Hydrocarbon Storage on Small-Pore Cu-Zeolite SCR Catalyst

Abstract

In this study we investigated the interaction of short-and long-chain hydrocarbons (HCs), represented by propene (C 3 H 6 ) and n-dodecane (n-C 12 H 26 ), 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, CO 2 , and H 2 O by an oxygen-rich mixture at elevated temperatures or by using NO 2 as an oxidant at lower temperatures.

Review of Hydrocarbon Poisoning and Deactivation Effects on Cu-Zeolite, Fe-Zeolite, and Vanadium-Based Selective Catalytic Reduction Catalysts for NOx Removal from Lean Exhausts

“…These results, considering the short exposure time, are also consistent with the work of Kumar et al, 19 where the amount of C 12 H 26 directly adsorbed at temperatures below 300 °C and in the presence of O 2 on state-of-the-art commercial Cu small pore zeolites was found to be limited (chabazite structure, pore opening of 3.8 Å). However, it must be remembered that the large HC impact on small pore zeolite catalysts may be affected by temperature, since these molecules start to decompose into smaller fractions at T > 320 °C (HC cracking).…”

“…Heavy Hydrocarbons. Kumar et al 19 methodically investigated the heavy (n-C 12 H 26 ) hydrocarbon storage capacity of a commercial small pore Cu-zeolite. In particular, the behavior of dodecane storage at sufficiently high temperatures in an oxidative environment was discussed.…”

Vehicular Emissions in Review

“…More recently, Kumar, et al, [71] looked at the behavior of long-and short-chained hydrocarbons (n-dodecane and propene) on a small-pored (0.38 nm) copper zeolite in the chabazite family. Even this type of zeolite can store a significant amount of large hydrocarbons (2.8 g/liter at 350°C), but they are stored on the outside of the zeolite chrystallites after breaking down into carbon-rich deposits.…”

Cu-SSZ-13 as pre-turbine NOx-removal-catalyst: Impact of pressure and catalyst poisons

“…Diesel oxidation catalyst (DOC) and Diesel particulate filter (DPF)) would result in an exposure to higher amounts of unburned hydrocarbons, particulate matter and less NO2. The latter supports the so-called Fast-SCR reaction, while the hydrocarbons may deposit as coke on the zeolite surface or enter the pores, depending on the size [16]. Particulate matter is usually too large to enter the zeolite pores but can also be converted [17].…”