Shaohua Xie

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.

Dual-templating synthesis of three-dimensionally ordered macroporous La0.6Sr0.4MnO3-supported Ag nanoparticles: controllable alignments and super performance for the catalytic combustion of methane

Highly dispersed Ag nanoparticles supported on high-surface-area 3DOM La0.6Sr0.4MnO3 were successfully generated via the dimethoxytetraethylene glycol-assisted gas bubbling reduction route. The macroporous materials showed super catalytic performance for methane combustion.

Morphologically Controlled Synthesis of Porous Spherical and Cubic LaMnO3 with High Activity for the Catalytic Removal of Toluene

A morphology-controlled molten salt route was developed to synthesize porous spherical LaMnO3 and cubic LaMnO3 nanoparticles using the as-prepared porous Mn2O3 spheres as template. The porous LaMnO3 spheres with an average pore size of about 34.7 nm and the cubic LaMnO3 nanoparticles with a good dispersion were confirmed by scanning electron microscope, transmission electron microscope, and N2 adsorption-desorption measurements. The mechanism of morphological transformation from the porous spherical structure to the cubic particle in the molten salt was proposed. The porous spherical LaMnO3 and cubic LaMnO3 catalysts exhibited high catalytic performance for the combustion of toluene, and the latter performed better than the former. Under the conditions of toluene/oxygen molar ratio = 1/400 and space velocity = 20,000 h(-1), the temperature required for 10, 50, and 90% toluene conversion was 110, 170, and 220 °C over the cubic LaMnO3 catalyst, respectively. Based on the results of X-ray photoelectron spectroscopic and hydrogen temperature-programmed reduction characterization, we deduce that the higher surface Mn(4+)/Mn(3+) molar ratio and better low-temperature reducibility enhanced the catalytic performance of cubic LaMnO3. Taking the facile morphology-controlled synthesis and excellent catalytic performance into consideration, we believe that the well-defined morphological LaMnO3 samples are good candidate catalytic materials for the oxidative removal of toluene.

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.

Catalytic removal of volatile organic compounds using ordered porous transition metal oxide and supported noble metal catalysts

Most of volatile organic compounds (VOCs) are harmful to the atmosphere and human health. Catalytic combustion is an effective way to eliminate VOCs. The key issue is the availability of high performance catalysts. Many catalysts including transition metal oxides, mixed metal oxides, and supported noble metals have been developed. Among these catalysts, the porous ones attract much attention. In this review, we focus on recent advances in the synthesis of ordered mesoporous and macroporous transition metal oxides, perovskites, and supported noble metal catalysts and their catalytic oxidation of VOCs. The porous catalysts outperformed their bulk counterparts. This excellent catalytic performance was due to their high surface areas, high concentration of adsorbed oxygen species, low temperature reducibility, strong interaction between noble metal and support and highly dispersed noble metal nanoparticles and unique porous structures. Catalytic oxidation of carbon monoxide over typical catalysts was also discussed. We made conclusive remarks and proposed future work for the removal of VOCs.

Efficient Removal of Methane over Cobalt-Monoxide-Doped AuPd Nanocatalysts

To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au-Pd alloy nanoparticles (NPs) to generate high-performance Au-Pd-xCoO/three-dimensionally ordered macroporous (3DOM) Co3O4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO-CoO active sites, which was beneficial for the improvement in adsorption and activation of CH4 and catalytic performance. The Au-Pd-0.40CoO/3DOM Co3O4 sample performed the best (T90% = 341 °C at a space velocity of 20 000 mL g-1 h-1). Deactivation of the 3DOM Co3O4-supported Au-Pd, Pd-CoO, and Au-Pd-xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd-CoO/3DOM Co3O4 catalyst at high temperatures (680-800 °C) might be due to decomposition of the PdOy active phase into aggregated Pd0 NPs. The Au-Pd-xCoO/3DOM Co3O4 nanocatalysts exhibited better thermal stability and water tolerance ability compared to the 3DOM Co3O4-supported Au-Pd and Pd-CoO nanocatalysts. We believe that the supported Au-Pd-xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

Catalytic performance enhancement by alloying Pd with Pt on ordered mesoporous manganese oxide for methane combustion

Ordered mesoporous Mn 2 O 3 (meso-Mn 2 O 3 ) and meso-Mn 2 O 3 -supported Pd, Pt, and Pd-Pt alloy x (Pd y Pt)/meso-Mn 2 O 3 ; x =(0.10-1.50) wt%; Pd/Pt molar ratio ( y )=4.9-5.1 nanocatalysts were prepared using KIT-6-templated and poly(vinyl alcohol)-protected reduction methods, respectively. The meso-Mn 2 O 3 had a high surface area, i.e., 106 m 2 /g, and a cubic crystal structure. Noble-metal nanoparticles (NPs) of size 2.1-2.8 nm were uniformly dispersed on the meso-Mn 2 O 3 surfaces. Al-loying Pd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd 5.1 Pt)/meso-Mn 2 O 3 gave the best performance; T 10% , T 50% , and T 90% (the temperatures required for achieving methane conversions of 10%, 50%, and 90%) were 265, 345, and 425℃, respectively, at a space velocity of 20000 mL/(g·h). The effects of SO 2 , CO 2 , H 2 O, and NO on methane combustion over 1.41(Pd 5.1 Pt)/meso-Mn 2 O 3 were also examined. We conclude that the good catalytic performance of 1.41(Pd 5.1 Pt)/meso-Mn 2 O 3 is associated with its high-quality porous structure, high adsorbed oxy-gen species concentration, good low-temperature reducibility, and strong interactions between Pd-Pt alloy NPs and the meso-Mn 2 O 3 support.

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.