Activity For Toluene Oxidation Research Articles

Template and interfacial reaction engaged synthesis of CeMnO x hollow nanospheres and their performance for toluene oxidation.

A series of well-dispersed CeMnOx hollow nanospheres with uniform diameter and thickness were synthesized by a novel approach combining the template method and interfacial reaction. A SiO2 template was used as a hard template for preparation of SiO2@CeO2 nanospheres by solvothermal reaction. SiO2@CeMnOx could be formed after KMnO4 was reacted with SiO2@CeO2 by interfacial reaction between MnO4− and Ce3+. Among all the prepared catalysts, CeMnOx-3 with a moderate content of Mn (15 wt%) exhibited the lowest temperature for complete combustion of toluene (280 °C). Moreover, it showed high stability for 36 h with toluene conversion above 97.7% and good water tolerance with 5 vol% H2O. With characterization, we found that the reaction between Ce and Mn in the Ce–Mn binary oxides gave rise to increased Ce3+ and oxygen vacancies, which led to the formation of enhanced reducibility and more surface-absorbed oxygens (O22−, O2− and O−), and improved the catalytic performance further.

Atomically dispersed Ag on δ-MnO2viacation vacancy trapping for toluene catalytic oxidation

Atomic dispersion of Ag on δ-MnO2was achievedviaH2O2-induced Mn vacancy trapping. Single-atom Ag could activate adjacent lattice oxygen, facilitating methyl oxidation and benzene ring cleavage to improve toluene oxidation activity.

Study on spinel - typed catalyst NiCo2O4 for total oxidation of toluene

Toluene is a component of volatile organic compounds which need to be converted into non-poisonous one. Thus, we study the spinel-typed catalyst as NiCo2O4 for total oxidation of toluene because the advantage of spinel catalyst is multi- defective. Based on the sol-gel method, the catalysts NiCo2O4 were successfully prepared with different ratios of Ni/Co. The characteristic properties of catalysts were evaluated by XRD, BET, H2-TPR and EPR experiments. Amongst these ratios, the catalyst with ratio Ni/Co as 0.5 had the best activity in the total oxidation of toluene, as 100% conversion reached at 250 oC.

Enhanced catalytic performance for toluene purification over Co3O4/MnO2 catalyst through the construction of different Co3O4-MnO2 interface

Co 3 O 4 /α-MnO 2 , Co 3 O 4 /β-MnO 2, and Co 3 O 4 /γ-MnO 2 catalysts were successfully prepared by a secondary hydrothermal method to construct interfaces between different phase MnO 2 and Co 3 O 4 , and then comparatively studied the influences of different MnO 2 -Co 3 O 4 interfaces on the properties of the obtained Co 3 O 4 /MnO 2 catalysts. Combined with the results of various characterizations, it was clear that the MnO 2 -Co 3 O 4 interface enhanced the catalytic activity of α-MnO 2 to a greater extent compared to that of β-MnO 2 -Co 3 O 4 and γ-MnO 2 . • Co 3 O 4 -MnO 2 interfaces were prepared by a secondary hydrothermal method. • The impact of MnO 2 -Co 3 O 4 interfaces mainly lay in the content of Mn 3+ . • Co 3 O 4 /α-MnO 2 exhibited high and stable activity for toluene oxidation. • Co 3 O 4 /α-MnO 2 possessed greater redox performance and maximum defect concentration. Co 3 O 4 was successfully anchored on the surfaces of different phase MnO 2 to investigate the effects of different Co 3 O 4 -MnO 2 interfaces on catalytic combustion of toluene over Co 3 O 4 /MnO 2 catalysts. The results of various characterizations illustrated that the construction of Co 3 O 4 -MnO 2 interfaces significantly increased the vacancy contents of Co 3 O 4 /MnO 2 catalysts and improved their redox properties and lattice oxygen mobility, which greatly enhanced the abilities to catalyze the oxidation of toluene. In particular, the Co 3 O 4 -MnO 2 interface showed much stronger effects on Co 3 O 4 /α-MnO 2 and Co 3 O 4 /γ-MnO 2 compared to that on β-MnO 2 , which resulted in a more significant enhancement in the catalytic activity of Co 3 O 4 /α-MnO 2 and Co 3 O 4 /γ-MnO 2 . Moreover, Co 3 O 4 /α-MnO 2 , the best catalyst, could achieve toluene conversion of 90% at 248 °C, which decreased by 22 °C in comparison with the pure α-MnO 2 . More importantly, Co 3 O 4 /α-MnO 2 could completely oxidize toluene to carbon dioxide and water at 260 °C, while α-MnO 2 could not decompose toluene thoroughly within the test temperature. The 100 h on stream test showed that the Co 3 O 4 /α-MnO 2 had excellent stability and was a catalyst with great potential in practical applications. In addition, the in-situ DRIFTS results also showed that the presence of abundant oxygen vacancies contributes to the adsorption of toluene on the Co 3 O 4 /α-MnO 2 surface, methyl dehydrogenation and the formation of benzoate.

