Pt/Co_3O_4/3DOM Al_2O_3:Highly effective catalysts for toluene combustion

Three-dimensionally ordered macro-/mesoporous alumina（3DOM Al2O3）-supported cobalt oxide and platinum nanocatalysts（xPt/yCo3O4/3DOM Al2O3,Pt mass fraction（x%）= 0-1.4%,Co3O4 mass fraction（y%） = 0-9.2%） were prepared using poly（methyl methacrylate） templating,incipient wetness impregnation and polyvinyl alcohol-protected reduction.The resulting xPt/yCo3O4/3DOM Al2O3 samples displayed a high-quality 3DOM architecture with macropores（180-200 nm in diameter） and mesopores（4-6 nm in diameter） together with surface areas in the range of 94 to 102m^2/g.Using these techniques,Co3O4 nanoparticles（NPs,18.3 nm） were loaded on the 3DOM Al2O3 surface,after which Pt NPs（2.3-2.5 nm） were uniformly dispersed on theyCo3O4/3DOM Al2O3.The1.3Pt/8.9Co3O4/3DOM Al2O3 exhibited the best performance for toluene oxidation,with a T（90%） value（the temperature required to achieve 90%toluene conversion） of 160 ℃ at a space velocity of20000 mL g^（-1） h^（-1）.It is concluded that the excellent catalytic performance of the 1.3Pt/8.9Co3O4/3DOM Al2O3 is owing to well-dispersed Pt NPs,the high concentration of adsorbed oxygen species,good low-temperature reducibility,and strong interaction between the Pt and Co3O4 NPs,as well as the unique bimodal porous structure of the support.

Toluene Combustion over Pd-Ce_(0.4)Zr_(0.6)O_2 Directly Washcoated Monolithic Catalysts

A Ce0.4Zr0.6O2 washcoat was prepared using an impregnation method, which acted as a host for the active Pd component to prepare a Pd-Ce0.4Zr0.6O2/substrate monolithic catalyst for toluene combustion. The catalyst was characterized by scanning electron microscopy （SEM）, Raman spectroscopy, Brunauner-Emmett-Teller （BET）, and carbon monoxide tonperature-programmed reduction （CO-TPR）. It was found that the washcoat had strong vibration-shock resistance according to an ultrasonic test. The Pd-Ce0.4Zr0.6O2/substrate monolithic catalyst calcined at 400 ℃ showed 95% toluene conversion at a temperature as low as 210 ℃. Furthermore, the lowest temperature for 95% toluene conversion was increased by 40℃ after the catalyst calcined at 900℃, indicating that the catalyst had good thermal stability. The results revealed that the developed catalyst in this study was promising for eliminating volatile organic compounds （VOCs）.

Catalytic combustion of toluene over Pd-based monolithic catalysts with a novel washcoat Ce_(0.8)Zr_(0.15)La_(0.05)O_δ

Two novel washcoats Ce0.8Zr0.15La0.05Oδ and Ce0.8Zr0.2O2 was prepared by an impregnation method, which acted as a host for the active Pd component to prepare Pd/Ce0.8Zr0.15La0.05Oδ/substrate and Pd/Ce0.8Zr0.2O2/substrate monolithic catalysts for toluene combustion. The washcoats was characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauner-Emmett-Teller (BET), and H2-temperature-programmed reduction (H2-TPR). The result indicated that both the washcoats had strong vibration-shock resistance according to ultrasonic test. Doping La3+ into CeO2-ZrO2 solid solution could generate more oxygen vacancies, and could inhibit the sinter of CeO2-ZrO2 solid solution when calcined at high temperatures (800, 900 and 1000 °C). The washcoat Ce0.8Zr0.15La0.05Oδ had much better redox properties. The reductive temperature of Ce4+ species shifted to low temperature by 60 °C when the washcoats calcined at high temperatures (800, 900 and 1000 °C). The Pd/Ce0.8Zr0.15La0.05Oδ/substrate monolithic catalyst calcination at 500 °C had the best catalytic activity and the 95% toluene conversion at a temperature as low as 190 °C. When calcined at low temperature (500 and 700 °C), the catalytic activity has little improvement, however, when calcined at high temperature, the catalytic activity of Pd/Ce0.8Zr0.15La0.05Oδ/substrate monolithic catalysts had significant improvement. As catalyst washcoat, the Ce0.8Zr0.15La0.05Oδ had better thermal stability than the washcoat Ce0.8Zr0.2O2, the developed Pd/Ce0.8Zr0.15La0.05Oδ/ substrate monolithic catalyst in this work was promising for eliminating Volatile organic compounds.

Confining shell-sandwiched Ag clusters in MnO_(2)-CeO_(2)hollow spheres to boost activity and stability of toluene combustion

Supported noble metal catalysts have the promising application in volatile organic compounds(VOCs)catalytic combustion but suffer from the deactivation due to noble metal sintering at high temperatures.Herein,we report the construction of shellsandwiched MnO_(2)-Ag-CeO_(2)hollow spheres with remarkable sintering resistance and high activity in toluene combustion.Ag clusters were sandwiched between outer MnO_(2)and inner CeO_(2)shell to enlarge and stabilize metal–support active interface.The unique hollow structure could alter the electronic states of catalysts sites and increase the adsorbed site of reactant molecules.Meanwhile,Mn–Ag–Ce multi-interfaces in MnO_(2)-Ag-CeO_(2)could facilitate the sustainable activation and the stable release of oxygen species via a tandem transfer.The oxygen species at Ag–Mn interface perimeter were instantly replenished by Ag–Ce interface to accelerate a deep oxidation of intermediates,guaranteeing the opening of benzene ring to generate maleic anhydride.This investigation provides a promising method for constructing efficient and sintering-resistant cluster catalysts for VOCs oxidation.

