Zr/HZSM-5 catalyst for NO reduction by C2H2 in lean-burn conditions Original Research Article

Zr-based zeolite catalysts were investigated for the first time in selective catalytic reduction of NO by hydrocarbon (HC-SCR). Highly dispersed zirconium species, especially the amorphous ultrafine zirconium oxide in the catalyst, considerably enhanced the activity for selective catalytic reduction of NO by acetylene (C2H2-SCR), both by accelerating the NO oxidation to NO2 and enlarging the NO2 adsorption capacity of the catalyst under the reaction conditions. Thus a durable and active Zr/HZSM-5 catalyst giving 89% of NO conversion to N2 at 350 °C in 1600 ppm NO, 800 ppm C2H2, and 9.95% O2 in helium was obtained. For the C2H2-SCR of NO, it was suggested that acidic sites with strong acidity on the Zr-based HZSM-5 catalysts are indispensable to initiate the aimed reaction via the route of NO oxidation to NO2, which explains the higher activity for the reaction obtained over the Zr/HZSM-5 catalyst sample with lower SiO2/Al2O3 ratio. The zirconium species could only functioned in the presence of protons in the C2H2-SCR of NO, so a synergistic effect between the zirconium species and protons of the Zr/HZSM-5 catalyst was proposed.