Propane-CO ₂ Coupling Reaction over Isolated Cr Active Centers in the Beta Zeolite

The propane–CO 2 coupling reaction (CO 2 -PDH) enables propylene production with simultaneous CO 2 utilization. Elucidating the nature of active sites and the role of CO 2 remains challenging due to catalyst heterogeneity and parallel pathways. Herein, we construct a well-defined catalytic platform comprising isolated metal sites embedded in the Beta zeolite framework. Among the metals examined (V, Nb, Ta, Cr, Mo, and W), Cr-Beta exhibits the best performance, achieving 66.9% propane conversion and 51.2% propylene yield with syngas coproduction (H 2 /CO = 0.82). Characterizations identify the active site as a pseudotetrahedral framework Cr species, {(≡SiO) 3 Cr···(HO–Si≡)}. Framework Cr═O species, generated during air pretreatment, serve as the active centers for initial oxidative dehydrogenation and are subsequently reduced to tetrahedral Cr sites. These reduced Cr sites catalyze CO 2 -PDH by coupling propane dehydrogenation with the reverse water–gas shift reaction, while CO 2 simultaneously promotes propane conversion through a formate-mediated surface hydrogen consumption pathway that shifts thermodynamic equilibrium and suppresses coke formation via the reverse Boudouard reaction. This work provides mechanistic insight into active-site evolution and CO 2 participation in alkane–CO 2 co-conversion, offering guidance for the rational design of efficient catalysts for simultaneous fossil-resource valorization and CO 2 utilization.