Abstract
Abstract The reaction network of the NO x storage and reduction over Pt−Ba/Al 2 0 3 ‘lean NO x trap’ catalysts is presented in this paper. The NO x storage was investigated at first. The collected results showed that a dual pathway is operating when starting from NO/O 2 mixtures: the first route implies the well-known oxidation of NO to NO 2 , and its subsequent adsorption via disproportionation to form nitrates (nitrate route), whereas the second novel route consists of a stepwise oxidation of NO in the presence of oxygen to form nitrite ad-species, which are progressively oxidized to nitrates (nitrite route). Then the reduction of stored NO x with hydrogen is addressed. The bulk of data points out that the reduction of stored nitrates occurs under near isothermal conditions through a Pt-catalysed surface reaction that does not involve the thermal desorption of the stored nitrates as a preliminary step. A specific role of a Pt−Ba interaction was suggested, which plays a role in the NO x storage phase as well. The effect of the operating conditions (temperature, presence of CO 2 and water) on both adsorption-reduction phases has been also analysed.
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