(691c) Using Atomic Layer Deposition to Understand Support Effects on Co2c Formation in ZnO-Modified Co Catalysts during Syngas Reaction

Growing energy demand is depleting non-renewable fossil fuel-based energy sources and necessitating the development of new strategies for energy production to meet society’s needs. Recently, interest has risen in using Co₂C catalysts to convert syngas (CO + H₂) to oxygenates, which are valuable fuels and feedstocks. We previously demonstrated that introducing a ZnO promoting overlayer on Co/SiO₂ using atomic layer deposition (ALD) significantly enhances oxygenate selectivity by enabling Co₂C formation during syngas reaction. ALD offers the capability of depositing precise amounts of promoters on catalysts, allowing atomic-level control over surface composition and the ability to modify both metal nanoparticles and oxide supports.

Although some studies suggest that the support influences the formation and performance of Co₂C, these support effects are not well understood. In this study, we characterize Co catalysts modified with ZnO ALD on SiO₂, carbon, CeO₂, and Al₂O₃ to understand how the support influences Co₂C. We show that under syngas conditions, ZnO-promoted Co undergoes a phase transformation to Co₂C on SiO₂, carbon, and CeO₂ but not on Al₂O₃, resulting in improved oxygenate selectivity on all supports except Al₂O₃. We then demonstrate that the properties of the SiO₂ support can be tuned using Al₂O₃ ALD. As increasing amounts of Al₂O₃ are deposited on the SiO₂, the catalyst shows decreased Co₂C formation and oxygenate selectivity, approaching the behavior of the bulk Al₂O₃-supported catalyst. In-situ XANES reveals that Al₂O₃ prevents Co₂C formation by enabling the ZnO to transform into ZnAl₂O₄ during catalyst reduction. Thus, the promoter can both modify the active catalyst phase and strongly interact with the support, significantly impacting catalyst performance. This work demonstrates the capability of ALD to systematically modify catalyst nanoparticles and supports, and tune and understand catalyst performance. With this understanding, we can apply ALD to promote catalysts towards higher oxygenates for sustainable fuel synthesis.