Hydrodechlorination catalysis of Pd-on-Au nanoparticles varies with particle size

Trichloroethene (TCE), a common carcinogen and groundwater contaminant in industrialized nations, can be catalytically degraded by Au nanoparticles partially coated with Pd (“Pd-on-Au NPs”). In this work, we synthesized Pd-on-Au NPs using 3, 7, and 10 nm Au NPs with Pd surface coverages between 0–150% and studied how particle size and composition influenced their TCE hydrodechlorination (HDC) activity. We observed volcano-shape dependence on both Au particle size and Pd surface coverage, with 7 nm Au NPs with Pd coverages of 60–70% having maximum activity. Using extended X-ray absorption fine-structure spectroscopy, we found a strong correlation between catalytic activity and the presence of 2-D Pd ensembles (as small as 2–3 atoms). Aberration-corrected scanning transmission electron microscopy further confirmed the presence of Pd ensembles. The Pd dispersion and oxidation state generally changed from isolated, metallic Pd atoms to metallic 2-D Pd ensembles of varying sizes, and to partially oxidized 3-D Pd ensembles, as Pd surface coverage increased. These changes occurred at different surface coverages for different Au particle sizes. These findings highlight the importance of controlling particle size and surface coverage in bimetallic catalysts.

Graphical abstractThe groundwater clean-up reaction of trichloroethene hydrodechlorination, catalyzed by Pd-on-Au nanoparticles, varies with volcano-shape dependence on both Au particle size and Pd surface coverage. Pd takes several forms on the nanoparticle surface, with metallic two-dimensional ensembles found in the most active catalyst compositions.Figure optionsDownload full-size imageDownload high-quality image (81 K)Download as PowerPoint slideHighlights► Aqueous trichloroethene hydrodechlorination is most rapid with 7 nm Pd-on-Au particles. ► Catalysis of palladium-on-gold nanoparticles changes with Au particle size. ► Volcano-shape dependence on both Au particle size and Pd surface coverage is seen. ► Metallic two-dimensional Pd ensembles correlate with high catalytic activity.