Toluene Conversion Research Articles

Steam reforming of toluene as model compounds of biomass tar by Fe–K-based biochar nano-catalysts at mild temperatures

Development of efficient catalysts for steam reforming of biomass tar is crucial for the widespread application of biomass gasification. In this work, a novel biochar nano-catalyst (BN) is conveniently prepared via one-step catalytic pyrolysis, using K and Fe to adjust the surface structure of the biochar, thereby enhancing the activity for toluene reforming. Fe–K/BN is tested in a fixed-bed reactor for steam reforming of toluene, a model compound of biomass tar, achieving a 100% toluene conversion rate at 650 °C. Fe–K/BN is activated in situ with steam to increase their specific surface area and enhance the O-containing functional groups on the surface, improving toluene adsorption and reforming. Finally, the stability of Fe–K/BN is tested in the simulated syngas, maintaining a 100% toluene conversion rate during a 26-h continuous catalytic reforming experiment. This work provides a promising strategy for the design of an active and stable catalyst for toluene reforming, which has potential for application of tar steam reforming during biomass gasification.

Reaction site-isolation for simultaneous removal of NOx and toluene: A reverse strategy to realize bifunctional catalysis

In this study, 3V5W/Cu@Ti catalyst with the function of reaction site-isolation was prepared to achieve the simultaneous removal of NO and toluene. The catalyst was prepared through the hard template and impregnation method, and V-W, and Cu species were introduced into the outer and inner layers of the hollow spherical shell TiO2, respectively. Under the coexistence of multi-pollutants, toluene was completely removed with NO conversions above 90% at 250 ℃. Even at high temperatures of 350-400 ℃, complete conversions of NO and toluene were maintained with apparent lower by-products than those for other catalysts. DFT calculations and activation energy(Ea) indicate that NH3 tends to adsorb and react at the V/W sites on the catalyst's outer layer, while toluene is more likely to adsorb and react at the Cu sites on the inner layer. The Ea and DFT results were well-consistent with the catalytic reactivity, revealing the achievement of reaction site-isolation.

Hydroxylated SiO2-modified {0 0 1}-TiO2 nanosheets as a surface multifunctional photocatalyst for enhanced degradation of gaseous toluene

The relatively weak activity and serious deactivation of anatase TiO2 nanosheet catalysts with highly exposed {001} facets ({001}-TiO2) limits its wide application in photocatalytic degradation of gaseous pollutants. Herein, we propose a hybrid photocatalyst composed of {001}-TiO2 and SiO2 with numerous hydroxyl groups (denoted as {001}-TiO2/HO-SiO2). The catalyst showed excellent performance for gaseous toluene degradation under UV illumination, with 99.2 % removal efficiency and 204.7 μmol L−1 CO2 yield (about 85.9 % mineralization efficiency) within 120 min. It also demonstrated superior durability over five consecutive cycles of toluene photodegradation. The modification of HO–SiO2 on {001}-TiO2 facilitate the selective adsorption of toluene on the catalyst surface by H-bonding interaction, and make the major poisoning species, benzoic acid, easily desorb from the surface, reducing the catalyst inactivation. Most importantly, we found that the formed TiOSi bond promotes the separation of photogenerated electron–hole pairs, and provides abundant available electrons for the formation of reactive oxygen radicals and the left holes for the conversion of toluene to benzyl radicals or oxidation of H2O to hydroxyl radicals, which results in the improved activity. This study highlights the importance of the introduction of secondary components with special functions on TiO2, which is helpful for the design of photocatalysts with high performance and anti-deactivation ability for treatment of volatile organic compounds.

