Activity For Toluene Combustion Research Articles

Study on Pt-structured anodic alumina catalysts for catalytic combustion of toluene: Effects of competitive adsorbents and competitive impregnation methods

Novel competitive impregnation methods were used to prepare high dispersion Pt-structured anodic alumina catalysts. It is found that competitive adsorbents owning different acidity result in different Pt loading amount and also exert great effects on Pt distribution, particle size and redox ability. The suitable adsorption ability of lactic acid led to its best activity for catalytic combustion of toluene. Co-competitive and pre-competitive impregnation methods were also compared and the mechanisms of two competitive methods were proposed. Co-competitive impregnation made Pt distribute more uniformly through pore channels and resulted in better catalytic activity, because of the weaker spatial constraint effect of lactic acid. Furthermore, the optimized Pt-structured anodic alumina catalyst also showed a good chlorine-resistance under moisture atmosphere, because water could promote the reaction of dichloromethane (DCM) transformation and clean chloride by-products to release more active sites.

Controlled synthesis of α-MnO2 nanowires and their catalytic performance for toluene combustion

α-MnO2 nanowires with a length about 6–10μm and an average diameter of 20nm were synthesized through a facile hydrothermal process without any templates or surfactants. The products were characterized by X-ray powder diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, hydrogen temperature-programmed reduction techniques, X-ray photoelectron spectroscopy and surface area analysis. The effects of the hydrothermal temperature and the concentration of CH3COOH on the crystal phase and morphology of the final products were studied in detail. The hydrothermal temperature and the concentration of CH3COOH play crucial roles in determining the crystal phase and morphology of the products. The possible formation mechanism of the α-MnO2 nanowires was investigated and discussed. Additionally, the as-prepared α-MnO2 nanowires showed higher catalytic activity for toluene combustion than the commercial MnO2, suggesting their potential applications in the elimination of volatile organic compounds.

Pd–Co based spinel oxides derived from pd nanoparticles immobilized on layered double hydroxides for toluene combustion

Noble metal nanoparticles (noble metal NPs, noble metal=Ag, Pt and Pd) have been successfully immobilized on CoAl-layered double hydroxide (CoAl-LDHs) layers using a simple and facile self-redox process to afford noble metal NPs immobilized on CoAl-LDHs (N–CoAl-LDHs, N=Ag, Pt and Pd). In addition, the CoAl-LDHs and N-CoAl-LDHs were calcined in air at 600°C to afford the CoAlO and N-CoAlO catalysts for toluene combustion. The catalytic and characterization results indicated that the Pd–CoAlO catalyst exhibited the highest catalytic activity because it possessed the highest low-temperature reducibility and the most abundant surface Co3+ and surface adsorbed oxygen species. In addition, the noble metal NP sizes of the N–CoAlO catalysts affected the catalytic activity for toluene combustion, and the existence of catalytically active PdO contributes to the excellent catalytic activity of the Pd–CoAlO catalyst for toluene combustion. The comparison experiments reveal that the PdO phase and CoAlO support play significant role in the toluene combustion and they participate cooperatively in the reaction process. In addition, the in situ DRIFTS results indicated that the benzoate species are the main intermediate species in toluene combustion, which should be further oxidized by O2 to the final products (i.e., CO2 and H2O).

Catalytic oxidation of toluene over Au–Co supported on SBA-15

Au–Co supported on mesoporous silica materials SBA-15 was prepared with about 15wt.% cobalt then deposition-precipitation with 2wt.% Au. The results showed that while SBA-15 provided the long ordered arrangement of the channels for support, mixtures of cobalt oxides and gold nanoparticles are dispersed in the mesoporous channels. The sample exhibited excellent catalytic activity for toluene combustion, a complete decomposition (about 100%) of toluene had been achieved at the reaction temperature over 573K and space velocity 30,000h−1. The kinetics showed that the activation energy of the sample was 96.06kJ/mol (22.96kcal/mol) and frequency factor was 1.05×1010s−1, respectively. All these results indicate that while mesoporous materials give a high surface area support for metals, cobalt offers active supports for gold particles, which might be a combined way to overcome the shortcomings of low specific area for reducible transition metal oxides and low activity for inert oxides.

