Evidence of Preferential Aluminum Site Loss during Reaction-Induced Dealumination.

Understanding the mechanism of steam-induced dealumination of zeolite catalysts is of high relevance for tuning their performance and stability in multiple industrial processes. A combination of Al and H-H double-quantum single-quantum magic angle spinning nuclear magnetic resonance and diffuse-reflectance ultraviolet-visible spectroscopies identified a preferential dealumination of tetrahedral aluminum sites in H-ZSM-5 zeolites. Framework aluminum atoms facing channels display reactivity toward steam higher than that of those in their intersections. Dealumination randomly occurs on isolated and proximate sites. However, the concentration of the latter sites decays more prominently. These findings contribute to a better understanding of the stability of zeolite catalysts in the presence of steam.