Widening the operating window of Pt/ZSM-5 catalysts for efficient NOx removal in H2-SCR: Insights from thermal aging

Abstract

NOx emissions from various sources cause serious environmental problems and harm human health. The selective catalytic reduction of NOx by hydrogen (H2-SCR) using Pt/ZSM-5 catalysts has attracted significant attention due to its effective removal of NOx at low temperatures. However, Pt/ZSM-5 has a narrow operating window because of the excessive oxidation of NO to NO2 at high temperatures. In this study, Pt/ZSM-5 catalysts were prepared by thermal aging treatment of fresh Pt/ZSM-5 at various temperatures to prevent the excessive oxidation of NO to NO2 at high temperatures, and these catalysts were applied to the H2-SCR reaction. The fresh Pt/ZSM-5 catalyst showed high NOx conversion at low temperatures, reaching 93% at 75 °C. However, the conversion rapidly declined as the temperature increased, dropping to 50% at 200 °C. In contrast, when the catalyst was thermally aged, the NOx conversion increased at all temperatures, and the operating window was significantly widened. Especially, Pt/ZSM-5 aged at 850 °C, maintained 84% NOx conversion even at 200 °C. Various characterizations, including XRD, NH3-TPD, STEM, CO-DRIFTS, and probe reactions revealed that the oxidation ability of the thermally aged catalysts decreased due to the sintering of Pt, resulting in widen operating windows. This study provides insights into the development of Pt-based catalysts for H2-SCR applications that can improve NOx reduction efficiency over a wide temperature range.