Yunsheng Xia

Mesoporous chromia with ordered three-dimensional structures for the complete oxidation of toluene and ethyl acetate.

Mesoporous chromia with ordered three-dimensional (3D) hexagonal polycrystalline structures were fabricated at 130, 180, 240, 280, and 350 degrees C in an autoclave through a novel solvent-free route using KIT-6 as the hard template. The as-obtained materials were characterized (by means of X-ray diffraction, transmission electron microscopy, N(2) adsorption-desorption, temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques) and tested as a catalyst for the complete oxidation of toluene and ethyl acetate. We found that with a high surface area of 106 m(2)/g and being multivalent (Cr(3+), Cr(5+), and Cr(6+)), the chromia (meso-Cr-240) fabricated at 240 degrees C is the best among the five in catalytic performance. According to the results of the temperature-programmed reduction and X-ray photoelectron spectroscopy investigations, it is apparent that the coexistence of multiple chromium species promotes the low-temperature reducibility of chromia. The excellent performance of meso-Cr-240 is because of good 3D mesoporosity and low-temperature reducibility as well as the high surface area of the chromia. The combustion follows a first-order reaction with respect to toluene or ethyl acetate in the presence of excess oxygen, and the corresponding average activation energy is 79.8 and 51.9 kJ/mol, respectively, over the best-performing catalyst.

P123-PMMA dual-templating generation and unique physicochemical properties of three-dimensionally ordered macroporous iron oxides with nanovoids in the crystalline walls.

Three-dimensionally (3D) ordered macroporous (3DOM) iron oxides with nanovoids in the rhombohedrally crystallized macroporous walls were fabricated by adopting the dual-templating [Pluronic P123 and poly(methyl methacrylate) (PMMA) colloidal microspheres] strategy with ferric nitrate as the metal precursor in an ethanol or ethylene glycol and methanol mixed solution and after calcination at 550 °C. The possible formation mechanisms of such architectured materials were discussed. The physicochemical properties of the materials were characterized by means of techniques such as XRD, TGA/DSC, FT-IR, BET, HRSEM, HRTEM/SAED, UV-vis, XPS, and H(2)-TPR. The catalytic properties of the materials were also examined using toluene oxidation as a probe reaction. It is shown that 3DOM-structured α-Fe(2)O(3) without nanovoids in the macroporous walls was formed in the absence of P123 during the fabrication process, whereas the dual-templating strategy gave rise to α-Fe(2)O(3) materials that possessed high-quality 3DOM structures with the presence of nanovoids in the polycrystalline macropore walls and higher surface areas (32-46 m(2)/g). The surfactant P123 played a key role in the generation of nanovoids within the walls of the 3DOM-architectured iron oxides. There was the presence of multivalent iron ions and adsorbed oxygen species on the surface of each sample, with the trivalent iron ion and oxygen adspecies concentrations being different from sample to sample. The dual-templating fabricated iron oxide samples exhibited much better low-temperature reducibility than the bulk counterpart. The copresence of a 3DOM-structured skeleton and nanovoids in the macropore walls gave rise to a drop in the band-gap energy of iron oxide. The higher oxygen adspecies amounts, larger surface areas, better low-temperature reducibility, and unique nanovoid-containing 3DOM structures of the iron oxide materials accounted for their excellent catalytic performance in the oxidation of toluene.

Three-dimensionally ordered and wormhole-like mesoporous iron oxide catalysts highly active for the oxidation of acetone and methanol.

Three-dimensionally (3D) ordered and wormhole-like mesoporous iron oxides (denoted as Fe-KIT6 and Fe-CA) were respectively prepared by adopting the 3D ordered mesoporous silica KIT-6-templating and modified citric acid-complexing strategies, and characterized by a number of analytical techniques. It is shown that the Fe-KIT6-400 and Fe-CA-400 catalysts derived after 400°C-calcination possessed high surface areas (113-165 m(2)/g), high surface adsorbed oxygen concentrations, and good low-temperature reducibility, giving 90% conversion below 189 and 208°C for acetone and methanol oxidation at 20,000 mL/(g h), respectively. It is believed that the good catalytic performance of Fe-CA-400 and Fe-KIT6-400 was related to factors such as higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and 3D mesoporous architecture.

