Catalytic Combustion Of Toluene Research Articles

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.

Mn-Ag bimetals supported on plate-like ZSM-5 as efficient and stable catalysts for the catalytic combustion of toluene: Synergistic effects and catalytic mechanisms

Ag-modified MnO2 loaded on plate-like ZSM-5 (PZ5) with different Ag/Mn ratios were synthesized by an in-situ growth method and used as catalysts for toluene combustion, as a probe molecule of volatile organic compounds (VOCs). The results showed that Ag doping greatly enhanced the toluene combustion activity (Mn50Agy/PZ5). Among them, Mn50Ag0.04/PZ5 showed the highest catalytic activity for toluene combustion with 90 % conversion of toluene at 234 °C (T90), and the reaction rate calculated per unit mass of Mn was 1.22×10−7 at 220 °C, which was 2.7 times higher than that of MnO2. In addition, Mn50Ag0.04/PZ5 exhibited excellent long-term stability and water resistance. Various characterizations indicated that the excellent performance of Mn50Ag0.04/PZ5 was attributed to its higher Mn2++Mn3+/Mn4+ ratios, higher reducibility, and more active surface adsorbed oxygen species. Finally, in-situ DRIFTS studies confirmed that Ag doping did not alter the catalytic combustion pathway of toluene over the Mn50Ag0.04/PZ5 catalyst but could accelerate the rate of conversion of toluene to the final products because the transfer of electrons from Ag+ to lattice oxygen persuaded the weaken of the Mn-O bond, and then made it easier for bulk lattice oxygen to migrate towards the Ag-MnO2 interface or catalysts’ surface, thus showing the better catalytic performance for toluene combustion.

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.

Catalytic combustion of toluene performance over MnOx catalysts: Effect of KMnO4 content

MnOx samples were prepared and applied to the catalytic combustion of toluene. The results indicated that the KMnO4 content was important to the catalytic performance. Cat‐0.2 (0.2 g KMnO4) possessed the best catalytic performance, and more than 90% of toluene conversion was 255°C. Moderate amounts of KMnO4 facilitated the generation of mixed crystalline phases and structural defects, which led to the generation of more oxygen vacancies. In addition, the Cat‐0.2 possessed high contents of Oads/(Oads + Olatt) and Mn3+/(Mn3+ + Mn4+), which promoted the emergence‐annihilation cycle of oxygen vacancies and facilitated the reaction process of toluene. The reaction pathway of toluene was investigated via in situ DRIFTS, in which the by‐products included benzyl alcohol, benzaldehyde, benzoate, maleic anhydride, and short‐chain carbonate. Among them, benzoate was the main intermediate in the catalytic oxidation process of toluene.

Constructing surface oxygen defects at CuO–Co3O4 interface to boost toluene oxidation over CuO/Co3O4 catalysts

As a typical heterogeneous catalytic process, the catalytic combustion of toluene over Co3O4-based catalysts is strongly depends on the surface properties of catalysts, especially the concentration of surface oxygen defects. Here, a novel way was proposed to construct chemically bonded CuO–Co3O4 interface by chemical deposition of CuO onto Co3O4 nanoflowers. The interfacial refinement effect between CuO and Co3O4 support disrupted the ordered atomic arrangement and created countless unsaturated coordination sites at CuO–Co3O4 interface, inducing a significant generation of surface oxygen defects. Surface-rich oxygen vacancies enhanced the capacity of 20%CuO/Co3O4–R to adsorb and activate oxygen species. Benefiting from this, 90 % toluene conversion was reached at 228 °C over 20%CuO/Co3O4–R, which was much lower than that over 20%CuO/Co3O4–S prepared by impregnation method and CuO/Co3O4-mix obtained by mechanically mixing way. In-situ DRIFTS analysis revealed that toluene could be directly decomposed into benzaldehyde at the highly defective CuO–Co3O4 interface, leading to toluene oxidation following the path of toluene → benzaldehyde → benzoate → maleic anhydride → water and carbon dioxide over 20%CuO/Co3O4–R, which was significantly different from decomposition mechanism over 20%CuO/Co3O4–S. Additionally, 20%CuO/Co3O4–R displayed terrific recyclability and outstanding stability, showing good application potential.

Mesoporous Silica MCM-41 from Fly Ash as a Support of Bimetallic Cu/Mn Catalysts for Toluene Combustion.

