Activity For Toluene Oxidation Research Articles

Photothermal catalytic oxidation performance of cerium-based perovskite catalyst CeBO3 under full-spectrum: Effect of B-site elements

In this paper, a series of cerium-based perovskite catalysts were prepared by sol-gel method combined with high-temperature calcination method, and Mn, Cr and Ni were selected as B-site elements, respectively, and characterized as well as tested for the catalytic activity of toluene oxidation. The CeMnO3 catalyst has the smallest grain size (4.33 nm), the largest specific surface area (39.65 m2/g) and the largest Oads/Olatt ratio (0.65). Based on its good low-temperature reduction performance, abundant adsorbed oxygen content, higher light absorption capacity and other characteristics, CeMnO3 exhibits outstanding photothermal catalytic oxidation of toluene under full-spectrum condition of 550 mW/cm2, and its photothermal catalytic T90% is only 233 °C. The photothermal catalytic oxidation reaction of CeMnO3 follows the Mars-van Krevelen mechanism. The introduction of light in thermal catalysis produces photothermal synergy, which has a better effect than single thermal catalysis and has a positive effect on the degradation of toluene.

Simultaneous Catalytic Oxidation of Benzene and Toluene over Pd-CeZrOx Catalysts

Since actual industrial emissions contain a wide range of volatile organic compounds, studies into the simultaneous catalytic degradation of multi-component VOCs are essential. This work developed Pd-CeZrOx samples for the simultaneous elimination of benzene and toluene. Firstly, CeZrOx supports were synthesized using several methods (co-precipitation, CTAB template co-precipitation, and sol–gel method). Pd active species were then added into the 1.0Pd-CeZrOx samples using the impregnation procedure. XRD, BET, NH3-TPD, Raman, EPR, XPS, and H2-TPR were utilized to analyze the as-prepared Pd-CeZrOx samples. The catalytic performance tests reveal that the performance of 1.0Pd-CeZrOx-CTAB outperforms that of 1.0Pd-CeZrOx-PM and 1.0Pd-CeZrOx-CASG, and 1.0Pd-CeZrOx-CTAB displays superior catalytic activity for both benzene and toluene oxidation. The improved redox properties, the abundant surface oxygen vacancies, and the surface Pd2+ species of the 1.0Pd-CeZrOx-CTAB sample may be responsible for the simultaneous degradation activity of benzene and toluene.

Boosting toluene destruction by engineering surface acidity–alkalinity in defective cobalt oxide catalyst

The surface acidity and alkalinity of catalysts played a decisive role in the destruction of Volatile organic compounds (VOCs). In this study, a series of Co3O4 catalysts were synthesized under different temperatures by calcining metal organic frameworks (MOFs). By controlling the temperature, the organic linkers were effectively eliminated, resulting in catalysts with a high specific surface area due to the preservation of the parent structure of the MOFs. Among the catalysts tested, Co3O4−350 (calcined at 350 °C) demonstrated the highest catalytic activity for toluene oxidation (T90 =231 ℃) and reliable water resistance (3 vol.% water vapor). The efficacy was attributed to the high ratio of reactive oxygen species and high valence Co species, weaken Co−O bond strength as well as high concentration of oxygen vacancies. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrate that acidity–alkalinity is crucial in the adsorption and activation, while oxygen vacancies were found to be essential for deep oxidation.

Impact of Cu content on the activity of TiO2-based catalysts for toluene oxidation

Toluene is one of the most toxic contaminants in industrial waste gases, it can enter the body through the respiratory system and skin. Long-term exposure to it can lead to skin inflammation and neurasthenia, and even cause lesions in organs. Over the years, catalytic oxidation technology has been extensively employed to the remove of toluene, and oxides, especially copper oxide, is considered to be an effective catalyst technology and has been extensively studied. In this work, we introduced CuO as an active species to investigate the impact of Cu content in TiO2@CuO (TC-x, x=1, 2, 3, and 5) catalyst on the activity, reusability, and stability of toluene oxidation. The result demonstrated that the addition of Cu species, facilitating the generation of active oxygen obviously reduced the complete oxidation temperature of toluene. Among them, TC-3 catalyst exhibited the highest activity (T50 = 234 ℃, T90 = 289 ℃, and T100 = 310 ℃, with Ctoluene=1000 ppm, WHSV=20,000 mL/ (g h)), great reusability, and stability for toluene degradation. According to the in-situ DRIFTS, the ultimate degradation products of toluene were CO2 and H2O, which were clean and free of secondary pollution.

