(382ao) Effect of Ordered Aluminosilicates on Non-Thermal Plasma-Assisted Ammonia Reactions

Alternatives to industrial high temperature and pressure Haber-Bosch ammonia (NH₃) synthesis include use of direct electricity from renewable sources. Beyond its large-scale production for fertilizers, NH₃ is also an attractive energy carrier so the direct electrification of its production and decomposition would circumvent the intermittent nature of green energy. One such technology is dielectric barrier discharges (DBD)-assisted catalysis, but its NH₃ energy yields are currently too low. Moreover, porous oxide supports (traditionally inactive for thermal catalysis) surprisingly account for most of the NH₃ yield, as opposed to their loaded metal nanoparticles, indicating that presence and identity of packed beds alter plasma dynamics and properties. Ordered structures, like silica-based SBA-15, have demonstrated promising performance, but ordered γ-alumina has not been similarly studied due to its complex syntheses, despite the beneficial acid site functionality and higher dielectric constant of γ-alumina. Thus, we explored the systematic effects of different ordered structures (i.e., SBA-15 and MCM-41) and acid site incorporation (conformal γ-alumina coatings in Al₂O₃-SBA-15 and Al incorporated tetrahedrally in Al-MCM-41) on both plasma-assisted NH₃ production and decomposition. Both Al₂O₃-SBA-15 and Al-MCM-41 exhibited higher overall NH₃ synthesis energy yields than their parent ordered silicas, where overall accounts for NH₃ recovered after the reaction via temperature-swing desorption. In terms of steady-state energy-yields, Al-MCM-41 performed similarly to MCM-41 but Al₂O₃-SBA-15 outperformed SBA-15, so perhaps the conformal γ-alumina coatings are more effective at altering the plasma properties and reaction rates. Al-MCM-41 still exhibited similar mass-normalized overall energy yield to that of Al₂O₃-SBA-15, highlighting the importance of product shielding by adsorption at acid sites. That being said, Al-MCM-41 demonstrated less NH₃ recovery than Al₂O₃-SBA-15, possibly due to the different type (Bronsted and Lewis, respectively) and density of acid sites found in the Al-incorporated silica ordered structures. The promising performance of these ordered aluminosilicates for DBD-assisted NH₃ synthesis motivated our investigation of systematically-modified zeolites (i.e., composition, structure and dielectric properties) alongside ordered porous oxide supports for DBD-assisted NH₃ decomposition. NH₃ adsorbed in the acid-site functionalized supports appears to desorb under DBD exposure, allowing for energy efficient extraction of the shielded NH₃ energy carrier for higher energy yields. 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. These results inform the rational design of porosity and functionality of dielectric porous supports to optimize plasma properties, catalytic activity, NH₃ adsorption/desorption, and therefore the energy yield of DBD-assisted NH₃ reactions.

Research Interests

My graduate research career focused on ordered porous oxide synthesis, zeolite post-synthetic modifications and their use in non-thermal plasma-assisted NH₃ reactions, alongside a project on electrocatalytic NH₃ synthesis from gaseous N₂. These various projects have taught me kinetic analysis and reactor design in catalytic systems, especially novel, non-thermal reactors. Post-graduation, I hope to harness these skills in the energy storage field such as battery research, and even in fields with thermal catalysis, such as chemical manufacturing and pharmaceutical reactor design.