Single atom catalysis is attracting widespread attention as it allows decreasing the amount of costly noble metals in environmental catalysis (e.g., CO oxidation). Preparing single atoms of metals like Pd, Pt and Au on typical supports is however not straightforward. We used flame spray pyrolysis (FSP) to synthesize Pd/CeO2 catalysts in a facile and reproducible way by mixing acetylacetonate precursors of Pd and Ce. FSP of a solution of these precursors in a CH4/O2 flame resulted in 5 nm CeO2 octahedra with a surface area of 155 m2/g. TEM showed that this catalyst did not contain visible Pd or PdO particles. The room-temperature CO oxidation activity of this catalyst was substantially higher than that of Pd/CeO2 prepared by impregnation of Pd on FSP-prepared ceria or hydrothermally synthesized Pd nanorods. A room temperature in situ FTIR study of adsorbed CO was carried in the presence and absence of oxygen. Under reducing conditions (no oxygen), the Pd-oxide precursor in the conventional catalyst is reduced and agglomerates to small metallic Pd clusters. The spectra are very different in the presence of oxygen: bands due to reduced metal clusters are absent and instead new bands are observed that by use of DFT calculations can be linked to highly dispersed PdmOx as well as isolated PdOx clusters. The more active FSP-prepared sample contains only isolated Pd atoms in relatively small amounts. All of these data indicate the highly dynamic nature of the active Pd phase under reducing and oxidizing conditions. In summary, we employed a facile and scalable FSP approach to prepare a highly active Pd/CeO2 catalyst, which displays unprecedented activity in low-temperature CO oxidation.

Unprecedented CO oxidation performance of Pd/CeO2 prepared by flame spray pyrolysis

253rd National Meeting (2017)

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