Mechanistic study of Pd-BEA as a model catalyst for PNA+DOC integration
Yuntao Gu, University of Virginia
The increasing demand of fuel efficiency and progressively more stringent emission regulations have further motivated cold start exhaust remediation research. Although cold start emission control remains challenging, previous work has shown that zeolite supported Pd catalysts are able to trap NOx at low temperature and subsequently release the NOx, such that the NOx emitted during cold start can be minimized, this concept is commonly referred to as passive NOx adsorber, or PNA. NOx storage performance with the existence of CO and hydrocarbons has also been reported in recent studies showing that PNAs are more efficient in some diesel exhaust conditions. Meanwhile, it has long been reported that Pd-based and bimetallic Pt-Pd catalysts have significant diesel oxidation activity. This study focuses on the integrated catalytic performance of a PNA+DOC catalyst, as well as the reaction mechanism in the combined system. Pd-BEA was synthesized as a model catalyst for PNA+DOC integration, as was a Pt/Pd/Al2O3 oxidation catalyst. Transient NOx adsorption experiments and temperature programmed desorption/oxidation were used to evaluate both the NOx storage and diesel oxidation catalyst performances. DRIFTS was used to help understand the reaction mechanism of the integrated system under different gas conditions.