Enhanced electrocatalytic C[sbnd]H amination of toluene via tailored interfacial microenvironment

Electrocatalytic CH amination of hydrocarbons is a promising avenue for the synthesis of high-value CN compounds. However, efficient activation of CH bonds remains a significant challenge in electrocatalytic CN coupling. Herein, we present a novel strategy to enhance the electrocatalytic conversion of toluene to N-benzylacetamide through a Ritter–type reaction by engineering a hydrophobic electrode–electrolyte interface using polytetrafluoroethylene (PTFE)-coated carbon paper (CP). The hydrophobic CP-based electrode exhibited a superior N-benzylacetamide productivity of 1860.9 mmol m−2h−1 and a substantially higher Faradaic efficiency (FE) of 70.1 % compared to pure CP (41.5 %). Experimental results and density functional theory (DFT) calculations reveal that the PTFE coating promotes toluene adsorption and efficiently lowers the energy barrier for toluene dehydrogenation. Additionally, the hydrophobic interface effectively hinders water adsorption on the electrode, suppressing the competitive water oxidation reaction. This study underscores the crucial role of interfacial engineering in optimizing electrocatalytic CN coupling reactions for the sustainable synthesis of high-value amide compounds.

Valorization of carbonaceous co-product obtained from iron ore-catalyzed methane cracking as support for Pd catalysts in toluene hydrogenation reaction

Iron ore has been proven as an abundant and sustainable catalyst in the production of hydrogen by catalytic cracking of methane. One of the main challenges is the identification of suitable market niches for the utilization of the resulting iron-carbon hybrid in order to make this process economically viable. This study examines the feasibility of using the iron-carbon hybrid obtained from methane cracking as support of Pd catalysts for the hydrogenation of toluene (350 ºC, 35 bar of H2 at room temperature and 90 min). Before supporting Pd, Fe-C hybrid was subjected to different acid functionalization treatments (nitric and/or phosphoric acids). The results indicate that sequential oxidation with nitric acid, followed by phosphoric acid, is the most effective strategy for achieving the highest catalytic activity (1294 mmolToluene gPd⁻¹) and conversion (27 %). Toluene conversion was 1.8 and 14.2 times higher than with the catalysts treated with nitric and phosphoric acid separately. Therefore, this work proves the possibility of employing carbon/Fe hybrid materials obtained in iron ore catalyzed methane cracking as catalytic supports in industrial relevant reactions.

Nano-MnOx prepared by redox method for toluene oxidation removal from air

Catalytic oxidation is an efficient VOCs removal technology with great potential and development advantages. The key to the oxidative elimination of VOCs lies in the development and application of the catalyst with high efficiency. In this work, the nano-MnOx catalysts were prepared by redox method and the catalytic oxidation performance of toluene was studied. The calcination temperature could effectively change the surface chemical composition and the nano-MnOx catalyst structures, which could effectively regulate the number of active centers on the catalyst surface to improve the adsorption, activation, and oxidation ability of the nano-MnOx catalysts for toluene molecules. The nano-MnOx catalyst dominated by the MnO2 phase, which was prepared at the calcination temperature of 400 °C, had a high specific surface area, developed porosity, abundant reactive oxygen species, and oxygen vacancies. The structural characteristics are conducive to the adsorption, activation, and oxidation of toluene molecules, and thus exhibited excellent toluene catalytic oxidation activity. At the reaction temperature of 140 °C, the toluene oxidation conversion was as high as 99.4 %, and the toluene conversion remained above 96.6 % after experiencing a 690 min stability test.

Unveiling the role of oxygen vacancy of manganese oxide coating on Ni foam to magnetocaloric catalytic oxidation of toluene

Using a pulsed-voltage technique, the manganese oxide (MnOx) coating on Ni foam (NF) was regulated to encourage magnetocaloric oxidation, which lowers volatile organic compounds (VOCs). The MnOx/NF was obtained by electrodeposition of MnOx onto NF. Subsequently, MnOx/NF-PV was obtained by pulsed-voltage modification. According to the structural characterization, the pulsed-voltage modification changed the interaction between the coating and the support, resulting in increased toluene adsorption capacity, oxygen desorption capability, oxygen vacancy (OV) quantity of MnOx/NF-PV. The MnOx/NF-PV exhibits excellent catalytic performance, with a 90 % conversion of toluene at 170 °C, where OV play an important role as electronic intermediates in magnetocaloric oxidation reactions. Furthermore, compared to traditional thermal catalysis, electromagnetic induction heating (EMIH) can promote the reactivity of OV in magnetocaloric catalysts by increasing the activation and dissociation of oxygen species and thus catalytic activity, which was demonstrated in the 18O isotope exchange experiment.