One-pot hydrothermal preparation and catalytic performance of porous strontium ferrite hollow spheres for the combustion of toluene

Strontium ferrite (SFO) hollow spheres with or without porous shells were fabricated via a novel one-pot hydrothermal route with the assistance of glucose and/or ethylenediamine. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic performance was evaluated for the combustion of toluene. It is shown that the SFO samples possessed an orthorhombic structure and displayed a porous hollow spherical morphology with a surface area of 18–27m2/g. The SFO sample (SFO-3) derived hydrothermally at 170°C with a glucose/ethylenediamine volumetric ratio of 0.3/1.0 exhibited the highest surface area and oxygen adspecies concentration and the best low-temperature reducibility. Among the SFO samples, the SFO-3 sample showed the best catalytic activity for toluene combustion, and the T10%, T50%, and T90% were ca. 145, 255, and 298°C at a space velocity of 20,000mL/(gh), respectively. It is concluded that the good catalytic performance of SFO-3 was associated with its surface oxygen species concentration and better low-temperature reducibility.

A facile route to cage-like mesoporous silica coated ZSM-5 combined with Pt immobilization

Uniform core–shell composites with cage-like mesoporous silica (CmesoSiO2) shells and zeolite HZSM-5 cores have been synthesized by a facile acid-catalyzed sol–gel coating process. The mesoporous silica shells are uniform and coated on the anisotropic HZSM-5 crystal faces, and the shell-thicknesses can be tuned from 25 to 70 nm. The core–shell composites possess a high surface area (∼862 m2 g−1) and pore volume (∼0.66 cm3 g−1), large pore sizes (3.2–8.2 nm) and unchanged zeolite micropore properties. The silica shells are composed of cage-like mesopores and entrances (ranging from 3.2 to 8.2 nm) as well as a plenty of micropores. Pt nanocatalysts with an average particle size of ∼3.2 nm have been successfully encapsulated into the micropores and partial mesopores of the cage-like silica shells. The catalytic oxidation of toluene shows that the Pt/HZ@CmesoSiO2 composite presents an equivalent activity for toluene combustion at the light-off temperature of ∼195 °C (T50%) relative to the mixture catalyst (198 °C of T50%), but more excellent catalytic durability without activity loss (193 °C of T50%) after a 100 h test.

Structural changes during toluene complete oxidation on supported EuFeO3 monitored by in situ 151Eu and 57Fe Mössbauer spectroscopy

Pure EuFeO3 and ceria were prepared via a sol–gel citrate route and were calcined at 700°C. Separately, a 20wt% EuFeO3/CeO2 was prepared via incipient wetness impregnation of calcined ceria with citrate precursors and calcined in the same conditions. SBET, XRD, toluene chemisorption, toluene–TPD and in situ 151Eu and 57Fe Mössbauer investigations were performed. All characterization data indicate the formation of a well-dispersed EuFeO3 at the surface of CeO2. During the oxidation of toluene 151Eu and 57Fe Mössbauer spectroscopy suggested a cooperative effect of the cations. The catalysts were tested in total oxidation of toluene. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuFeO3. All structural changes during operation time were reversible.

A comparative study of bulk and 3DOM-structured Co3O4, Eu0.6Sr0.4FeO3, and Co3O4/Eu0.6Sr0.4FeO3: Preparation, characterization, and catalytic activities for toluene combustion

Three-dimensionally ordered macroporous (3DOM) and bulk Co3O4, Eu0.6Sr0.4FeO3 (ESFO), and 3 wt% Co3O4/Eu0.6Sr0.4FeO3 (3Co3O4/ESFO) were fabricated using the PMMA-templating (3DOM-Co3O4 and 3DOM-ESFO), citric acid-assisted hydrothermal (Co3O4-bulk and ESFO-bulk), and incipient wetness impregnation (3Co3O4/3DOM-ESFO and 3Co3O4/ESFO-bulk) methods, respectively. Physicochemical properties of these materials were characterized by means of various techniques, and their catalytic activities were evaluated for toluene combustion. Compared to the nonporous Co3O4 and ESFO samples, the 3DOM-Co3O4, 3DOM-ESFO, and 3Co3O4/3DOM-ESFO samples exhibited higher oxygen adspecies concentrations and better low-temperature reducibility. The 3Co3O4/3DOM-ESFO sample showed the best catalytic activity for toluene combustion, giving the T50% and T90% of 251 and 269°C at 20,000mL/(gh), respectively. The apparent activation energies of these samples were in the range of 72–88kJ/mol. We believe that the higher oxygen adspecies concentration, better low-temperature reducibility, and synergistic action between Co3O4 and 3DOM-structured ESFO were responsible for the excellent catalytic performance of 3Co3O4/3DOM-ESFO.

