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

Abstract

Abstract Two copper-exchanged zeolites, Cu/SSZ-13 and Cu/BEA, were studied as catalysts for the selective reduction of NO x by NH 3 (NH 3 -SCR). Their activities for standard SCR (NO x = NO) and fast SCR (NO x = 50% NO + 50% NO 2 ) were measured before and after sulfur poisoning at 250 °C. The effect of 30 ppm SO 2 and a mixture of 24 ppm SO 3 + 6 ppm SO 2 was evaluated. The repetition of subsequent activity measurements served as regeneration method in SCR conditions. SO 2 deactivated Cu/SSZ-13 whereas Cu/BEA was only moderately affected. SO 3 led to stronger deactivation of both catalysts than SO 2 . 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. NH 3 temperature-programmed desorption (NH 3 -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 SO 2 interacts with the ZCuOH sites on Cu/SSZ-13, causing the strong poisoning.