Hydrogen in plasma-assisted hydrocarbon selective catalytic reduction

Abstract Onboard plasma reforming has strong potential for use in supplying reductants for hydrocarbon selective catalytic reduction (HC SCR) of NO x in vehicle exhaust. However, the role of hydrogen as an additional reductant with various catalysts at various temperatures remains unclear. Here we investigated the de-NO x performance of HC SCR with Pt-based and Ag/Al 2 O 3 catalysts at various temperatures using hydrogen and hydrocarbons supplied directly or generated onboard by plasma reforming using engine bench-level tests. Further, we clarified the specific role of hydrogen in the process. We found that with Pt-based catalysts, hydrogen is oxidized to H 2 O or promotes full oxidation of hydrocarbon, thus having no positive effect. By contrast, with Ag/Al 2 O 3 , hydrogen only promotes partial oxidation of hydrocarbon to yield surface intermediates that significantly facilitate SCR. Furthermore, reductants generated by plasma reforming exhibit better de-NO x performance than directly supplied gas mixtures. Thus, onboard plasma onboard reforming can be an important strategy for effective HC SCR.