Oxide-supported single-atom Pt materials are prepared by combining surface organometallic chemisorption with atomic layer deposition (ALD). Here Pt is supported as a discrete monatomic "pincer" complex, stabilized by an atomic layer deposition (ALD) derived oxide overcoat, and then calcined at 400 °C under O 2 . ALD-derived Al 2 O 3 , TiO 2 , and ZnO overlayers are effective in suppressing Pt sintering and significantly stabilizing single Pt atoms. Furthermore, this procedure decreases the overall Pt nuclearity (∼1 nm average particle diameter) versus bare Pt (∼3.8 nm average diameter), as assayed by aberration corrected HAADF-STEM. The TiO 2 and ZnO overcoats are significantly more effective at stabilizing single-atom Pt species and decreasing the overall Pt nuclearity than Al 2 O 3 overcoats. Vibrational spectroscopy of adsorbed CO also shows that oxidized Pt species commonly thought to be single Pt atoms are inactive for catalytic oxidation of adsorbed CO. CO chemisorption measurements show site blockage by the ALD overcoats.

The surface structure of (110) faceted strontium titanate nanoparticles synthesized via solvothermal method has been resolved using high-resolution electron microscopy (HREM). We demonstrate that the surface is a titania-rich structure containing tetrahedrally coordinated TiO units similar to the family of (n × 1) reconstructions observed on (110) surfaces of bulk crystalline strontium titanate. When compared with prior results for (001) terminated strontium titanate single crystals made with traditional transmission electron microscopy (TEM) sample preparation techniques, the results demonstrate that many models for oxide nanoparticles need to be revisited. This work serves as a reminder that attention must be paid to the surface of nanoparticles. Even with a simple perovskite as the starting point the end result can be very complex. As more materials are synthesized on the nanoscale, this will become increasingly important to take into consideration.

Through high-resolution electron microscopy, the surface structure of barium titanate and strontium titanate nanoparticles are found to be terminated by a TiO 2 double layer. These results confirm prior observations of TiO 2 -rich surface reconstructions on strontium titanate nanoparticles made hydrothermally at high pH and single crystals prepared with wet chemical etching. Of all the reconstructions observed on single crystals for these two materials, we report for first time the √13 × √13R33.7°structure on the {001} facets of hydrothermally prepared barium titanate and strontium titanate nanocrystals. The aqueous environment common to the two preparation methods preferentially leaves strontium and barium depleted from the A-sites near the surface and leads to TiO 2 -terminated surfaces for both materials. Analysis indicates that the observed structures are the thermodynamic lowest energy structures in aqueous conditions.

Single crystal SrTiO3 nanocuboids having primarily TiO2-(001) surfaces and nanododecahedra having primarily (110) surfaces were created by two separate hydrothermal synthesis processes. Pd nanoparticles grown on the two sets of STO nanopolyhedra by atomic layer deposition show different morphologies and CO oxidation performance. Transmission electron microscopy and small-angle X-ray scattering show that 2–3 nm Pd nanoparticles with 3–5 nm interparticle distances decorate the STO surfaces. When the number of ALD cycles increases, the growth of the Pd nanoparticles is more significant in size on TiO2-(001)-STO surfaces, while that on (110)-STO surfaces is more predominant in number. High resolution electron microscopy images show that single crystal and multiply twinned Pd nanoparticles coexist on both types of the STO nanopolyhedra and exhibit different degrees of adhesion. The CO oxidation reaction, which was employed to determine the dependence of catalytic activity, showed that the Pd catalytic performance was dominated by the coverage of CO, which is more directly related to Pd nanoparticle size than to shape. CO turnover frequency analysis and diffuse reflectance infrared Fourier transform spectroscopy show that regardless of the shape or degrees of wetting, larger Pd nanoparticles (∼3 nm) have lower catalytic activity due to high CO coverage on nanoparticle facets. Smaller nanoparticles (∼2 nm) have more edge and corner sites and exhibit 2–3 times higher TOF at 80 and 100 °C.

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