Cu–Mn–Ce ternary mixed-oxide catalysts for catalytic combustion of toluene

Cu-Mn, Cu-Mn-Ce, and Cu-Ce mixed-oxide catalysts were prepared by a citric acid sol-gel method and then characterized by XRD, BET, H_2-TPR and XPS analyses. Their catalytic properties were investigated in the toluene combustion reaction. Results showed that the Cu-Mn-Ce ternary mixed-oxide catalyst with 1：2：4 mole ratios had the highest catalytic activity, and 99% toluene conversion was achieved at temperatures below 220°C. In the Cu-Mn-Ce catalyst, a portion of Cu and Mn species entered into the Ce O2 fluorite lattice, which led to the formation of a ceria-based solid solution. Excess Cu and Mn oxides existed on the surface of the ceria-based solid solution. The coexistence of Cu-Mn mixed oxides and the ceria-based solid solution resulted in a better synergetic interaction than the Cu-Mn and Cu-Ce catalysts, which promoted catalyst reducibility, increased oxygen mobility, and enhanced the formation of abundant active oxygen species.

Pd/silicalite-1: An highly active catalyst for the oxidative removal of toluene

Catalytic combustion is thought as an efficient and economic pathway to remove volatile organic compounds, and its critical issue is the development of high-performance catalytic materials. In this work, we used the in situ synthesis method to prepare the silicalite-1(S-1)-supported Pd nanoparticles(NPs). It is found that the as-prepared catalysts displayed a hexagonal prism morphology and a surface area of 390-440 m^(2)/g. The sample(0.28Pd/S-1-H)derived after reduction at 500°C in 10 vol% H_(2)showed the best catalytic activity for toluene combustion(T50%= 180℃ and T90%= 189℃ at a space velocity of 40,000 m L/(g·hr), turnover frequency(TOFPd) at 160℃ = 3.46 × 10^(-3)sec^(-1), and specific reaction rate at 160℃ = 63.8μmol/(gPd·sec)), with the apparent activation energy(41 k J/mol) obtained over the bestperforming 0.28Pd/S-1-H sample being much lower than those(51-70 k J/mol) obtained over the other samples(0.28Pd/S-1-A derived from calcination at 500℃ in air, 0.26Pd/S-1-im derived from the impregnation route, and 0.27Pd/ZSM-5-H prepared after reduction at 500℃ in 10 vol% H_(2)). Furthermore, the 0.28Pd/S-1-H sample possessed good thermal stability and its partial deactivation due to CO_(2) or H_(2)O introduction was reversible, but SO_(2) addition resulted in an irreversible deactivation. The possible pathways of toluene oxidation over 0.28Pd/S-1-H was toluene → p-methylbenzoquinone → maleic anhydride, benzoic acid, benzaldehyde → carbon dioxide and water. We conclude that the good dispersion of Pd NPs, high adsorption oxygen species concentration, large toluene adsorption capacity, strong acidity,and more Pd~0 species were responsible for the good catalytic performance of 0.28Pd/S-1-H.

Hydrothermal-treated Pt/Al_(2)O_(3) as an excellent catalyst for toluene total oxidation

The preparation of highly active supported noble metal catalysts with a low noble metal loading has always been the ultimate goal of researchers working on catalysis.Hydrothermally treated Pt/Al_(2)O_(3)(Pt/Al_(2)O_(3)-H)exhibits better catalytic activity than that(Pt/Al_(2)O_(3)-C)treated via the conventional calcination approach.At the high space velocity of100,000 m L/(g·hr),the temperature that correspond to 50%toluene conversion(T50)of Pt/Al_(2)O_(3)-H is 115℃ lower than that of Pt/Al_(2)O_(3)-C,and the turnover frequency(TOF)value can reach 0.0756 sec-1.The mechanism by which the hydrothermal approach enhances Pt/Al_(2)O_(3) activity has been investigated.The structure associated with the high catalytic activity of Pt nanoparticles(NPs)can be retained via hydrothermal treatment.Furthermore,the support is transformed to AlO(OH)with numerous surface hydroxyl groups,which in turn can facilitate the adsorption of toluene.And the synergistic effects of Pt NPs and AlO(OH)increases the contents of Pt in oxidation state and active oxygen,which are beneficial for toluene oxidation.

Preparation of 3D micro/nanostructured CeO2： Influence of organic/inorganic acids

CeO2 is an important porous material with a wide range of applications in the abatement of volatile organic compounds （VOCs）. In this paper, we prepared a series of novel three-dimensional （3D） micro/nanostructured CeO2 materials via a solvothermal method. Organic acid-assisted synthesis and inorganic acid post-treatment were used to adjust the Ce02 microstructures. The size of the 3D micro/nanostructures could be controlled in the range from 180nm to 1.5 μm and the surface morphology changed from rough to smooth with the use of different organic acids. The CeO2 synthesized with acetic acid featured a hierarchical porosity and showed good performance for toluene catalytic combustion： a T50 of 187 ℃ and a T90 of 195 ℃. Moreover, the crystallite size, textural properties, and surface chemical states could be tuned by inorganic acid modification. After treatment with HNO3, the modified CeO2 materials exhibited improved catalytic activity, with a T50 of-175 ℃ and a T90 of -187 ℃. We concluded that the toluene combustion activity is related to the porosity and the amount of surface active oxygen of the CeO2. Both these features can be tuned by the co-work of organic and inorganic acids.