Surface oxygen vacancies induced by cu-doping in hexagonal ZnMn2O4 nanoplates for high efficiency photothermocatalytic oxidation of toluene

The exploitation of efficient and stable photothermal catalyst for the deep mineralization of volatile organic compounds (VOCs) is crucial and challenging. Herein, a photothermal catalyst with abundant oxygen defects was prepared for the first time via Cu-doped ZnMn2O4 hexagonal nanoplate. Experimental characterization results reveal that Cu doping enhances not only the ZnMn2O4 defect contents but also the light absorption and thermal conversion ability of ZnMn2O4. Compared to the undoped ZnMn2O4 (ZMO), the ZnMn2O4 with optimal Cu doping amount (ZMO-4Cu) exhibits excellent photothermal catalytic performance (94% toluene conversion and 87% toluene mineralization) and good resistance to low concentration SO2 under full-spectrum light irradiation. Experimental characterizations and theoretical calculations jointly demonstrated that the oxygen vacancies of ZMO-4Cu surface are more conducive to the adsorption of O2, effectively reduce the oxygen dissociation energy of ZMO-4Cu, thus generating abundant active oxygen species and improving the photothermal catalytic activity for toluene oxidation. In situ IR experiments disclosed that photothermal catalysis is more conducive to the toluene deep oxidation than thermal catalysis. This work provides new insights for the design of high efficiency photothermal catalysis for the deep oxidation of VOCs.

Tuning the Metal-Support Interaction by Modulating CeO2 Oxygen Vacancies to Enhance the Toluene Oxidation Activity of Pt/CeO2 Catalysts.

In this research, a range of Pt/CeO2 catalysts featuring varying Pt-O-Ce bond contents were developed by modulating the oxygen vacancies of the CeO2 support for toluene abatement. The Pt/CeO2-HA catalyst generated a maximum quantity of Pt-O-Ce bonds (possessed the strongest metal-support interaction), as evidenced by the visible Raman results, which demonstrated outstanding toluene catalytic performance. Additionally, the UV Raman results revealed that the strong metal-support interaction stimulated a substantial increase in oxygen vacancies, which could facilitate the activation of gaseous oxygen to generate abundant reactive oxygen species accumulated on the Pt/CeO2-HA catalyst surface, a conclusion supported by the H2-TPR, XPS, and toluene-TPSR results. Furthermore, the results from quasi-in situ XPS, in situ DRIFTS, and DFT indicated that the Pt/CeO2-HA catalyst with a strong metal-support interaction led to improved mobility of reactive oxygen species and lower oxygen activation energies, which could transfer a large number of activated reactive oxygen species to the reaction interface to participate in the toluene oxidation, resulting in the relatively superior catalytic performance. The approach of tuning the metal-support interaction of catalysts offers a promising avenue to develop highly active catalysts for toluene degradation.

Highly Dispersed Ni Atoms and O3 Promote Room-Temperature Catalytic Oxidation.

Transition metal oxides are promising catalysts for catalytic oxidation reactions but are hampered by low room-temperature activities. Such low activities are normally caused by sparse reactive sites and insufficient capacity for molecular oxygen (O2) activation. Here, we present a dual-stimulation strategy to tackle these two issues. Specifically, we import highly dispersed nickel (Ni) atoms onto MnO2 to enrich its oxygen vacancies (reactive sites). Then, we use molecular ozone (O3) with a lower activation energy as an oxidant instead of molecular O2. With such dual stimulations, the constructed O3-Ni/MnO2 catalytic system shows boosted room-temperature activity for toluene oxidation with a toluene conversion of up to 98%, compared with the O3-MnO2 (Ni-free) system with only 50% conversion and the inactive O2-Ni/MnO2 (O3-free) system. This leap realizes efficient room-temperature catalytic oxidation of transition metal oxides, which is constantly pursued but has always been difficult to truly achieve.

Modulating the Electronic Structures of Pt on Pt/TiO2 Catalyst for Boosting Toluene Oxidation.