Insight into the effects of oxygen vacancy on the toluene oxidation over α-MnO2 catalyst

In order to clarify the role of oxygen vacancy (OV), five α-MnO2 catalysts with abundant OVs are fabricated via a novel and facile redox-precipitation approach and employed to the toluene oxidation in air. The concentration of OVs in α-MnO2 catalysts is regulated via the alkyl chain length of alcohols, and its correlation with catalytic performances is scientifically investigated based on various characterization technologies and density functional theory (DFT) calculation. The α-MnO2-C2 catalyst exhibits excellent catalytic activity (T90 = 217 °C), stability, and water resistance for toluene oxidation in air. The OVs can induce the new bandgap states (BGS), which upshift the antibonding orbitals relative to the Fermi level (Ef), eventually favoring the formation of adsorbed active oxygen species. Furthermore, the OVs cause an increase in the amount of Mn3+, resulting in the elongated Mn–O bonds due to the strong Jahn-Teller effect of Mn3+. Therefore, the synergistic effects of OVs benefit toluene oxidation through L-H and MvK mechanisms over the prepared α-MnO2-Cx catalysts. This work reveals the important role of OVs in the promotion of toluene catalytic oxidation activity and also may provide new insights for the design of high-performance VOCs oxidation elimination catalyst.

Investigation into the Phase–Activity Relationship of MnO2 Nanomaterials toward Ozone‐Assisted Catalytic Oxidation of Toluene

AbstractManganese dioxide (MnO2), with naturally abundant crystal phases, is one of the most active candidates for toluene degradation. However, it remains ambiguous and controversial of the phase–activity relationship and the origin of the catalytic activity of these multiphase MnO2. In this study, six types of MnO2 with crystal phases corresponding to α‐, β‐, γ‐, ε‐, λ‐, and δ‐MnO2 are prepared, and their catalytic activity toward ozone‐assisted catalytic oxidation of toluene at room temperature are studied, which follow the order of δ‐MnO2 > α‐MnO2 > ε‐MnO2 > γ‐MnO2 > λ‐MnO2 > β‐MnO2. Further investigation of the specific oxygen species with the toluene oxidation activity indicates that high catalytic activity of MnO2 is originated from the rich oxygen vacancy and the strong mobility of oxygen species. This work illustrates the important role of crystal phase in determining the oxygen vacancies’ density and the mobility of oxygen species, thus influencing the catalytic activity of MnO2 catalysts, which sheds light on strategies of rational design and synthesis of multiphase MnO2 catalysts for volatile organic pollutants’ (VOCs) degradation.

Catalytic enhancement of small sizes of CeO2 additives on Ir/Al2O3 for toluene oxidation

Catalytic combustion of VOCs is one of the most promising technologies for removal of VOCs. Developing new and highly performance catalyst is very important for the application of this technology. Here, we report the fabrication of catalysts Ir/Ce/γ-Al2O3 for complete oxidation of toluene, via confining the particles size of CeO2 additives. The catalysts are analyzed by XRD, H2-TPR, O2-TPD, TEM, HRTEM, XPS, Raman and in-situ DRIFTS. The catalyst Ir/Ce(A)/Al2O3 contains small CeO2 nanoparticles (<5 nm) loaded with ultrafine nanoparticles of Ir0 (<2 nm), exhibiting higher catalytic activity for toluene oxidation than the control catalyst with large CeO2 additives. The results from XRD, TEM, Raman and XPS show the formation of a strong interaction between the IrO2 and the small CeO2 nanoparticles, resulting in the enhanced catalytic activity. This novel means for synthesizing the iridium-based catalyst promises the catalytic oxidation of VOCs.

