Toluene Combustion Research Articles

Novel Pd-loaded self-standing hierarchical pore structure silicalite for low temperature toluene catalytic combustion

A novel Pd-loaded self-standing hierarchical pore structure silicalite were obtained by a handy polymer form board assisted hydrothermal method. The selected foam-shaped form board of a polyurethane (PU) foam monolith was regarded as the precursor of the self-standing hierarchical pore structure silicalite. The fruiting silicalite can steadily hold unique macroporous network structure and shape of the anterior original PU foam board . By means of the BET and BJH pore size distribution tests, the as-synthesis silicalite demonstrated hierarchical pore structure. The method of in-situ reduction was wielded to load palladium on the silicalite, and the catalytic performance of the catalyst to decompose toluene was tested at multiple burning temperatures. The experimental results revealed that the Pd-loaded catalyst can effectively decompose toluene at nearly 230°C, realizing low-temperature catalytic combustion of toluene.

The abundant oxygen vacancies of the Co–Ce mixed oxides towards catalytic combustion toluene

A series of catalysts (Co3O4/Beta-60, CeO2/Beta-60, CoCeOx/Beta-60) were prepared by constant volume impregnation method and were applied to the catalytic oxidation toluene. The characterization results showed that some Co ions were embedded into the lattice of CeO2 to form CoCeO2-δ solid solution that promoted the formation of a large number of oxygen vacancies and generation of active oxygen species for the deep oxidation of toluene. The mobility of active oxygen species and reducibility for CoCeOx/Beta-60 were both improved. Therefore, CoCeOx/Beta-60 showed the superior catalytic performance, the conversion of toluene was 90% when the temperature was 307 °C. The combination between the zeolite carrier and the active components endowed the supported catalyst with excellent stability. Additionally, the in situ DRIFTS results displayed that the oxidation of toluene over CoCeOx/Beta-60 followed the MvK mechanism and L-H mechanism. Adsorbed toluene could be oxidized by not only active adsorbed oxygen on oxygen vacancies but also the lattice oxygen species. However, gaseous oxygen was paramount importance for the total oxidation of toluene for the reason that the gaseous oxygen could be activated through the oxygen vacancies generated to fill the active oxygen species after the depletion of active adsorbed oxygen and lattice oxygen. The study systematically reviewed the data for the catalytic combustion of toluene, aiming to provide new avenues for the preparation and application of catalysts with excellent catalytic activity.

Boosting sulfur tolerance and catalytic performance in toluene combustion via Enhanced-mechanism of Ce-Fe dopants incorporation of LaCoO3 perovskite

In-depth mechanism of catalytic reaction could help to guide the development of efficient catalysts with high tolerance to sulfur. Here, to seek optimized dopants to improve both sulfur tolerance and activity of Co-based perovskite catalysts for the removal of volatile organic compounds (VOCs), a series of La1−xCexCo1−yFeyO3 perovskites were prepared and then tested for toluene combustion before and after SO2 poisoning. Results showed that both sulfur tolerance and catalytic activity could be improved by adding Ce and/or Fe dopants with a suitable ratio, in which Ce dopant has advantages in catalytic activity, while Fe dopant is better for sulfur tolerance. Multiple in-situ and ex-situ characterization analysis indicated that dopants can alter the oxidation state of B-site, reducibility and oxygen vacancy content to varying degrees, thus increasing the catalytic activity. In addition, the ceria generated by Ce dopants could limits the sulfurization of the main active phase, Fe dopants would lead to highly stable and SO2-insensitive perovskite lattices, while co-doping of Ce and Fe elements could interact to form Ce-Fe solid solution and making the formed sulfate more mobile and decomposable after heating. This study presents a catalytic reaction enhanced-mechanism to provide theoretical basis and novel insights for the application of perovskite catalysts.

Enhancement of toluene oxidation performance over La1-xCoO3-δ perovskite by lanthanum non-stoichiometry

La1-xCoO3-δ catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method, and their catalytic performance in toluene combustion was investigated. The results showed that the catalytic activity and stability of A-site nonstoichiometric La1-xCoO3-δ were improved to a certain extent compared with pure LaCoO3 perovskite. Among them, the La0.9CoO3-δ catalyst gave the best catalytic performance for toluene oxidation. It achieved 90% toluene conversion at 205°C under the conditions of a WHSV (weight hourly space velocity) of 22,500 mL/(g·hr) and a 500 ppmV-toluene concentration. Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance. It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO3 changed the surface element state of the catalyst and increased the oxygen vacancy content, thus, combined with improved reducibility, improving toluene degradation on the catalyst.

