Isolated Cr Active Centers in the Beta Zeolite Framework for Propane Dehydrogenation

Conventional supported metal catalysts in propane dehydrogenation (PDH) face critical challenges due to sintering-induced deactivation at high reaction temperatures. Herein, we develop a series of highly stable atomically dispersed metal-Beta catalysts by embedding single metal atoms (such as V, Cr, Fe, Zn, and Ga) into the dealuminated H-Beta zeolite framework. Unlike the pristine H-Beta zeolite with Brønsted acid sites, the embedded metals possess a distorted tetrahedral structure and typical Lewis acidic properties, which exhibit good C–H bond activation rather than C–C bond activation observed on Brønsted acid sites. Among these metal-Beta zeolites, the Cr-Beta zeolite with an ultralow density of ∼128 framework atoms per Cr atom exhibits notable performance in PDH. Through HAADF-STEM, X-ray absorption spectroscopy (XAS), and isotope labeling FTIR, the local coordination environment of framework-embedded Cr species is unambiguously identified as a distorted tetrahedral geometry {(≡SiO)3Cr···(HO–Si≡)} with three Cr–O–Si bonds and one Cr···OH–Si linkage. Kinetic investigations and deuterium-labeling results demonstrate that propane activation occurs on isolated Cr Lewis sites with adjacent O atoms that facilitate the reception and release of hydrogen species. These findings provide valuable strategies for the rational design of supported metal catalysts for alkane activation and offer great insights into recognizing the local coordination structures of heteroatoms in zeolites.