Nature of Cu Active Centers in Cu-SSZ-13 and Their Responses to SO2 Exposure

Abstract

The effect(s) of SO2 on the two types of active sites on Cu-SSZ-13 NH3–SCR catalysts, Z2Cu and ZCuOH, were investigated. Two Cu-SSZ-13 catalysts with Si:Al ratios of 6 and 30 were synthesized, and they provide very different distributions of these two active sites. Inductively coupled plasma optical emission spectroscopy (ICP-OES), H2 temperature-programmed reduction (H2-TPR), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were utilized to characterize catalyst samples and quantify the amounts of total Cu, Z2Cu and ZCuOH. In situ DRIFTS results show that Z2Cu and ZCuOH responses to low-temperature (<200 °C) SO2 poisoning were site-dependent. Results of SO2 and SO2 + NH3 temperature-programmed desorption (TPD) and DRIFTS experiments, supplemented with DFT calculations, revealed that the different observed responses correspond to different sulfur intermediates that form. On Z2Cu sites, SO2 only adsorbs when it is cofed with NH3 via formation of ammonium sulfate, with its fingerprin...