Higher Oxygen Adspecies Concentration Research Articles

Influence of preparation method on catalytic performance of three-dimensionally ordered macroporous NiO–CuO for CO oxidation

A series of three-dimensionally ordered macroporous (3DOM) nickel−copper mixed oxides (with the NiO/CuO molar ratios of 3 : 3, 3 : 2, and 3 : 1) calcined at various temperatures (450, 550, and 650 ​°C) were prepared using the dual-templating (Pluronic P123 and polymethyl methacrylate (PMMA)) method in a mixed solution of ethylene glycol and methanol with different volumetric ratios (1 : 2, 1 : 1.5, and 1 : 1). The sample obtained after the use of P123 and PMMA exhibited a much higher catalytic activity for CO oxidation, over which a complete CO conversion was achieved at 138 ​°C, CO/O2 volumetric ratio ​= ​2 : 5, and space velocity ​= ​60,000 mL/(g h), and this catalyst possessed good stability in the presence of water vapor in the feed stream. The large surface area, high oxygen adspecies concentration, good low-temperature reducibility, and unique nanovoid 3DOM structure were accountable for the superior catalytic performance of the sample prepared by the dual P123- and PMMA-templating method.

3D ordered honeycomb-shaped CuO⋅Mn2O3: Highly active catalysts for CO oxidation

Highly 3D ordered honeycomb-shaped xCuO⋅Mn2O3 (CuO content (x) = 10, 20, and 30 wt%) catalysts with various CuO contents were synthesized by adopting a colloidal crystal template method with poly(methyl methacrylate) (PMMA) as template, and the as-prepared catalysts were used in oxidation of CO. The catalysts possessed a macro-mesoporous structure. The catalytic performance at low temperatures improved significantly with a rise in CuO content. The light-off temperature (10 % conversion) and the temperature for CO complete conversion were 71 and 98 oC over 30 wt% CuO⋅Mn2O3, respectively. Good stability of the 30 wt% CuO⋅Mn2O3 catalyst was also observed under the dry and wet (in the presence of water vapor) conditions. It is concluded that high catalytic activity of 30 wt.% CuO.Mn2O3 was related to its unique pore structure, high oxygen adspecies concentration, and oxygen vacancy.

Catalytic Oxidation of VOCs over SmMnO3 Perovskites: Catalyst Synthesis, Change Mechanism of Active Species, and Degradation Path of Toluene.

Highly active samarium manganese perovskite oxides were successfully prepared by employing self-molten-polymerization, coprecipitation, sol-gel, and impregnation methods. The physicochemical properties of perovskite oxides were investigated by XRD, N2 adsorption-desorption, XPS, and H2-TPR. Their catalytic performances were compared via the catalytic oxidation of toluene. The perovskite prepared by self-molten-polymerization possessed the highest catalytic capacity, which can be ascribed to its higher oxygen adspecies concentration (Olatt/Oads = 0.53), higher surface Mn4+/Mn3+ ratio (Mn4+/Mn3+ = 0.95), and best low-temperature reducibility (H2 consumption = 0.27; below 350 °C). The most active catalyst also exhibited good cycling and long-term stability for toluene oxidation. After a multistep cycle reaction and a long-term reaction of 42 h, the toluene conversion maintained above 99.9% at 270 °C. Mechanistic study hinted that lattice oxygen was involved in toluene oxidation. The oxidation reaction was dependent on the synergism of lattice oxygen, adsorbed oxygen, and oxygen vacancies. The degradation pathway of toluene, researched by diffuse reflectance infrared Fourier transform spectroscopy and online mass spectrometry technologies, demonstrated that a series of organic byproducts existed at a relatively low temperature. This work provides an efficient and practical method for selecting highly active catalysts and for exploring the catalytic mechanism for the removal of atmospheric environmental pollution.

Influence of group VIB metals on activity of the Ni/MgO catalysts for methane decomposition

Mesoporous 55 wt.% Ni/MgO and group VIB metal (Cr, Mo or W)-doped catalysts were prepared using the facile "one-pot" evaporation-induced self-assembly in ethanol and wetness impregnation methods, respectively. Physicochemical properties of the as-prepared catalysts were characterized by means of the BET, XRD, SEM, TEM, HAADF, XPS, H2-TPR, TPO, and Raman techniques. The doping of Cr to 55 wt% Ni/MgO improved catalytic activity and stability for the decomposition of methane under harsh reaction conditions. The maximal initial methane conversions of 80, 87, and 75% were achieved over the 55 wt.% Ni−xCr/MgO (denoted as 55Ni−xCr/MgO; x = 5, 10, and 15 wt.%) at 675 oC and GHSV = 48,000 mL/(g h), respectively. It is concluded that the high catalytic efficiency of the Cr-doped sample in methane decomposition was associated with its high surface area, high oxygen adspecies concentration, and good low-temperature reducibility. In addition, multi-walled carbon filaments with metal-encapsulated carbon particles were deposited on the Cr-doped catalysts, and the ordered carbon filaments with different diameters and good crystallinity were produced on the surface of the 55Ni−10Cr/MgO catalyst.

