Understanding Support Effects of ZnO-Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition

Co₂C, an emerging catalyst for the conversion of syngas to oxygenates, shows support-sensitive behavior that has not yet been fully explained. Here, we characterize Co catalysts modified with ZnO atomic layer deposition on SiO₂, carbon, CeO₂, and Al₂O₃ supports. We find that under syngas conditions, ZnO-promoted Co transforms into Co₂C on SiO₂, carbon, and CeO₂, but not on Al₂O₃. Moreover, the support affects the extent of carburization: while the SiO₂-supported catalyst carburizes completely, carbon- and CeO₂-supported catalysts show incomplete conversion of Co to Co₂C. These three catalysts also exhibit different oxygenate selectivities. In contrast, the modified Al₂O₃-supported catalyst retains the Fischer-Tropsch catalytic properties of metallic Co. By depositing increasing amounts of Al₂O₃ by ALD on the SiO₂ support, decreasing Co₂C formation and oxygenate selectivity occurs. In-situ XANES reveals that Al₂O₃ prevents Co₂C formation by enabling the ZnO to restructure into ZnAl₂O₄ during reduction. Thus, in addition to modifying the active catalyst phase, the promoter can also strongly interact with the support, significantly impacting catalyst performance.