Low-Temperature Combustion of Toluene over Cu-Doped SmMn2O5 Mullite Catalysts via Creating Highly Active Cu2+-O-Mn4+ Sites.

Catalytic combustion of volatile organic compounds (VOCs) at low temperatures is still an urgent issue to be solved. Herein, low-temperature combustion of toluene over Cu-doped SmMn2O5 mullite catalysts via creating highly active Cu2+-O-Mn4+ sites has been originally demonstrated. Cu-doped SmMn2O5 mullite catalysts exhibited 90% conversion of toluene at 206 °C and displayed robust stability even in the presence of water. It has been demonstrated that Cu doping created Cu2+-O-Mn4+ active composite sites that were more exposed after removing surface Sm species via acid-etching. Benefiting from this, the redox and oxygen activation ability of catalysts was significantly enhanced. The consumption of benzaldehyde and benzoic acid as intermediate species and the CO2 generation ability were apparently promoted, which were the direct reasons for the enhanced low-temperature combustion of toluene. This work provides novel ideas for the development of high-performance catalysts for low-temperature VOC combustion, which has great industrial application prospects.

Tuning the structure of Co3O4@MnOx catalyst by in situ redox approach for enhancing activity of the catalytic combustion of toluene

A novel in-situ redox method is proposed to prepare Co3O4 based catalysts with a core-shell-like structure toward the catalytic oxidation of toluene. The results of XRD, SEM and HRTEM reveal that Co3O4@MnOx with a core-shell-like structure was obtained after the precursor was partially oxidized by potassium permanganate. The as-prepared Co3O4@MnOx catalyst exhibits considerably high efficiency for the catalytic combustion of toluene, achieving 90% conversion of toluene at 233 ​°C that is at least 65 ​°C lower than that of the sole Co3O4 sample. The real reason is that Co3O4@MnOx is remarkably active than the other samples was explored by analyzing the results of a series of characterizations including Raman, XPS, TEM and H2-TPR. The results show that the catalytic activity of the samples is affected by the amount of Co3+ species, the concentration of oxygen species, and the content of oxygen vacancies to some extent, however, the result of H2-TPR indicates that their reactivity rather than the absolute content is the decisive factor for the activity of these catalysts. In addition, Co3O4@MnOx presents a satisfactory long-term stability, suggesting its great potential in industrial application.

Nb-modified CoOx as efficient catalysts for toluene oxidation

A series of NbCoOx catalysts with different Nb/Co molar ratios were synthesized via a slurry method to investigate the catalytic activity of oxidizing toluene. Among them, Nb0.67Co0.33Ox exhibited the highest toluene combustion efficiency. It was found that the incorporation of amorphous niobium provided the surface acid sites and abundant oxygen vacancies for the adsorption and activation of the reactants which was demonstrated by NH3-TPD, XRD, UV–vis DRS, XPS and Toluene-TPD. Furthermore, the strong interaction between niobium and cobalt can also affect its physical and chemical properties related to SEM, H2-TPR and XPS. Multiply TP-experiments were conducted to investigate the migration and transformation of oxygen species and find out that the reaction followed the MVK mechanism.

Hollow mesoporous aluminosilicate spheres imbedded with Pd nanoparticles for high performance toluene combustion

In the past few decades, persistent efforts have been directed toward the stabilization of Pd nanoparticles during catalytic reaction processes carried out at relatively higher temperatures. In this study, small-sized Pd nanoparticles imbedded into hollow mesoporous aluminosilicate sphere catalysts (Pd/HMAS-1) have been synthesized. The physical and chemical properties of Pd/HMAS-1 were studied by the means of XRD, TEM, and XPS analysis. The prepared Pd/HMAS-1 catalyst was evaluated for its catalytic performance in the combustion of toluene. Pd/HMAS-1 showed excellent activity for toluene oxidation with T90 at 150 °C, which was much higher than that of Pd/HMAS-2 (T90 at 220 °C) with Pd nanoparticle supported on the external surface of HMAS and Pd/HMAS-CTAB (T90 at 200 °C) with perpendicular pore channel occupied by CTAB. Furthermore, Pd/HMAS-1 exhibited an outstanding long-term stability and maintained the conversion efficiency of 100 % at 200 °C for 20 h. The superior catalytic performance of Pd/HMAS-1 has been attributed to the confinement effect of ordered mesopore in stabilizing Pd nanoparticles and improvement in mass transfer efficiency and active Pd metal accessibility. Furthermore, the oxidation pathway of toluene over Pd/HMAS-1 was proposed based on the analysis of key intermediates generated during the catalytic combustion process by in situ-DRIFTS analysis. This study provides a promising strategy to design novel high-performance ordered mesoporous zeolite-confined metal/metal oxide catalysts for industrial VOCs combustion.

