluene by the catalyst were identified using gas chromatography-mass spectrometry (GC-MS). The possible mechanism of toluene oxidation was inferred by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Moreover, LaCoO3 exhibits a predominant resistance to high-temperature hydrothermal conditions. This work provides a scalable and innovative approach to fabricating exceptionally effective catalysts for the efficient purification of VOCs.

Bimetallic Fe-Mn loaded H-ZSM-5 zeolites for excellent VOCs catalytic oxidation at low-temperatures: Synergistic effects and catalytic mechanisms

The development of catalysts with high adsorption and low-temperature catalytic characteristics for the decomposition of volatile organic compounds (VOCs) is of great importance for air purification. Herein, H-ZSM-5 (proton form Zeolite Socony Mobil-5) zeolite -supported Fe-Mn elements were synthesized via a two-step procedure (hydrothermal and precipitation methods). These zeolite-supported bimetal Fe-Mn catalysts exhibited a mesoporous structure, uniform distribution of Fe-Mn elements, excellent catalytic-oxidation capacity for toluene at low-temperatures, and high stability. Due to interactive synergies between the bimetallic Fe and Mn, the Fe2-Mn1/H-ZSM-5 (ratio of Fe and Mn was 2:1 with a total amount of 15 % to H-ZSM-5) exhibited 100 % toluene-conversion at 200 °C and T90 = 195 °C (temperature of toluene-conversion at 90 %) with GHSV = 20,000 mL/(g∙h). Its distinguishing catalytic-oxidation abilities at low temperatures were due to abundant oxygen-vacancies, adequate acidic-sites and various active oxygen-species, which improved the adsorption of toluene and expedited its degradation. The Fe2-Mn1/H-ZSM-5 catalyst also demonstrated a good resistance to humidity and renewable catalytic properties over five cyclic tests. The in-situ DRIFTS and LC-MS results revealed that toluene was decomposed to benzyl-alcohol, benzaldehyde, benzoate-acid, formates or/and acetate step by step, and finally CO2 and H2O. The mechanism of toluene oxidation over Fe2-Mn1/H-ZSM-5 catalysts was proposed and elucidated via the Mars–van-Krevelen (MVK) model. This study comprehensively explored the adsorption and decomposition kinetics of VOCs over bimetal decorated H-ZSM-5, which was useful toward the design of highly efficient catalysts for the removal of VOCs.

Properties and characterization of red mud modified by hydrochloric, sulfuric, and nitric acid for the catalytic oxidation of toluene

In this paper, red mud (RM), a solid waste with high alkalinity generated by the alumina production industry, was modified using three different acids. The catalytic efficiency of HNO3-MRM was the best, and the T10, T50, and T90 were 280 ℃, 325 ℃, and 361 ℃, respectively. The CO2 selectivity of HNO3-MRM was better than those of HCl-MRM and H2SO4-MRM. Further, the HNO3-MRM catalyst maintained high stability at 420 ℃. This good catalytic performance of HNO3-MRM is related to its high specific surface area, Fe3+ content, surface adsorbed oxygen content, and surface acidic sites. The reaction rate linearly increases with the number of surface acidic sites on the catalyst, indicating that surface acidity is an important factor affecting the catalytic activity of toluene. H2SO4 solution forms calcium sulfate with Ca2+ in the RM, resulting in a lower catalytic activity for H2SO4-MRM. Fe2O3, Al2O3, and SiO2 were the main components of HNO3-MRM. Fe2O3 was the active component of the catalyst, which played the role of the catalytic oxidation of toluene. Al2O3 and SiO2 were used as catalyst carriers. Moreover, the catalytic mechanism of toluene oxidation over the HNO3-MRM catalyst was studied. The catalytic oxidation of toluene on HNO3-MRM catalysts may have two simultaneous reaction paths. The first reaction path would be toluene → species benzyl→ benzaldehyde→ benzoic acid→ heptaldehyde→ CO2 and H2O. The second reaction path would be toluene → benzene →phenol → maleic acid →CO2 and H2O.

Catalytic Oxidation Mechanism of Toluene over CexMn1-xO2: The Role of Oxygen Vacancies in Adsorption and Activation of Toluene.

