Atomic layer deposition (ALD) was employed to synthesize supported Pt–Pd bimetallic particles in the 1 to 2 nm range. The metal loading and composition of the supported Pt–Pd nanoparticles were controlled by varying the deposition temperature and by applying ALD metal oxide coatings to modify the support surface chemistry. High-resolution scanning transmission electron microscopy images showed monodispersed Pt–Pd nanoparticles on ALD Al2O3- and TiO2-modified SiO2 gel. X-ray absorption spectroscopy revealed that the bimetallic nanoparticles have a stable Pt-core, Pd-shell nanostructure. Density functional theory calculations revealed that the most stable surface configuration for the Pt–Pd alloys in an H2 environment has a Pt-core, Pd-shell nanostructure. In comparison to their monometallic counterparts, the small Pt–Pd bimetallic core–shell nanoparticles exhibited higher activity in propane oxidative dehydrogenation as compared to their physical mixture.

The atomic layer deposition (ALD) of metal oxides on metal surfaces is of great importance in applications such as microelectronics, corrosion resistance, and catalysis. In this work, Al 2 O 3 ALD using trimethylaluminum (TMA) and water was investigated on Pd, Pt, Ir, and Cu surfaces by combining in situ quartz crystal microbalance (QCM), quadrupole mass spectroscopy (QMS), and scanning tunneling microscopy (STM) measurements with density functional theory (DFT) calculations. These studies revealed that TMA undergoes dissociative chemisorption to form monomethyl aluminum (AlCH 3 *, the asterisk designates a surface species) on both Pd and Pt, which transform into Al(OH) 3 * during the subsequent water exposure. Furthermore, the AlCH 3 * can further dissociate into Al* and CH 3 * on stepped Pt(211). Additional DFT calculations predicted that Al 2 O 3 ALD should proceed on Ir following a similar mechanism but not on Cu due to the endothermicity for TMA dissociation. These predictions were confirmed by in situ QCM, QMS, and STM measurements. Our combined theoretical and experimental study also found that the preferential decoration of low-coordination metal sites, especially after high temperature treatment, correlates with the differences in free energy between Al 2 O 3 ALD on the (111) and stepped (211) surfaces. These insights into Al 2 O 3 growth on metal surfaces can guide the future design of advanced metal/metal oxide catalysts with greater durability by protecting the metal against sintering and dissolution and enhanced selectivity by blocking low-coordination metal sites while leaving (111) facets available for catalysis. ■ INTRODUCTIONThe growth of metal oxide thin films on metal surfaces is of tremendous importance for applications such as microelectronics 1 and corrosion resistance. 2−4 In heterogeneous catalysis, overcoating supported metal catalysts with porous metal oxide films to obtain a core−shell structure is an effective way to protect the metal catalyst against sintering, coking, and leaching under severe reaction conditions thereby improving catalyst stability. 5−12 In catalyst synthesis, the thickness of this protective layer must be carefully controlled to minimize the mass transfer resistance. The self-limiting, layer-by-layer ALD method enables atomic-level control over the thickness and composition of the protecting layer; therefore, it appears as a promising way to address this issue. 13−15 Among the ALD metal oxides, 11,12,16−25 alumina is the most frequently applied protective coating. 11,12,17,18,20−25 For example, Van Duyne et al. demonstrated that a subnanometer thick ALD Al 2 O 3 overcoating layer on silver nanoparticles can stabilize and maintain the activity of the silver nanoparticles for surface-enhanced Raman spectroscopy. 21,22 Weimer et al. prepared ALD aluminum alkoxide hydride overcoatings on Pt/SiO 2 catalysts using alternating exposures to TMA and ethylene glycol and subsequently thermally decomposed these films to form highly porous Al 2 O 3 . 26 They discovered that th...

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Combining Clarke's model with first‐principles calculation of average sound velocity, the minimum lattice thermal conductivities (κmin) of Y3Al5O12 (YAG), YAlO3 (YAP) and Y4Al2O9 (YAM) are predicted to be 1.59, 1.61, and 1.10 W·(m·K)−1, respectively. The weak Y–O polyhedra provide “weak zones” that scattering phonons and lead to the low κmin of ternary Y–Al–O compounds. In addition, the extremely low κmin of YAM is attributed to its higher levels of local disorder of crystal structure and weaker chemical bonding compared with those of YAG and YAP. Inspired by theoretical predictions, dense and phase‐pure YAM is synthesized and the experimental thermal conductivity is only 1.56 W·(m·K)−1at 1273 K. Finally, YAM is highlighted as a potential thermal barrier material for its low thermal conductivities at temperatures from 473 to 1273 K.

As promising TBC (thermal barrier coating) candidates, perovskite oxides own designable properties for their various options of cations and structural diversity, but limited comprehensions of structure-property relationship delay their engineering applications. In this work, mechanical/thermal properties of ABO 3 (A=Sr, Ba;B=Ti, Zr, Hf) perovskites and their anisotropic nature are predicted employing density functional theory. Their theoretical minimum thermal conductivities range from 1.09 to 1.74 WÁm À1 ÁK À1 , being lower than Y 2 O 3 partially stabilized ZrO 2 . Reduced thermal conductivities up to 16% along particular directions are reached after considering thermal conductivity anisotropy. All compounds own high hardness while SrZrO 3 , SrHfO 3 , and BaHfO 3 possess well damage tolerance. We found that small electronegativity discrepancy leads to big anisotropy of chemical bond, Young's/shear moduli and thermal conductivities, together with good damage tolerance. These results suggest that the next generation TBCs with extra low thermal conductivity should be achieved through combining material design and orientation-growth tailoring. K E Y W O R D S density functional theory, mechanical properties, perovskites, thermal conductivity