Au/MnOx/3DOM SiO2: Highly active catalysts for toluene oxidation

Three-dimensionally ordered macro-/mesoporous silica (3DOM SiO2)-supported manganese oxide and gold nanocatalysts (yAu/zMnOx/3DOM SiO2, y=0–0.95wt%; z=2.7–15.4wt% (weight percentage of Mn2O3)) were prepared using the polymethyl methacrylate-templating, incipient wetness impregnation, and polyvinyl alcohol-protected reduction methods, respectively. It is shown that the yAu/zMnOx/3DOM SiO2 samples displayed a high-quality 3DOM architecture with macropores (180–200nm in diameter) and mesopores (4–6nm in diameter) and a surface area of 220–318m2/g. MnOx nanoparticles (NPs) with a size of 18.7–25.7nm were dispersed on the surface of 3DOM SiO2, and Au NPs with a size of 3.6–3.8nm were uniformly dispersed on the surface of zMnOx/3DOM SiO2. The 0.93Au/11.2MnOx/3DOM SiO2 sample performed the best (the temperature required for achieving a 90% toluene conversion was 255°C at space velocity=20,000mL/(g h)) for toluene oxidation. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between Au and MnOx NPs as well as the unique bimodal porous structure were responsible for the good catalytic performance of 0.93Au/11.2MnOx/3DOM SiO2.

3DOM BiVO4 supported silver bromide and noble metals: High-performance photocatalysts for the visible-light-driven degradation of 4-chlorophenol

Three-dimensionally ordered macroporous (3DOM) photocatalysts BiVO4 (denoted as 3D-BiV), AgBr/3D-BiV, and 0.17wt% M/AgBr/3D-BiV (MAu, Pt, and Pd) were prepared using the polymethyl methacrylate-templating, low-temperature deposition, and polyvinyl alcohol-protected reduction methods, respectively. The as-prepared BiVO4 possessed a good-quality 3DOM structure and a high surface area. It is found that the AgBr and noble metals were uniformly distributed on the surface of 3D-BiV. Among the M/AgBr/3D-BiV samples, the 0.17wt% Pd/AgBr/3D-BiV sample showed the highest photocatalytic activity for the degradation of 4-chlorophenol (4-CP) under visible light illumination (i.e., complete 4-CP degradation could be achieved within 150min), which was associated with its good 3DOM structure, high surface oxygen adspecies concentration, easy transfer and separation of photogenerated carriers, and synergistic effect between AgBr or Pd nanoclusters and BiVO4.

Au/Ce0.6Zr0.3Y0.1O2 Nanorods: Highly Active Catalysts for the Oxidation of Carbon Monoxide and Toluene

The Ce0.6Zr0.3Y0.1O2 (CZY) nanorods and its supported nanosized gold (xAu/CZY, Au loading (x) = 0.4–4.7 wt %) were prepared using the cetyltrimethylammonium bromide-assisted hydrothermal and polyvinylpyrrolidone-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of CO and toluene. It is shown that the CZY in xAu/CZY was cubic in crystal structure, surface areas of CZY and xAu/CZY were in the range of 68–79 m2/g, and the Au nanoparticles (NPs) with a size of 3.1–3.9 nm were well dispersed on the surface of CZY nanorods. Among the xAu/CZY samples, the 4.7Au/CZY sample possessed the highest adsorbed oxygen concentration and the best low-temperature reducibility, and showed the highest catalytic activity at a space velocity of 20 000 mL/(g h): the T50% and T90% (temperatures required for achieving reactant conversions of 50 and 90%) were 32 and 60 °C for CO oxidation and 218 and 265 °C for toluene oxidation, respectively. Deactivation of water vapor addition was reversible, a result due to the competitive adsorption of H2O and toluene as well as oxygen on the sample surface. The apparent activation energies (27–37 and 39–53 kJ/mol) obtained over xAu/CZY were lower than those (42 and 88 kJ/mol) obtained over CZY for CO and toluene oxidation, respectively. On the basis of the characterization results and activity data, we conclude that the excellent catalytic performance of 4.7Au/CZY was associated with its higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between Au NPs and CZY nanorods as well as better Au NPs dispersion.