Synthesis and Characterization of Wormhole-Like Mesoporous SnO2 with High Surface Area

Abstract High-surface-area wormhole-like mesoporous SnO2 with a tetragonal rutile-type structure was fabricated adopting the hydrothermal strategy using poly(ethylene glycol) (PEG) as the template, tin chloride as the tin source, and urea as the precipitating agent. The effects of PEG with different molecular weights and its concentration, hydrothermal temperature, and calcination temperature on the pore structure and morphology of SnO2 were examined. The physical properties of these materials were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, selected-area electron diffraction, infrared spectroscopy, and ultraviolet-visible diffuse reflection spectroscopy. It is shown that the PEG template could be removed by washing, no significant impact of PEG molecular weight was observed on the surface area of the mesoporous SnO2 samples, but the factors such as PEG concentration, hydrothermal temperature, and calcination temperature exerted considerable influence on the pore structure of the SnO2 samples. After the hydrothermal treatment at 120 °C for 29 h with the molar ratio of PEG (with a molecular weight of 6000 g/mol) to Sn of 0.01, a wormhole-like mesoporous SnO2 sample with a high surface area of 161 m2/g and an average pore size of 2.6 nm was generated. The SnO2 samples exhibited good behavior in UV-light absorption. These porous materials are suitable for use as catalysts, supports, and gas sensors.

A comparative investigation of NdSrCu1−xCoxO4−δ and Sm1.8Ce0.2Cu1−xCoxO4−δ (x: 0–0.4) for NO decomposition

Abstract A series of single-phase T-structured NdSrCu 1− x Co x O 4−δ with oxygen vacancies and T′-structured Sm 1.8 Ce 0.2 Cu 1− x Co x O 4−δ ( x : 0–0.4) with oxygen excess were prepared using ultrasound-assisted citric acid complexing method, and characterized by means of techniques such as thermogravimetric analysis and NO temperature-programmed desorption (NO-TPD). The catalytic activities of these materials were evaluated for the decomposition of NO. It was found that the NdSrCu 1− x Co x O 4−δ catalysts were of oxygen vacancies whereas the Sm 1.8 Ce 0.2 Cu 1− x Co x O 4−δ ones possessed excessive oxygen (i.e., over-stoichiometric oxygen); with a rise in Co doping level, the oxygen vacancy density of NdSrCu 1− x Co x O 4−δ decreased while the over-stoichiometric oxygen amount of Sm 1.8 Ce 0.2 Cu 1− x Co x O 4−δ increased. The NO-TPD results revealed that NO could be activated much easier over the oxygen-deficient perovskite-like oxides than over the oxygen-excessive perovskite-like oxides, with the NdSrCuO 3.702 catalyst showing the best efficiency in activating NO molecules. Under the conditions of 1.0% NO/helium, 2800 hr −1 , and 600–900°C, the catalytic activity of NO decomposition followed the order of NdSrCuO 3.702 > NdSrCu 0.8 Co 0.2 O 3.736 > NdSrCu 0.6 Co 0.4 O 3.789 > Sm 1.8 Ce 0.2 Cu 0.6 Co 0.4 O 4.187 > Sm 1.8 Ce 0.2 Cu 0.8 Co 0.2 O 4.104 > Sm 1.8 Ce 0.2 CuO 4.045 , in concord with the sequence of decreasing oxygen vacancy or oxygen excess density. Based on the results, we concluded that the higher oxygen vacancy density and the stronger Cu 3+ /Cu 2+ redox ability of NdSrCu 1− x Co x O 4−δ account for the easier activation of NO and consequently improve the catalytic activity of NO decomposition over the catalysts.

Concurrent catalytic removal of typical volatile organic compound mixtures over Au-Pd/α-MnO2 nanotubes

α-MnO2 nanotubes and their supported Au-Pd alloy nanocatalysts were prepared using hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Their catalytic activity for the oxidation of toluene/m-xylene, acetone/ethyl acetate, acetone/m-xylene and ethyl acetate/m-xylene mixtures was evaluated. It was found that the interaction between Au-Pd alloy nanoparticles and α-MnO2 nanotubes significantly improved the reactivity of lattice oxygen, and the 0.91wt.% Au0.48Pd/α-MnO2 nanotube catalyst outperformed the α-MnO2 nanotube catalyst in the oxidation of toluene, m-xylene, ethyl acetate and acetone. Over the 0.91wt.% Au0.48Pd/α-MnO2 nanotube catalyst, (i) toluene oxidation was greatly inhibited in the toluene/m-xylene mixture, while m-xylene oxidation was not influenced; (ii) acetone and ethyl acetate oxidation suffered a minor impact in the acetone/ethyl acetate mixture; and (iii) m-xylene oxidation was enhanced whereas the oxidation of the oxygenated VOCs (volatile organic compounds) was suppressed in the acetone/m-xylene or ethyl acetate/m-xylene mixtures. The competitive adsorption of these typical VOCs on the catalyst surface induced an inhibitive effect on their oxidation, and increasing the temperature favored the oxidation of the VOCs. The mixed VOCs could be completely oxidized into CO2 and H2O below 320°C at a space velocity of 40,000mL/(g·hr). The 0.91wt.% Au0.48Pd/α-MnO2 nanotube catalyst exhibited high catalytic stability as well as good tolerance to water vapor and CO2 in the oxidation of the VOC mixtures. Thus, the α-MnO2 nanotube-supported noble metal alloy catalysts hold promise for the efficient elimination of VOC mixtures.