Surface hydroxyl groups commonly exist on the catalyst and present a significant role in the catalytic reaction. Considering the lack of systematical researches on the effect of the surface hydroxyl group on reactant molecule activation, the PtOx/TiO2 and PtOx-y(OH)y/TiO2 catalysts were constructed and studied for a comprehensive understanding of the roles of the surface hydroxyl group in the oxidation of volatiles organic compounds. The PtOx/TiO2 formed by a simple treatment with nitric acid presented greatly enhanced activity for toluene oxidation in which the turnover frequency of toluene oxidation on PtOx/TiO2 was around 14 times as high as that on PtOx-y(OH)y/TiO2. Experimental and theoretical results indicated that adsorption/activation of toluene and reactivity of oxygen atom on the catalyst determined the toluene oxidation on the catalyst. The removal of surface hydroxyl groups on PtOx promoted strong electronic coupling of the Pt 5d orbital in PtOx and C 2p orbital in toluene, facilitating the electron transfers from toluene to PtOx and subsequently the adsorption/activation of toluene. Additionally, the weak Pt-O bond promoted the activation of surface lattice oxygen, accelerating the deep oxidation of activated toluene. This study clarifies the inhibiting effect of surface hydroxyl groups on PtOx in toluene oxidation, providing a further understanding of hydrocarbon oxidation.

Design and optimization of CuCo-LDO catalysts via ZIF-67 sacrificial templates for enhanced toluene oxidation: A comprehensive study on morphology, structure, and catalytic activity

The investigation into the development of an active transition-metal oxide catalyst with controllable morphology for the degradation of volatile organic compounds (VOCs) is a subject of considerable importance and warrants further exploration. In this study, ZIF-67 was prepared and employed as a sacrificial template, with varying quantities of Cu ions incorporated to synthesize layered copper-cobalt double oxide (CuCo-LDO) featuring a modifiable surface state. A comprehensive characterization of the CuCo-LDO catalysts was conducted, encompassing structural properties, morphology, surface chemical state, and redox properties, utilizing a range of analytical techniques. Subsequent evaluations included testing the catalytic activity for toluene oxidation and assessing stability performance. The results revealed that differing Cu contents played a pivotal role in inducing changes in the morphology and structure of CuCo-LDO, thereby significantly influencing its oxidation activity towards toluene. Notably, the flower-like structure of 3CuCo-LDO (Cu% = 20.14 wt.%) exhibited outstanding toluene oxidation activity attributable to its unique structure and composition. This research contributes novel insights to the design of highs-performance catalysts targeting volatile organic compounds.

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

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

Unveiling the crucial active sites responsible for CO, n-heptane, and toluene oxidation over Pt/ZrO2 catalyst

The surface Pt species and adsorbed oxygen on the Pt/ZrO2 catalyst were successfully modulated by altering the preparation methods, resulting in distinct catalytic behaviors for CO, n-heptane, and toluene oxidation. The Pt/ZrO2 catalyst was initially prepared via wetness impregnation and subsequently reduced in an H2 atmosphere to obtain the Pt/ZrO2-R catalyst. In contrast, the Pt/ZrO2-E catalyst was synthesized using ethanol solvent (also serving as a reducing agent) instead of water during wetness impregnation. Moreover, the pre-prepared Pt nanoparticles were loaded onto the ZrO2 surface using polyvinylpyrrolidine (as a protective and structure directing agent) dissolved in ethanol solvent to fabricate the Pt/ZrO2-EP catalyst. Among these catalysts, the Pt/ZrO2-R exhibits superior catalytic activity towards CO oxidation due to its abundant metallic Pt species. It is found that activity of Pt/ZrO2 catalyst for n-heptane oxidation is positively correlated with its surface adsorbed oxygen concentration, thus the highest activity is achieved over the Pt/ZrO2-EP catalyst possessing a higher concentration of surface adsorbed oxygen species. Unlike CO and n-heptane oxidation, toluene oxidation activity is affected by multiple factors, it is primarily promoted by synergistic catalysis between metallic Pt species (Pt0) and surface adsorbed oxygen species over the Pt/ZrO2-EP catalyst. Our preliminary findings underscore that precise modulation of sensitive active sites on surfaces plays a critical role in specific catalytic reactions.

Mesoporous Si-WO3-supported Pt catalysts with high catalytic performance and excellent water resistance for toluene oxidation

