Non-dissociative adsorption of glycerol on the (111) surface of Ni and Pt-based metallic systems: Hints on reforming activity from d-band center

Abstract

In the context of catalyst design, particularly for glycerol conversion, glycerol adsorption on Pt3Ni(111) and Pt3Ni/Pt(111) surfaces has been studied using spin-polarized density functional theory within a non-local van der Waals approach (optB86b-vdW). Pure Ni and Pt metals, and Ni/Pt/Pt and Pt/Ni/Pt bimetallic systems were also studied for comparison purposes. Compared to the glycerol adsorption energy (Eads) predicted by the generalized gradient approximation (PBE), optB86b-vdW predicts an adsorption up to 70% stronger, though both functionals predict the same lowest energy adsorption sites. Glycerol adsorption does not change the segregation state of the catalyst, and involves either charge polarization or a small charge transfer to the substrate. Eads was found to be dependent not only on the nature of the three metallic atoms closest to glycerol, but also on their nearest neighbors lying both on the surface (L1) and subsurface (L2) atomic layers. For all the surfaces, Eads was predominantly determined by the stability of the non-covalent interaction between one of the lone pairs of the oxygen atom closest to L1 and its closest metallic atom in L1. In addition to the surface energy (γ), the occupied d-band center relative to the Fermi level, εd-εF, was found to correlate remarkably well with Eads when modelling of van der Waals forces is improved. Since Eads energy has been found to correlate well with the reforming yield for non-supported Ni and Pt-based catalysts, we suggest a dual descriptor based on both εd-εFL1 and Eads to estimate the reforming yield of these systems within the scope of a fundamental surface science study.