Catalytic oxidation has been extensively studied as a promising technology for the removal of toluene from industrial waste gases and indoor air. However, the debate regarding the oxidation mechanism is far from resolved. CexMn1-xO2 catalysts with different mixing ratios are prepared by the sol-gel method and found to exhibit better catalytic activities for toluene oxidation than a single oxide. Characterizations and theoretical calculations reveal that the doped Mn increases the number of oxygen vacancies and the ability of oxygen vacancies to activate aromatic rings, which promotes the rate-determining step of toluene oxidation, i.e., ring-opening reactions. The oxidation products detected by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Vocus proton transfer reaction mass spectrometry (Vocus-PTR-MS) show that the doped Mn significantly improves the ring-opening efficiency and subsequently yields more short-chain products, such as pyruvic acid and acetic acid. A comprehensive oxidation pathway of toluene is refined in this work.

Pt–Co bimetals supported on UiO-66 as efficient and stable catalysts for the catalytic oxidation of various volatile organic compounds

Bimetallic catalysts exhibit excellent synergistic catalytic performance for volatile organic compounds (VOCs) oxidation. However, it remains challenging to design more active, selective, and stable bimetallic catalytic systems for the practical oxidation of various VOCs. Here, by integrating porous metal-organic frameworks as support, platinum as catalytic center, and cobalt as promoter, we obtained a synergistic and stable Pt–Co/UiO-66 catalytic system, with highly dispersed active sites for various VOCs oxidation. Pt–Co/UiO-66 exhibited better catalytic performances than monometallic constituents in toluene, n-hexane, and ethyl acetate oxidation. Besides, Pt–Co/UiO-66 showed high reusability, water or CO2 resistance, long-term activity over 120 h, and structural stability. Furthermore, the reaction pathway and mechanism of toluene oxidation were investigated by in-situ diffuse reflectance infrared Fourier transform spectroscopy and online gas chromatography-mass spectrometer. We believe that this work will provide a useful idea for developing effective bimetallic catalysts in environmental catalysis.

Insights into the reaction mechanism of toluene oxidation by isotope dynamic experiment and the kinetics over MCeZr/TiO2 (M = Cu, Mn, Ni, Co and Fe) catalysts

Catalytic properties of multiple metals deposited on TiO2 nanoparticles were investigated in the oxidation of toluene. Isovolume impregnation method prepared the catalysts containing Cu, Mn, Ni, Co, and Fe deposited on TiO2, including CeO2 and ZrO2. The effects of loaded metal oxides on the structure and activity of initial catalysts were investigated using various characterization techniques. Toluene's removal efficiency and CO2 selectivity in the catalyst system were classified as follows: CuCeZr/T > MnCeZr/T > NiCeZr/T > CoCeZr/T > FeCeZr/T. Presence of water vapor exhibits an inhibitory effect on the conversion of toluene, which diminishes at higher temperatures. One contribution of this paper is to obtain the oxidation pathway of toluene and the relationship between the activation energy of all-inclusive and elementary reactions based on the variation of infrared spectrum using Freeman-Carroll method. Another contribution is to clarify the share of Langmuir-Hinshelwood and Mars-van Krevelen mechanisms during the oxidation of toluene over CuCeZr/T catalyst by transient response experiments of isotopically labeled oxygen. These findings provide a feasible method for the design and synthesis of transition metal oxide catalysts for industrial applications.

High-efficiency palladium/halloysite nanotubes catalyst for toluene catalytic oxidation: Characterization, performance and reaction mechanism

