期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：26
页码：7903-7908
DOI：10.1073/pnas.1506939112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceSupported metal nanoparticles often exhibit properties differing from those of their single-crystal counterparts. There have been several suggested explanations for this, including quantum size effects, strong metal support interactions, and some interplay between facets. In this article, we show that the support morphology can also have a decisive role in the nanoparticle properties. Using scanning tunneling microscopy, we show that Pd nanocrystals formed across steps of a TiO2 support have a curved top facet, where unusual adsorption behavior of CO is found. Calculations suggest that the different adsorption behavior arises from strain originating in the curved top facet. Our observations open the way for the tailoring of nanoparticle functionality by tuning the morphology of the support. Supported metal nanoparticles form the basis of heterogeneous catalysts. Above a certain nanoparticle size, it is generally assumed that adsorbates bond in an identical fashion as on a semiinfinite crystal. This assumption has allowed the database on metal single crystals accumulated over the past 40 years to be used to model heterogeneous catalysts. Using a surface science approach to CO adsorption on supported Pd nanoparticles, we show that this assumption may be flawed. Near-edge X-ray absorption fine structure measurements, isolated to one nanoparticle, show that CO bonds upright on the nanoparticle top facets as expected from single-crystal data. However, the CO lateral registry differs from the single crystal. Our calculations indicate that this is caused by the strain on the nanoparticle, induced by carpet growth across the substrate step edges. This strain also weakens the CO-metal bond, which will reduce the energy barrier for catalytic reactions, including CO oxidation.