In situ reaction-induced strong metal-support interaction to enhance catalytic performance and stability of toluene oxidation

The construction of strong metal-support interaction (SMSI) represents an attractive strategy to enhance the catalytic performance of the catalysts. Herein, the SMSI state over the Pt/TiO2 catalyst that inductively formed with a toluene atmosphere at a temperature below 300 °C is reported. During this process, the Pt species is covered by TiOx overlayers, while the Pt species is endowed to an electron-sufficient state, and more defects on the surface are produced simultaneously. Owing to the existence of formed SMSI, the interface of Pt and TiO2 with an improved redox property is conducive for oxygen species activation to expedite toluene conversion. The experimental results demonstrate that the catalysts with SMSI state exhibit improved catalytic activity and stability (5 vol% water and 800 °C thermal treatment). This work posits that the SMSI state of noble metal-supported catalysts can be dynamically produced during toluene conversion, which paves a novel method for designing efficient catalysts for the practical elimination of VOCs.

Surfactants govern the fabrication of sulfur-enriched heterojunction catalysts for highly selective photocatalytic conversion of toluene

Photocatalytic selective oxidation of toluene represents a milder and more environmentally friendly strategy for the synthesis of benzaldehyde. In order to enhance catalytic performance, efficient carrier separation and transport are crucial in the photocatalytic process. This study focused on the preparation of ZnS@ZnIn2S4 with sulfur vacancies and heterostructures, combining the advantages properties of ZnS and ZnIn2S4 in photocatalysis. The effects of ZnS and surfactants on the catalytic properties of the composites were studied in depth. Characterization tests revealed that surfactant-modified ZnS@ZnIn2S4 exhibited a higher concentration of sulfur defects, which facilitated electron trapping and promoted photogenerated carrier separation and utilization. Additionally, the present study also demonstrated that the incorporation of ZnS and surfactants could reduce the crystal size of ZnIn2S4, thereby facilitating the exposure of additional active sites. The synergistic effect of the aforementioned advantages enabled toluene to undergo oxidation at a conversion rate of 39% in the presence of oxygen, resulting in the production of benzaldehyde with an exceptional selectivity of 92%. This finding offers valuable insights for future endeavors in designing photocatalytic C-H bond oxidation catalysts.

Enhancing Ce-Co interfacial effects via special petal-pollen morphology construction to achieve efficient toluene removal

Interfacial effects provide an effective means to construct multi-metal interactions and design efficient catalysts for VOCs purification, while morphology construction remains a common tactic to optimize the efficiency of these catalysts. In the present work, the Co-Ce bimetal interface was effectively constructed by morphological regulation, and the coupling of the interfacial effect modulation and the special morphological structure was realized, resulting in superior catalyst performance. Among the series catalysts, CeCoOx-H demonstrated the optimized activity with 90 % toluene conversion at 250 °C while maintaining good results in a 50 h stability test. And the systematic characterization revealed that the structural changes and interfacial effects induced by morphological modulation would increase the structural defects, improving surface reactive oxygen and oxygen vacancy content, oxygen storage capacity, oxygen motivity and low-temperature reductivity, which account for promising catalytic performance of CeCoOx-H. Furthermore, in-situ DRIFTS revealed the following decomposition routes for toluene on the CeCoOx-H catalyst surface: toluene → benzyl alcohol → benzaldehyde → benzoate → phenol → maleate → acetate → formate → carbon dioxide. In particular, the decomposition of benzaldehyde and benzoate may be the key steps in toluene catalytic oxidation. Also, the characterization unveiled that the rich adsorption sites brought by the interfacial construction are not negligible in boosting the catalytic performance.

