Abstract
Heterogeneous catalysis, which is widely used in the chemical industry, makes a great use of supported late-transition-metal nanoparticles, and bimetallic catalysts often show superior catalytic performances as compared to their single metal counterparts. In order to optimize catalyst efficiency and discover new active combinations, an atomic-level understanding and control of the catalyst structure is desirable. In this work, the structure of catalytically active AuRh bimetallic nanoparticles prepared by colloidal methods and immobilized on rutile titania nanorods was investigated using aberration-corrected scanning transmission electron microscopy. Depending on the applied post-treatment, different types of segregation behaviours were evidenced, ranging from Rh core – Au shell to Janus via Rh ball – Au cup configuration. The stability of these structures was predicted by performing density-functional-theory calculations on unsupported and titania-supported Au-Rh clusters; it can be rationalized from the lower surface and cohesion energies of Au with respect to Rh, and the preferential binding of Rh with the titania support. The bulk-immiscible AuRh/TiO2 system can serve as a model to understand similar supported nanoalloy systems and their synergistic behaviour in catalysis.
Highlights
Both carried out in large excess of hydrogen around 300 °C
With the aim of gaining insights into the structure of the catalytically active phase, the catalyst submitted to thermal treatments in hydrogen has been investigated in details by aberration-corrected scanning transmission electron microscopy (AC-Scanning transmission electron microscopy (STEM))
Au-Rh nanoparticles were synthesized by conventional colloidal chemical co-reduction in water, using chloride salts as metal precursors, polyvinyl alcohol (PVA) as surfactant, and NaBH4 as reducing agent, as previously reported[15]
Summary
Both carried out in large excess of hydrogen around 300 °C. In this work, with the aim of gaining insights into the structure of the catalytically active phase, the catalyst submitted to thermal treatments in hydrogen has been investigated in details by aberration-corrected scanning transmission electron microscopy (AC-STEM). As previously shown by infrared spectroscopy and TEM, the heating of AuRh/TiO2 to 350 °C under H2 flow leads to the complete removal of the PVA surfactant from the NP surface without significant change of the mean particle size[15].
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