Yttrium-modified Co3O4 as efficient catalysts for toluene and propane combustion: Effect of yttrium content

A series of Y-modified cobalt oxides with various Y/(Co+Y) molar ratios (0.25 %, 0.5 %, 1 %, 3 % and 5 %) were prepared to study the effect of Y content on toluene and propane combustion. The characterization of the catalysts revealed that proper Y incorporation resulted in smaller crystallite sizes, larger specific surface areas, more oxygen vacancies and weaker Co−O bonds. As such, the Y-modified Co3O4 showed enhanced low-temperature reducibility, boosted oxygen mobility and better catalytic activity. However, excess Y (> 1 %) aggregates on the surface of Co3O4 and forms yttrium carbonate species, hindering the catalyst activity. A volcano-type relationship between the Y content and the catalytic activity was established. The optimal catalyst 1 % Y-Co (with Y/(Co+Y) molar ratio of 1 %) exhibited toluene oxidation rate of 24 nmol g−1 s−1 at 220 °C and propane oxidation rate of 69 nmol g−1 s−1 at 180 °C. Besides, 1 % Y-Co presented perfect cycling stability and long-term durability in propane oxidation. Regarding its low cost, high efficiency and good stability, 1 % Y-Co is a promising catalyst for the practical elimination of hydrocarbon emissions.

Assembling core-shell SiO2@NiaCobOx nanotube decorated by hierarchical NiCo-Phyllisilicate ultrathin nanosheets for highly efficient catalytic combustion of VOCs

Configuring Ni-based catalyst with superior activity and stability is one efficient strategy in achieving its application for VOCs catalytic combustion. Here, we report the rational design and synthesis of core-shell SiO2@NiaCobOx nanotube derived from three-layered C@SiO2@NiCo-Phyllosilicate nanofiber. Through a typical hydrothermal strategy, the hierarchical NiCo-Phyllosilicate ultrathin nanosheets are fitly grown on the surface of order mesoporous SiO2 nanotube, which is obtained through thermal treatment of core-shell C@SiO2 nanofiber in air. Whereafter, a core-shell SiO2@Ni2Co1Ox nanotube is obtained to achieve the highly efficient conversion of VOCs in the presence of 5vol%H2O. We observe this special structural design can own superior redox ability, provide active oxygen species (Oads), and generate the abundant acid sites. Ideally, the low-temperature catalytic combustion of toluene over the core-shell SiO2@Ni2Co1Ox nanotube is realized through the combined action of Marse-van Krevelen (MvK) and Langmuir-Hinshelwood (L-H) mechanism. Simultaneously, a good thermal stability and water resistance is also achieved, which benefits from the guided growth of order mesoporous SiO2 nanotube, the presence of strong interactions (Ni-O-Si band) and the contribution of surface -OH groups in the special “fibrous” structure of phyllosilicate.

Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2, CeO2–Y2O3 and La2O3 as coatings

CeO2, La2O3, and CeO2–Y2O3 oxides were coated on the surface of spherical granular Al2O3 (3–5 mm) through impregnation method, and proved as better supports of Pd and Pt catalysts. The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions, as well as the catalytic performance, were investigated. Results show that the H2PtCl6·6H2O adsorption rates of the Al2O3 carriers modified by Ce, La, and CeY increase significantly. These rare earth coatings can adsorb almost all H2PtCl6·6H2O in the solution. Compared with Pt/Al2O3 catalyst, Pt/Ce–Al2O3 and Pt/CeY–Al2O3 catalysts have better degradation performance for toluene, and the T90 temperatures are both about 147 °C. According to X-ray photoelectron spectroscopy (XPS) characterization, Pt0 is an important active species for catalytic oxidation reaction of toluene. After CeO2 modification to the conventional Pt/Al2O3 catalyst, the proportion of Pt0 increases from 74.5% to 82.1%. When the Pt0 content in the metal state is improved, the redox activity of the catalyst is promoted correspondingly.

