Catalysts For Oxidation Of Toluene Research Articles

A review on Fe2O3‐based catalysts for toluene oxidation: catalysts design and optimization with the formation of abundant oxygen vacancies

Volatile organic compounds (VOCs) are typical pollutants with hazards for humans and the environment, and can be efficiently mitigated by catalytic combustion. Fe2O3‐based catalysts are a promising choice due to their low cost and strong redox ability. Several attempts have been made to promote the catalytic performance of Fe2O3 at low temperatures. This review summarizes the research progress on Fe2O3‐based catalysts for the oxidation of toluene, one of the most common and harmful VOC. Firstly, the properties and catalytical performance for Fe2O3‐based catalysts were summarized, and the reaction mechanisms for toluene oxidation on the surface of Fe2O3 were detailed to comprehend the role of oxygen vacancy. Then, the modification for single Fe2O3 catalysts, including synthesis parameters, structure and morphology control, has been introduced to reveal the correlation between physicochemical properties of catalysts and their activity. In addition, composite Fe2O3 catalysts, which can promote catalytic performance significantly due to the synergetic effect between different components, were comprehended. Finally, waste‐derived Fe2O3 catalysts with sustainable merit as converting waste into worth have been discussed. Moreover, the advanced machine learning tools, which are helpful in accelerating catalyst design, configuration optimization and reactivity prediction, have been introduced as an emerging research opportunity for the future.

Light-driven photothermocatalytic performance of the Pt/Co3O4 catalyst for toluene oxidation

Light-driven photothermocatalytic oxidation is a promising method for the elimination of volatile organic compounds (VOCs). The Co3O4, 0.46 Pt/Co3O4 and 0.97 Pt/Co3O4 catalysts were fabricated via the simple molten salt and incipient wetness impregnation method. Compared with Co3O4 and 0.46 Pt/Co3O4, the 0.97 Pt/Co3O4 catalyst showed higher photothermocatalytic performance for toluene oxidation under simulated solar irradiation intensity of 900 ​mW ​cm−2, with the toluene conversion and CO2 yield being up to 98.3 % and 96.0 %, respectively. The better activity was ascribed to its outstanding strong light absorption and low temperature reducibility. Meanwhile, 0.97 Pt/Co3O4 also exhibited an excellent photothermocatalytic stability and H2O resistance. The Vis−IR light played a key role in the photothermocatalytic oxidation of toluene in the whole solar spectrum. This work benefited the synthesis of catalysts with good photothermocatalytic activity for environment friendly treatment of VOCs.

New insights into the catalytic mechanism of VOCs abatement over Pt/Beta with active sites regulated by zeolite acidity

Zeolite-supported noble metal catalysts have good low-temperature activity and efficacy in eliminating VOCs contaminants. Regulating the nature of active sites is beneficial for improving the catalytic oxidation performance and decreasing coke deposition for further increase in the durability. In this work, Pt/Beta catalysts for toluene oxidation with different valence states, location, and dispersion of Pt were achieved through regulation of active sites using the acidity of zeolites with different Si/Al ratios. It was revealed that Ptδ+ were highly dispersed on the low Si/Al ratio of 6 including isolated Z[Pt2+(OH)]+ originated from Pt2+ ions anchored on ion-exchange sites (strong Brønsted acid sites) of Beta zeolites, while Pt0 nanoparticles were the main active sites of Beta zeolites with the high Si/Al ratio of 260 without H2 post-treatment. The Pt/Beta catalysts with high silica had better catalytic oxidation performance than that with low silica because Pt0 had stronger activation ability towards O2 as well as more facile oxygen replenishment than Ptδ+. It was noted that the key role of OH groups led to the enhanced oxidation of toluene driven by water vapor. Both high-silica and low-silica Pt/Beta catalysts exhibited excellent durability for 60 h of operation with no detectable decrease in catalytic performance and followed similar toluene oxidation pathways, forming intermediates including alkoxides, carboxylates, and anhydrides. The difference was that the quantity of gaseous benzene generated on high-silica Pt/Beta was much lower than that on low-silica Pt/Beta, indicating that Pt0 rather than Ptδ+ was conducive to the benzene ring opening reaction. The strong ability of Pt0 to activate O2 and the reduction of Ptδ+ into Pt0 during the reaction process could be responsible for the excellent durability and similar reaction pathways towards both low-silica and high-silica Pt/Beta. This study provides guidance for the regulation of active sites and design of efficient zeolite-based catalysts for VOCs abatement.

