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Please use this identifier to cite or link to this item: http://hdl.handle.net/1860/286

Title: Thermal stability and catalytic application of MnOx-ZrO2 oxide powders (The)
Authors: Zhao, Qiang
Keywords: Manganese oxides -- Thermomechanical properties;Materials engineering
Issue Date: 24-May-2004
Abstract: MnOx-ZrO2 mixed oxide is an active catalyst for combustion, oxidation, and oxygen storage applications. MnOx-ZrO2 mixture also has large reversible adsorption capability for NOx, which makes it a promising candidate for NOx abatement in automobile emission control. However, MnOx-ZrO2 mixed oxide has not been used extensively because the processing and the thermal stability of resulting powders have not been studied systematically. It is critical to have thermally stable catalytic material because the application temperature can reach as high as 1000oC during service. In this study, we focused on improving the thermal stability of oxide powders, such as MnOx, ZrO2, and MnOx-ZrO2, by controlling the processing methods and parameters. For pure MnOx made from the precipitation method using Mn(NO3)2 aqueous solution and ammonium hydroxide, we found that lower concentration of Mn(NO3)2 solution and larger amount of ammonium hydroxide resulted in higher surface area powders. For pure ZrO2, we found curing hydrous zirconia in the mother liquid produced ZrO2 powders with larger pore volume and pore size. The specific surface area was also significantly enhanced by curing for the synthesized powders before calcination or after low temperature calcinations, and this improvement could be preserved to high temperatures if SiO2 was doped in ZrO2. A Monte Carlo simulation model examining the effect of primary particle packing on the specific surface area was used to explain the curing result. MnOx-ZrO2 mixtures had higher surface area than the single component oxide at 500 and 700 oC because composite powders sintered less. The sintering behavior of composite powders at 900 oC was opposite to that at 500 oC and the specific surface area of MnOx-ZrO2 decreased drastically at 900 oC. Curing ZrO2 first or using La dopant could significantly enhance the specific surface area of MnOx-ZrO2 at 900 oC. Through the tests of the redox property and NO storage capability we found a close relationship between the enhanced thermal stability and better catalytic performance.
URI: http://dspace.library.drexel.edu/handle/1860/286
Appears in Collections:Drexel Theses and Dissertations

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