Nanoplate-aggregate Co3O4 microspheres for toluene combustion

Nanoplate-aggregate microspherical Co3O4 was prepared by an ethylenediamine-assisted hydrothermal route and characterized by means of numerous techniques. Their catalytic activities for toluene combustion were evaluated. The Co3O4 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 Co3O4 sample with a surface area of 66 m2 g−1 had a higher adsorbed oxygen concentration and better low-temperature reducibility than bulk Co3O4. Over the Co3O4 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 Co3O4 microsphere sample was related to its large surface area, high oxygen adspecies concentration, and good low-temperature reducibility.

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 34−38m2/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.

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.

Three-Dimensionally Ordered Macroporous La0.6Sr0.4MnO3 Supported Ag Nanoparticles for the Combustion of Methane

A series of Ag nanoparticles (NPs) supported on three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4MnO3 (yAg/3DOM La0.6Sr0.4MnO3; y = 0, 1.57, 3.63, and 5.71 wt %) were successfully prepared with high surface areas (38.2–42.7 m2/g) by a facile novel reduction method using poly methacrylate colloidal crystal as template in a dimethoxytetraethylene glycol (DMOTEG) solution. Physicochemical properties of these materials were characterized by means of numerous techniques, and their catalytic activities were evaluated for the combustion of methane. It is shown that the yAg/3DOM La0.6Sr0.4MnO3 materials possessed unique nanovoid-like 3DOM architectures, and the Ag NPs were well dispersed on the inner walls of macropores. Among the La1–xSrxMnO3 (x = 0.2, 0.4, 0.6, 0.8) and yAg/3DOM La0.6Sr0.4MnO3 (y = 0, 1.57, 3.63, and 5.71 wt %) samples, 3.63 wt % Ag/3DOM La0.6Sr0.4MnO3 performed the best, giving T10%, T50%, and T90% (temperatures corresponding to methane conversion =10, 50, and 90%) of 361, 454, and 524 °C, respectively, and the highest turnover frequency (TOFAg) value of 1.86 × 10–5 (mol/molAg s) at 300 °C. The apparent activation energies (39.1–37.5 kJ/mol) of the yAg/3DOM La0.6Sr0.4MnO3 samples were much lower than that (91.4 kJ/mol) of the bulk La0.6Sr0.4MnO3 sample. The effects of water vapor and sulfur dioxide on the catalytic activity of the 3.63 wt % Ag/3DOM La0.6Sr0.4MnO3 sample were also examined. It is concluded that its super catalytic activity was associated with its high oxygen adspecies concentration, good low-temperature reducibility, large surface area, and strong interaction between Ag and La0.6Sr0.4MnO3 as well as the unique nanovoid-walled 3DOM structure.

Gold Supported on Iron Oxide Nanodisk as Efficient Catalyst for The Removal of Toluene

In the present study, nanodisk-like Fe2O3 was first prepared using the hydrothermal method, and then its supported gold catalysts (xAu/Fe2O3 nanodisk, x = 0.71–6.55 wt %) were fabricated using the polyvinyl alcohol-protected reduction method. Under the reaction conditions of toluene concentration = 1000 ppm, toluene/O2 molar ratio = 1/400, and space velocity = 20 000 mL/(g h), 6.55Au/Fe2O3 nanodisk performed the best (T50% = 200 °C and T90% = 260 °C). The apparent activation energies (46–50 kJ/mol) obtained over the xAu/Fe2O3 nanodisk were smaller than that (65 kJ/mol) obtained over the Fe2O3 nanodisk for toluene oxidation. We conclude that the high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au nanoparticles and the Fe2O3 nanodisk are responsible for the high catalytic performance of the 6.55Au/Fe2O3 nanodisk.

Porous FeOx/BiVO4–δS0.08: Highly efficient photocatalysts for the degradation of Methylene Blue under visible-light illumination

Porous S-doped bismuth vanadate with an olive-like morphology and its supported iron oxide (y wt.% FeOx/BiVO4–δS0.08, y = 0.06, 0.76, and 1.40) photocatalysts were fabricated using the dodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnation methods, respectively. It is shown that the y wt.% FeOx/BiVO4–δS0.08 photocatalysts contained a monoclinic scheetlite BiVO4 phase with a porous olive-like morphology, a surface area of 8.8–9.2 m2/g, and a bandgap energy of 2.38–2.42 eV. There was co-presence of surface Bi5+, Bi3+, V5+, V3+, Fe3+, and Fe2+ species in y wt.% FeOx/BiVO4–δS0.08. The 1.40 wt.% FeOx/BiVO4–δS0.08 sample performed the best for Methylene Blue degradation under visible-light illumination. The photocatalytic mechanism was also discussed. We believe that the sulfur and FeOx co-doping, higher oxygen adspecies concentration, and lower bandgap energy were responsible for the excellent visible-light-driven catalytic activity of 1.40 wt.% FeOx/BiVO4–δS0.08.

