Direct Conversion of Syngas into Methyl Acetate, Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether

Abstract

Selective conversion of syngas (CO/H₂ ) into C₂₊ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu-Zn-Al oxide/H-ZSM-5 and zeolite mordenite (H-MOR) catalysts separated by quartz wool (denoted as Cu-Zn-Al/H-ZSM-5|H-MOR) and also at higher temperatures (603-643 K) without significant deactivation using spinel-structured ZnAl₂ O₄ |H-MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl₂ O₄ |H-MOR|ZnAl₂ O₄ gives ethanol as the major product, while ethylene is formed with a layer-by-layer ZnAl₂ O₄ |H-MOR|ZnAl₂ O₄ |H-MOR combination. Close proximity between ZnAl₂ O₄ and H-MOR increases ethylene selectivity to 65 %.