Enhanced Performance of Supported Ternary Metal Catalysts for the Oxidation of Toluene in the Presence of Trichloroethylene

Chlorinated volatile organic compounds (CVOCs), even in small quantities, can cause Pt-based catalyst poisoning. Improving the low-temperature chlorine resistance of catalysts is of vital importance for industrial application, although it remains challenging. Considering actual industrial production, a TiO2-supported ternary metal catalyst was prepared in this work to study the catalytic oxidation of multicomponent VOCs (toluene and trichloroethylene (TCE)). Among all of the samples, PtWRu/TiO2 and PtWCr/TiO2 exhibited the best catalytic performance for toluene oxidation. In the mixed VOC oxidation, the PtWCr/TiO2 sample showed the best catalytic activity for toluene combustion (a toluene conversion of 90% was achieved at 258 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 215 °C were 44.9 × 10−6 mol gPt−1 s−1 and 26.2 × 10−5 s−1). The PtWRu/TiO2 sample showed the best catalytic activity for TCE combustion (a TCE conversion of 90% was achieved at 305 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 270 °C were 9.0 × 10−6 mol gPt−1 s−1 and 7.3 × 10–5 s−1). We concluded that the ternary metal catalysts could greatly improve chlorine desorption by increasing the active lattice oxygen mobility and surface acidity, thus reducing chlorinated byproducts and other serious environmental pollutants. This work may serve as a reasonable design reference for solving more practical industrial production emissions of multicomponent VOCs.

Rational Design and Construction of Monolithic Ordered Mesoporous Co3O4@SiO2 Catalyst by a Novel 3D Printed Technology for Catalytic Oxidation of Toluene.

Here, we report a novel 3D printed layered ordered mesoporous template that can encapsulate active Co-MOFs species in a confined way to achieve the goal of monolithic catalyst. The monolithic OM-Co3O4@SiO2-S catalyst can maintain a macroscopic porous layered structure and a microscopic ordered mesoporous structure. This monolithic OM-Co3O4@SiO2-S catalyst has excellent catalytic performance (T90 = 236 °C), water resistance, and thermal stability in the catalytic combustion of toluene. The catalytic performance of the monolithic OM-Co3O4@SiO2-S catalyst is much better than that of many monolithic catalysts reported in the former. Among them, the introduction of binder aluminum phosphate (AP) can effectively enhance the rheological properties of the printing ink, achieve the purpose of ink writing monolithic layered porous material, enrich the acidic point of the monolithic catalyst, and increase the number of reactive oxygen species. This work reveals a novel monolithic catalyst forming strategy that can combine the advantages of ordered mesoporous materials with active species to form macro-layered porous materials and provide ideas and an experimental basis for the elimination of VOCs in industrial applications.

Synthesis of quantitative sulfur-poisoned Pd/γ-Al2O3 and its deactivation mechanism for catalytic combustion of toluene

A series of Pd/γ-Al2O3 with different degrees of sulfur poisoning have been successfully prepared by in-situ thermal decomposition of (NH4)2SO4. The influence of sulfur poisoning on toluene combustion was evaluated. The samples were characterized by XRD, N2 adsorption/desorption, HRTEM, FT-IR, TG, XPS, NH3-TPD and H2-TPR. The results indicated that the no-poisoned Pd/γ-Al2O3 showed the highest activity, which was attributed to the cooperation of Pd0 and Pd2+ species. However, all sulfur-poisoned catalysts showed a decline in activity, which was quantitatively related to the amount of (NH4)2SO4. It was found that the Pd0 active sites were more easily contaminated by sulfur species than the Pd2+ active sites, resulting in the deactivation of the catalysts. In addition, γ-Al2O3 also reacted with sulfur to produce aluminum sulfur, which led to a significant increase in the strong acid site of the catalyst, while no beneficial effect was observed during our study.

Confining shell-sandwiched Ag clusters in MnO2-CeO2 hollow spheres to boost activity and stability of toluene combustion

Confining shell-sandwiched Ag clusters in MnO2-CeO2 hollow spheres to boost activity and stability of toluene combustion

Effects of sulfur poisoning on physicochemical properties and performance of MnO2/AlNi-PILC for toluene catalytic combustion

AlNi pillared clay (AlNi-PILC) was synthesized firstly, and then MnO2 was supported via wetness impregnation from nitrate precursors. Sulphation was performed by in-situ decomposing ammonium sulfate with different concentrations over MnO2/AlNi-PILC. Catalysts before and after sulfur poisoning were characterized by XRD, N2 adsorption/desorption, HRTEM, XPS, H2-TPR and NH3-TPD. MnO2/AlNi-PILC exhibited high catalytic activity, allowing the complete toluene combustion. Structure of the catalyst was obviously damaged after sulfur poisoning. (001) crystal plane strength of AlNi-PILC was decreased significantly. Meanwhile, the specific surface area and pore volume reduced with increase of sulfate concentration. Sulfur species were readily formed on the surface of poisoned catalyst and deposited in the pore structure of AlNi-PILC, which resulted in significant impacts on the structural stability, acidity and the number of active species. These changes were responsible for the decreased catalytic performance.

