Hydrocarbon Storage on Small-Pore Cu-Zeolite SCR Catalyst 2013-01-0508
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.