DOI: 10.1002/cphc.200900597 Where does Hydrogen Adsorb on Ru Nanoparticles? A Powerful Joint 2 H MAS-NMR/DFT Approach Lionel A. Truflandier, [b] Iker Del Rosal, [a] Bruno Chaudret, [c] Romuald Poteau, [a] and Iann C. Gerber* [a] Several studies have shown that 2 H NMR, among many other techniques, is a versatile tool for the study of hydrogen coordi- nation modes in transition metal complexes [1] or clusters. [2] Thanks to 1 H gas-phase and 2 H solid-state MAS-NMR spectro- scopy, the coexistence of ancillary organic ligands, with mobile and reactive hydride ligands coordinated to ruthenium nano- particles (NPs) has been observed. [3] Similar results were also found in the case of Ru NPs embedded in the cavities of metal-organic frameworks (MOFs). [4] However, secure assign- ment of the experimental information is hardly straightforward, as few reliable reference data are available for different bond- ing situations and chemical environments. As a matter of fact, solid-state NMR spectra of molecular compounds with non- equivalent deuterons generally consist of a complex superposi- tion of subspectra with different shapes, which depend on the motion of the corresponding deuterons. [5] Here, the need for systematic theoretical studies for better interpretation of NMR spectra is clear. Recently, some of the authors have proposed the foundation of this work, with molecular density functional theory (DFT) calculations of quadrupole coupling constants Q cc and the asymmetry parameter h Q , (see the Supporting Information for definitions) of deuteron in ruthenium complexes [6] directly comparable with the experimental data. [1g] There is no doubt now that joint theoretical/experimental studies are a very pow- erful approach to complete the partial understanding of deu- teron solid-state NMR spectra. Herein, we propose to explore the stability and to estimate quadrupole coupling parameters of deuterium atoms, on and below the surface of Ru NPs at low coverage, by means of DFT calculations on an infinite Ru(0001) slab surface model. Moreover, new quantitative in- sights into the kinetic behavior of chemically adsorbed hydro- gen atoms are brought with the help of diffusion barrier esti- mations for surface hopping and subsurface paths. These in- vestigations should form a first basis for the assignment of deuteron MAS-NMR spectra of ruthenium NPs. At a coverage value of 1/4 monolayer (ML), high-symmetry adsorption sites on the Ru surface, as depicted in Figure 1, were considered, yielding energetic and structural parameters in good agreement with the literature. [7] The Fcc site is slightly more stable than the Hcp site, while sites with less local sym- metry order, namely On-top and Bridge, respectively lie 3 and 10 kcal mol À1 higher. Note that the terminal (On-top) and the two-fold (Bridge) sites are distinguished from the other sites by an imaginary frequency, which indicates that these states are saddle points at this particular low coverage value. The subsurface sites, Ts and Os, are significantly higher in energy, 24.2 and 8.7 kcal mol À1 respectively. Consequently, unless cov- erage increases significantly or co-adsorption species can rea- sonably invert their energy sign, there is a very low probability that hydrogen atoms can be found in these four-and six-fold sites at low coverage values. In the context of NPs, informations about surface diffusion processes are of great interest in many aspects, such as the transport of species in catalyzed reactions, for surface nano- [a] I. Del Rosal, Prof. R. Poteau, Dr. I. C. Gerber UniversitØ de Toulouse INSA, UPS, LPCNO, IRSAMC 135 avenue de Rangueil, F-31077 Toulouse (France) and CNRS UMR 5215 (IRSAMC) F-31077 Toulouse, France Fax: (+ 33) 56-559-697 E-mail : igerber@insa-toulouse.fr [b] Dr. L. A. Truflandier CEA Saclay DSM/IRAMIS/SIS2M, CEA/CNRS, LSDRM F-91191 Gif-sur-Yvette (France) [c] Dr. B. Chaudret Laboratoire de Chimie de Coordination du CNRS 205 route de Narbonne, F-31077 Toulouse (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.200900597. Figure 1. Left panel: Views of subsurface and surface adsorption sites with adsorption energies in kcal mol À1 . Diffusion barrier energies corresponding to the hopping process are also shown. Right panel : a) Solid-state 2 H NMR spectra of Ru NPs stabilized by HDA from ref. [3]. b) and c) Simulations of the resonances using the theoretical quadrupolar parameters collected in Table 1. The simulated spectrum of the partially mobile Ru ÀD (in black) was realized using experimental parameters Q cc = 66 kHz, h Q = 0.30 (ref. [3]). d) Simulation of the “rigid C ÀD” component using Q cc = 160 kHz, h Q = 0.02 (ref. [3]). ChemPhysChem 2009, 10, 2939 – 2942  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2939