Local coordination environment of isolated Fe sites in zeolite affects the catalytic performance for propane dehydrogenation

In order to elucidate the intrinsic relationship between the local coordination environment of the tetrahedrally coordinated metal sites bound to zeolite framework and their catalytic performance in propane dehydrogenation (PDH) reaction, Fe-S-1, Fe-S-1-Na and FeAlPO 4 –5 catalysts with different isolated iron sites were constructed, characterized and evaluated. The catalytic performance tests demonstrated that the C H activation efficiency of the isolated Fe sites decreased in a sequence of {(≡SiO) 3 Fe(HO − Si≡)} > {Fe(OP≡) 4 } > {(≡SiO) 3 Fe(NaO − Si≡)}, while the propylene selectivity followed a trend of {(≡SiO) 3 Fe(NaO − Si≡)} > {(≡SiO) 3 Fe(HO − Si≡)} > {Fe(OP≡) 4 }. Through detailed reaction mechanism study using density functional theory calculations, the rate-determining step (RDS) of PDH is the first dehydrogenation step of propane to propyl intermediate. The intrinsic activity of different Fe sites is closely related to their effective charge redistribution ability during the reaction, which is profoundly affected by its local coordination environment. Isolated Fe sites exhibit activity proportional to their charge transfer efficiency in the initial dehydrogenation step. Higher extent of Fe reduction corresponds to greater catalytic activity, whereas propylene selectivity decreases with increased reduction. This work established the relationship between the catalytic properties of isolated Fe sites embedded in zeolite with their local coordination structure, opening up new prospect for the optimization design of PDH catalysts.