Dynamics of Two-Step CO Oxidation Light-Off on Pt/ $$\gamma$$ γ -Al $$_2$$ 2 O $$_3$$ 3 and Pd/ $$\gamma$$ γ -Al $$_2$$ 2 O $$_3$$ 3 in the Presence of C $$_3$$ 3 H $$_6$$ 6

Abstract

Although the kinetics of CO and hydrocarbon (HC) oxidation reactions on three-way catalyst and diesel oxidation catalysts for automotive exhaust gas aftertreatment has been studied for a couple of decades, there are still some phenomena affecting the catalyst performance and pollutant conversion that need to be better understood and controlled. Two-step CO light-off is an undesired effect that significantly delays the process of reaching full CO conversion in the exhaust gas mixture including also hydrocarbons. In such a case CO light-off curve exhibits a plateau or shoulder where the CO conversion does not increase or even temporarily decreases with temperature, though there is enough O\(_2\) available for both CO and HC oxidation. The onset of hydrocarbon oxidation may inhibit the CO conversion due to blocking of active catalytic sites by adsorbed reaction intermediates. Furthermore, CO can be released as a by-product of the hydrocarbon oxidation. In this contribution we present the results of a systematic experimental study exploring these phenomena on Pt/\(\gamma\)-Al\(_2\)O\(_3\) and Pd/\(\gamma\)-Al\(_2\)O\(_3\) catalysts. Pt/\(\gamma\)-Al\(_2\)O\(_3\) showed larger decrease of CO conversion caused by accumulation of the surface intermediates. On the contrary, the production of CO by incomplete C\(_3\)H\(_6\) oxidation was higher on Pd/\(\gamma\)-Al\(_2\)O\(_3\). Overall extent of the two-step CO light-off effect was higher on Pt/\(\gamma\)-Al\(_2\)O\(_3\).