Hydrogen production from a combination of the water-gas shift and redox cycle process of methane partial oxidation via lattice oxygen over LaFeO3 perovskite catalyst.
ABSTRACT A redox cycle process, in which CH4 and air are periodically brought into contact with a solid oxide packed in a fixed-bed reactor, combined with the water-gas shift (WGS) reaction, is proposed for hydrogen production. The sole oxidant for partial oxidation of methane (POM) is found to be lattice oxygen instead of gaseous oxygen. A perovskite-type LaFeO3 oxide was prepared by a sol-gel method and employed as an oxygen storage material in this process. The results indicate that, under appropriate reaction conditions, methane can be oxidized to CO and H2 by the lattice oxygen of LaFeO3 perovskite oxide with a selectivity higher than 95% and the consumed lattice oxygen can be replenished in a reoxidation procedure by a redox operation. It is suggested that the POM to H2/CO by using the lattice oxygen of the oxygen storage materials instead of gaseous oxygen should be possibly applicable. The LaFeO3 perovskite oxide maintained relatively high catalytic activity and structural stability, while the carbonaceous deposits, which come from the dissociation of CH4 in the pulse reaction, occurred due to the low migration rate of lattice oxygen from the bulk toward the surface. A new dissociation-oxidation mechanism for this POM without gaseous oxygen is proposed based on the transient responses of the products checked at different surface states via both pulse reaction and switch reaction over the LaFeO3 catalyst. In the absence of gaseous-phase oxygen, the rate-determining step of methane conversion is the migration rate of lattice oxygen, but the process can be carried out in optimized cycles. The product distribution for POM over LaFeO3 catalyst in the absence of gaseous oxygen was determined by the concentration of surface oxygen, which is relevant with the migration rate of lattice oxygen from the bulk toward the surface. This process of hydrogen production via selective oxidation of methane by lattice oxygen is better in avoiding the deep oxidation (to CO2) and enhancing the selectivity. Therefore, this new route is superior to general POM in stability (resistance to carbonaceous deposition), safety (effectively avoiding accidental explosion), ease of operation and optimization, and low cost (making use of air not oxygen).
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ABSTRACT: Hydrogen production by steam reforming of toluene as a model aromatic hydrocarbon has been investigated with various Ni/perovskite catalysts. Among them, Ni/LaAlO3 catalyst showed high catalytic activity. Partial substitution of the La site of LaAlO3 support with other elements (Sr, Ba or Ca) was conducted for the Ni/LaAlO3 catalyst, and substitution with 30% Sr promoted catalytic activity and selectivity to hydrogen. Optimization for the Ni loading amount over Ni/La0.7Sr0.3AlO3−δ catalyst revealed that 5 wt% Ni/La0.7Sr0.3AlO3−δ had the highest toluene conversion and the smallest amount of carbon deposition. To elucidate the role of doped Sr, the catalytic natures of Sr-substituted catalyst Ni/La0.7Sr0.3AlO3−δ and Sr-supported catalyst Ni/Sr/LaAlO3 were compared. Results show that Sr-ions should be incorporated in the LaAlO3 perovskite structure to show high catalytic performance. Based on results of transient response test with H218O on Ni/La0.7Sr0.3AlO3−δ, Ni/Sr/LaAlO3, and Ni/LaAlO3 at reaction temperature of 873 K, the formation of 18O-products was observed only on Ni/La0.7Sr0.3AlO3−δ catalyst derived from redox between the lattice oxygen in the perovskite and water. Lattice oxygen in the La0.7Sr0.3AlO3−δ support worked as active oxygen species to enhance its catalytic nature.Applied Catalysis A General 01/2013; 451:160–167. · 3.67 Impact Factor
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ABSTRACT: BaTi1−xInxO3−δ perovskites (called BITx) were evaluated as supports of nickel catalysts for methane oxidation in the absence of gas-phase oxygen. Ni/BaTi1−xInxO3−δ (x = 0 and 0.3) catalysts were studied, by temperature programmed surface reaction of methane (TPSR-CH4) and pulses at 850 °C. In these conditions, the only oxygen source is the oxide bulk support. TPSR-CH4 results suggest that the support is able to oxidize the methane producing H2 and CO at temperatures above 750 °C. Ni/BT and Ni/BIT0.7 catalysts, showed a high selectivity towards partial oxidation products. Ni/BIT0.7 catalyst was more stable than Ni/BT due to the existence of Ni–In alloys which catalyze less the cracking reaction. Moreover, the higher ionic conductivity of BIT0.7 facilitates the O2− ions diffusion to the surface and promotes the oxidation of carbonaceous deposits formed on the metal–support interface preventing thus catalyst deactivation.Catalysis Today 11/2010; 157(s 1–4):177–182. · 3.31 Impact Factor
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ABSTRACT: A series of Fe2O3/Al2O3, Fe2O3/CeO2, Ce0.7Zr0.3O2, and Fe2O3/Ce1−x Zrx O2 (x = 0.1–0.4) oxides was prepared and their physicochemical features were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and H2-temperature-programmed reduction (H2-TPR) techniques. The gas–solid reactions between these oxides and methane for syngas generation as well as the catalytic performance for selective oxidation of carbon deposition in O2-enriched atmosphere were investigated in detail. The results show that the samples with the presence of Fe2O3 show much higher activity for methane oxidation compared with the Ce0.7Zr0.3O2 solid solution, while the CeO2-contained samples represent higher CO selectively in methane oxidation than the Fe2O3/Al2O3 sample. This suggests that the iron species should be the active sites for methane activation, and the cerium oxides provide the oxygen source for the selective oxidation of the activated methane to syngas during the reaction between methane and Fe2O3/Ce0.7Zr0.3O2. For the oxidation process of the carbon deposition, the CeO2-containing samples show much higher CO selectivity than the Fe2O3/Al2O3 sample, which indicates that the cerium species should play a very important role in catalyzing the carbon selective oxidation to CO. The presence of the Ce–Zr–O solid solution could induce the growth direction of the carbon filament, resulting in a loose contact between the carbon filament and the catalyst. This results in abundant exposed active sites for catalyzing carbon oxidation, strongly improving the oxidation rate of the carbon deposition over this sample. In addition, the Fe2O3/Ce0.7Zr0.3O2 also represents much higher selectivity (ca. 97 %) for the conversion of carbon to CO than the Fe2O3/CeO2 sample, which can be attributed to the higher concentration of reduced cerium sites on this sample. The increase of the Zr content in the Fe2O3/Ce1−x Zrx O2 samples could improve the reactivity of the materials for methane oxidation, but it also reduces the selectivity for CO formation.Rare Metals 04/2013; · 0.81 Impact Factor