In this study, the halloysite treated with nitric acid was designed as a functionalized support material for favoring surface availability and dispersion of nanometric palladium (Pd) nanoparticles. The prepared supported catalysts were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed desorption (O2-TPD). The catalytic performance and reaction mechanism of toluene oxidation were evaluated and proposed. Scanning and transmission electron microscopy images showed that 4–5 nm diameter Pd nanoparticles were uniformly dispersed on the external and edge surfaces of the A-Hal nanotubes and no obvious aggregations observed. The Pd nanoparticles were mainly present in the zero-valent state. The ratio of metallic Pd to Pd oxide species and adsorbed (Oads) to lattice (Olatt) presented a maximum value of 2.54 and 23.0, respectively, when the Pd loading was 0.5%. The prepared support catalysts exhibited a satisfactory catalytic performance and cycling stability for toluene conversion. Among the analyzed samples, the 0.5% Pd/A-Hal catalyst exhibited the highest catalytic activity for toluene oxidation, stability, and water resistance. Toluene conversions of 50% and 90% were obtained at 167 and 185 °C, respectively. In situ diffuse reflection Fourier transform spectroscopy measurements confirmed the intermediates generated during toluene oxidation and revealed that toluene oxidation occurred via the benzyl alcohol → benzaldehyde → benzoic acid → maleic anhydride reaction pathway over the obtained catalysts. These results were attributed to the high content of metal Pd species, abundant Oads species, and low-temperature reducibility. These results indicate that Hal support catalysts are promising materials for application in environmental protection.

An overlooked oxidation mechanism of toluene: computational predictions and experimental validations.

Secondary organic aerosols (SOAs) influence the Earth's climate and threaten human health. Aromatic hydrocarbons (AHs) are major precursors for SOA formation in the urban atmosphere. However, the revealed oxidation mechanism dramatically underestimates the contribution of AHs to SOA formation, strongly suggesting the importance of seeking additional oxidation pathways for SOA formation. Using toluene, the most abundant AHs, as a model system and the combination of quantum chemical method and field observations based on advanced mass spectrometry, we herein demonstrate that the second-generation oxidation of AHs can form novel epoxides (TEPOX) with high yield. Such TEPOX can further react with H2SO4 or HNO3 in the aerosol phase to form less-volatile compounds including novel non-aromatic and ring-retaining organosulfates or organonitrates through reactive uptakes, providing new candidates of AH-derived organosulfates or organonitrates for future ambient observation. With the newly revealed mechanism, the chemistry-aerosol box modeling revealed that the SOA yield of toluene oxidation can reach up to 0.35, much higher than 0.088 based on the original mechanism under the conditions of pH = 2 and 0.1 ppbv NO. This study opens a route for the formation of reactive uptake SOA precursors from AHs and significantly fills the current knowledge gap for SOA formation in the urban atmosphere.

Insight into the surface reaction mechanism of toluene oxidation over a composite CeOx/La1-xCexMnO3 catalyst using DRIFTS

In this work, La1-xCexMnO3 catalysts at different Ce concentrations were synthesized by the hydrothermal method, characterized and tested in the toluene oxidation reaction. The results show the formation of a composite catalyst of the CeOx/La1-xCexMnO3 type at Ce/Mn molar ratio > 0.3. In this composite catalyst, a synergistic effect promoting its catalytic activity was observed between CeOx and La1-xCexMnO3, which was enhanced by the existence of Ce3+ species in CeOX and promotion of Mn4+ species. A surface mechanism was proposed by in-situ DRIFTS measurements, which helped identify two different mechanisms by taking into account either the rich or poor surface active Olat present on the unsubstituted LaMnO3 catalyst and composite CeOx/La1-xCexMnO3 catalysts, respectively. According to the DRIFTS observations, the oxidation to benzoate species could be the most important step during the catalytic oxidation of toluene by the composite catalyst.

Boosting the VOCs purification over high-performance α-MnO2 separated from spent lithium-ion battery: Synergistic effect of metal doping and acid treatment

Spent lithium-ion batteries and VOCs both pose a significant threat to the environment and human health. In this work, a series of high-performance α-MnO2 catalysts with metal dopant and acid treatment are synthesized from acid leaching solution of cathode materials, which were separated from spent lithium-ion manganese battery (SLMB). Compared with pure α-MnO2, all SLMB-MnO2 (α-MnO2 prepared from SLMB) exhibit better catalytic activities of VOCs oxidation. Among them, SLMB-MnO2-2, with a molar ratio value of KMnO4 to Mn2+ of 2, exhibits the best catalytic activity (T90 = 224 °C and 297 °C for toluene and chlorobenzene oxidation, respectively). By comparison of their physicochemical properties, it can be found that SLMB-MnO2-2 possesses a larger specific surface and abundant mesopores, better redox ability at low temperature, much more generation of oxygen vacancies, and abundant adsorbed oxygen species. Moreover, the suitable dopant of copper and appropriate concentration of acid treatment play a synergistic role in enhancing the catalytic performance of VOCs oxidation on SLMB-MnO2-2. Furthermore, combined with in-situ DRIFTS and TD/GC–MS, the catalytic mechanism of toluene oxidation is explored on SLMB-MnO2-2.

