Cu‐Promoted Pt/Ce_0.5Zr_0.5O_x Catalyst for Ammonia Production Reaction of Passive SCR from Nitric Oxide and Hydrogen

Abstract

In response to stricter emission regulations, lean-burn engines have attracted more and more attention. However, lean burn engines would inevitably lead to the increase in NO x emissions. The researchers combined Three-Way Catalyst (TWC) and Selective Catalytic Reduction (SCR) to propose "passive SCR", which makes the engine periodically switch between rich and lean burn. During rich combustion, ammonia is produced by the TWC catalyst, stored in the downstream SCR, and reacts with NO x during lean combustion, in which increasing the ammonia yield on the TWC catalyst is the key. In this study, the self-propagating high-temperature synthesis method was used to modify the catalyst by adding copper to improve the ammonia production efficiency. The conversion rate of catalysts with different copper doping ratios from NO to ammonia was measured. Through XRD, BET, H 2 -TPR, TEM, HRTEM, XPS, in-situ DRIFTS, etc., the improvement mechanism of copper doping was analysed. The results showed that Pt 0.01 Cu 0.1 Ce 0.45 Zr 0.45 O x had the highest catalytic activity, the widest reaction temperature window (300-550 °C) with the conversion greater than 96 %. The characterization results showed that appropriate amount of copper doping can adjust the valence distribution, form more oxygen vacancies, and improve the distribution of active species. The in-situ DRIFTS further demonstrated that the conversion from bridged to monodentate and bidentate nitrate may be the key factors on the catalyst surface.