Nanocrystalline perovskites for catalytic combustion and oxygen separation

Nanocrystalline perovskites (Lal-xAMnl-yByO3) were successfully synthesized with higher surface area and smaller grain size by chemical co-precipitation compared to solid-state and complexation/combustion synthesis routes. The choice of solvent, base and suspension pH in co-precipitation was found to strongly affect the chemical stoichiometry of the resulting material. Stoichiometric La0.5Sr0.sMnO3 was successfully obtained at a high pH using isopropanol as the solvent and tetraethylammonium hydroxide as the base. La0.sSr0.sMnO3 was derived with a ultrafine grain size of 13 nm and a high surface area of 43 m2/g at 650⁰C, and maintained its nanocrystalline microstructure on heating to 1000⁰C, with a grain size of 25 nm and a surface area of 19 m2/g. The catalytic activity of these perovskites was investigated for different A- and B-site substitutions. Among LaBO3 perovskites, the catalytic activity was found to decrease in the order: Mn > Fe [approx.] Ni > Co, with LaMnO3 showing the lowest light-off temperature of 420⁰C. The intrinsic catalytic activity at 650C decreased in the order: Ni > Co > Fe > Mn. Substitution of Group IIA metals for La3+ was found to increase the reaction rate of LalxAxMnO3, while higher valency dopants did not change or decreased catalyst activity. In the case of Ca2+ and Sr +dopants, intrinsic activity of Lal-xAxMnO3 was found to increase with doping level until x = 0.4 and 0.6, respectively. La0.4Sr0.6MnO3 exhibited the lowest light-off temperature of 3800C, with a reaction rate that was 2.5 times higher than LaMnO3. Methane TPR experiments showed that methane oxidation over the perovskites occurred by methane adsorption on the catalyst surface via hydrogen abstraction.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Sangar, Neeraj, 1974-

Advisor dc:contributor.advisor

• Jackie Y. Ying.

• Chemical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/17562

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/17562