Experimental studies on intracrystalline diffusion of NO and NH3 in Cu-CHA

Equilibrium adsorption and intracrystalline diffusion of NO and NH3 in Cu-CHA were experimentally studied using constant volumetric method. The saturated amount of adsorbed NO on Cu-CHA at 373 K linearly increases with Cu loading, which indicates that Cu sites are the adsorption site of NO on Cu-CHA. Temperature dependence of adsorption equilibrium constant of NO gives the adsorption enthalpy (-24 kJ mol-1), regardless of the Cu loading. The activation energy for NO diffusivity in Cu-CHA was evaluated from its temperature dependence of intracrystalline diffusivity (7.0 kJ mol-1). The intracrystalline diffusivity of NO in Cu-CHA is lower than that in Cu-ZSM-5, which can be ascribed to the narrower pore size of CHA. Intracrystalline diffusivity and effective diffusivity of NO were lower than those of NH3 in Cu-CHA. The Weisz-Prater Parameter was calculated using the NH3-SCR reaction rate on Cu-CHA at 508 K and the effective diffusivity of NO. The calculated result indicates that intracrystalline diffusion of NO in Cu-CHA limits the NH3-SCR reaction under the present conditions.

Automated summary

The equilibrium adsorption and intracrystalline diffusion of NO and NH3 in Cu-CHA were studied experimentally using constant volumetric method. The adsorbed amount of NO on Cu-CHA at 373 K increases linearly with Cu loading, indicating that Cu sites are the adsorption site of NO. The calculated result shows that the intracrystalline diffusion of NO in Cu-CHA limits the NH3-SCR reaction.