Sulfur poisoning and hydrothermal aging effects on a Cu-SSZ-13 selective catalytic reduction (SCR) catalyst

Yu-Ren  Chen, University of Virginia

Cu-SSZ-13 catalysts are widely used for selective catalyst reduction (SCR) to reduce NOx. However, they still suffer from sulfur poisoning and hydrothermal aging. Literature shows that mild hydrothermal aging does not affect the zeolite structure, but changes the Cu distribution from ZCuOH to Z2Cu. Literature also shows that ZCuOH sites have better oxidation activity than Z2Cu sites. This caused the catalyst’s oxidation activity to decrease after mild hydrothermal aging. Our experimental data show that such mild hydrothermal aging can protect the catalysts from SO2 poisoning, but not from SO3 poisoning. Analyzing results from experiments with different SO2 exposure temperatures and O2 concentrations during the SO2 those exposure suggests that the sulfur poisoning effect follows the trend in the catalyst’s oxidation activity. This indicates that the catalyst oxidation activity is related to the severity of sulfur poisoning, likely through SO2 oxidation to SO3 and SO3 being the primary poison.