Comparative Study of SO2 and SO2/SO3 Poisoning and Regeneration of Cu/BEA and Cu/SSZ-13 for NH3 SCR

Abstract

Two copper-exchanged zeolites, Cu/SSZ-13 and Cu/BEA, were studied as catalysts for the selective reduction of NOx by NH3 (NH3-SCR). Their activities for standard SCR (NOx = NO) and fast SCR (NOx = 50% NO + 50% NO2) were measured before and after sulfur poisoning at 250 °C. The effect of 30 ppm SO2 and a mixture of 24 ppm SO3 + 6 ppm SO2 was evaluated. The repetition of subsequent activity measurements served as regeneration method in SCR conditions. SO2 deactivated Cu/SSZ-13 whereas Cu/BEA was only moderately affected. SO3 led to stronger deactivation of both catalysts than SO2. However, also for this case, the Cu/BEA was significantly less affected than Cu/SSZ-13, even though Cu/BEA contained larger amount of stored sulfur. One possible reason for this could be the large pores of Cu/BEA, where the sulfur species possibly resulted in less sterical hindrance than in the small pore SSZ-13 structure. NH3 temperature-programmed desorption (NH3-TPD) showed no loss of storage sites upon sulfur treatment and subsequent regeneration. Partial activity recovery was observed after a period in SCR conditions at 400 °C and 500 °C. Temperature at 300 °C was insufficient to regenerate the catalysts. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NO adsorption suggested that SO2 interacts with the ZCuOH sites on Cu/SSZ-13, causing the strong poisoning.

N2O Formation during NH3-SCR over Different Zeolite Frameworks: Effect of Framework Structure, Copper Species, and Water

“…The Cu/SSZ-13 sample deactivates slower during SO 2 exposure than the other two catalysts but reaches a lower conversion during time on stream (see Figure S15, SI). These results are in line with the recent study by Auvray et al 32 where it was reported that Cu/BEA was significantly less affected than Cu/SSZ-13 from SO 2 or SO 3 , and the reason for this was suggested to be less steric hindrance of Cu/BEA by sulfur species.…”

How changes in Cu-SSZ-13 catalytic oxidation activity via mild hydrothermal aging influence sulfur poisoning extents

“…Contrary to the results shown above and the associated literature discussed, here the hydrothermal aging treatment did not mitigate the extent of SO 3 poisoning. Literature has consistently shown that SO 3 leads to a higher level of SCR catalyst deactivation compared to SO 2 , 34,36,59 with one explanation being higher levels of copper sulfate formation. 34 Our results show a similar trend in that the extent of SO 3 poisoning is higher compared to SO 2 poisoning, see Fig.…”

Mechanism for So2 Poisoning of Cu-Cha During Low Temperature Nh3-Scr

“…One important finding is that the presence of HSO 4 (NH 4 ) hinder O 2 adsorption in Cu-CHA. The structure of the zeolite has been measured to affect the SO 2 -induced deactivation [56,24]. Recently, the poisoning with SO 2 and SO 3 of Cu-CHA was compared to poisoning of Cu-BEA [24].…”

“…The structure of the zeolite has been measured to affect the SO 2 -induced deactivation [56,24]. Recently, the poisoning with SO 2 and SO 3 of Cu-CHA was compared to poisoning of Cu-BEA [24]. It was observed that the deactivation of Cu-CHA was more severe than that of Cu-BEA even if Cu-CHA accumulated only 10 % of the sulfur accumulated in Cu-BEA.…”

“…The mechanism behind the deactivation is not well understood and the degree of deactivation appears to depend on numerous variables such as temperature, gas composition, Cu loading, Si/Al ratio and the state of the Cu-ion (ZCuOH or Z 2 Cu) [19,22,23]. Moreover, SO 2 and SO 3 shows differences in the degree of induced deactivation, with SO 3 being more severe [24]. Presence of SO 3 in the exhaust stream could originate from the diesel oxidation catalyst (DOC) commonly placed upstream of the NH 3 -SCR catalyst.…”