Hydrocarbon Storage on Small-Pore Cu-Zeolite SCR Catalyst

In this study we investigated the interaction of short- and long-chain hydrocarbons (HCs), represented by propene (C₃H₆) and n-dodecane (n-C₁₂H₂₆), respectively, with a state-of-the-art small-pore Cu-Zeolite SCR catalyst. By varying HC adsorption conditions, we determined that physisorption was the primary mechanism for some minor HC storage at low temperatures (≺ 200°C), while chemical transformation was involved in more substantial HC storage at higher temperatures (200-400°C). The latter was evidenced by the oxygen-dependent and thermally activated nature of the storage process, and further confirmed by the carbon-rich composition of the deposits. The nature of HC-derived deposits of different origins and amounts was further probed using the standard SCR reaction at kinetically challenging conditions (at 200°C), as well by ammonia adsorption/desorption experiments. The resulting observations indicate that the carbonaceous deposits originating from long-chain HCs accumulate solely on the outer surface of the zeolite crystallites, while short-chain HCs can access both the external surface and the pores. The stored HCs can be readily removed in the form of CO, CO₂, and H₂O by an oxygen-rich mixture at elevated temperatures or by using NO₂ as an oxidant at lower temperatures.