Resumen de Advanced modelling of metallic nanomaterials for catalysis
Nanoparticles are highly relevant for catalysis due to their nanostructure, which increases the fraction of surface atoms, and the size dependent morphology and properties. Catalytic properties of nanoalloys also depend on the composition and chemical ordering. Therefore, it is important to understand how geometrical and topological features of mono- and bimetallic nanoparticles affect their stability and reactivity of the exposed surface sites.
This Thesis deals with computational study of monometallic and bimetallic nanoparticles using methods based on Density Functional Theory (DFT). First, the exchange-correlation functional PBE was identified to reproduce experimental bulk and surface properties of Transition Metals overall more accurately than other examined functionals VWN, PBEsol, RPBE and TPSS. The performance was further improved by choosing exchange and correlation parameters between those of PBE and PBEsol functionals or restoring the linear spin approximation of PBEsol. The d-band center was found the most robust and transferrable among the studied electronic descriptors for different functionals.
For different monometallic Pd nanoparticles it was shown that their energies can be quantitatively described using linear dependence on the quantity of atoms with different coordination numbers. Whereas employing such morphological features as number of corner sites, length of the edges, particle area and volume allowed only a qualitative energy prediction.
Equilibrium chemical ordering for bare PdRh, PtNi, PtAu, PtAg, and PtCu bimetallic nanoparticles at low temperature was determined employing the so-called Topological Method parameterized on DFT data. Effects of temperature and reactive environment on the chemical ordering were also evaluated. A remarkable experimental finding of our collaborators is that CO molecules can bind stronger on some core@shell Cu@Pt particles than on pure Pt particles. It was rationalised by DFT calculations of specific surface sites, such as single Pt atom surrounded by surface Cu atoms, under-coordinated Pt atom, Pt adatom and vacancies with missing Pt atoms.
