(Invited) Atomic Layer Deposition of Nanoalloys of Noble and Non-Noble Metals

Tuesday, 3 October 2017: 16:00
Chesapeake L (Gaylord National Resort and Convention Center)
R. K. Ramachandran, J. Dendooven (Department of Solid State Sciences, Ghent University), M. Filez (Utrecht University), V. V. Galvita, H. Poelman, E. Solano (Ghent University), M. M. Minjauw (Department of Solid State Sciences, Ghent University), G. B. Marin (Ghent University), and C. Detavernier (Ghent University, Dept. of Solid-state Sciences)
Bimetallic nanoparticles (BMNPs) play a pivotal role in optical, magnetic and electronic applications, and are true workhorses during the catalytic transformation of chemicals. In particular, supported Pt nanoparticles alloyed with In, Ga or Sn are highly selective catalysts for the dehydrogenation of propane to propylene. It is well established that the size and composition of the nanoparticles strongly impact the catalytic properties and performance. Yet, conventional synthesis strategies lack proper control over the nanoparticle morphology and composition. ALD has proven its potential for the size and composition controlled synthesis of supported BMNPs, but has to date only been applied for the synthesis of binary noble metal nanoparticles like Pt-Pd, Pt-Ru and Pd-Ru BMNPs. Extension of this approach to BMNPs containing non-noble metals has so far been hampered by unfavorable ALD chemistries to deposit non-noble metals in their elemental state. As a consequence, a strong need has arisen to develop alternative ALD-strategies which can deal with non-noble metals also.

We report a new ALD based procedure for the tailored synthesis of BMNPs containing a non-noble metal next to a noble metal (ACS Nano, 2016, 10, 8770–8777), here exemplified for nanoalloys containing In as non-noble and Pt as noble metal. Figure 1a schematically describes the steps involved in the fabrication process of the Pt-In BMNPs. Thin layers of In2O3 and Pt are sequentially deposited by ALD, yielding a Pt/In2O3 bilayer structure. These bilayers are then subjected to a temperature programmed reduction (TPR) in hydrogen to induce the formation of Pt-In nanoalloys. The BMNP formation during TPR was followed by in situ XRD measurements (Figure 1b) and was further confirmed by ex situ XAS (Figure 1c) and SEM measurements. The composition of the formed bimetallic alloys can be tuned by controlling the ratio of the deposited thickness of Pt to the thickness of In2O3. Figure 2a presents the relation between the as-deposited Pt/(Pt+In) atomic ratio and the alloy phase(s) obtained after TPR. In addition, our method enables tuning of the particle size with high precision in a range from 1 to 30 nm by changing the total thickness of the ALD-grown Pt/In2O3 bilayer (Figure 2b). Tuning of the particle size while keeping the composition the same can thus be achieved by scaling the layer thicknesses of the Pt and In2O3 layers while keeping the Pt/(Pt+In) atomic ratio constant.

Finally, successful BMNP synthesis was achieved on mesoporous silica, resulting in high surface area nanocatalysts which showed promising high activity for propane dehydrogenation.