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Chemists identify active sites enabling direct syngas conversion to light olefins

Zinc chromite (ZnCrO_x) 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 ZnCrO_x composite oxides.

Recently, a research team led by Prof. Bao Xinhe and Prof. Fu Qiang from the Dalian Institute of Chemical Â鶹ÒùÔºics (DICP) of the Chinese Academy of Sciences has revealed that monodispersed ZnO_x species, anchored on ZnCr₂O₄ spinel surface, are the key active sites for syngas conversion to light olefins. This work was 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 ZnO_x species, uniformly distributed up to a loading of 16.0 wt%, on the spinel surface (denoted as ZnCr₂O₄@ZnO_x).

A linear correlation between CO conversion and surface ZnO loading confirmed that the ZnO_x overlayer is the active site, which can efficiently activate both H₂ and CO. When combined with SAPO-34 zeolite, the ZnCr₂O₄@ZnO_x catalyst achieved high catalytic performance with 64% CO conversion and 75% light olefins selectivity among total hydrocarbons.

Moreover, the ZnO_x 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 ZnO_x 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.