C.T. Au

The decomposition of NO on CNTs and 1 wt% Rh/CNTs

Carbon nanotubes (CNTs) and CNTs-supported rhodium were tested as catalysts for NO decomposition. For the fresh catalysts, 100% NO conversion was achieved at 600°C over CNTs; when 1 wt% Rh was loaded on CNTs, 100% NO conversion was achieved at 450°C. If the catalysts were pre-reduced in H2 at or above 300°C, 100% NO conversions were observed at 300°C. XPS investigation indicated that there was still metallic rhodium (BE=307.2 eV) on Rh/CNTs after heating in air at 500°C for 2 h and after the NO decomposition reaction. As for a 1 wt% Rh/Al2O3 sample, the rhodium (BE = 308.2 eV) was completely in the form of Rh2O3 after similar treatments. These results suggest that compared to γ-Al2O3, the CNTs material is more capable of keeping the rhodium in its metallic state. The results obtained in H2-TPR studies support this conclusion. In addition, TEM investigation revealed that the rhodium particles distributed rather evenly over CNTs with a particle diameter of around 8 nm. We propose that CNTs can be used as a material for the facilitation of NO decomposition.

RE0.6Zr0.4−xYxO2 (RE = Ce, Pr; x = 0, 0.05) solid solutions: an investigation on defective structure, oxygen mobility, oxygen storage capacity, and redox properties

Abstract We have examined the crystal structures, surface textures, oxygen mobility, oxygen storage capacity, and redox behaviors of RE0.6Zr0.4−xYxO2 (RE=Ce, Pr; x=0, 0.05) solid solutions. According to the results of X-ray diffraction (XRD) studies, there are two cubic phases (Ce0.75Zr0.25O2, major; ZrO1.87, minor) in Ce0.6Zr0.4O2 (denoted as CZ hereafter) and Ce0.6Zr0.35Y0.05O2 (CZY), but only one cubic phase in Pr0.60Zr0.40O2 (PZ) and Pr0.60Zr0.35Y0.05O2 (PZY). These nanosized materials are porous and have large surface areas. As revealed by the Ce 3d and Pr 3d results of X-ray photoelectron spectroscopic (XPS) investigations, the doping of Y3+ ions into the CZ and PZ lattices resulted in an increase in concentration of oxygen vacancies and Ce3+ and Pr4+ ions. The results of H2 (or CO)–O2 titration and temperature-programmed reduction (TPR)–reoxidation experiments indicate the presence of a reversible redox behavior of Ce4+/Ce3+ in CZY and Pr4+/Pr3+ in PZY. The results of 18 O / 16 O exchange studies show that, with the presence of oxygen vacancies, the lattice O2− mobility on/in CZY and PZY enhanced. Based on such outcomes, we conclude that, by incorporating Y3+ ions into CZ and PZ, one can enhance (i) lattice oxygen mobility, (ii) Ce3+ and Pr4+ concentrations, and (iii) oxygen uptake capacity. We observed that PZY is superior to CZY in redox behavior, oxygen mobility, and oxygen storage capacity.

Carbon dioxide reforming of methane to syngas over SiO2-supported rhodium catalysts

Abstract The decomposition of CH4 and CO2 as well as the reaction between CH4 and CO2 over SiO2-supported rhodium catalysts has been investigated in the temperature range of 600–800°C over a pulse reactor. The initial activities for methane decomposition and CO2 decomposition increased with the increase of rhodium loading; whereas the activity for CO formation in the CH4+CO2 reaction was almost unaffected by the rhodium loading over catalysts with rhodium loading >0.05%. Different reaction behaviors of methane reforming with CO2 were observed at 700°C and 800°C. At 700°C, CO2 conversion was higher than CH4 conversion; whereas at 800°C, CH4 conversion was higher than CO2 conversion. The bond order conservation-Morse potential (BOCMP) calculations indicate that the oxygen at on-top site can promote the dissociation of methane on the Rh(111) surface. Normal deuterium isotope effect was observed to be more noticeable on the methane conversion reaction than on the CO formation reaction, while no such effect was observed on the CO2 conversion reaction. The mechanism for CO and H2 formation in the reforming of methane with CO2 is discussed based on the results of the present work.

Magnesia-carbon nanotubes (MgO-CNTs) nanocomposite: novel support of Ru catalyst for the generation of COx-free hydrogen from ammonia

Magnesia–carbon nanotubes (abbreviated as MgO–CNTs) nanocomposites were prepared by impregnation of CNTs with Mg(NO3)2·6H2O in ethanol solution, followed by drying at 353 K and calcination at 873 K, respectively. The nanocomposites are thermally more stable than CNTs in a H2 flow. The use of the nanocomposites as support yielded more efficient Ru catalysts for the generation of COx-free hydrogen from NH3 decomposition.

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.