Enhanced performance of photocatalytic oxidation of indoor toluene over Pd/TiO2 catalyst by tuning surface defect concentrations

An effective approach for the elimination of indoor gaseous toluene through photocatalytic oxidation involves the engineering of surface defects on catalysts. In this study, the concentrations of surface oxygen defects in PdTi-xN (x = 10, 30) catalysts were controlled using the sodium borohydride solid-phase reduction method, and their performances in the photocatalytic oxidation of indoor gaseous toluene were evaluated. PdTi–10 N demonstrated high photocatalytic efficiency for toluene oxidation, achieving 84% toluene conversion and approximately 75% CO2 mineralization. Characterization results indicated that surface oxygen defects can enhance the separation of photo-generated electrons and holes, facilitating their interaction with Pd0 species to form Ti3+ species. More reactive oxygen species (·OH-and ·O2−) were generated on PdTi–10 N due to the synergistic effect of surface oxygen defect and Ti3+ species, which played a significant role as the toluene oxidation. This work provides a new insight for the design and development of high-performance Pd/TiO2 catalysts in the field of indoor VOCs treatment.

A Green and Efficient Electrocatalytic Route for the Highly‐Selective Oxidation of C–H Bonds in Aromatics over 1D Co3O4‐Based Nanoarrays

Electrocatalytic oxidation of C‐H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value‐added chemicals. Herein, a highly selective and continuous‐flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4‐based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D‐Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained with selectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm‐2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable, and continuous‐flow process for precise control over production selectivity of value‐added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

A Green and Efficient Electrocatalytic Route for the Highly-Selective Oxidation of C-H Bonds in Aromatics over 1D Co3O4-Based Nanoarrays.

Electrocatalytic oxidation of C-H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value-added chemicals. Herein, a highly selective and continuous-flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4-based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D-Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained withselectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm-2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable,and continuous-flow process for precise control over production selectivity of value-added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

Heterogeneous toluene nitration with mixed acid in microreactors: Reaction regime, characteristics and kinetic models

It is critical for reactor design and process safety to determine the reaction kinetics for toluene nitration. Herein, a continuous-flow platform based on capillary microreactors was established. First, reaction regimes for toluene nitration and its consecutive side reaction (MNT (mononitrotoluene) nitration) were identified. On this basis, the influence of process parameters on conversion of toluene, selectivity of MNT and DNT (dinitrotoluene) and their isomer distribution were meticulously examined, including molar ratio of reactants, sulfuric acid strength, reaction temperature, and residence time. Subsequently, reaction kinetic models coupled with mass transfer were developed, allowing the simultaneous kinetic determination for toluene nitration and MNT nitration. It was found that the logarithm of the observed kinetic constant is proportional to the sulfuric acid strength. The kinetic parameters under 72.7 to 80.1 wt% sulfuric acid strengths were obtained. The outcomes provide a basis for process intensification and optimization of toluene nitration as well as other similar aromatics.

Dry reforming of toluene over Ni/pyrochlore catalysts with A-site Sr doping

Dry reforming with CO2 is one potential method for tar removal and further production of syngas in biomass gasification, but the crucial catalysts with good reaction characteristics are still being developed. In the work, Ni/pyrochlore was proposed to be utilized as catalysts in the dry reforming of tar, and thermodynamic calculation, reaction progress test, and materials characterization were conducted to reveal dry reforming characteristics over Ni/pyrochlore catalysts and the reaction mechanism behind. Results show that YS0.2C catalyst exhibits the best activity (toluene and CO2 conversion of 70.1% and 79.5%) and stability among all catalysts under the optimized conditions of 700 °C with a CO2/toluene molar ratio of 7. Analysis on physicochemical properties of the catalysts indicate Sr doping can effectively promote catalytic reforming by enhanced interaction between Ni and support, CO2 adsorption and oxygen mobility. The work offers a promising catalyst type in improving tar removal by dry reforming.

Dry reforming of toluene for syngas production over Ni-based perovskite-type oxides

Developing efficient Ni-based catalysts and understanding the mechanism of tar removal are crucial for upgrading biomass gasification technology. Literature has identified the superior performance of Ni-based catalysts in reforming tar model compounds like toluene under a steam atmosphere. In this work, we have synthesized La1-xCexNiO3 catalysts and examined their activity with benchmark A2BO4-type perovskites in dry reforming of toluene (DRT). Catalytic experiments revealed that La0.25Ce0.75NiO3 catalysts exhibited superior activity and stability regarding toluene conversion (85.4%) compared to La0.5Ce1.5NiO4. The structural study, conducted through various techniques, highlighted the easier reducibility of Ni from the ABO3 perovskite lattice, leaving higher oxygen vacancies, and higher basicity for reactant adsorption in DRT. Besides, in-situ DRIFTS experiments confirmed the *CHO-participated pathway of syngas generation from DRT. The findings suggested potential pathways for designing catalysts to support biomass gasification while contributing to global carbon reduction.