The main outcome of this research was to demonstrate the opportunity to obtain a stable and well-ordered structure of MCM-41 synthesized from fly ash. A series of bimetallic (Cu/Mn) catalysts supported at MCM-41 were prepared via grinding method and investigated in catalytic toluene combustion reaction to show the material's potential application. It was proved, that the Cu/Mn ratio had a crucial effect on the catalytic activity of prepared materials. The best catalytic performance was achieved with sample Cu/Mn(2.5/2.5), for which the temperature of 50% toluene conversion was found to be 300 °C. This value remains in line with the literature reports, for which comparable catalytic activity was attained for 3-fold higher metal loadings. Time-on-stream experiment proved the thermal stability of the investigated catalyst Cu/Mn(2.5/2.5). The obtained results bring a valuable background in the field of fly ash utilization, where fly ash-derived MCM-41 can be considered as efficient and stable support for dispersion of active phase for catalyst preparation.

Catalytic combustion of toluene over cerium modified CuMn/Al2O3/cordierite monolithic catalyst

Catalytic combustion is an effective approach to remove volatile organic compounds, in which the development of highly active and durable catalyst is extremely crucial. Herein, a series of CuMnCex/Al2O3/cordierite monolithic catalysts were synthesized by using the ultrasonic-assisted impregnation method. The physicochemical properties were comprehensively characterized via the BET, XRD, SEM, EDX, H2-TPR, O2-TPD, XPS and EPR techniques. The results showed that the catalytic activity of CuMnCex/Al2O3/Cor for toluene combustion was strongly affected by the Ce content. The CuMnCe2/Al2O3/Cor monolithic catalyst showed the best catalytic activity with toluene conversion of 90% at 263 °C under toluene concentration of 1 g/L and space velocity of 78000 mL/(g·h). Meanwhile, the well-dispersed CeO2 in the CuMn matrix not only improved the content of oxygen vacancies and the mobility of oxygen species, but also enhanced the low-temperature reducibility of the catalyst. Moreover, the CuMnCe2/Al2O3/Cor monolithic catalyst exhibited an excellent stability in the long-term test and cycle ability test.

Engineering Co3O4@3DOM LaCoO3 multistage-pore nanoreactor with superior SO2 resistance for toluene catalytic combustion.

Sulfur dioxide poisoning is a significant factor in catalyst deactivation during the catalytic combustion of volatile organic compounds. In this study, we prepared the LaCoO3 and Co3O4 composite catalysts using both the Ship-in-Bottle and Building-Bottle-Around-Ship approaches. Three-dimensionally ordered macropores (3DOM LaCoO3) were utilized as nanoreactors to protect the active sites during the catalytic combustion of toluene, preventing SO2 poisoning. Additionally, we grew ZIF-67 confined in the nanoreactor to create a multistage-pore structure. The Co3O4@3DOM LaCoO3 catalysts exhibited excellent activity in the complete catalytic oxidation of toluene. Various characterization studies confirmed the presence of a significant number of Co3+ species and an abundance of surface weak acid sites in the Co3O4@3DOM LaCoO3 catalysts, which synergistically enhanced the conversion of VOCs at low temperatures. Notably, the multistage pore structure provided a favorable reaction environment, accelerating the adsorption and diffusion of toluene and intermediates, resulting in excellent sulfur resistance of the catalysts. Moreover, XPS analysis confirmed a strong interaction between Co3O4 and LaCoO3, promoting rapid electron transfer and increasing the activation of O2-. In situ DRIFTS experiments verified that toluene mainly follows the MvK mechanism over Co3O4@3DOM LaCoO3 catalysts, indicating the following reaction pathway: toluene adsorption → benzyl alcohol → benzaldehyde → benzoate → anhydride → CO2 and H2O.

Sulfur-tolerant mechanism in catalytic combustion of toluene over Co/5Mg-γ-Al2O3 catalyst: Dual functions of MgO

Using toluene catalytic combustion as a probe reaction, simulating quantitative sulfur poisoning by in situ thermal decomposition of ammonium sulfate solution, the study used MgO modified γ-Al2O3 to support cobalt-based catalyst, and the result displayed that the catalyst exhibited excellent sulfur poisoning resistance. The successful construction of MgO-Al2O3 heterogeneous interface weakened the interaction between Co and Al and reduced the production of inactive CoAl2O4. Besides that, it fixed sulfur species and formed MgSO4 to protect active components. The dual function of MgO have been proved by various characterization experiments. The modification of γ-Al2O3 by the appropriate amount of MgO could improve the catalytic activity of Co/γ-Al2O3. Meanwhile, T100 increased from 300 °C to 330 °C after 1.6 wt% sulfur poisoning and we concluded that the decrease in catalytic performance was not caused by the loss of active Co, but by the decrease of specific surface area and lattice oxygen activity.

