In-situ studies of oxidation/reduction of copper in Cu-CHA SCR catalysts: comparison of fresh and SO2-poisoned catalysts

•Cu-SSZ-13 catalysts for SCR were studied as fresh and SO2-poisoned samples.•In-situ Cu K-edge XANES studies of the oxidation/reduction of Cu in these catalysts was correlated with SCR performance and catalyst characterization.•H2-TPR was used to determine Cu sites present in the catalyst.•Cu K-edge XANES spectra were used to follow oxidation and reduction of these Cu ion sites for fresh and SO2-poisoned samples.•Differences in the ease of Cu ion reduction is observed for fresh vs. SO2-poisoned samples in different temperature regions.