Enhancement of SO₂ resistance and hydrothermal stability of Cu-SAPO-34 via Al₂O₃ coating for NO_x selective catalytic reduction with NH₃ in diesel exhaust

Cu-based zeolites are one kind of efficient catalyst in the selective catalytic reduction of NOx with NH3 (NH3-SCR) in diesel exhaust, but the SO2 resistance and hydrothermal stability of the catalyst need to be improved. Herein, in this work, a series of Al2O3-coated Cu-SAPO-34 catalysts were prepared by chemical liquid deposition (CLD) to enhance the SO2 resistance and hydrothermal stability simultaneous. The optimal Al2O3-coated Cu-SAPO-34 catalyst showed >90 % NO conversion at 180-500 degrees C, and presented significant enhanced SO2 resistance and hydrothermal stability in comparison to the uncoated Cu-SAPO-34 catalyst. It was found that the Al2O3 shell served as the sacrificial layer, reacted with SO2, which could limit the competitive adsorption between SO2 and NO on the Cu-SAPO-34, and reduce the formation of sulfate species. Moreover, the Al2O3 shell also limited the aggregation of Cu species and enhanced the stability of the catalysts during hydrothermal aging. This work provides a facile method for construction of efficient practical NH3-SCR catalysts.