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Jin Y.,Tianjin Key Laboratory of Catalysis Science and Technology | Wang G.,Tianjin Key Laboratory of Catalysis Science and Technology | Li Y.,Tianjin University
AIChE 2012 - 2012 AIChE Annual Meeting, Conference Proceedings | Year: 2012

Methane catalytic decomposition reaction (MCD) has received much attention in recent years as a potential route for the direct production of COx (CO/CO2)-free hydrogen because of its environmentally benign, energy efficient and process simple characteristics, which produces an especially suitable feed for low temperature hydrogen fuel cells, e.g. proton exchange membrane fuel cells (PEMFC) and alkaline fuel cells. Besides of generating COx-free hydrogen, MCD produces valuable carbon nanotubes (CNTs) and nanofibers (CNTs) with great application potentials. The catalysts used for MCD are usually group 8-10 transition metals, such as Ni, Fe and Co. The co-precipitated nickel-based catalysts are very active and stable at low temperatures (e.g. 773-873 K). MCD is endothermic and high reaction temperature is advantageous for obtaining high concentration hydrogen. However, the durability of the Ni/Al2O3 catalyst declines swiftly with the increase of the reaction temperature. To improve its durability and delay its deactivation at expected reaction temperatures, the third component, such as metals, or oxides were introduced. In this work, the influence of the doping of iron to co-precipitated Ni-Al catalysts on the stability and activity of the reaction was investigated. The mixed oxide was prepared from the precursor which possesses a well-crystallized hydrotalcite-like anionic clay structure. In the mixed metal oxides obtained from calcination of the co-precipitated precursors, NiO phase dominates and the iron oxide is uniformly dispersed in NiO phase. The constant temperature reaction result indicates that the addition of iron enhances the stability of the Ni/Al2O3 catalyst greatly. Since the diffusion coefficient of carbon atoms through iron metal is three orders of magnitude higher than that through nickel metal. Modification of the catalyst with doping iron increases the carbon diffusion rate thus enhances the stability of the catalyst at high temperatures. The carbon yield of the prepared Ni-Fe/Al2O3 catalyst (mole ratio of Ni-Fe-Al=2:1:1) at 923 K was 851.3 g C/ g cat which is the highest yield in the literature reported and the reaction lasted more than 200 h. This work provides a new catalyst which is extremely stable for MCD reaction and is promising for the H2 production for PEMFC. Source

Rui Z.,Tianjin Key Laboratory of Catalysis Science and Technology | Rui Z.,Arizona State University | Ding J.,Tianjin Key Laboratory of Catalysis Science and Technology | Li Y.,Tianjin Key Laboratory of Catalysis Science and Technology | And 2 more authors.
Fuel | Year: 2010

Perovskite-type SrCo0.8Fe0.2O3-δ (SCF) has been prepared by a liquid citrate method and used to produce O2-CO2 gas mixture for oxyfuel combustion. Oxygen is desorbed and an oxygen-enriched carbon dioxide stream is obtained when SCF is exposed in a carbon dioxide stream at high temperature. Oxygen is adsorbed when SCF is regenerated in an air stream. A carbonation-reaction mechanism for O2-desorption has been identified with the evidences of XRD and TGA analysis. It is found that the theoretical oxygen sorption capacity decreases with the increase of temperature. The sorption kinetics over a temperature range of 700-900 °C has been examined by TGA experiment. Both desorption and sorption processes exhibit a high reaction rate in an initial stage followed by a slower rate in a second stage. It is difficult to reach the theoretical oxygen sorption capacity during the whole temperature range due to the slow oxygen desorption rate. Optimal temperatures for oxygen sorption and desorption processes are determined to be 900 and 850 °C, respectively. Multiple sorption and desorption cycles indicate that SCF sorbent has high reactivity and cyclic stability. Comparison with the reference La0.1Sr0.9Co0.5Fe0.5O2.6 (LSCF) and Sr0.5Ca0.5Co0.5Fe0.5O2.47 (SCCF) sorbents shows that SCF has faster carbonation reaction at high temperature, i.e., 850 and 900 °C, and much higher theoretical oxygen sorption capacities. © 2009 Elsevier Ltd. All rights reserved. Source

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