Unravelling the role of oxygen species in toluene oxidation over Co3O4-base catalysts: In situ DRIFTS coupled with quasi in situ XPS

The present work elucidated the role of oxygen species in toluene oxidation over Co3O4-base catalysts. Co3O4 nanoneedles, nanoflowers, nanocubes, and nanoplates (denoted as Co3O4-n, Co3O4-f, Co3O4-c, and Co3O4-p) were employed to anchor Pt nanoparticles by an electrostatic adsorption method. The catalytic activity of the Pt/Co3O4 catalyst for toluene oxidation was significantly enhanced compared to that of Co3O4. Among these catalysts, Pt/Co3O4-p exhibited outstanding catalytic activity with the temperature for 90 % toluene conversion (T90 = 167 °C) at 82 °C lower than Co3O4-p (T90 = 249 °C). The low-temperature reducibility was obviously enhanced by the Pt nanoparticles, which weakened the Co-O bond energy, and improved the capacity of oxygen mobility and the concentration of surface adsorbed oxygen. The results of in situ DRIFTS demonstrated benzoate was identified as the dominant intermediate in toluene oxidation toward Co3O4-based catalysts. Furthermore, combined with the results of quasi in situ XPS showed that oxidizing toluene largely into benzoate primarily by the active adsorbed oxygen species at low reaction temperature (50 °C), mainly following the Langmuir-Hinshelwood mechanism, while oxidizing toluene into CO2 mostly by the lattice oxygen species at high reaction temperature (180–250 °C), largely following the Mars-van Krevelen mechanism.

Unravelling the correlation of dielectric barrier discharge power and performance of Pt/CeO2catalysts for toluene oxidation

Two “volcano” peaks in the relevant activity curve showcased that plasma discharge power had a significant impact on the activity of Pt/CeO2-Pxcatalysts and modulating discharge power could be regarded as an efficient method to optimize catalyst performance.

Dielectric barrier discharge plasma modified Pt/CeO2 catalysts for toluene oxidation: Effect of discharge time

This work demonstrated that a dielectric barrier discharge plasma was applied to modify the performance of catalyst. The Pt/CeO2 catalyst was treated with various plasma discharge time to reveal the effect of plasma on the performance of Pt/CeO2 catalyst for toluene oxidation. It is interesting that two volcanic peaks appeared at discharge time of 30 min (Pt/CeO2-PT3) and 3 h (Pt/CeO2-PT6). Compared to Pt/CeO2 without plasma treatment, their catalytic activities (T90) decreased by 24 °C for Pt/CeO2-PT3 and 34 °C for Pt/CeO2-PT6, respectively. By contrast, the Pt/CeO2-PT5 (2 h) showed the lowest activity due to the surface carbon deposition. We demonstrated that the plasma discharge time significantly affects the Pt particle size, CeO2-rod length, oxygen vacancies, and redox ability of the Pt/CeO2 catalyst by using the characterizations of X-ray power diffraction patterns (XRD), specific surface area (BET), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2-TPR). The linear relationship between catalytic activities and turnover frequency values (TOFPt and TOFOv) were observed in the discharge time ≤1 h. Furthermore, we found that discharge time has a more profound impact on oxygen vacancy than Pt particle.

