Dielectric barrier discharge (DBD)-assisted catalysis is a promising technology for sustainable chemical synthesis but suffers from low energy yields, which motivates fundamental studies on plasma/catalyst interactions. Here, we investigate DBD and catalyst contributions to the reaction rate using a relevant probe reaction (i.e., equilibrium-limited NH3 synthesis and decomposition) on a suite of porous oxides with varied elemental composition and structures. While these oxides are often supports for metal nanoparticles, it has been shown that they have significant NH3 synthesis yields without metal, so we simplify this study to be metal-free. We investigated DBD-assisted NH3 decomposition in the presence of Al-incorporated and parent ordered SiO2 at various dilute feed concentrations, building upon reported high NH3 synthesis energy yields of these materials (relative to non-ordered SiO2 and γ-Al2O3). The ordered SiO2 materials investigated are SBA-15 and MCM-41; Al was incorporated via conformal γ-Al2O3 coatings in synthesized SBA-15 (Al2O3-SBA-15; primarily Lewis acid sites) and incorporated tetrahedrally into the MCM-41 backbone (isolated Bronsted acid sites) in the Al-MCM-41 analog. Acid sites within the ordered SiO2 not only adsorb and shield synthesized NH3 from the DBD, but they also immobilize these energy carriers for easy integration into the NH3 decomposition process regime. Upon DBD exposure, we observe an initial spike in NH3 concentration above the feed, which is absent for the parent SiO2 and the empty reactor. As such, NH3 likely desorbs under the electric bias, demonstrating energy-efficient decomposition of the shielded NH3 energy carriers and providing insight on the extent of DBD interaction with the pore volume near the surface. The steady-state NH3 decomposition rates across feed concentrations in the presence of these Al-incorporated ordered SiO2 as well as zeolites were studied to understand the overall rate law dependence on composition, structure and dielectric properties. Quantifying the overall rate law for a suite of catalysts provides a robust understanding of DBD-assisted NH3 decomposition kinetics; it is key to decoupling forward and reverse rates in the equilibrium-limited reactors as well as elucidating the mechanism of this simple probe reaction in the complex DBD-assisted catalytic environment.
