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

•The pore size affects the hydrothermal stability of zeolite supported Cu catalysts.•Small pore catalysts are more stable than large or medium pore catalysts.•In situ XRD experiments were performed to understand the pore size effects.•Destructive Cu/Al2O3 interaction is minimized on the small pore zeolite catalysts.•This is attributed to the steric restriction in the small pore zeolite structure.