Catalytic Oxidation of Toluene over Fe-Rich Palygorskite Supported Manganese Oxide: Characterization and Performance

A series of Fe–rich palygorskite supported manganese oxide (X%Mn–Pal) catalysts were prepared by co-precipitation method and used as catalysts for toluene oxidation. The components and structure of the as-prepared catalysts were characterized by XRD, Raman, TEM, XPS, and in situ DRIFTS. The results showed that the 15%Mn–Pal catalyst exhibited the highest catalytic activity (T90 = 227 °C) and excellent cycling stability for the oxidation of toluene compared with other catalysts. The characterization results indicated that remarkable activity of the 15%Mn–Pal catalyst for toluene oxidation should be ascribed to the abundant surface oxygen vacancies. In situ DRIFTS results elucidated that benzoate was the main intermediate, which can be further oxidized into H2O and CO2. The objectives of this study are to (i) investigate the synergistic effect between Fe and Mn for toluene oxidation, (ii) develop an efficient catalyst for toluene abatement with high activity and low–cost, and (iii) promote the application of natural Fe–rich palygorskite in the control of VOCs.

Controllable synthesis of MnO2/iron mesh monolithic catalyst and its significant enhancement for toluene oxidation

A series of monolithic MnO2/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth. MnO2 can grow firmly on the IM substrates surface with a shedding rate of only 0.14%. Due to the highest Oads and high-valent Mn4+ and Fe3+ elements, the temperature at 50% and 90% toluene conversion (T50% and T90%) was 252 and 265 °C, respectively for the best performance catalyst (hydrothermal temperature of 80 °C, hydrothermal time of 12 h, and precursor manganese ion concentration of 0.03 mol/L). The catalysts also presented good water resistance and cycle performance. In-situ DRIFTS results suggesting that toluene was first rapid transformed into the reaction intermediate species (benzoate species) and then converted to CO2 and H2O. Therefore, this work provides a new direction for the research and application of IM-based monolithic catalysts.

Low thermal oxidation of gaseous toluene over Cu/Ce single-doped and co-doped OMS-2 on different synthetic routes

In this study, cryptomelane-type manganese oxide (K-OMS-2) was used as a catalyst for the thermal oxidation of toluene. The catalyst was synthesized via the hydrothermal route and doped with Cu, Ce, and co-doped with the same metals by ex-situ and in-situ methods. The effects of dopant type, dopant concentration, and dopant impregnation method on the thermal catalytic activity of K-OMS-2 were examined. Initially, 1%, 2%, and 4% by mole Cu or Ce were incorporated by wet impregnation to the hydrothermally synthesized K-OMS-2 and in-situ direct hydrothermal method. The physicochemical properties were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and thermal gravimetric analysis (TGA) techniques. Gaseous toluene was made to react with the doped catalysts in a packed bed reactor attached to gas chromatography equipment to measure the amount of unreacted toluene. Results showed K-OMS-2 doped with 4% by mole Cu and 1% by mole Ce gave excellent thermal catalytic efficiency results at 180 °C reaction temperature. Meanwhile, K-OMS-2 co-doped with Ce and Cu with a mole ratio of 0.25:3.75 per 100 moles of K-OMS-2 gave the best catalytic activity and complete oxidation at 180 °C reaction temperature. Comparing K-OMS-2 doped with the same metal ratios, in situ doped catalysts led to higher toluene removal percentages. Meanwhile, the 72-h stability test showed that the optimum co-doped catalysts are capable of entirely oxidizing toluene even after prolonged and continuous use.

Vanadium(V) Complexes Supported on Porous Mil-100(Fe) as Catalysts for the Peroxidative Oxidation of Toluene

Vanadium(V) Complexes Supported on Porous Mil-100(Fe) as Catalysts for the Peroxidative Oxidation of Toluene

Construction of Cu-Ce interface for boosting toluene oxidation: Study of Cu-Ce interaction and intermediates identified by in situ DRIFTS