Reducing emissions of volatile organic compounds (VOCs) is an integral part of improving the quality of the atmospheric environment. Catalytic oxidation has become an effective means of treating low and medium concentration VOCs exhausts due to its advantages in terms of removal efficiency, energy saving and environmental protection. Due to the unique inherent properties of supported precious metal catalysts, they show good catalytic efficiency in VOCs emission reduction. In this study, the mesoporous Si-WO3 support was first synthesized by the P123-assisted sol-gel method, and the xPt/Si-WO3 catalysts with the actual loadings (x = 0.19, 0.48, and 0.81 wt%) of Pt nanoparticles (NPs) were then obtained, physicochemical properties of these materials were characterized using a variety of techniques, and their catalytic activities and water resistance for the oxidation of toluene were evaluated. The results showed that Pt NPs with an average particle size of 2.3−3.3 nm were highly dispersed on the mesoporous Si-WO3 support, and the 0.81Pt/Si-WO3 sample exhibited the highest catalytic activity for toluene oxidation at a space velocity of 20,000 mL/(g h) (T50% = 167 °C and T90% = 180 °C; specific reaction rate at 160 °C = 8.54 µmol/(gPt s), turnover frequency (TOFPt) at 160 °C = 1.67 × 10−3 s−1, and apparent activation energy = 45 kJ/mol). The good catalytic performance of 0.81Pt/Si-WO3 was associated with its large surface area, well dispersed Pt NPs, high adsorbed oxygen species concentration, large toluene adsorption capacity, and strong interaction between Pt NPs and mesoporous Si-WO3. The 0.81Pt/Si-WO3 sample possessed excellent water resistance, and the introduction of 5 vol% or 10 vol% water vapor to the reaction system enhanced toluene oxidation since part of water vapor participated in the oxidation of toluene. In addition, the toluene oxidation pathway might obey the sequence of (adsorbed toluene + adsorbed oxygen species) → benzyl alcohol → (benzoic acid and benzaldehyde) → maleic anhydride → (carbon dioxide and water).

Mn-MIL-100 non-thermally derived MnOx catalysts for toluene oxidation

Herein, a novel preparation method via non-thermal derivation by using Mn-MIL-100 as the precursor to synthesize MnOx catalysts was proposed. The synthesized catalysts were applied to toluene oxidation. Characterizations and experiments results showed that the more surface Mn3+, Oads species, large surface area, better low-temperature reducibility and higher lattice oxygen mobility of Mn-Na2CO3 prepared via Na2CO3 treatment induced its great catalytic activity for toluene oxidation.

Manufacturing AAl2O4 (A=Cu, Co, Ni, Zn) Spinel Catalysts for Toluene Combustion: Elucidating the A‐site Replacement Effect on the Reactivity

AbstractTo decode the A‐site substitution effect on the reactivity of Al‐based spinel complex oxides, a series of AAl2O4 (A=Cu, Co, Ni, Zn) compounds were manufactured and tested by toluene combustion. It was confirmed that a pure spinel crystalline phase has been successfully synthesized for all the catalysts. The toluene and CO oxidation activity are sequenced as CuAl2O4>CoAl2O4>NiAl2O4>ZnAl2O4. As discovered, both active surface O2− and acid sites are the two critical factors to determine the reactivity, which can adsorb and activate the reactants effectively to form active intermediates, possibly following a Mars‐van‐Krevelen pathway. The activity improves positively with the amount increasing of these two kinds of active sites, thus showing an evident A‐site replacement effect. CuAl2O4 owns the biggest numbers of these two kinds of active sites, thereby exhibiting the optimal catalytic activity. Moreover, it also shows good stability in a dry feed, and considerable ability to resist water vapor and sulfur poisoning. In‐situ DRIFTS results have indicated that benzyl, benzoate, benzaldehyde and benzoquinone might be the major reaction intermediates.

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.

A bimetallic MOF-derived MnCo spinel oxide catalyst to enhance toluene catalytic degradation.

MnCo spinel oxide catalysts were successfully synthesized by the calcination of bimetallic Mn/Co-MOFs as sacrificial templates. The derived catalysts exhibited optimal catalytic activity, reusability and thermal stability for toluene oxidation, which was ascribed to their large specific surface area, higher number of octahedral metal ions and the weakest metal-oxygen bonds.

High catalytic performance of thermally treated Mn-rich limonite for catalytic oxidation of toluene

Abstract The development of active and low-cost transition metal oxide-based catalysts was vital for the catalytic oxidation of toluene. This study aimed to prepare Fe-Mn oxide catalysts by Mn-rich limonite, and investigate the catalytic activity and mechanism for toluene oxidation. The natural Mn-rich limonite was thermally activated at different temperatures and these thermally activated samples exhibited different oxidation activities. YL-300, obtained through thermal treatment at 300°C, exhibited excellent catalytic activity, showing 90% toluene conversion at 239°C (1000 ppm toluene) and remarkable catalytic stability even in the presence of water vapor (5 vol.%). The amount of oxygen vacancies in the catalyst was regulated by tuning the thermal treatment temperatures. Optimal thermal treatment facilitated the increase of oxygen vacancies and enhanced the oxygen mobility and redox capacity of YL-300, contributing to the complete oxidation of toluene to H2O and CO2. The oxidation of toluene was greatly influenced by the adsorbed oxygen species. This study demonstrates the potential of Mn-rich limonite as a promising catalyst for toluene oxidation, thereby promoting the utilization of natural mineral materials in the field of environmental pollution control.