Catalytic combustion of toluene over Fe–Mn mixed oxides supported on cordierite

The catalytic combustion of toluene over Fe–Mn mixed oxides supported on cordierite was investigated. The catalysts were synthesized by the impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area measurement. The effects of the mole ratio of Fe to Mn, the loading of Fe–Mn mixed oxides on the catalyst support and the calcination temperature were all investigated. The results indicate that Fe–Mn/cordierite catalysts with a 4 mol ratio of Fe to Mn, used with 10wt% loading, and calcined at 500°C showed the highest catalytic activities as measured by the oxidation of toluene. Compared to unsupported powder catalysts of Fe–Mn mixed oxides, the Fe–Mn/cordierite catalyst showed higher activity for the catalytic combustion of toluene with less active component.

A new route to preparation of palladium catalysts for VOC combustion

Methyltheophylline is known to be effective and highly selective extractant for Pd in the solvent extraction process. The high selectivity for Pd extraction might be due to the formation of chelate complex of Pd and methyltheophylline. The chelate complexes made insoluble precipitate in organic solvent when it became a certain condition. Partially-oxidized Pd nanoparticles below 100 nm were obtained by calcination of the precipitate. Pd/γ-Al 2O 3 and Pd/cordierite honeycomb catalysts were prepared by conventional impregnation method using the organic solvent containing Pd extracted from aqueous solution, and their catalytic activities for toluene combustion were compared with that of the Pd catalysts prepared from PdCl 2 aqueous solution. Consequently, the Pd catalyst prepared by using Pd extracted organic solvent showed remarkably higher activity for toluene combustion than that prepared from PdCl 2 aqueous solution.

Catalytic Combustion of Toluene on Cu-Mn Complex Oxides Prepared by Urea-Based Hydrothermal Method

Catalytic combustion of toluene on Cu-Mn complex oxides was investigated. The catalysts were prepared by urea-based hydrothermal method and characterized by XRD and SEM. It was found that both the decrease of the Cu/Mn molar ratio and the increase of reaction time contributed to improving catalytic activity for toluene combustion. The temperature for 99% conversion of toluene (T99) was lowered to 210°C. The main crystalline phases of Cu-Mn complex oxides were CuO and Cu0.45Mn0.55O2. It was showed that the existence and high dispersion of Cu-Mn complex oxides were related to the catalytic combustion activity.

Preparation of CuxCo1-x/Al2O3/Cordierite Monolithic Catalysts and the Catalytic Combustion of Toluene

A series of Cu x Co 1- x /Al 2 O 3 /cordierite ( x = 0–1) catalysts were prepared using cordierite as a support, a boehmite primer sol as the first washcoat layer and copper as well as cobalt oxides as the activity washcoat layer. The structure of the catalysts was characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and temperature-programmed reduction. Toluene was chosen as a model compound to evaluate the catalytic activity in a conventional fixed-bed quartz reactor. The results indicate that Cu-Co-O was present when the Cu content was low. CuO diffraction peaks were observed when the Cu content was high. Both Co 2+ and Co 3+ exist on the surface of the obtained monolithic catalysts while Cu 2+ is the main Cu species. The addition of a certain amount of copper oxide improved the reducibility of the cobalt oxide, which enhanced the catalytic activity of the catalysts. All the obtained catalysts showed good activity for the catalytic combustion of toluene. The Cu 0.5 Co 0.5 /Al 2 O 3 /cordierite catalyst showed the best catalytic activity. Toluene was completely oxidized at 315 °C. 摘要：以堇青石蜂窝陶瓷为基底, Al 2 O 3 浆料为过渡胶体, Cu 和 Co 为催化活性组分, 制备了一系列 Cu x Co 1- x /Al 2 O 3 /堇青石 ( x = 0−1) 整体式催化剂. 采用 X 射线衍射、X 射线光电子能谱、扫描电镜和程序升温还原等手段对催化剂进行了表征. 以甲苯为模型化合物, 在微型固定床反应器上评价了催化剂的催化性能. 结果表明, 当 Cu 含量较低时, 在整体式催化剂上形成了Cu-Co-O 固溶体; 当 Cu 含量较高时, 可以检测到 CuO. 在催化剂表面, Co 以 Co 2+ 和 Co 3+ 形式存在, 而 Cu 主要以 Cu 2+ 形式存在. 适量 Cu 的加入可以改善催化剂中 Co 的氧化还原性能, 有利于催化剂活性的提高. 在所制备的催化剂中, Cu 0.5 Co 0.5 /Al 2 O 3 /堇青石整体式催化剂活性最高, 在315 o C 可以完全催化燃烧消除甲苯. Cu x Co 1- x /Al 2 O 3 /cordierite monolithic catalysts were prepared and their catalytic performance during toluene combustion was evaluated. The catalysts show good activity for the catalytic combustion of toluene.