Unveiling the water-resistant mechanism of Cu(I)-O-Co interfaces for catalytic oxidation

The development of low-temperature and water-resistant heterogeneous catalysts without noble metals is vital in the effective treatment of atmospheric pollutants in practical application. Herein, we report that Cu(I)-O-Co interfaces of ultrafine CuOx on Co3O4 prepared by co-precipitation exhibit promising low-temperature activity and good water resistance. Experiment results together with density functional theory (DFT) calculations not only verify that Cu+ species are stabilized over Cu(I)-O-Co interfaces because of the strong interaction between Cu2O1 and Co3O4, but also demonstrate that the Cu(I)-O-Co interface facilitates oxygen species activation for promoting catalytic oxidation and reduces the accumulation of hydroxyl and bicarbonate species on the surface of CuOx/Co3O4. DFT calculations also reveal that the CO oxidation rate-limiting step via the dissociation pathway under dry conditions is the Co-OO-Cu species dissociation while the CO coupling with the adsorbed O2 becomes the rate determining step for CO oxidation through the direct pathway over Cu(I)-O-Co interface under humid conditions. Further, the CuOx/Co3O4 catalyst also exhibits superior and stable catalytic activity for toluene oxidation, comparable with partial supported noble metal catalysts (T90 = 190 °C). The present work gives a useful strategy for the rational design of low-temperature and water-resistant non-precious-based catalysts to be applicable in CO and toluene removal in practical applications.

Microwave-assisted synthesis of manganese oxide catalysts for total toluene oxidation

Oxygen vacancy on the heterogeneous catalyst is of great importance to the catalysis of volatile organic compound (VOC) oxidation. Herein, microwave radiation with special energy-excitation is successfully utilized for the post-processing of a series of manganese oxides (MnOx) to generate oxygen vacancies. It is found that the MnOx catalyst with 60 min of microwave radiation demonstrates higher activity for toluene oxidation with a T50% of 210 °C and a T100% of 223 °C, which is attributed to the higher concentration of oxygen vacancies derived from the rich phase interface defects resulted from the microwave radiation. Furthermore, the Mn-MW-60 catalyst possesses excellent thermal stability and water vapor tolerance even under 20 vol% H2O atmospheres within 60 h. In situ DRIFTS analysis verifies that both surface and lattice oxygen species simultaneously participate the oxidation process, and all reactions over different environments follows two different pathways. Meanwhile, it is proposed that those oxygen vacancies derived from microwave radiation could facilitate the rate-controlling step of opening the aromatic ring based on the electron back-donation, thereby leading to the increment of catalytic activity.

Optimized Synthesis Routes of MnOx-ZrO2 Hybrid Catalysts for Improved Toluene Combustion

In this contribution, the three Mn-Zr catalysts with MnxZr1−xO2 hybrid phase were synthesized by two-step precipitation route (TP), conventional coprecipitation method (CP) and ball milling process (MP). The components, textural and redox properties of the Mn-Zr hybrid catalysts were studied via XRD, BET, XPS, HR-TEM, H2-TPR. Regarding the variation of synthesis routes, the TP and CP routes offer a more obvious advantage in the adjustment of the concentration of MnxZr1−xO2 solid solution compared to the MP process, which directly commands the content of Mn4+ and oxygen vacancy and lattice oxygen, and thereby leads to the enhanced mobility of reactive oxygen species and catalytic activity for toluene combustion. Moreover, the TP-Mn2Zr3 catalyst with the enriched exposure content of 51.4% for the defective (111) lattice plane of MnxZr1−xO2 exhibited higher catalytic activity and thermal stability for toluene oxidation than that of the CP-Mn2Zr3 sample with a value of 49.3%. This new observation will provide a new perspective on the design of bimetal catalysts with a higher VOCs combustion abatement.

