Huanggen Yang

Controlled Generation of Uniform Spherical LaMnO3, LaCoO3, Mn2O3, and Co3O4 Nanoparticles and Their High Catalytic Performance for Carbon Monoxide and Toluene Oxidation

Uniform hollow spherical rhombohedral LaMO3 and solid spherical cubic MOx (M = Mn and Co) NPs were fabricated using the PMMA-templating strategy. Hollow spherical LaMO3 and solid spherical MOx NPs possessed surface areas of 21-33 and 21-24 m(2)/g, respectively. There were larger amounts of surface-adsorbed oxygen species and better low-temperature reducibility on/of the hollow spherical LaMO3 samples than on/of the solid spherical MOx samples. Hollow spherical LaMO3 and solid spherical MOx samples outperformed their nanosized counterparts for oxidation of CO and toluene, with the best catalytic activity being achieved over the solid spherical Co3O4 sample for CO oxidation (T50% = 81 °C and T90% = 109 °C) at space velocity = 10,000 mL/(g h) and the hollow spherical LaCoO3 sample for toluene oxidation (T50% = 220 °C and T90% = 237 °C) at space velocity = 20,000 mL/(g h). It is concluded that the higher surface areas and oxygen adspecies concentrations and better low-temperature reducibility are responsible for the excellent catalytic performance of the hollow spherical LaCoO3 and solid spherical Co3O4 NPs. We believe that the PMMA-templating strategy provides an effective route to prepare uniform perovskite-type oxide and transition-metal oxide NPs.

Preparation and high catalytic performance of Au/3DOM Mn2O3 for the oxidation of carbon monoxide and toluene.

Three-dimensionally ordered macroporous (3DOM) Mn2O3 and its supported gold (xAu/3DOM Mn2O3, x=1.9-7.5wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Mn2O3 and xAu/3DOM Mn2O3 samples exhibited a surface area of 34-38m(2)/g. The Au nanoparticles (NPs) with a size of 3.0-3.5nm were uniformly dispersed on the skeletons of 3DOM Mn2O3. The 5.8Au/3DOM Mn2O3 sample performed the best, giving the T90% (the temperature required for a conversion of 90%) of -15°C at space velocity (SV)=20,000mL/(gh) for CO oxidation and 244°C at SV=40,000mL/(gh) for toluene oxidation. The apparent activation energies (30 and 54kJ/mol) over 5.8Au/3DOM Mn2O3 were much lower than those (80 and 95kJ/mol) over 3DOM Mn2O3 for CO and toluene oxidation, respectively. The effects of SV, water vapor, CO2, and SO2 on catalytic activity were also examined. It is concluded that the excellent catalytic performance of 5.8Au/3DOM Mn2O3 was associated with its high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au NPs and 3DOM Mn2O3 as well as high-quality porous architecture.

Ultralow Loading of Silver Nanoparticles on Mn2O3 Nanowires Derived with Molten Salts: A High-Efficiency Catalyst for the Oxidative Removal of Toluene

Using a mixture of NaNO3 and NaF as molten salt and MnSO4 and AgNO3 as metal precursors, 0.13 wt % Ag/Mn2O3 nanowires (0.13Ag/Mn2O3-ms) were fabricated after calcination at 420 °C for 2 h. Compared to the counterparts derived via the impregnation and poly(vinyl alcohol)-protected reduction routes as well as the bulk Mn2O3-supported silver catalyst, 0.13Ag/Mn2O3-ms exhibited a much higher catalytic activity for toluene oxidation. At a toluene/oxygen molar ratio of 1/400 and a space velocity of 40,000 mL/(g h), toluene could be completely oxidized into CO2 and H2O at 220 °C over the 0.13Ag/Mn2O3-ms catalyst. Furthermore, the toluene consumption rate per gram of noble metal over 0.13Ag/Mn2O3-ms was dozens of times as high as that over the supported Au or AuPd alloy catalysts reported in our previous works. It is concluded that the excellent catalytic activity of 0.13Ag/Mn2O3-ms was associated with its high dispersion of silver nanoparticles on the surface of Mn2O3 nanowires and good low-temperature reducibility. Due to high efficiency, good stability, low cost, and convenient preparation, 0.13Ag/Mn2O3-ms is a promising catalyst for the practical removal of volatile organic compounds.