Efficient oxidation and stable removal of toluene over controlled metal-organic framework derived MnFeOx catalysts

For VOCs oxidation technology, significant room for enhancement still exists in terms of catalytic performance of commonly used transition metal oxide-based catalysts. In this work, we designed MnFeOx oxides catalysts by using in situ pyrolysis of MnFe bimetallic MOF-74 as efficient and stable catalysts for toluene oxidation and this bimetallic framework was synthesized by metal doping. The preferred Mn2Fe3Ox-500 (Mn/Fe molar ratio of 2:3, calcination T=500 °C) catalyst exhibited excellent catalytic activity and stability towards toluene which was significantly superior the control MnOx-500 catalyst. Under simulated industrial real-exhaust conditions, the Mn2Fe3Ox-500 catalyst maintained better resistance at higher air velocities, in addition to exhibiting excellent stability and good water resistance. The superior toluene oxidation activity of Mn2Fe3Ox-500 catalyst can be associated with its high reducibility of metal active species, abundance of oxygen species, and the well dispersion of Fe2O3 and MnOx species. In addition, suggested potential degradation pathways for toluene over the Mn2Fe3Ox-500 catalyst. For the exhaust gas purification industry, this work will be beneficial in exploring the mechanistic level of MOF materials in the field of VOCs removal.

Enhancing plasma-catalytic toluene oxidation: Unraveling the role of Lewis-acid sites on δ-MnO2

The emission of volatile organic compounds (VOCs) into the air, primarily due to human activities, has caused significant environmental pollution and health concerns. In response, the development of advanced environmental catalysts is crucial, and δ-MnO2 has emerged as a promising material for efficient VOC oxidation. However, the identification of the specific active sites and the underlying oxidation mechanisms of this material remain unclear, hindering the development and optimization of high-activity catalysts. Herein, we present a strategy to remove the internal water and hydrated cations from δ-MnO2, thereby unblocking the inter-lamellar gaps and exposing the internal Lewis-acid sites, while maintaining other physical and chemical characteristics of the sample unchanged. Notably, the well-defined δ-MnO2 catalysts with more accessible interlayer Lewis-acid sites exhibited significantly enhanced catalytic activity in toluene oxidation, demonstrated in both two-stage plasma catalysis and single-stage ozonation processes. A quantitative analysis of Lewis-acid sites and initial toluene reaction rates revealed that these Lewis-acid sites serve as the active centers for toluene adsorption and activation, and the heterogeneous reaction between toluene and ozone follows the Langmuir-Hinshelwood mechanism. Moreover, in-depth analysis of byproducts showed that δ-MnO2 rich in Lewis-acid sites promoted the oxidation of intermediates, such as esters, hydrazides, and ketones, leading to a more complete toluene oxidation. This work not only fully explores the potential of δ-MnO2 as a catalyst, but also provides valuable insights into the elucidation of unknown catalytic active sites, potentially paving the way for the rational design of more efficient catalysts for VOC oxidation.

Catalytic oxidation of toluene over Co3O4-CeO2 bimetal oxides derived from Ce-based MOF

A series of Co–Ce oxide catalysts with different molar ratios were prepared by impregnation and pyrolysis using a Co-loaded Ce-based metal–organic framework as a precursor. Physicochemical properties of the catalysts were characterized by N2 adsorption–desorption measurements, X-ray diffraction, H2 temperature-programmed reduction, Raman analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, thermal desorption-gas chromatography-mass spectrometry and scanning electron microscopy. Toluene was selected as a reference to evaluate catalytic performance. Results show that the catalyst prepared at a Co/(Ce+Co) molar ratio of 0.3 exhibits excellent catalytic activity in the catalytic oxidation of toluene. The temperature at 90 % conversion of toluene (T90) is 262 °C which is significantly lower than the catalyst prepared by the traditional preparation method. The specific surface area is not the main factor affecting the reaction. The high activity is due to the better low temperature reducibility, abundant lattice defects, more active oxygen species, higher surface Ce3+ species (oxygen vacancies). What's more, 30Co-Ce has superior stability at different conversion rates and tolerance in the presence of water vapor. The results stated above indicate that the surface properties of the Co-Ce catalysts significantly affected the toluene combustion reaction.