Water-Induced Framework Oxygen Exchange in Zeolites

In the present work, the zeolitic framework oxygen exchange mechanisms in the presence of water molecules were systematically studied using density functional theory (DFT) calculations. The oxygen atoms of water molecules exchanging with different framework bridging oxygen sites in zeolites such as Si-O-Al, Si–O(H)-Al, and Si–O–Si in H-FAU zeolite and Si–O–Al, Si–O(H)-Al, and P–O–Al in SAPO zeolite were examined. It was found that the second water molecule kinetically promotes the oxygen exchange by stabilizing the transition states. DFT results indicate the framework oxygen exchange possibility follows the order of Si-O(H)-Al > Si-O-Al > Si-O-Si in H-FAU and Si-O-Al > Si-O(H)-Al > P-O-Al in H-SAPO. Notably, the Si-O(H)-Al site in H-FAU has the highest oxygen exchange possibility while the Si-O-Si site is the least, which is consistent with experimental observation.