Polymer template assisted construction of spherical Co3O4@meso-SiO2 yolk-shell nanoreactors for catalytic combustion of volatile organic compounds

Co3O4@SiO2 yolk-shell materials containing Co3O4 nanoparticles protected against aggregation and easily accessible for gaseous reactants inside a mesoporous SiO2 shell were developed for the catalytic combustion of volatile organic compounds (VOCs). Spherical polymer templates with an appropriate cation adsorption capacity were used as scaffolding for the construction of these structures by the bottom-up strategy. An application of polystyrene led to accumulation of introduced cobalt phase within the SiO2 layer and favored the formation of catalytically inactive Co silicate species. On the other hand, poly(maleic anhydride-co-divinylbenzene) modified with diethylenetriamine gave improved penetration of the composite interior by Co2+ cations and highly dispersed Co3O4 nanoparticles after calcination. The latter materials appeared excellent nanoreactors for the catalytic combustion of toluene. The real role of the active phase was determined by characterization of the developed catalysts with XRD, N2 adsorption, SEM-EDS, TEM, UV–Vis-DR, FT-IR, H2-TPR, isothermal oxidation-reduction analyses, XPS, XAS and electrochemical measurements.

Low-content Pt loading on a post-treatment-free zeolite for efficient catalytic combustion of toluene

One of the main techniques for removing volatile organic compounds (VOCs) from the environment is catalytic combustion technology. Noble metal-loaded Zeolite catalysts have a promising future in the field of VOCs catalysis. In this study, NaA, NaX, NaY and ZSM-5 were produced by a simple hydrothermal method, and Pt particles were loaded onto the zeolite. Among the four zeolite-supported Pt catalysts with similar loading loads, Pt/NaA has the best catalytic oxidation performance of toluene, and the total conversion of toluene can be achieved at 160 °C. At the same time, it has good repeatability, and stability. A series of characterizations indicate the synthesis of pure phase NaA zeolites and the presence of a number of acid sites, active oxygen and Pt0 species. The presence of these active substances promoted the adsorption and final oxidation of VOCs by the catalyst, which enabled Pt/NaA to exhibit the most excellent catalytic oxidation performance for toluene. In situ DRIFTS showed that surface reactive oxygen species in Pt/NaA acted as an important role in the catalytic oxidation of toluene. The preparation of high efficiency zeolite catalysts by simple synthesis method has broad future in the field of VOCs treatment.

Catalytic oxidation of toluene by binary metal oxide Cr2O3/CeO2 from MIL-101 (Cr)

Volatile organic compounds (VOCs) not only pollute the environment, but also seriously damage human health. Studies have shown that CeO2 doped with Cr and other metal elements can significantly improve its catalytic activity. In this paper, MIL-101 (Cr) was selected as the precursor of Cr2O3, and x wt%Cr2O3/CeO2 catalysts (x = 5, 10, 15) with different loadings were prepared by impregnation method. The physicochemical properties of the catalysts were characterized by XRD, SEM, BET, XPS and H2-TPR, and their catalytic performance was evaluated by toluene catalytic combustion. The results show that 10 wt%Cr2O3/CeO2 exhibits the best catalytic activity for toluene combustion, and the conversion of toluene can reach 90% at 263 °C. This can be attributed to the relatively high specific surface area (118 m2 g−1), the highest surface adsorbed oxygen content (Oads/Ototal = 0.251), oxygen vacancy content, more surface Ce3+ species and Cr6+ species, and the best low-temperature reducibility.

Oxygen vacancy engineering on copper-manganese spinel surface for enhancing toluene catalytic combustion: A comparative study of acid treatment and alkali treatment