Preparation and characterization of rare earth orthovanadates for propane oxidative dehydrogenation

High purity rare earth orthovanadates (REVO4), YVO4, LaVO4, CeVO4, NdVO4, SmVO4 and EuVO4, were prepared by the citrate method. XRD, FT-IR, LRS and TPR techniques were employed to characterize these orthovanadates. The catalytic performance of SmVO4, LaVO4 and YVO4 in the oxidative dehydrogenation of propane can compete with that of Mg3V2O8. The selectivity of propene over CeVO4, NdVO4 and EuVO4 was relatively lower. The correlation between the reducibility and the selectivity of the catalysts implied that the V4+/V3+ couple might be involved in the dehydrogenation process.

Hydrothermal Fabrication and Catalytic Properties of La1-xSrxM1-yFeyO3 (M = Mn, Co) That Are Highly Active for the Removal of Toluene

A series of La(1-x)Sr(x)M(1-y)Fe(y)O(3) (M = Mn, Co; x = 0, 0.4; y = 0.1, 1.0) perovskite-type oxide catalysts have been fabricated via a strategy of citric acid complexation coupled with hydrothermal treatment. The materials are characterized by a number of analytical techniques. The oxidation of toluene is used as a probe reaction for the evaluation of catalytic performance. It is found that both La(0.6)Sr(0.4)FeO(3) and LaFeO(3) exhibit high activities. The partial substitution of manganese and cobalt with iron can significantly improve the catalytic performance of La(0.6)Sr(0.4)MnO(3) and La(0.6)Sr(0.4)CoO(3). At toluene/O(2) molar ratio = 1/200 and space velocity = 20,000 h(-1), the catalytic activity decreases in the sequence of La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) > La(0.6)Sr(0.4)FeO(3) > La(0.6)Sr(0.4)Mn(0.9)Fe(0.1)O(3) > LaFeO(3) > La(0.6)Sr(0.4)CoO(3) > La(0.6)Sr(0.4)MnO(3). Compared to the Fe-free counterparts, the La(0.6)Sr(0.4)Mn(0.9)Fe(0.1)O(3) and La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) catalysts are, respectively, 50 and 85 degrees C lower with regard to the temperature required for complete toluene oxidation. Toluene can be completely oxidized at 245 degrees C over La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3). The excellent catalytic performance of La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) can be attributed to the presence of (i) Fe(3+)-O-Fe(4+) couples, (ii) a transition of electronic structure, and (iii) a trace amount of Co(3)O(4).

P123-assisted hydrothermal synthesis and characterization of rectangular parallelepiped and hexagonal prism single-crystalline mgo with three-dimensional wormholelike mesopores.

By adopting the strategy of dissolution-recrystallization under hydrothermal conditions (at 240 degrees C for 72 h) in the presence of a triblock copolymer (Pluronic P123), we fabricated nano- and microparticles of single-crystalline MgO of rectangular parallelepiped and hexagonal prism morphologies. The MgO crystallites display three-dimensional wormholelike mesopores and have a surface area as high as 298 m(2)/g even after calcination at 550 degrees C for 3 h.

The effect of calcination temperature on the catalytic performance of 2 wt.% Mo/HZSM-5 in methane aromatization

We observed that, at a calcination temperature (Tc) of 500 or 700 ◦ C, the catalytic performance of 2 wt.% Mo/HZSM-5 for methane aromatization was compatible with that reported in the literature. When Tc was set at or above 750 ◦ C, the catalyst deactivated and ethylene was the dominant product. The results of our analytic studies suggested that at T c = 500 ◦ C, the Mo species were not uniformly distributed, but existed as microcrystalline MoO3, polymolybdate, and other Mo entities. At T c = 700 ◦ C, Mo species were dispersed on the external surface as well as diffused into the channels of the zeolite. At or above a calcination temperature of 750 ◦ C, dealumination as well as reduction in crystallinity of the zeolite became considerable. The results of atomic absorption spectrophotometric analysis confirmed that the loss of Mo during calcination was insignificant. With the partial destruction of HZSM-5 zeolite and the disappearance of Bronsted acid sites, the 2 wt.% Mo/HZSM-5 material ceased to function as a catalyst for methane aromatization.

Sol–Gel-Generated La2NiO4 for CH4/CO2 Reforming

A stable La2NiO4 catalyst active in CH4/CO2 reforming has been prepared by a sol–gel method. The catalyst was characterized by techniques such as XRD, BET, TPR and TG/DTG. The results show that the conversions of CH4 and CO2 in CH4/CO2 reforming over this catalyst are significantly higher than those over a Ni/La2O3 catalyst prepared by wet impregnation and those over a La2NiO4/γ-Al2O3 catalyst. The TG/DTG outcome confirmed that the amount of carbon deposition observed in the former case was less than that observed in the latter two cases, a phenomenon attributable to the uniform dispersion of nanoscale Ni particles in the sol–gel-generated La2NiO4 catalyst.