Enhanced emissions of NHb>3b>, Nb>2b>O and Hb>2b> from a Pd-only TWC and supported Pd model catalysts: Light-off and sulfur level studies

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• 作者：Isidro Mejí ; a-Centeno^a ; ^b ; Salvador Castillo^b ; Gustavo A. Fuentes^a ; ^{gfuentes@xanum.uam.mx}
• 关键词：Ammonia ; Nitrous oxide ; Hydrogen ; Palladium ; TWC ; Greenhouse gases ; Sulfur level in fuel
• 刊名：Applied Catalysis B ; Environmental
• 出版年：2012
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：30 May, 2012
• 卷：119-120
• 期：Complete
• 页码：234-240
• 文件大小：786 K

摘要

In this work we study the formation of NHb>3b>, Nb>2b>O and Hb>2b> side products during operation of three-way catalytic converters (TWC) in a simulated engine exhaust. We used a commercial Pd-only TWC and supported Pd model catalysts in light-off and during constant temperature tests under rich conditions. Nb>2b>O is observed primarily during light-off and its low temperature formation (110-320 掳C) proceeds via reduction of NO by CO when Ob>2b> is present, or by Hb>2b> in its absence. We detected also Nb>2b>O formation at 500 掳C that has not been reported previously, proceeding via reduction with CO.

NHb>3b> is formed in the 200-600 掳C range via reduction of NO by Hb>2b>. The Hb>2b> required to produce NHb>3b> is generated via steam reforming and water gas-shift reactions over the catalysts. On a molar basis, the Hb>2b> emission is about five-fold higher than that of NHb>3b> during cold start of TWC.

We determined the effect of SOb>2b> level during constant temperature experiments at 500 掳C, extending the work of Gandhi and Shelef . In CeOb>2b>-containing catalysts the interaction with SOb>2b> favors the production of Nb>2b>O, but lowers that of NHb>3b>, apparently by suppressing selectively the reaction path leading to Hb>2b> needed for the reaction.

Our study suggests that the use of low and ultra-low sulfur gasoline by cars equipped with TWC lowers the emission of Nb>2b>O to the atmosphere during high temperature operation but enhances the production of NHb>3b> and Hb>2b>. This is a matter of concern because NHb>3b> is involved in the formation of nano, fine and ultra fine inorganic particles in the atmosphere.