ZnOx overlayer confined on ZnCr2O4 spinel for direct syngas conversion to light olefins

ZnCrO x oxides coupled with zeolites (OXZEO) allow direct conversion of syngas into light olefins, while active sites in the composite oxides remain elusive. Herein, we find that ZnO particles physically mixed with ZnCr 2 O 4 spinel particles can be well dispersed onto the spinel surfaces by treatment in syngas and through a reduction-evaporation-anchoring mechanism, forming monodispersed ZnO x species with uniform thickness or dimension on ZnCr 2 O 4 up to a dispersion threshold ZnO loading of 16.0 wt% (ZnCr 2 O 4 @ZnO x ). A linear correlation between CO conversion and surface ZnO loading clearly confirms that the ZnO x overlayer on ZnCr 2 O 4 acts as the active structure for the syngas conversion, which can efficiently activate both H 2 and CO. The obtained ZnCr 2 O 4 @ZnO x catalyst combined with SAPO-34 zeolite achieves excellent catalytic performance with 64% CO conversion and 75% light olefins selectivity among all hydrocarbons. Moreover, the ZnO x overlayer is effectively anchored on the ZnCr 2 O 4 spinel, which inhibits Zn loss during the reaction and demonstrates high stability over 100 hours. Thus, a significant interface confinement effect is present between the spinel surface and the ZnO x overlayer, which helps to stabilize ZnO x active structure and enhance the catalytic performance.