The role of pore size on the thermal stability of zeolite supported Cu SCR catalysts

A comparison study on the hydrothermal stability of Cu SCR catalysts supported on an 8-ring small pore chabazite and a 12-ring large pore beta zeolite was performed to understand why small pore zeolite supported Cu catalysts are in general hydrothermally more stable than medium pore or large pore zeolite supported Cu catalysts and how different pore sizes affect the hydrothermal stability of the catalysts. In situ XRD hydrothermal experiments show that, even though the parent chabazite and beta zeolites have comparable hydrothermal stability and both can maintain their zeolite framework structure after a 900 °C hydrothermal exposure, the presence of Cu in the Cu/beta catalyst accelerates the collapse of the BEA framework structure at temperatures above 800°C whereas Cu in the Cu/chabazite catalyst has little effect on the CHA framework structure. The loss of beta zeolite framework structure is due to a detrimental Cu/Al₂O₃ interaction. It is proposed that the constricting dimensions of the small openings in a small pore zeolite can hinder the destructive Cu/Al₂O₃ interaction as well as the zeolite dealumination process, hence significantly improving the hydrothermal stability of the small pore zeolite supported Cu catalyst.