(12f) CO2 Hydrogenation over Mechano-Chemically Prepared Transition Metal-Based Ceria Catalysts

One promising route to mitigating CO₂ is using point source CO₂ capture technologies to create high purity CO₂ that can be upgraded to value added products, such as methane. Due to the high thermodynamic stability of CO₂, catalytic routes are often required to convert CO₂ into high value products. The thermo-catalytic approach is often favored due the robust nature of the process, which can be readily scaled to demand and easily integrated into existing point source CO₂ sites. However, while several advances have been made in the mechanistic understanding of CO₂ hydrogenation, there is still need for spectroscopic evidence that unambiguously link changes in the surface to shifts in the reaction mechanism.

In this study, transition metal based (Pd, Ru, Ni) ceria supported catalysts will be explored for CO₂ hydrogenation into methane. The use of mechano-chemically prepared ceria supported catalysts both increase the dispersion of the metal species and generates novel active sites due to the high energy synthesis method of ball milling the catalysts, which bypasses the need for additional drying/calcining steps. This resulted in catalysts that exhibit nearly a factor of two higher methane yield than conventionally prepared catalysts made via incipient wetness impregnation. Furthermore, by exposing the catalysts to an oxidative pretreatment, the catalytic activity is considerably increased relative to a reductive pretreatment, suggesting a synergy between the ceria and the metal centers. The precise nature of the active site will be unraveled via DRIFTS and AP-XPS, to elucidate the relevant surface species in addition to the coordination environment of the metals, respectively. Ultimately, this work seeks to establish a strong structure/activity relationship between the synthesis method, catalytic pretreatment, and overall CO₂ hydrogenation activity with spectroscopic evidence to better understand the reaction mechanism across distinct catalytic systems.