Nanostructured catalysts expose a high surface area available for chemical reactions, thus yielding high activity with a low fraction of metal loading. This is much convenient in terms of both volume and cost, the latter being determined by the fact that the most efficient catalysts are often based on precious metals. Furthermore, in the world of nanostructures, materials show novel and unexpected properties, considerably different with respect to the conventional behavior at large scales: pros and cons that still need to be deeply understood.

By combining advanced experimental techniques with accurate calculations within the framework of quantum mechanics, the effects induced by carbon monoxide on platinum nanoclusters have been investigated. Carbon monoxide is indeed a key ingredient in many relevant synthesis and chemical conversion reactions in modern catalytic systems. The model nanocatalysts (from few up to tens of atoms in a particle) were obtained by exploiting self-assembling processes on a single graphene sheet. The latter, when grown on an iridium single crystal termination, yields a Moiré superstructure that acts as a template for an ordered clusters growth, a process that can be controlled in a precise way. The study put in evidence that the presence of a gas phase induces relevant structural changes in the particles due to the carbon monoxide coordination to the many non-equivalent and active adsorption sites available at the surface of the metallic clusters. Small particles undergo a complex restructuring process, thus becoming mobile at the graphene surface and yielding coalescence phenomena that contribute to the degradation of the overall catalytic performance. More, also the graphene network gets involved, so that even the underlying supporting metal surface takes part in the diffusion mechanisms. Therefore, we can surely say that “small” is … surprising!

The work was performed within the framework of a collaboration between the experimental group led by Dr. Erik Vesselli and the theoretical group of Prof. Maria Peressi, both from the Physics Department, with the contribution of Prof. Giovanni Comelli, Nicola Podda and Dr. Carlo Dri, and from PhD students Zhijing Feng, Manuel Corva (Nanotechnology) and Fatema Mohamed (Physics). International collaborators also contributed to the work. The results have been recently published in the high impact factor journal ACS Nano.

Supports from CERIC Consortium, MAECI (Progetto di Grande Rilevanza con l’Argentina), ICTP, and UniTs through FRA 2015 and the agreement with CINECA for high performance computing are greatly acknowledged.

Experimental and Theoretical Investigation of the Restructuring Process Induced by CO at Near Ambient Pressure: Pt Nanoclusters on Graphene/Ir(111)

Nicola Podda, Manuel Corva, Fatema Mohamed, Zhijing Feng, Carlo Dri , Filip Dvorák, Vladimir Matolin, Giovanni Comelli, Maria Peressi, and Erik Vesselli

ACS Nano, 2017, 11 (1), pp 1041–1053

http://pubs.acs.org/doi/abs/10.1021/acsnano.6b07876