Preparation and application of honeycomb NH3-SCR catalyst based on small crystal-sized FeCu-ZSM-5 zeolite

A small crystal-sized FeCu-ZSM-5 zeolite was prepared by the controlled synthesis chemistry, and used as the active component to fabricate a coated honeycomb-type NH3 selective catalytic reduction (NH3-SCR) catalyst. The systematic characterizations indicate that the FeCu-ZSM-5 zeolite obtained under optimal conditions has an average crystal size of 0.61 μm. Compared with the conventional one (4.28 μm), FeCu-ZSM-5 zeolite with small crystal size exhibits a larger specific surface area (312 m2/g), a higher total acid amount (1.01 mmol/g), a higher proportion of isolated Cu2+ and Fe3+ active species, as well as better dispersion and stronger metal interactions, thus displaying superior catalytic performance in the NH3-SCR reaction. The catalyst stability test conducted at 300 °C consistently maintained excellent denitrification performance. On this basis, the formulation and process parameters of the coating slurry were systematically optimized with small crystal-sized FeCu-ZSM-5 zeolite as the active component and natural mineral honeycomb as the support. The results show that when the solid content in the slurry is 18 wt%, the amount of inorganic binder is 3 wt%, and a two-step coating process is adopted, the obtained honeycomb catalyst has a coating loading of 131 g/L with a coating shedding rate of only 0.16%. This honeycomb catalyst exhibits an NH3-SCR activity window ranging from 245 to 380 °C, which is wider than that of the catalyst based on the conventional-sized FeCu-ZSM-5 zeolite. Furthermore, under flue gas condition with a water content of no more than 5 vol%, this small crystal-sized honeycomb catalyst can maintain a NO conversion of above 90% within the temperature range of 250-380 oC, demonstrating good water resistance. Through the synergistic optimization of small crystal-sized zeolite and coating process, this work provides a potential high-performance and low-cost catalyst technical solution for ultra-low NOx emissions of industrial flue gas.