A facile hydrothermal method was applied to gain stably and highly efficient CuO-CeO2 (denoted as Cu1Ce2) catalyst for toluene oxidation. The changes of surface and inter properties on Cu1Ce2 were investigated comparing with pure CeO2 and pure CuO. The formation of Cu-Ce interface promotes the electron transfer between Cu and Ce through Cu2+ + Ce3+ ↔ Cu+ + Ce4+ and leads to high redox properties and mobility of oxygen species. Thus, the Cu1Ce2 catalyst makes up the shortcoming of CeO2 and CuO and achieved high catalytic performance with T50 = 234 °C and T99 = 250 °C (the temperature at which 50% and 90% C7H8 conversion is obtained, respectively) for toluene oxidation. Different reaction steps and intermediates for toluene oxidation over Cu1Ce2, CeO2 and CuO were detected by in situ DRIFTS, the fast benzyl species conversion and preferential transformation of benzoates into carbonates through C=C breaking over Cu1Ce2 should accelerate the reaction.

Modifying Y zeolite with chloropropyl for improving Cu load on Y zeolite as a super Cu/Y catalyst for toluene oxidation.

Developing an efficient catalyst is desirable when for example moving from a noble metal-based catalyst to a transition metal-based one for VOC removal. In this work, the chloropropyl-modified NaY zeolite (NaY-CPT) was first synthesized in an extremely dense system through introducing 3-chloropropyl-trimethoxysilane (CPT) in the aluminosilicate sol. Then the Cu/Y-CPT catalyst was fabricated by impregnating Cu species on the NaY-CPT zeolite and the highly effective Cu/Y based catalyst has been achieved for catalytic toluene oxidation. The structure evolution of CPT modified sol and its effect on texture properties of NaY-CPT and thereby reduction ability of Cu/Y catalyst were systematically investigated by synchrotron radiation small angle X-ray scattering (SR-SAXS), EXAFS and other characterization. The CPT modified sol can promote the formation of more active aluminosilicate species, greatly accelerating crystal growth and improving framework Si/Al ratio of NaY zeolite. Due to the presence of the CPT group, the Cu/Y-CPT catalyst enhanced the interaction between Cu species and the zeolite matrix, resulting in small sized CuO nanoparticles (2.0–4.0 nm) anchoring to NaY-CPT. The Cu/Y-CPT catalyst renders more isolated Cu2+ species and adsorbed oxygen species, which are reactive in the oxidation reaction due to their high reducibility and mobility. Finally, the Cu/Y-CPT catalyst exhibits 90% toluene conversion at 296 °C (T90), lower than the value of 375 °C on the conventional Cu/Y-con catalyst. Meanwhile, the optimal Cu/Y-CPT catalyst also gives higher toluene conversion and stability in moisture conditions.

Effect of Na+ on catalytic performance of CoCe/ZSM-5 catalysts for oxidation of toluene

A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene. To study the effect of Na+ on catalytic performance of CoCe/ZSM-5 catalysts, a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized. The experimental results show that 0.71 wt% Na+ can inhibit active growth, generate more active small crystal grains, and promote improvement of the catalytic activity by the grain boundary segregation block mechanism, and the catalyst with 0.71 wt% of Na shows toluene conversion of 90 vol% at 250 °C. Over 0.71 wt% of Na+ content will neutralize the acid centre of the catalyst, lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.

Effect of calcination temperature on properties of waste alkaline battery-based catalysts for deep oxidation of toluene and o-xylene

To evaluate waste alkaline battery (WB) as a catalyst for deep oxidation of toluene and o-xylene, we investigated how calcination temperature influenced the catalytic activity of WB-based catalyst for catalyst preparation. Physicochemical properties of WB-based catalysts were characterized by BET (Brunauer Emmett Teller) analysis, XRD (X-ray diffraction), SEM/EDX (scanning electron microscope/energy dispersive X-ray), TGA/DTA (thermo gravimetric analysis/differential thermal analysis), and H2-TPR (hydrogen temperature programmed reduction). Major elements of WB-based catalysts were carbon, manganese, zinc, and iron. The catalytic activity of WB-based catalyst was significantly influenced by calcination temperatures ranging from 300 °C–600°C. An increase calcination temperature resulted in a significant decrease in the BET surface area and concentrations of surface carbon and chlorine of the WB-based catalyst, while levels of other components increased. The average pore diameter of the WB-based catalyst calcined at 400 °C (WB (400) catalyst) was the smallest. The concentrations of manganese and iron in WB (400) catalyst were the highest, while those of manganese and iron in the WB-based catalyst calcined at 300 °C (WB (300) catalyst) were the lowest. Therefore, a good performance of WB (400) catalyst was likely due to its higher concentrations of manganese and iron and smaller pore size. When GHSV (gas hourly space velocity) was 40,000 h−1, toluene and o-xylene were completely oxidized on WB (400) catalyst at 430 °C and 440 °C, respectively.

