Single Atom-Based Catalysts Prepared By Atom Trapping and Their Catalytic Properties for Emission Control Applications

Carlos Eduardo Garcia Vargas

doi:10.7273/000005261

Emission control catalysts must exhibit robust thermal/hydrothermal stability and high activity at the lowest possible temperatures. Upcoming environmental regulations require current catalytic formulations to further improve low-temperature activity (<150°C) while making the most efficient use or replacement of platinum group metals (PGMs). Single Atom catalysts have positioned as promising catalyst design tools to address these challenges, which make 100% use efficiency of PGMs while exhibiting advantageous electronic properties due to unique structure and interactions with supports. Recently, Pt1 single atoms were stabilized in square planar coordination at ceria surface step defects via high-temperature calcination (Atom Trapping), showing remarkable thermal/hydrothermal stability (high surface area) and low-temperature activity. This dissertation focuses on investigating the mechanisms of single atom stabilization on CeO2 for metals different than Pt, while exploiting the resulting catalytic properties for emission control applications. At high temperature calcination conditions, metals mobilize via likely surface diffusion and are stabilized in near square planar form due to inability to form solid solutions with CeO2. Cu/CeO2 catalyst prepared by atom trapping is a representative case in which a non-PGM metal can stabilize CeO2 from sintering while exhibiting remarkable low-temperature oxidation activity. A combined experimental and theoretical study revealed that dual low-temperature activity/high thermal stability properties are achieved due to unique electronic properties of Cu1 sites, which allows for dynamic charge shuttling with the support and promotes lattice oxygen activation that facilitates multiple oxidation pathways. Rh/CeO2 exhibited the highest surface area retention with remarkable low-temperature activity and stability under dynamic redox environments commonly encountered in gasoline vehicle emissions. Cationic Rh-carbonyl complexes resulting from atom trapping synthesis exhibited improved metal-support interaction reflected in higher lattice oxygen availability and stronger anchoring of Rh1 to CeO2. Finally, the atom trapping approach was leveraged as a catalyst design strategy to overcome inhibition by H2O competitive adsorption of low temperature methane abatement from natural gas emissions. Pt1 sites prepared by atom trapping were used as anchoring species for Pd active phase. The resulting Pd species exhibited 2-dimensional rafts-like morphology whose remarkable low-temperature methane oxidation and water tolerance was rationalized by improved C-H bond activation and higher water dissociation barrier.

Single Atom-Based Catalysts Prepared By Atom Trapping and Their Catalytic Properties for Emission Control Applications

Files and links (1)

Abstract

Metrics

Details