Effect of PS Microspheres with Different Size on the NH3-SCR Activity of Ce, Cu and La Modified Hierarchical Porous ZSM-5 Catalyst

Abstract

Microporous zeolite is commonly employed as the catalyst for selective catalytic reduction of NO_x using NH₃ as reducing agent (NH₃-SCR) because of its strong acidity and exceptional hydrothermal stability. However, the channel of microporous zeolite limits mass transfer under low temperature. Hierarchical porous molecular sieves can overcome the above imperfections. Hierarchical pore (microporous/mesoporous/macroporous) ZSM-5 molecular sieves were prepared using polystyrene(PS) microspheres with different particle size as the hard templates and then the ion exchange method was utilized to introduce the active components Ce, Cu, and La. In addition, the effect of PS microspheres with different size and H₂O+SO₂ on denitrification performance was also investigated. The results exhibited that the specific surface area of the hierarchical pore ZSM-5 was the smallest when the size of polystyrene microspheres was the largest. The NO_x conversion of all supported hierarchical porous catalysts is more than that of supported microporous ZSM-5 catalyst in the low temperature (200 °C), which was because that the presence of the mesopores favored diffusion-control in the low temperature, expediting the reactant transport. Furthermore, the supported hierarchical pore ZSM-5 catalyst exhibited excellent denitrification performance in a wide temperature range of 250–500 °C (the conversion of NO_x exceeded 80 % and the N₂ selectivity was approaching 100 %). More importantly, the supported hierarchical pore ZSM-5 catalyst demonstrated notably superior water and SO₂ resistance in comparison to the supported micropore ZSM-5 catalyst.