A theoretical study of the stability of Cu2+ ion in IM-5 zeolite and the interaction of Cu-IM-5 with NO

Experimentally, Cu-exchanged IM-5 zeolite has been found to exhibit excellent catalytic activity in NOx reduction. Unfortunately, the origin of such property still remains obscure due to the rather complex structure of IM-5. In this paper, we made the first attempt to provide a theoretical rationalization. By calculating the (Al, Cu) location energies, the stability of both Cu2+ and hydroxyl-Cu2+ (i.e., [CuOH]+) was considered and compared to those in ZSM-5. It was shown that [CuOH]+ located in IM-5 is comparable to that in ZSM-5. The most favorable location of Cu2+ cation is in 6-membered ring in the wall of unusual two-dimensional medium-pore channel of IM-5. Moreover, through calculating the interaction of NO with copper-exchanged zeolite (Cu-IM-5), the most active center is Cu2+ located in the 5-membered ring. The relatively high adsorption energies and numerous active centers in Cu-IM-5 might rationalize why Cu-IM-5 is more active than Cu-ZSM-5 in experiment of NO reduction. Thus, our theoretical results provide support that Cu-IM-5 is a more active and hydrothermically more stable catalyst than Cu-ZSM-5.