Porous Cube‐Aggregated Co3O4 Microsphere‐Supported Gold Nanoparticles for Oxidation of Carbon Monoxide and Toluene

Porous cube-aggregated monodisperse Co3O4 microspheres and their supported gold (xAu/Co3O4 microsphere, x=1.6-7.4 wt %) nanoparticles (NPs) were fabricated using the glycerol-assisted solvothermal and polyvinyl alcohol-protected reduction methods. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene and CO. It is shown that the cubic Co3O4 microspheres were composed of aggregated cubes with a porous structure. The gold NPs with a size of 3.2-3.9 nm were uniformly deposited on the surface of Co3O4 microspheres. Among the Co3O4 microsphere and xAu/Co3O4 microsphere samples, the 7.4Au/Co3O4 microspheres performed the best, giving T90 % values (the temperature required for achieving a CO or toluene conversion of 90 % at a weight hourly space velocity of 20 000 mL g(-1)  h(-1)) of -8 and 250 °C for CO and toluene oxidation, respectively. In the case of 3.0 vol % water vapor introduction, a positive effect on CO oxidation and a small negative effect on toluene oxidation were observed over the 7.4Au/Co3O4 microsphere sample. The apparent activation energies obtained over the xAu/Co3O4 microsphere samples were in the ranges of 40.7-53.6 kJ mol(-1) for toluene oxidation and 21.6-34.6 kJ mol(-1) for CO oxidation. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between gold NPs and Co3O4 as well as the porous microspherical structure were responsible for the excellent catalytic performance of 7.4Au/Co3O4 microsphere.

Nanoplate-aggregate Co3O4 microspheres for toluene combustion

Abstract Nanoplate-aggregate microspherical Co 3 O 4 was prepared by an ethylenediamine-assisted hydrothermal route and characterized by means of numerous techniques. Their catalytic activities for toluene combustion were evaluated. The Co 3 O 4 sample obtained using 1.0 ml of ethylenediamine and a hydrothermal treatment at 140 °C for 12 h had a nanoplate-aggregate microspherical morphology. This microspherical Co 3 O 4 sample with a surface area of 66 m 2 g −1 had a higher adsorbed oxygen concentration and better low-temperature reducibility than bulk Co 3 O 4 . Over the Co 3 O 4 microsphere sample, the temperatures required for 50% and 90% toluene conversions were 230 and 254 °C, respectively, at a space velocity of 20000 ml g −1 h −1 . The good catalytic performance of the Co 3 O 4 microsphere sample was related to its large surface area, high oxygen adspecies concentration, and good low-temperature reducibility.

Pt/Co3O4/3DOM Al2O3: Highly effective catalysts for toluene combustion

Abstract 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 102 m2/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 the yCo3O4/3DOM Al2O3. The 1.3Pt/8.9Co3O4/3DOM Al2O3 exhibited the best performance for toluene oxidation, with a T90% value (the temperature required to achieve 90% toluene conversion) of 160 °C at a space velocity of 20000 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.

Article (Special Issue on Environmental Catalysis and Materials)Pt/Co3O4/3DOM Al2O3: Highly effective catalysts for toluene combustion

Abstract 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 102 m2/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 the yCo3O4/3DOM Al2O3. The 1.3Pt/8.9Co3O4/3DOM Al2O3 exhibited the best performance for toluene oxidation, with a T90% value (the temperature required to achieve 90% toluene conversion) of 160 °C at a space velocity of 20000 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.