Designing a dumbbell-brush-type Co3O4 for efficient catalytic toluene oxidation

A series of cobalt oxide (Co3O4) catalysts in dumbbell-brush-type, mesoporous nanosheets and nanorods morphologies were successfully prepared and used as catalysts for toluene oxidation. Tailoring Co3O4 morphology not only changed their physico-chemical properties but also remarkably enhanced their catalytic performance, and the formation of oxygen species of different reactivity. Dumbbell-brush-type Co3O4 exhibited the best catalytic activity due to abundant surface Co3+ species, which contributed to superficial oxygen mobility and the formation of more reactive oxygen species. In situ DRIFTS studies confirmed the presence of key reaction intermediates, such as benzaldehyde, benzoate, carbonate and formate species.

Pt/Al2O3 with ultralow Pt-loading catalyze toluene oxidation: Promotional synergistic effect of Pt nanoparticles and Al2O3 support

A kind of highly efficient and low cost supported-Pt catalyst for oxidation of toluene is obtained through controlling both the chemical state of Pt active sites and surface properties of supports. The optimized Pt/Al2O3 catalyst with Pt loading as low as 0.1 wt% could completely convert toluene (1000 ppm) to CO2 at about 180 ℃ under a space velocity of 24,000 mL g−1 h−1. It also exhibits a high stability and moisture resistance properties under reaction atmosphere. TOF value calculated with the dispersion of Pt can reach 0.0685 s-1, representing a high utilization efficiency of Pt. A series of characterizations are carried out to investigate the key factors affecting the catalytic performance of Pt/Al2O3, and disclose the concrete role of Pt and Al2O3 in the activation of molecular oxygen and toluene. In situ DRIFTS and EPR results show that Pt is the active center for O2 activation. Metallic Pt nanoparticles (Pt0) can activate the molecular O2 even at room temperature. Al2O3 offers sites for the adsorption of toluene and desorption of CO2 product. The weak and medium strength of acid-base sites favorite the adsorption and desorption process. The oxidation of toluene over Pt/Al2O3 obeys modified L-H mechanism. The synergistic effect of metallic Pt nanoparticles and suitable Al2O3 support is critical for obtaining highly efficient Pt-based catalysts with low Pt contents for toluene oxidation.

Facile synthesis of NaOH-promoted Pt/TiO2 catalysts for toluene oxidation under visible light irradiation

NaOH-promoted Pt/TiO2 catalysts are successfully prepared by a facile impregnation method assisted by NaOH and tested for the toluene oxidation reaction under visible light irradiation. Keeping molar ratio of Pt:Na = 1:8, the 0.1Pt-Na/TiO2 catalyst (0.1 mol% Pt) shows excellent catalytic performance with more than 60% of toluene conversion at 45 °C and achieving total toluene removal at 280 °C, which is significantly better than 0.1Pt/TiO2 catalyst. The structures and properties of catalysts are characterized by XRD, SEM, N2 adsorption, XPS and UV–vis spectra. The positively charged Pt species stabilized by NaOH are the most active sites for photo-thermal catalyzing toluene oxidation. The influence of Pt loading and the effect of supports (active TiO2 and inert Al2O3) are also discussed.

