Ab initio study of Pt clusters on TiO2 (110)

A. MALDONADO; S.B. RAMOS; C.I.N. MORGADE; G. F. CABEZA

La Plata

Workshop; VI Workshop on Novel Methods for Electronic Structure Calculations; 2015

Departamento de Electrotecnia - Universidad Nacional de La Plata

TiO2 is a widely used material due to its electronic and catalytic properties, which are of interest for technological applications. In catalysis it is generally used as support for different catalyzers, such as for example Pt, which is important for the water shift reaction (WSR) for H2 production [1]. Due to the high catalytic activity of Pt nanoclusters (NCs), they are placed over TiO2 in search for improving the sensibility of the material.In this work we use an ab initio modeling method based on the DFT+U, previously used [2], to investigate the structural, cohesive and magnetism of Pt4, with planar and tetrahedral geometries, and Pt13 with octahedral symmetry deposited over (110) of TiO2 in its rutile phase. We use the projected augmented wave (PAW) method and the Vasp code [3], combined with exchange and correlation functions. We determine the equilibrium structure, energy of adsorption, charge transfer effects and electronic density of states, to characterize different aspects of the metal-oxide interaction. We evaluate the relative stability of both isolated and supported geometries over the surface,the electronic densities and charge transfer effects, comparing with previous theoretical results [4]. For the isolated Pt4 cluster thetetrahedral geometry is more stable than the planar one. However when deposited over TiO2 the relative stability is reversed; this effect is correlated with the higher number of Pt-Ti bonds that tend to stabilize the system. This result is in good agreement with Jiang et al. [4] who used a similar study based on exchange and correlation potentials of the type PBE. However, an important difference is observed for the electronic behavior; according to [4]the system Pt4/TiO2 is semiconductor, while our results indicate that the system has metallic character. In our case the use of XC potential of the type PBE + U let us correctly treat the gap for TiO2(110),and therefore better results are expected.Besides,our results for Pt4/TiO2 are also in line with the experimental observations of Watanabe etal. [5], who find planar configurations for clusters with sizes lower than 7. For Pt13/TiO2, our results predict a strong restructuration of the cluster, that evolves from an initial octahedral configuration, to a more disordered configuration in more contact to the surface in the sense of increasing the Pt-Ti bonds. References[1] C. Vignatti, M. Avila, C. Apesteguía, T. Garetto, Inter. J. of  Hyd. Energy 35 (2010) 7302.[2] C. I. N. Morgade, Ch. I. Vignatti, M. S. Avila, G. F. Cabeza, J. of  Mol. Cat. A: Chemical 407 (2015) 102.[3] G. Kresse, J. Joubert, Phys. Rev. B 59 (1999) 1758.[4] D. Jiang, S. H. Overbury, Sheng Dai, J. Phys. Chem. C 116 (2012) 21880.[5] Y. Watanabe, X. Wu, H. Hirata and N. Isomura, Catal. Sci. Technol. 1(2015) 1490.