Catalytic oxidation of toluene over ZIF-8 composited with Mn by different methods

ZIF-8 composites with Mn (Mn-ZIF-8 & Mn/ZIF-8) were prepared by two methods for the complete catalytic oxidation of toluene. The results revealed that catalytic activity increased with the increasing content of manganese, and the activities of the two series composites were different from each other. The Mn[Formula: see text]-ZIF-8 prepared by the methanol thermal method showed the best catalytic performance, which had the lowest T[Formula: see text] of toluene conversion, compared with the series of Mn/ZIF-8 catalysts. The resulting composites were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), thermogravimetric analysis (TG) and X-ray photoelectron spectroscopy (XPS). It was concluded that Mn, as the active species, might partly replace Zn in the frame of Mn-ZIF-8 for the catalytic oxidation of toluene at lower temperatures.

Catalytic Ozonation of Low Concentration Toluene over MnFeOx-USY Catalyst: Effects of Interactions between Catalytic Components and Introduction of Gas Phase NOx.

A series of Mn and Fe metal oxide catalysts loaded onto USY, as well as single metal oxides, were prepared and characterized. The effects of interactions between the catalytic components and the introduction of gas phase NO on the catalytic ozonation of toluene were investigated. Characterization showed that there existed strong interactions between MnOx, FeOx, and USY, which enhanced the content of oxygen vacancies and acid sites of the catalysts and thus boosted the generation of reactive oxygen species and the adsorption of toluene. The MnFeOx-USY catalyst with MnOx and FeOx dimetallic oxides exhibited the most excellent performance of catalytic ozonation of toluene. On the other hand, the presence of NOx in reaction gas mixtures significantly promoted both toluene conversion and mineralization, which was attributed to the formation of nitrate species on the catalysts surface and thus the increase of both acid sites and toluene oxidation sites. Meanwhile, the reaction mechanism between O3 and C7H8 was modified in which the strong interactions between MnOx, FeOx, and USY accelerated the reaction progress based on the L-H route. In addition, the formation of the surface nitrate species not only promoted reaction progress following the L-H route but also resulted in the occurrence of the reaction via the E-R route.

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

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

Enhancing Oxygen Activation Ability by Composite Interface Construction over a 2D Co3O4-Based Monolithic Catalyst for Toluene Oxidation.

Developing robust metal-based monolithic catalysts with efficient oxygen activation capacity is crucial for thermal catalytic treatment of volatile organic compound (VOC) pollution. Two-dimensional (2D) metal oxides are alternative thermal catalysts, but their traditional loading strategies on carriers still face challenges in practical applications. Herein, we propose a novel in situ molten salt-loading strategy that synchronously enables the construction of 2D Co3O4 and its growth on Fe foam for the first time to yield a unique monolithic catalyst named Co3O4/Fe-S. Compared to the Co3O4 nanocube-loaded Fe foam, Co3O4/Fe-S exhibits a significantly improved catalytic performance with a temperature reduction of 44 °C at 90% toluene conversion. Aberration-corrected scanning transmission electron microscopy and theoretical calculation suggest that Co3O4/Fe-S possesses abundant 2D Co3O4/Fe3O4 composite interfaces, which promote the construction of active sites (oxygen vacancy and Co3+) to boost oxygen activation and toluene chemisorption, thereby accelerating the transformation of reaction intermediates through Langmuir-Hinshelwood (L-H) and Mars-van Krevelen (MvK) mechanisms. Moreover, the growth mechanism reveals that 2D Co3O4/Fe3O4 composite interfaces are generated in situ in molten salt, inducing the growth of 2D Co3O4 onto the surface lattice of 2D Fe3O4. This study provides new insights into enhancing oxygen activation and opens an unprecedented avenue in preparing efficient monolithic catalysts for VOC oxidation.