Catalytic combustion of toluene on Pt zeolite coated cordierite foams

The catalytic properties of Pt based cordierite foam catalysts have been evaluated in catalytic combustion of toluene (800 ppm in air). The catalysts contain identical Pt content (0.1%) which was introduced by three different ways: Pt ion exchange on MFI zeolite and then coating on the foam; Pt ion exchange after zeolite coating and finally Pt directly wet impregnated on the cordierite foam. The catalytic behaviour of Pt foam based catalysts was compared with that of PtMFI zeolite under powder form. Pt exchanged MFI supported on the cordierite foams present an improvement of activity for toluene combustion of about 50 °C on the light off temperature ( T 50%). The enhanced performance of the structured catalysts is due not only to the open structure of foams and homogeneous thin layers catalyst deposited on their cell walls, but also to the fact that the size and location of Pt particles present in MFI zeolite are changed during the dipping step. Indeed, as prepared Pt samples and those used in the preparation of the slurry were observed by transmission electron microscopy revealing that the chemical interaction of PtMFI zeolite with the binder and detergent, both present in the slurry, leads to an increase of Pt particles size which were found to migrate from internal pores to the external surface of zeolite crystallites thereby increasing catalytic activity.

Effect of drying and calcination on the toluene combustion activity of a monolithic CuMnAg/γAl2O3/cordierite catalyst

AbstractBACKGROUND: This paper presents a mathematical modeling and factorial analysis of the toluene combustion activity of a cordierite monolith supported copper–manganese–silver mixed‐oxide catalyst in the drying and calcination processes, using response surface methodology. A central composite rotatable design is performed to collectively study the effect of drying temperature, calcination temperature and calcination time. Experimental results are provided to confirm the validity of the models developed.RESULTS: The calcination temperature is the most significant process factor affecting the catalytic combustion activity. It is also shown that the combustion activity increases in most cases with decreasing calcination time and that a moderate calcination or drying temperature is required to increase the combustion activity. The optimal factor levels are drying temperature 160 °C, calcination temperature 500 °C, and calcination time 3 h.CONCLUSIONS: There is significant scope to improve the combustion activity of the monolithic catalyst through the optimization of the drying and calcination process factors. Response surface methodology is an effective technique for mathematical modeling and factorial analysis of the catalytic activity of monolithic catalysts. Copyright © 2010 Society of Chemical Industry

A Study on the Relationship Between Low-Temperature Reducibility and Catalytic Performance of Single-Crystalline La0.6Sr0.4MnO3+δ Microcubes for Toluene Combustion

Single-crystalline La0.6Sr0.4MnO3+δ microcubes of cubic perovskite phase were prepared hydrothermally. The adopted temperature and time of hydrothermal treatment and the amount of KOH used had great effects on the low-temperature reducibility of La0.6Sr0.4MnO3+δ . The initial H2 consumption rate of La0.6Sr0.4MnO3+δ played a vital role in determining its catalytic activity for toluene combustion. It is concluded that the perovskite-type oxide catalyst with a higher initial H2 consumption rate displayed a higher catalytic activity for the addressed reaction.

