Metal-support interaction induced atomic dispersion and redispersion of Pd on CeO2 for passive NOx adsorption

Abstract

Atomically dispersed metal catalysts have attracted extensive attention in the fields of heterogeneous catalysis due to the enhanced intrinsic activity and selectivity in many energy and environment related reactions, while they suffer from sintering under harsh reaction conditions. Herein, atomically dispersed Pd/CeO2 was synthesized and investigated as a passive NOx adsorber (PNA) material. The strong interaction between CeO2 and Pd creates Pd-O-Ce linkages with 100% utilization of Pd for NOx trapping, being one of the most active oxide-based PNAs up to date. Although a sulfation treatment can substantially reduce NOx storage capacity (NSC) on the Pd/CeO2, a two-step desulfation process, including a cold plasma treatment and an oxidative calcination, can recover near 90% of its original NSC. Desulfation caused Pd aggregating into nanoparticles (NPs), while reconstruction of Pd-O-Ce moieties was achieved by prolonged oxidation at 500 °C, driving by the strong metal-support interaction between Pd and CeO2. The Pd/CeO2 system exemplifies the advantages of the metal and oxide support interaction for the atomic dispersion of Pd and redispersion of sintered Pd NPs. Monitoring this dynamic interaction enables the atomically dispersed metal structure to be modulated in controlled reaction environments, being such an example, the enhanced performance of Pd/CeO2 in PNA applications was shown in the present manuscript.