2020 Virtual AIChE Annual Meeting

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

Authors

Nathan, S. - Presenter, Stanford University
Hoffman, A. - Presenter, SLAC National Accelerator Laboratory
Asundi, A., Stanford University
Boubnov, A., Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
Hong, J., Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
Bare, S., SLAC National Accelerator Laboratory
Bent, S., Stanford University
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.