Insights into the size effect of ZnCr2O4 spinel oxide in composite catalysts for conversion of syngas to aromatics

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Direct conversion of syngas to aromatics (STA) over oxide-zeolite composite catalysts is promising as an alternative method for aromatics production. However, the structural effect of the oxide component in composite catalysts is still ambiguous. Herein, we investigate the size effect by selecting ZnCr2O4 spinel, as a probe oxide, mixing with H-ZSM-5 zeolite as a composite catalyst for STA reaction. The CO conversion, aromatics selectivity and space-time yield (STY) of aromatics are all significantly improved with the crystal size of ZnCr2O4 oxide decreases, which can mainly attribute to the higher oxygen vacancy concentration and thus the rapid generation of more C1 oxygenated intermediate species. Based on the understanding of the size–performance relationship, ZnCr2O4-400 with a smaller size mixing with H-ZSM-5 can achieve 32.6% CO conversion with 76% aromatics selectivity. The STY of aromatics reaches as high as 4.79 mmol gcat−1 h−1, which outperforms the previously reported some typical catalysts. This study elucidates the importance of regulating the size of oxide to design more efficient oxide-zeolite composite catalysts for conversion of syngas to value-added chemicals.