Researcher Identify Active Sites Enabling Direct Syngas Conversion to Light Olefins
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Zinc chromite (ZnCrOx) oxides coupled with zeolites (OXZEO) have shown great promise as the catalyst for the direct conversion of syngas into light olefins. However, identifying the specific active sites for this reaction remains elusive due to the structural complexity of the ZnCrOx composite oxides.
Recently, a research team led by Prof. BAO Xinhe who is a CAS Member and Prof. FU Qiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences revealed that monodispersed ZnOx species, anchored on ZnCr2O4 spinel surface, are the key active sites for syngas conversion to light olefins. This work was published in Nature Communications.
Researchers demonstrated that ZnO particles, when physically mixed with ZnCr2O4 spinel particles and treated in a syngas atmosphere, undergo a reduction-evaporation-anchoring process. This led to the formation of monodispersed ZnOx species, uniformly distributed up to a loading of 16.0 wt%, on the spinel surface (denoted as ZnCr2O4@ZnOx).
A linear correlation between CO conversion and surface ZnO loading confirmed that the ZnOx overlayer is the active sites, which can efficiently activate both H2 and CO. When combined with SAPO-34 zeolite, the ZnCr2O4@ZnOx catalyst achieved high catalytic performance with 64% CO conversion and 75% light olefins selectivity among total hydrocarbons.
Moreover, the ZnOx overlayer remained stably anchored on the ZnCr2O4 spinel, which inhibits Zn loss during the reaction and maintains high stability over 100 hours. This highlights a significant interface confinement effect between the spinel surface and ZnOx overlayer, which stabilizes the active sites and boosts catalytic performance.
"Our study provides a clear understanding of how interfacial confinement enhances catalytic activity, and provides a new approach for identifying active sites on supported catalyst surfaces," said Prof. FU.
Schematic depiction of the gas phase migration mechanism of ZnO species and the active site during syngas conversion (Image by FENG Xiaohui)
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