Co-immobilization of N-hydroxyphthalimide and cobaltous ions as a recyclable catalyst for selective aerobic oxidation of toluene to benzaldehyde

Selective aerobic oxidation of toluene to benzaldehyde has gained vast attentions due to its characteristics in environmental friendliness, atomic economy and a waiver of chlorine contamination. The separation, recovery and reuse of homogeneous catalysts will, however, be tricky. In this work, cobalt ions were immobilized by coprecipitation followed by a special washing, and the prepared cobalt-containing intermediate exhibited excellent textural properties and an exclusively low chemical state. 3-(Glycidoxypropyl) trimethoxysilicane (GPTMS) was used as a linking molecule to anchor N-hydroxyphthalimide (NHPI) onto the intermediate by C–O–N and Si–O–Si bonds, respectively, and a reliable covalent combination of NHPI was confirmed by the decomposition temperature and chemical states of N element in the co-immobilized NHPI/Co catalyst. The synthesized NHPI-GPTMS-CS catalyst exhibited a toluene conversion of 42.5% and a selectivity to benzaldehyde of 52.6% in hexafluoropropan-2-ol, which is much higher than the reactivity of toluene observed on the catalyst combination of commercial silica anchored NHPI (NHPI-GPTMS-SiO2) and homogeneous cobaltous ions, testifying an accessibility and a better synergy between N-oxyl radicals and cobaltous ions co-immobilized. There was no appreciable leaching of cobalt species and anchored NHPI observed for the co-immobilized catalyst and its activity for toluene oxidation was well remained, indicating an excellent reusable capability. It was observed that benzaldehyde is converted into benzoic acid, but benzyl alcohol into benzaldehyde and toluene via oxidation and disproportionation, respectively, over the synthesized co-immobilized catalyst. Toluene oxidation is suggested to proceed via a free radical mode and the produced water is one of the quenching agents.

Superior performance of Cu-Ce binary oxides for toluene catalytic oxidation: Cu-Ce synergistic effect and reaction pathways

A series of Cu-Ce binary oxides were synthesized via a facile co-precipitation method for toluene catalytic oxidation. The physicochemical properties of these samples were characterized by BET, XRD, SEM, TEM, H2-TPR, O2-TPD, and XPS. It reveals that Cu1Ce3 catalyst possesses a higher specific surface area, stronger Cu-Ce synergistic effect, and better low-temperature reducibility than other samples. Moreover, Cu1Ce3 catalyst exhibited superior toluene oxidation activity with 99.10% toluene removal efficiency and 97.28% CO2 selectivity at 200 °C, as well as satisfactory stability and moisture resistance. Therefore, Cu1Ce3 catalyst indicates a huge potential for practical applications, such as coal-fired flue gas and spray coating industry. The reaction pathways for toluene catalytic oxidation over the Cu1Ce3 catalyst were further illuminated by in-situ DRIFTs. In the main pathway, toluene molecules were firstly in contact with the interface lattice oxygen, then the abstraction of H atoms occurred on the methyl group, and benzyl alcohol is considered as the primary intermediate, during which the rate-determining step is the oxidation of benzyl alcohol. In the secondary pathway, a little proportion of toluene molecules were directly oxidized into benzoic acid by the chemisorbed oxygen species. In subsequent steps, all the intermediates were converted into CO2 and H2O. At last, it is confirmed that the toluene oxidation over Cu1Ce3 catalyst involves a Mars-van-Krevelen mechanism via this study.

Promotional effect of surface fluorine species on CeO2 catalyst for toluene oxidation

In this study, fluorine (F) modified cerium oxide (Fx-Ce) catalysts were prepared by co-precipitation method to investigate the impact of fluorine species on CeO2 catalyst for toluene oxidation. Compared to bared CeO2, the catalysis activity of Fx-Ce was further improved. The temperature of toluene conversion (T90% and T50%) for F3-Ce decreased by ΔT90% = 30°C and ΔT50% = 15°C, respectively. The characterizations of H2-TPR, O2-TPD, Raman, XPS certified that there was more chemisorbed oxygen, oxygen vacancies and Ce3+ ions on the F3-Ce than bared CeO2. DFT calculations demonstrated that the formation energy of oxygen vacancy on F3-Ce is reduced by surface-florine, which promotes the formation of oxygen vacancy. Meanwhile, Toluene-TPD indicated that fluorine-doping increased the adsorption capacity of toluene on CeO2. According to the above-mentioned results, F3-Ce has higher oxygen vacancy concentration, more active oxygen, and larger toluene adsorption capacity. Thus it has the optimal catalytic activity for toluene oxidation.