DRIFTS investigation of toluene oxidation on CeO2 nanoparticles

The oxidation mechanism of toluene on the surface of heat-treated CeO2 nanoparticles was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). When introduced to the CeO2 surface, toluene either chemisorbs to an oxygen bound to a single cerium atom creating monobound (m) benzyloxy or to an oxygen bound to two neighboring cerium atoms forming bridged (b) benzyloxy. From the DRIFTS analysis, benzoate production is directly dependent on the presence and oxidation of b-benzyloxy groups. Using temperature dependent peak height analysis of the DRIFTS spectra, the oxidation state of specific vs(OCO) bands of bidentate (bdt) benzoate groups are identified through pairing with their va(OCO) counterparts. Surface lattice oxygens and b‑hydroxyl groups are found to facilitate the chemisorption of toluene as the two surface benzyloxy groups. Once toluene reacts with the substrate, surface hydroxyls react with m-benzyloxy groups to create additional b-benzyloxy groups as well as enabling the transformation of b-benzyloxy groups to bdt-benzoate groups. The previously unclear intermediate transformation steps of toluene to bdt-benzoate on the surface of CeO2 and surface hydroxyls species role in said transformation is unveiled through the use of peak height analysis of the collected DRIFTS spectra.

Reheat treatment under vacuum induces pre-calcined α-MnO2 with oxygen vacancy as efficient catalysts for toluene oxidation

Engineering α-MnO2 with abundant oxygen vacancies is efficient to enhance its catalytic activity towards toluene oxidation. A simple and facile method was introduced to fabricate oxygen vacancies on α-MnO2 surface by reheating the pre-calcined samples under vacuum condition. The reheat treatment especially at 180 °C is beneficial for the formation of oxygen vacancies on α-MnO2 surface, enhancing the oxidation of toluene. The toluene conversion is up to 100% at 270 °C, which is 30 °C lower than that of α-MnO2 without reheat treatment. The apparent activation energy (16.8 kJ mol−1) of MnO2-180 catalyst is lowest among these catalysts, which is essential for accelerating the oxidation of toluene. In-situ DRIFTS results indicate that the MnO2-180 sample promotes the formation of benzaldehyde and the occurrence of ring-opening reaction, thus effectively improving the catalytic performance for toluene oxidation. A possible catalytic oxidation mechanism of toluene over α-MnO2 catalysts after reheat treatment was proposed.

Uniform platinum nanoparticles loaded on Universitetet i Oslo-66 (UiO-66): Active and stable catalysts for gas toluene combustion

Highly dispersed Pt nanoparticles supported UiO-66 catalysts were successfully prepared by the incipient wetness impregnation method. Their thermal catalytic performances were evaluated by toluene degradation. The physicochemical properties of the samples were characterized using a series of characterization methods. The catalytic activity of catalysts remained essentially unchanged in the high weight hourly space velocity, stability and water resistance test, which also indicated good catalytic performance. In the reusability test, the catalytic performance was found to be enhanced after the reaction, because of the catalyst might follow a Pt0-PtO synergistic catalytic mechanism (similar to Mars-van Krevelen mechanism) and there was a phase transition between Pt0 and PtO during the reaction. Firstly, the toluene adsorbed on the catalyst surface was oxidized by the activated lattice oxygen of the PtO. Then, consumption of oxygen atoms led to formation of oxygen vacancies, and finally the molecular oxygen adsorbed by Pt0 was activated and passed to the PtO to supplement the oxygen vacancies, forming a redox cycle. In addition, the possible catalytic oxidation mechanism of toluene was also revealed.