ZnCrOx oxides coupled with zeolites (OXZEO) enable the direct conversion of syngas into light olefins, but the identification of active sites remains elusive due to the structural complexity of the ZnCrOx composite oxides.

Recently, a research team led by Prof. BAO Xinhe and Prof. FU Qiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) made new progress in the research of construction of monodispersed ZnOx species and its interface confinement effect on syngas conversion to light olefins.

This work was published in Nature Communications on 19 April.

Schematic depiction of the gas phase migration mechanism of ZnO species and the active site during syngas conversion (Image by FENG Xiaohui)

The researchers showed that ZnO particles physically mixed with ZnCr2O4 spinel particles can be well dispersed onto the spinel surfaces by treatment in syngas and through a reduction-evaporation-anchoring mechanism, forming monodispersed ZnOx species with uniform thickness or dimension on ZnCr2O4 up to a dispersion threshold ZnO loading of 16.0 wt% (ZnCr2O4@ZnOx). A linear correlation between CO conversion and surface ZnO loading clearly confirms that the ZnOx overlayer on ZnCr2O4 acts as the active structure for the syngas conversion, which can efficiently activate both H2 and CO. The obtained ZnCr2O4@ZnOx catalyst combined with SAPO-34 zeolite achieves excellent catalytic performance with 64% CO conversion and 75% light olefins selectivity among all hydrocarbons. Moreover, the ZnOx overlayer is effectively anchored on the ZnCr2O4 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 ZnOx overlayer, which helps to stabilize ZnOx active structure and enhance the catalytic performance.

“Our study provides a detailed understanding of the positive role of oxide interface confinement effect in catalytic reactions and a new approach to identifying active sites on supported catalyst surfaces.” said Prof. FU.

This work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, and Photon Science Center for Carbon Neutrality. R.M. thanks support from the Dalian Innovation Support Plan for High Level Talents and DICP. The authors thank the fruitful discussions with Feng JIAO and Xiulian PAN.