Copper-manganese spinel is a low-cost VOCs catalytic combustion catalyst with good performance. Oxygen vacancy has excellent properties for oxygen activation and VOCs dehydrogenation activation, which is beneficial for the catalytic combustion of VOCs. In this study, a large number of oxygen vacancies were introduced on the copper-manganese spinel surface by selective dissolution method (acid treatment and alkali treatment) for catalytic combustion of toluene. Furthermore, the effects of acid treatment and alkali treatment on the catalytic performance, oxygen vacancy amount, physical and chemical properties, and toluene catalytic combustion mechanism of copper-manganese spinel were studied. Both acid treatment and alkali treatment can produce large quantities of oxygen vacancies on the copper-manganese spinel surface. The generation of surface oxygen vacancies can greatly improve the catalytic combustion activity of copper-manganese spinel. At 240 °C, the combustion rate of toluene increased by 8.8 times for the acid-treated catalyst and 11.2 times for the alkali-treated catalyst. The numerous surface oxygen vacancies, Mn3+/Mn4+ at the ratio of 1.11 and appropriate acidity result in the alkali-treated catalyst exhibiting excellent catalytic activity and stability for toluene combustion. This strategy provides a new method to further improve catalytic combustion activity of copper-manganese spinel and a reference for the development of the surface oxygen vacancy engineering of transition metal oxides.

One-pot solvothermal synthesis of highly dispersed, morphology- and crystal structure-tunable copper-manganese oxide for catalytic combustion of toluene at low temperatures

Copper-manganese composite oxide (CuMnOx) catalyst was prepared through an improved solvothermal reduction by short-chain dopamine (DA) with catechol structure for catalytic oxidation of toluene. The catalyst possessed the properties of controllable morphology, adjustable size, high dispersion and excellent catalytic activity. The regular hexagonal, square and spherical crystal particles with different crystal structures were synthesized by adjusting the molar ratio of copper and manganese during the reaction. Further investigation of the performance indicated that CuMnOx − 1 (Cu:Mn = 1:1) had high catalytic combustion activity with low temperatures of T50 (205 ℃) and T90 (221 ℃). Meantime, it has favorable stability with the basically unchanged conversion efficiency in 60 h of continuous testing.

Mesoporous Nanosized Manganese Dioxides for Efficient Toluene Oxidation

An efficient approach to synthetize the sandwich-like graphene-supported manganese oxides nanosheets (G-MnO[Formula: see text] had been developed for catalytic combustion of toluene by employing sandwich-like graphene-silica nanosheets (G-silica) as intermediates. The as-prepared G-MnO2 not only inherited the two-dimensional structure of reduced graphene, high specific surface areas, the unique mesoporous structure, good dispersion, but also possessed numerous nanoparticles of crystalline MnO2 with the size of about 5[Formula: see text]nm on each nanosheet. Such unique features had enhanced significantly the catalytic performance and catalytic stability of MnO2 for toluene oxidation. As a consequence, with the help of sandwich-like G-silica intermediates, the T[Formula: see text] and T[Formula: see text] of G-MnO2 for toluene was 240[Formula: see text]C (3.92[Formula: see text][Formula: see text][Formula: see text]mol [Formula: see text]g[Formula: see text][Formula: see text]h[Formula: see text] and 262[Formula: see text]C (7.06[Formula: see text][Formula: see text][Formula: see text]h[Formula: see text] respectively, and even after 30[Formula: see text]h at 288[Formula: see text]C, the conversion of toluene could still be maintained at 99.7% (GHSV[Formula: see text]60[Formula: see text]000[Formula: see text]mL[Formula: see text]g[Formula: see text][Formula: see text]h[Formula: see text].

Enhanced low-temperature catalytic combustion of toluene over Cu and Mn co-modified α-MnO2 with flower spheres

MnO2, MnO2-M and MnO2-CM were successfully obtained by one-pot hydrothermal method using different precursors, and were applied for the catalytic oxidation of toluene. A variety of characterization means were used to precisely define the physicochemical characteristics of these catalysts. The Cu and Mn co-modified MnO2-CM shows a nanosphere morphology which is made of worm-like particles. And it exhibits better low-temperature catalytic oxidation activity, long term activity stability and H2O resistance, in which the temperature of 90% toluene conversion is about 207 °C and the apparent activation energy of MnO2-CM is as low as 31.7 kJ∙mol−1. This is due to the strong interaction between Cu and Mn from the redox coupling reaction (Cu+ + Mn4+ ↔ Cu2+ + Mn3+) that contributes to produce more oxygen vacancies in MnO2-CM to enhance the gaseous oxygen activation and supplement of active oxygen species at low temperature, leading to stronger oxidation ability.