Au/3DOM La0.6Sr0.4MnO3: Highly active nanocatalysts for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4MnO3 (LSMO) and its supported gold (xAu/LSMO, x=3.4–7.9wt%) catalysts were prepared using the polymethyl methacrylate-templating and gas-bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. There were good correlations of surface-adsorbed oxygen species concentration and low-temperature reducibility with the catalytic activity of the sample for CO and toluene oxidation. Among the LSMO and xAu/LSMO samples, 6.4Au/LSMO performed the best, giving T50% and T90% values of −19 and 3°C for CO oxidation and 150 and 170°C for toluene oxidation, respectively. The apparent activation energies (31–32 and 44–48kJ/mol) obtained over xAu/LSMO were much lower than those (45 and 59kJ/mol) obtained over LSMO for the oxidation of CO and toluene, respectively. It is concluded that higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and LSMO are responsible for the excellent catalytic performance of 6.4Au/LSMO.

Au/3DOM LaCoO3: High-performance catalysts for the oxidation of carbon monoxide and toluene

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) LaCoO3 and its supported Au (xAu/3DOM LaCoO3, x=0–7.63wt%) catalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. 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 xAu/3DOM LaCoO3 samples displayed a 3DOM architecture and a high surface area of 24–29m2/g. The 7.63Au/3DOM LaCoO3 sample exhibited the highest adsorbed oxygen species concentration and the best low-temperature reducibility, and hence the best catalytic performance. Over 7.63Au/3DOM LaCoO3, the T10%, T50%, and T90% (corresponding to the temperatures required for achieving a reactant conversion of 10%, 50%, and 90%) were 136, 188, and 202°C for toluene oxidation at space velocity (SV)=20,000mL/(gh), and −61, −6, and 42°C for CO oxidation at SV=10,000mL/(gh), respectively. Over xAu/3DOM LaCoO3, the apparent activation energies were 31.4–37.4kJ/mol for toluene oxidation and 16.6–19.4kJ/mol for CO oxidation. We believe that the high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au and 3DOM LaCoO3 might account for the excellent catalytic performance of 7.63Au/3DOM LaCoO3.

In situ PMMA-templating preparation and excellent catalytic performance of Co3O4/3DOM La0.6Sr0.4CoO3 for toluene combustion

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4CoO3 (LSCO)-supported Co3O4 (x wt% Co3O4/3DOM LSCO; x=0, 2, 5, 8, and 10) were prepared using the in situ poly(methyl methacrylate)-templating strategy. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the combustion of toluene. It is shown that the x wt% Co3O4/3DOM LSCO samples displayed a 3DOM architecture and a high surface area of 29–32m2/g. Among the x wt% Co3O4/3DOM LSCO samples, the 8wt% Co3O4/3DOM LSCO sample possessed the highest adsorbed oxygen species concentration and the best low-temperature reducibility. The 8wt% Co3O4/3DOM LSCO sample showed the best catalytic performance for toluene combustion (the temperatures required for toluene conversions of 10, 50, and 90% were 158, 210, and 227°C at a space velocity of 20,000mL/(gh), respectively). The apparent activation energies (43–58kJ/mol) of the x wt% Co3O4/3DOM LSCO (x=0–10) samples were lower than those (59–67kJ/mol) of the 8wt% Co3O4/bulk LSCO and bulk LSCO samples. It is concluded that the excellent catalytic performance of 8wt% Co3O4/3DOM LSCO was associated with its high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Co3O4 and LSCO as well as high-quality 3DOM structure.

Enhanced visible-light photocatalytic activities of porous olive-shaped sulfur-doped BiVO4-supported cobalt oxides

Porous S-doped bismuth vanadate with an olive-like morphology and its supported cobalt oxide (y wt% CoOx/BiVO4−δS0.08, y = 0.1, 0.8, and 1.6) photocatalysts were fabricated using the dodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnation methods, respectively. It is shown that the y wt% CoOx/BiVO4−δS0.08 photocatalysts were single-phase with a monoclinic scheetlite structure, a porous olive-like morphology, a surface area of 8.8–9.2 m2/g, and a bandgap energy of 2.38–2.41 eV. There was the co-presence of surface Bi5+, Bi3+, V5+, V3+, Co3+, and Co2+ species in y wt% CoOx/BiVO4−δS0.08. The 0.8 wt% CoOx/BiVO4−δS0.08 sample performed the best for methylene blue degradation under visible-light illumination. The photocatalytic mechanism was also discussed. We believe that the sulfur and CoOx co-doping, higher oxygen adspecies concentration, and lower bandgap energy were responsible for the excellent visible-light-driven catalytic activity of 0.8 wt% CoOx/BiVO4−δS0.08.

