CLEERS Teleconference: Balaji Sukumar

Title: Effect of Hydrocarbon on SCR and NH₃ Oxidation Reactions

Balaji Sukumar, Ph.D. – Johnson Matthey

Abstract:

Selective Catalytic Reduction (SCR) catalyst followed by Ammonia Slip Catalyst (ASC) architecture (without any Diesel Oxidation Catalyst or particulate filter upstream) is being used in various off road applications. Vanadium SCR is preferred in such cases because of its high sulfur tolerance. In these applications, the effect of hydrocarbon (HC) from engine exhaust on the NOx reduction in SCR and NH₃ oxidation in ASC is to be understood for better catalyst design.

In this study, we examine the effect of Decane, Propylene and Toluene on both vanadium SCR and Cu- ASC performance. In V-SCR, the HC oxidation activity is in the order of decane > toluene > propylene which translates directly to its inhibition on NOx conversion. In the presence of HC, ammoxidation reaction takes place decreasing the ammonia to NOx ratio (ANR) thereby decreasing the NOx conversion. In Cu-ASC, NH₃ oxidation is inhibited by HCs in the order of propylene > toluene > decane. In addition, HC increases the selectivity of the catalyst towards NOx. This effect is attributed to the decrease in the top layer SCR activity and an increase in mass transfer resistance. Kinetic models to capture HC oxidation and inhibition in both V-SCR and Cu-ASC were also developed for catalyst design studies.