Toluene abatement on Ag-CeO2/SBA-15 catalysts: synergistic effect of silver and ceria

As a typical volatile organic compound, toluene is a hazardous material for human health and the environment, and currently, the development of catalysts for its oxidation into CO2 and water is crucial. The series of Ag-CeO2/SBA-15 catalysts is synthesized by wetness impregnation techniques and characterized by a number of physical-chemical methods (nitrogen [N2] physisorption, small angle X-ray scattering [SAXS], transmission electron microscopy [TEM], and temperature-programmed reduction [TPR]). The toluene sorption and catalytic properties in toluene oxidation are studied. Small silver [Ag] and cerium oxide [ceria, CeO2] particles with sizes below 3 nm are predominantly formed in the ordered structure of Santa Barbara Amorphous-15 [SBA-15]. The interactions between the Ag and CeO2 nanoparticles are established. Temperature-programmed desorption of toluene [TPD-C7H8] analysis shows that physical adsorption of toluene occurs on pristine SBA-15 material, while the introduction of either silver or ceria to SBA-15 leads to the appearance of additional strongly bound chemisorbed toluene on such sites. When both Ag and CeO2 are introduced, only chemisorbed toluene is formed over the Ag-CeO2/SBA-15 catalyst, and the highest catalytic activity in toluene oxidation is observed over this catalyst (T98% = 233 °C, 0.2% C6H5CH3) that is attributed to the synergistic effect of ceria [CeO2] and silver [Ag].

Efficient photocatalytic toluene selective oxidation over Cs3Bi1.8Sb0.2Br9 Nanosheets: Enhanced charge carriers generation and C–H bond dissociation

Inert C–H bonds activation at room temperature has been regarded as the control step in photocatalytic generation of valuable products from hydrocarbons. Herein, lead-free perovskite Cs3Bi1.8Sb0.2Br9 nanosheets with a proper amount of Sb in Cs3Bi2Br9 not only improves optical absorption due to anomalous band gap behavior, but also promotes the generation of holes (h+). The convergence of h+ on the surface of Cs3Bi1.8Sb0.2Br9 is crucial for the dissociation of toluene C(sp3)–H bond, which was proved by the density functional theory calculation and isotopic labelling results. The excellent activity in photocatalytic selective oxidation of toluene with a conversion rate of 5.83 mmol g−1h−1 under visible light is the highest ever achieved. This work sheds light on the modification of halide perovskites through the regulation of B-site cations for photocatalytic applications.

Enhanced Photocatalytic Activity for Selective Oxidation of Toluene over Cubic–Hexagonal CdS Phase Junctions

Enhanced Photocatalytic Activity for Selective Oxidation of Toluene over Cubic–Hexagonal CdS Phase Junctions

A highly dispersed Pt/copper modified-MnO2 catalyst for the complete oxidation of volatile organic compounds: The effect of oxygen species on the catalytic mechanism

Manganese oxide (MnO2) exhibits excellent activity for volatile organic compound oxidation. However, it is currently unknown whether lattice oxygen or adsorbed oxygen is more conducive to the progress of the catalytic reaction. In this study, novel hollow highly dispersed Pt/Copper modified-MnO2 catalysts were fabricated. Cu2+ was stabilized into the δ-MnO2 cladding substituting original K+, which produced lattice defects and enhance the content of adsorbed oxygen. The 2.03 wt% Pt Cu0.050-MnO2 catalyst exhibited the highest catalytic activity and excellent stability for toluene and benzene oxidation, with T100 = 160 °C under high space velocity (36,000 mL g−1 h−1). The excellent performance of catalytic oxidation of VOCs is attributed to the abundant adsorbed oxygen content, excellent low-temperature reducibility and the synergistic catalytic effect between the Pt nanoparticles and Cu0.050-MnO2. This study provides a comprehensive understanding of the Langmuir–Hinshelwood (L-H) mechanism occurring on the catalysts.

