(292f) Multi-Scale DFT/Reaxff Modeling of Hydrocarbon Reactions Over Pd/Ceria Catalysts

Catalyst design plays an indispensable role in optimizing processes to meet ever rising demands for efficient and clean energy technologies. Numerous experimental studies have demonstrated the high activity of ceria supported palladium catalysts for a range of applications, such as catalytic combustion, water-gas shift reaction, and solid-oxide fuel cells.  In this study, multi-scale computational techniques are used to characterize the structure, stability, and reactivity of the Pd/ceria surface. Density functional theory, including on site Coulombic interaction (DFT+U), provides quantum mechanical data describing the energetics of Pd/ceria interactions and hydrocarbon activation over the Pd/ceria surface. The data obtained from DFT+U calculations are used to parameterize a reactive force-field (ReaxFF) capable of describing long length and time scales via reactive molecular dynamic (RMD) simulations. RMD simulations are capable of investigating aspects of the system that are computationally intractable for ab initio methods, such as the dynamic restructuring of the catalyst surface during reaction. DFT+U results demonstrate that Ce_1-xPd_xO_2-δ mixed oxide surfaces are stable under catalytically relevant conditions (~5 atm, 300 K), and have significantly lower reaction barriers for methane C-H bond activation compared to pure CeO₂(111). The ReaxFF force-field for Pd/C/O/H accurately reproduces quantum-level data and is implemented in RMD simulations to investigate the activity of Pd and PdO nanoparticles toward hydrocarbon activation paths. These results will serve as a benchmark for comparison against the analogous ceria-supported systems. Combined with the Ce/O force-field, this multi-scale DFT/ReaxFF approach will determine the structure, stability, and activity of Ce_1-xPd_xO_2-δ mixed oxide surfaces and the corresponding hydrocarbon reaction paths.