Revealing the ZrO2 crystal effect of Pd/ZrO2 catalyst for toluene combustion: A combined DRIFTS and DFT study

The effect of ZrO2 crystalline phases on Pd/ZrO2 for catalytic combustion of toluene was investigated. It was found that Pd/t-ZrO2 showed superior activity when the toluene concentration was lower than 2000 ppm, while Pd/m-ZrO2 performed better with toluene concentration higher than 3000 ppm. Kinetic studies showed that the reaction order of toluene on Pd/t-ZrO2 and Pd/m-ZrO2 is 0 and 2, respectively. The catalytic activity was controlled by combined effect of PdO activity and quantity, which was correlated with the interaction between palladium and zirconia. The t-ZrO2 increased PdO species activity, while m-ZrO2 could enhance the amount of PdO. DFT results showed that the p-band center of the O of PdO on t-ZrO2 was higher, suggesting that PdO was more active. In situ-DRIFTS revealed that the reaction pathway of catalytic oxidation of toluene on Pd/ZrO2 was as follows: toluene was oxidized stepwise to benzyl alcohol, benzaldehyde, benzoic acid, CO2 and H2O.

Study on the mechanism of sulfur poisoning in toluene catalyzed by Co3O4/γ-Al2O3 sulfur tolerant catalyst containing spinel structure

In this paper, in-situ thermal decomposition of ammonium sulfate method was used to cause sulfur poisoning of Co3O4/γ-Al2O3 catalyst rapidly and quantitatively. The pore structure, valence state of active species, surface morphology and acidity of the catalyst before and after sulfur poisoning were characterized, and its influence on catalytic combustion of toluene was studied. The results showed the crystal shape of the catalyst changed little after sulfur poisoning. As sulfur poisoning gradually deepened, the formation of sulfate blocked the pores, the high-valence cobalt decreased, strong acid sites increased, and its catalytic activity for toluene combustion gradually decreased. Formation of cobalt sulfate was a main reason for the decline in catalyst activity. Spinel phase CoAl2O4 formed outside γ-Al2O3 framework can adsorb a large amount of sulfur species to form sulfate, protecting Co3O4 and delaying the deactivation of catalysts.

Study on the performance and sulfur tolerance mechanism of Pd/beta zeolite in catalytic combustion of toluene

Based on the method of quantitative pyrolysis of ammonium sulfate, sulfur tolerance of Pd/beta zeolite in catalytic conversion of toluene was explored in this paper. Changes in pore structure, valence, acidity, oxidation, and adsorption/desorption behavior were investigated in detail through XRD, N2 adsorption, HRTEM-EDS, XPS, H2-TPR, and NH3-TPD before and after sulfur poisoning. The results proved the structural stability of Pd/beta zeolite in the process of sulfur poisoning. Combined with FT-IR and ICP characterization results, the possible sulfur poisoning process and the intrinsic sulfur tolerance mechanism of Pd/beta zeolite were revealed: Active PdO/Pd reacted with sulfur species to produce inactive PdSO4 was regarded as a major cause of partial deactivation of Pd/beta zeolite. AlO4 units in beta zeolite were likely to combine with sulfur species to obtain Al2(SO4)3 and generate more acidic sites, and SiO4 units in beta zeolite were structurally stable enough to resist sulfur corrosion, guaranteeing the stability of the catalyst. The catalyst catalytic performance was not seriously affected after deep sulfur poisoning, exhibiting good resistance to sulfur poisoning.

Insights into enhancing SO2 tolerance for catalytic combustion of toluene over sulfated CeZrOx supported platinum catalysts

Supported platinum catalysts are widely used in the catalytic combustion of volatile organic compounds due to their excellent catalytic activity, but SO2 poisoning is one of the critical problems for the industrial application. In this work, a series of sulfated ceria-zirconia composite oxides (CeZrOx) supported platinum catalysts (Pt/CeZr-S) were prepared through the support sulfation strategy. In the catalytic combustion of toluene, the Pt/CeZr-S catalyst with 0.5 wt% Pt and 15 wt% sulfuric acid loading amounts exhibited the significantly increased activity compared with the reference Pt/CeZr catalyst. Moreover, the tolerance to SO2 poisoning of Pt/CeZr-S catalyst was greatly improved in the presence of 50 ppm SO2. Various characterization methods including XPS, NH3-TPD and in-situ DRIFTS were performed to reveal the structure-activity relationship and SO2 tolerance mechanism. The higher concentration of metallic Pt0 species resulting from the interaction of Pt species and acidic CeZr-S support contributed to the enhanced catalytic activity. Meanwhile, the increased acidity strength and total acidity amounts over Pt/CeZr-S catalysts could affect the sulfation process, resulting in significant inhibition of the adsorption and further accumulation of sulfur species.