Effect of pretreatment conditions on catalytic activity of Ag/SBA-15 catalyst for toluene oxidation

The catalytic oxidation of toluene over Ag/SBA-15 synthesized under different pretreatment conditions, including O2 at 500 °C (denoted O500), H2 at 500 °C (H500), and O2 at 500 °C followed by H2 at 300 °C (O500-H300) was studied. The pretreated samples were investigated by N2 physisorption, X-ray diffraction, and ultraviolet-visible diffuse reflectance. The pretreatment atmosphere greatly influences the status of the Ag and O species, which in turn significantly impacts the adsorption and catalytic removal of toluene. Ag2O and amorphous Ag particles, as well as a large amount of subsurface oxygen species, are formed on O500, and the subsurface oxygen enhances the interaction between Ag species and toluene, so O500 shows good activity at higher temperature. However, its activity at lower temperature is not as high as expected, with a reduced presence of Ag2O and lower adsorption capacity for toluene. H2 pretreatment at 500 °C is conducive to the formation of large Ag particles and yields the largest adsorption capacity for toluene, so H500 exhibits the best activity at lower temperatures; however, because of poor interaction between Ag and toluene, its activity at higher temperature is modest. The O500-H300 sample exhibits excellent catalytic activity during the whole reaction process, which can be attributed to the small and highly dispersed Ag nanoparticles as well as the existence of subsurface oxygen.

Insight into the enhanced performance of TiO2 nanotube supported Pt catalyst for toluene oxidation

Featuring an assembly of identical pores, TiO2 nanotube array (TiNT) makes an ideal monolith-like support of noble metal catalysts for volatile organic compounds combustion. Herein, the deep oxidation of gaseous toluene over Pt/TiNT and anatase TiO2 (ATiO2) particles supported Pt catalysts are studied and compared. Pt/TiNT demonstrates remarkably enhanced performance over Pt/ATiO2 powder catalyst, and ranges among the best performances of the state of the art Pt based catalysts. A toluene conversion of (>)95% at 185°C and a multiple heating-cooling cyclic stable performance with a time of (>)300h are achieved over 0.4wt% Pt/TiNT. In situ DRIFTS study indicates that toluene is sequentially oxidized to benzaldehyde, benzoate, aliphatic carboxylates species, CO and finally to CO2, and the decomposition of benzoate species is the key step. The unique performance of Pt/TiNT is attributed to its ordered monolith-like structure, well-dispersion and surface enrichment of Pt, and enhanced benzoate species decomposition rate.

Activity of catalysts consisting of Fe2O3 nanoparticles decorating entire internal structure of mesoporous Al2O3 bead for toluene total oxidation

Fe2O3 nanoparticles with a mean size of ∼1nm were evenly distributed inside the mesoporous Al2O3 with a diameter of ∼1mm using temperature-regulated chemical vapor deposition (TR-CVD), in which Fe(Cp)2 vapor and air were use as metal precursor and oxidizing agent, respectively. For comparison, NiO/Al2O3 was prepared by a similar method using Ni(Cp)2 vapor as Ni precursor, and the resulting structure showed NiO nanoparticles decorating only the shell part of the Al2O3 bead with a shell depth of ∼50μm. After post-annealing of these samples under air at 450–750°C, these structures were used as catalysts for oxidation of toluene in the reaction temperature range of 150–350°C. Fe2O3/Al2O3 showed significantly higher catalytic activity than NiO-based catalysts, which can be attributed to the unique structure of Fe2O3/Al2O3, i.e., very small catalytically active nanoparticles are distributed inside the entire structure of the mesoporous supporting material. 100% conversion of toluene into CO2 with a long-term stability of the catalytic activity was realized at 350°C using Fe2O3/Al2O3 under both dry and humid conditions with a toluene concentration of 10,000ppm in the feed gas. It is worth noting that the unique structure of the Fe2O3/Al2O3 is stable after air-post-annealing at 750°C. Our Fe2O3/Al2O3 catalysts are active for toluene oxidation, and stable upon annealing at high temperature, showing that one can use our Fe2O3/Al2O3 as a component of catalytic converter of harmful volatile organic compounds.