Catalytic Oxidation of Toluene into Benzaldehyde and Benzyl Alcohol Using Molybdenum-Incorporated Manganese Oxide Nanomaterials.

Oxidation of toluene (an organic pollutant), into useful chemical products, is of great interest nowadays. However, efficient conversion of toluene under mild and sustainable conditions is a thought-provoking task. Here, we report MnMoO4 nanomaterials (CH1–CH2), synthesized through a very facile solvothermal approach. Catalytic efficiencies of MnMoO4 nanomaterials were evaluated by direct oxidation of toluene via C–H activation. Toluene was converted into benzaldehyde and benzyl alcohol in the presence of H2O2 as an oxidant at 80 °C. The reaction parameters, that is, catalyst dose, time, and toluene concentration, were varied to obtain the optimal conditions for the oxidation process. The 40.62% maximum toluene conversion rate was obtained after 18 h of oxidation activity with 0.06 g of catalyst CH1. A maximum of 78% benzaldehyde selectivity was obtained with 0.06 g of catalyst CH1 after 18 h of toluene oxidation activity. Also, 62.33% benzyl alcohol selectivity was achieved using 0.1 g of catalyst CH1 after 1 h of activity. Several catalytic cycles were run with CH1 to evaluate catalyst reusability. Potential % toluene conversion was obtained for up to six cycles and their turnover frequencies were found to be 1.94–1.01 s–1. FTIR spectra of catalyst CH1 before and after recovery indicate no significant change. The good conversion rate of toluene and efficient selectivity toward benzaldehyde and benzyl alcohol indicates the robustness and high potential of these catalysts to oxidize toluene under a milder, greener, and hazardous chlorine-free environment.

Metal organic framework-templated fabrication of exposed surface defect-enriched Co3O4 catalysts for efficient toluene oxidation

Exposed surface defect-enriched Co3O4 catalysts derived from metal organic framework (MOF) were fabricated by the promotion of surface Mn species for toluene oxidation. The incorporation of Mn species into Co3O4 surface lattice could give rise to the local lattice distortion in spinel structure, resulting in highly exposed surface defect rather than bulk defect. More Co3+ species were also exposed on the surface of MnOx/Co3O4 samples owing to the electron transfer from Co to Mn species by the occupation of surface Mn in octahedral Co3+ sites. Accordingly, the low-temperature reducibility and high mobility of lattice oxygen were significantly improved in virtue of the highly exposed surface defect and predominately surface Co3+ sites, thus promoting the catalytic activity and stability for toluene oxidation. Moreover, the toluene conversion decreased with the increase of weight hourly space velocity (WHSV). In situ DRIFTS results confirmed the continuous oxidation process for toluene degradation, and the conversion of benzoate into maleic anhydride should be the rate-controlling step.

Simultaneously Enhanced Activity and Selectivity for C(sp3)\u2013H Bond Oxidation Under Visible Light by Nitrogen Doping

Selective oxidation of saturated C(sp3)–H bonds in hydrocarbon to target chemicals under mild conditions remains a significant but challenging task because of the chemical inertness and high dissociation energy of C(sp3)–H bonds. Semiconductor photocatalysis can induce the generation of holes and oxidative radicals, offering an alternative way toward selective oxidation of hydrocarbons under ambient conditions. Herein, we constructed N-doped TiO2 nanotubes (N-TNTs) that exhibited remarkable activity and selectivity for toluene oxidation under visible light, delivering the conversion of toluene and selectivity of benzaldehyde of 32% and > 99%, respectively. Further mechanistic studies demonstrated that the incorporation of nitrogen induced the generation of N-doping level above the O 2p valance band, directly contributing to the visible-light response of TiO2. Furthermore, hydroxyl radicals generated by photogenerated holes at the orbit of O 2p were found to be unselective for the oxidation of toluene, affording both benzaldehyde and benzoic acid. The incorporation of nitrogen was able to inhibit the generation of hydroxyl radicals, terminating the formation of benzoic acid.