Preparation of highly dispersed Pt/Hβ catalyst via supercritical fluid deposition and its catalytic performance for combustion of toluene

The emission of volatile organic compounds (VOCs) causes serious atmospheric environmental problems and catalytic combustion is one of the most promising methods in the treatment of VOCs. In this work, the Pt/Hβ catalyst was fabricated via supercritical fluid deposition (SFD) for the first time and its activity was evaluated for toluene catalytic combustion. The preparation conditions during the SFD process were optimized. Na2PtCl6 was selected as the precursor and 450 °C as the reduction temperature. The catalysts prepared by the SFD and impregnation (IM) were compared. The Pt/Hβ catalyst prepared by SFD had smaller size and higher dispersion and its T90 was 25 °C lower than that prepared by IM, which showed obvious size effect. For the similar activity, the Pt loading on catalyst prepared by SFD is only 50% of that on catalyst prepared by IM, showing obvious reduction effect for noble metal.

Active surface RuOx species originating from size-driving self-dispersion process for toluene catalytic combustion

Catalytic combustion method is an effective way to degrade aromatic volatile organic compounds (VOCs). The size of Ru species significantly affect the catalytic performance, while lack of enough concern for VOCs catalytic oxidation. In this work, we deposited a series of Ru nanoparticles (1.6, 2.9, and 3.6 nm) on CeO2 support for toluene catalytic combustion, and reported a size-dependent performance under oxidizing atmosphere. The catalytic performance was improved with the decrease of Ru size (T90 = 214 °C on 1.6RuCe-SD, compared to 228 °C of 3.6RuCe-SD, and 244 °C of RuCe-IM). The drastic activity improvement may result from the smallest size of Ru and the highest formation degree of coordinatively-unsaturated sites during a self-dispersion (redispersion) process. The active surface RuOx species originating from the smaller Ru contain a higher ratio of active Run+, oxygen vacancy, and stronger ability to facilitate dehydrogenation and aromatic ring breakage, thus eventually boosting the toluene combustion activity. This work brings forward a simple strategy to expose coordinatively-unsaturated sites based on size-driving self-dispersion for catalyst design for the elimination of typical VOCs and other environmental applications.

Boosting catalytic toluene combustion over Mn doped Co3O4 spinel catalysts: Improved mobility of surface oxygen due to formation of Mn-O-Co bonds

Catalytic combustion is considered as the most promising technology for removing VOCs over composite metal oxide catalysts. Herein, Mn doped Co3O4 spinel catalysts (MnaCo1-aOx) like spherical were successfully prepared via solvothermal method, and applied for catalytic toluene combustion. The physical and chemical properties of catalysts were analyzed by various characterization techniques such as XRD, N2 physical-adsorption, SEM, TEM, H2-TPR, O2-TPD, XPS and in-situ DRIFTS. Among these catalysts, Mn0.4Co0.6Ox shows optimal catalytic activity (T50 = 206 °C; T90 = 215 °C) and stability, and it can still maintain good activity even in presence of H2O. The amounts of the surface Co2+, Mn4+and lattice oxygen are improved based on the interaction between Co and Mn ions (Mn3+ + Co3+ → Mn4+ + Co2+), leading to far stronger oxidation ability of catalyst. The formation of the surface Mn-O-Co bonds on spinel catalysts MnaCo1-aOx improves the mobility of surface oxygen. In addition, the catalytic combustion of toluene over these catalysts follows the Mars-van Krevelen mechanism and the surface lattice oxygen plays a crucial role in the cycle of oxygen species based on in-situ DRIFTS results.

Remarkable Pd/SnO2 nano-rod catalysts with ultra-low Pd content for toluene combustion: Clarifying the effect of SnO2 morphology on the valence states of the supported Pd species and the vital role of Pd0

To develop efficient Pd/SnO2 catalysts with ultra-low Pd loadings for toluene combustion, nano-rod (SnO2-R) and nano-particle (SnO2-P) supports have been intentionally prepared. SnO2-P has a much larger surface area and lower crystallinity than SnO2-R, hence possessing richer surface-active O22- and O2- sites. HRTEM and XPS demonstrate that only Pd2+ is formed on Pd/SnO2-P. In contrast, a considerable amount of Pd0 is formed besides Pd2+ over Pd/SnO2-R, which is highly effective to adsorb/activate both toluene and O2 molecules. It was discovered that surface Pd0 plays a more critical role than the active oxygen sites. Therefore, Pd/SnO2-R demonstrates much higher activity than Pd/SnO2-P at the same Pd loading. With SnO2-R support, 9 times less Pd could be used to get a catalyst with rival activity than with SnO2-P. The reported results might shed some new lights for people to design highly efficient catalysts with ultra-low noble metal contents.