The apparent activity of the long-term offline SCR catalysts as well as the fresh one in a power plant were assessed and compared by the activity simulation experiment. The influence of crystal structure

morphology

specific surface area

pore size distribution and acidic active sites on the performance of catalysts were characterized and analyzed by XRD

SEM

BET and FTIR spectra. The results indicated that the denitration efficiency was 94. 12% and apparent activity was 0. 78 respectively

meanwhile he crystal structure maintained well and long-term offline catalysts are able to keep operating. The aggregation of particles

increase of average pore size

decrease of specific surface area（ reduced 12. 4%） and reduction of acidic active sites were the main reasons of the degradation of the catalyst activity.