The microemulsion preparation and high catalytic performance of mesoporous NiO nanorods and nanocubes for toluene combustion

Cubically crystallized mesoporous nickel oxide nanorods and nanocubes were fabricated by using a facile microemulsion strategy with cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) as surfactant. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic activities were evaluated for the combustion of toluene. It was shown that the morphology of the samples strongly depended on the nature of surfactant: when CTAB was used, the product was mesoporous NiO nanorods; when SDS was adopted, mesoporous NiO nanocubes were obtained. The NiO-CTAB-2 sample derived with a Ni2+/CTAB molar ratio of 0.364 displayed the highest surface area (ca. 46m2/g) and the best low-temperature reducibility. A clear correlation of oxygen adspecies concentration or low-temperature reducibility with catalytic performance was observed. The high catalytic activity (T50%=256°C and T90%=278°C at SV=20,000mL/(gh)) for toluene combustion of NiO-CTAB-2 was related to its larger surface area, higher oxygen adspecies concentration, and better low-temperature reducibility.

Au/3DOM Co3O4: highly active nanocatalysts for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous Co3O4 (3DOM Co3O4) and its supported gold (xAu/3DOM Co3O4, x = 1.1-8.4 wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Co3O4 and xAu/3DOM Co3O4 samples exhibited a surface area of 22-27 m(2) g(-1). The Au nanoparticles with a size of 2.4-3.7 nm were uniformly deposited on the macropore walls of 3DOM Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO and toluene oxidation. Among 3DOM Co3O4 and xAu/3DOM Co3O4, the 6.5Au/3DOM Co3O4 sample performed the best, giving a T90% (the temperature required for achieving a conversion of 90%) of -35 °C at a space velocity of 20 000 mL g(-1) h(-1) for CO oxidation and 256 °C at a space velocity of 40 000 mL g(-1) h(-1) for toluene oxidation. The effect of water vapor was more significant in toluene oxidation than in CO oxidation. The apparent activation energies (26 and 74 kJ mol(-1)) over 6.5Au/3DOM Co3O4 were lower than those (34 and 113 kJ mol(-1)) over 3DOM Co3O4 for CO and toluene oxidation, respectively. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and 3DOM Co3O4 were responsible for the excellent catalytic performance of 6.5Au/3DOM Co3O4.

Three-dimensionally ordered macroporous Eu0.6Sr0.4FeO3 supported cobalt oxides: Highly active nanocatalysts for the combustion of toluene

Three-dimensionally ordered macroporous (3DOM) Eu0.6Sr0.4FeO3-supported cobalt oxide nanocatalysts (yCoOx/3DOM-ESFO; ywt%=1, 3, 6, and 10) were prepared using the incipient wetness impregnation method. Physicochemical properties of the composite materials were characterized by means of numerous techniques, and their catalytic performance was evaluated for the combustion of toluene. It is shown that all of the samples displayed a well-defined 3DOM architecture with a surface area of 22–31m2g−1 and the loaded cobalt oxide nanoparticles with a diameter of 7–11nm were well dispersed on the surface of the 3DOM-ESFO support. Among the yCoOx/3DOM-ESFO samples, the 3CoOx/3DOM-ESFO and 6CoOx/3DOM-ESFO ones possessed the highest oxygen adspecies concentration and the best reducibility at low temperature, and hence showing the best catalytic performance (the temperatures required for 50 and 90% toluene conversions were ca. 250 and 270°C at a space velocity of 20,000mLg–1h–1, respectively) for toluene combustion. The apparent activation energies (ca. 72kJmol−1) of 3CoOx/3DOM-ESFO and 6CoOx/3DOM-ESFO were lower than that (81kJmol−1) of 3DOM-ESFO. It is concluded that the enhanced catalytic performance of 3CoOx/3DOM-ESFO and 6CoOx/3DOM-ESFO for toluene combustion was mainly related to their higher oxygen adspecies concentrations, stronger reducibility at low temperature, and better dispersion of cobalt oxide nanoparticles.