Toluene combustion on γ-Al 2O 3–CeO 2 catalysts prepared from boehmite and cerium nitrate

γ-Al 2O 3–Ce catalysts were obtained by the impregnation of boehmite with cerium nitrate at different Ce contents (1, 5, 10, 20 wt%) and tested in the catalytic combustion of toluene. The catalysts annealed at 650 °C showed a diminution of the BET specific surface areas as a function of the cerium content. At low cerium content, the XRD spectra showed the γ-Al 2O 3 phase, whereas at high cerium content, the γ-Al 2O 3 phase and cerium oxide were observed. A diminution of the Lewis acidity was shown by the FTIR-pyridine absorption spectra. Both Ce 3+ and Ce 4+in variable proportions were observed by XPS. It has been found that the activity for the toluene combustion can be related to the C 4+/Ce 3+ ratio obtained in the various catalysts. The higher the C 4+/Ce 3+ ratio is the higher the toluene combustion activity.

Combustion of Toluene over Titanium(IV) Oxide Catalyst

Combustion catalysts free from precious metals, such as platinum, for removal of volatile organic compounds were investigated. Common metal oxides (titanium(IV) oxide (TiO2), alumina and silica) were selected as candidates for a catalyst for combustion of toluene at low concentrations. Complete conversion of toluene was not achieved even at 500°C without catalysts, although the ignition point of toluene is 480°C. TiO2 exhibited the highest activity for combustion of toluene among representative metal oxides. Toluene was almost quantitatively converted to carbon dioxide (>99% yield) over TiO2 under the condition of appropriate contact time at 500°C.

In situ structural changes during toluene complete oxidation on supported EuCoO 3 monitored with 151Eu Mössbauer spectroscopy

Ceria–zirconia supported (10 and 20 wt.% EuCoO 3) versus bulk EuCoO 3 perovskite were prepared via citrate decomposition at 700 °C and tested for toluene complete oxidation. S BET, XRD, XPS, H 2-TPD and in situ 151Eu Mössbauer investigations were performed. Electron delocalization processes around the Eu cations are induced by the reaction, as proved via the evolution of the Mössbauer parameters. All characterization data indicate the formation of a well-dispersed EuCoO 3 at the surface of Ce 0.9Zr 0.1O 2 for the 10 wt.% loading and larger crystallite formation for 20 wt.% loading. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuCoO 3. All structural changes during operation time are reversible.

Catalytic combustion of toluene on platinum-containing monolithic carbon aerogels

Monolithic organic aerogels were prepared by the sol–gel procedure from the polymerisation reaction of resorcinol and formaldehyde in water. The organic aerogels were heat treated in inert atmosphere at either 500 or 1000°C to obtain the carbon aerogels. The catalysts were prepared by impregnation with an aqueous solution of [Pt(NH3)4]Cl2 or by dissolving this salt in the initial aerogel mixture. Supported catalysts were pretreated in He at 400°C or H2 at 300°C before their characterization by H2 chemisorption, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy or before testing their catalytic activity. Catalyst activities in toluene combustion were evaluated by conversion versus temperature (light-off curves) and conversion versus time catalytic tests. In the case of catalysts prepared by impregnation, the light-off curves for the total combustion of toluene were shifted to lower temperatures with increasing Pt particle size. This suggests that the reaction was sensitive to the Pt structure within the dispersion range of these catalysts. However, the reverse occurred with catalysts prepared by mixing the precursor in the initial aerogel mixture. Results found could be due to the different surface Pt content of these catalysts as revealed by X-ray photoelectron spectroscopy. This difference was related to the growth of large three-dimensional Pt particles on the surface of the less dispersed catalyst. This means that there is a critical Pt particle size above which the toluene combustion activity decreases with increasing Pt particle size, due to the reduction in active surface sites available for the combustion reaction. Other effect that might influence the activity of these last catalysts is the encapsulation of some Pt particles by the carbon matrix.

Toluene combustion over palladium supported on various metal oxide supports

Metal–support interaction in the catalytic combustion of toluene was studied using metal oxides with different acid–base properties as supports for Pd. The catalytic performance was correlated with XPS data and the reaction order for oxygen. These studies revealed that the affinity for oxygen of Pd surface changed according to the acid–base character of metal oxide over MgO, Al2O3, SiO2, SnO2, Nb2O5, and WO3. However, ZrO2 exhibited exceptional character in that metal Pd was unusually stabilized, which was derived from the weak interaction between Pd and support surface. The reason for high toluene combustion activity of Pd/ZrO2 was ascribed to the stabilization of metal Pd on ZrO2.