Elucidating Storage and Oxidation Mechanisms on Pd and Pt Catalysts: From Single Atoms to Nanoparticles



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Metal based catalysts have played a crucial role in the development of industrial catalytic processes, including the Haber-Bosch process for ammonia synthesis that uses metal-based catalyst. Platinum group elements have emerged as exceptional catalysts for various applications, including pollution abatement, battery materials, and the production of value-added chemicals. These metals are often dispersed as isolated single atoms or nanoparticles on a support to increase their effectiveness. The activity of these sites varies depending on the reaction, with Pd single atoms exchanged in zeolite pores being more favorable for NOx adsorption and larger Pt nanoparticles being preferred for methane activation. The automotive industry faces a significant challenge in reducing NOx emissions from diesel exhaust at low temperatures (<200 ℃). Passive NOx adsorber (PNA) emerged as a potential technology that uses Pd-exchanged zeolite materials to reduce NOx in diesel engine exhaust. Density functional theory (DFT) and reaction experiments were used in the current work to understand reaction mechanisms. The findings show that water oxidizes NO to NO2, resulting in the reduction of Pd which acts as storage site with stronger NO binding. However, the combined presence of water and CO can deactivate the catalyst. This understanding offers a new direction for the improvement of PNA material. Recent advancements in dynamic catalysis have demonstrated enhanced catalytic performance compared to static conditions. Dynamic reactor experiments along with DFT were used in this study to explore avenues to maximize hydrogen production during methane partial oxidation on Pt-based catalysts. The study found that feed modulation with varying concentrations of oxygen could enhance hydrogen production, and the mechanistic investigation confirmed the role of hydroxyl groups at the metal support interface in improving hydrogen selectivity. Additionally, DFT calculations were used to understand the electronic properties of Pt-based catalysts subjected to dynamic surface charge environments in catalytic condenser devices. Varying surface charge on the catalyst could help increase reaction rates in dynamic conditions. These findings provide valuable insights for the development of more efficient and effective dynamic catalytic processes, which are critical for sustainable growth while minimizing environmental impact.



Catalysis, DFT, Reaction mechanism


Portions of this document appear in: Onn, Tzia Ming, Sallye R. Gathmann, Silu Guo, Surya Pratap S. Solanki, Amber Walton, Benjamin J. Page, Geoffrey Rojas et al. "Platinum Graphene Catalytic Condenser for Millisecond Programmable Metal Surfaces." Journal of the American Chemical Society 144, no. 48 (2022): 22113-22127.