Study of thermal deactivation of a de-NOx commercial catalyst

Abstract

In the present paper, the thermal deactivation of a commercial de-NOx V2O5–WO3/TiO2 catalyst is investigated. In order to simulate long-term operation in gas firing samples of the catalyst are calcined at different temperatures from 773 to 1173K. The structural, morphological and chemico-physical changes caused by calcination at high temperatures are investigated by XRD, BET and Hg porosimetry measurements, FT-IR, FT-Raman and EPR spectroscopies, and the activity in the reduction of NO with ammonia, the direct oxidation of ammonia and the oxidation of SO2 is measured over the different catalyst samples. It is shown that sintering of the TiO2 support leads to aggregation of isolated vanadium ions; this favours the selective catalytic reduction (SCR) reaction at low temperatures, the oxidation of ammonia at high temperatures and the undesired oxidation of SO2 as well. Thus, it is expected that catalysts operated for long-term in gas firing at high temperatures are no longer appropriate for commercial use in the SCR process, because in spite of the greater activity in the de-NOx reaction, the temperature window is too narrow and the activity in the oxidation of SO2 is too high.