The influence of Mg on the C adsorption on Ni(100): A DFT study

Abstract

In this work, we performed density functional theory (DFT) calculations to study carbon adsorption on the Ni(1 0 0) surface and absorption in the bulk of nickel-based catalysts. The ideal catalyst surface was modeled as a five-layer Ni(1 0 0) slab. We also studied the influence of magnesium, considered as an atomic substitutional impurity, on carbon adsorption and migration into the bulk. To study the effect of Mg on the structure of Ni-based catalysts, we replaced a Ni atom by a Mg atom, on the surface and also in the bulk. Then, we relaxed the Mg and Ni positions. Our results showed that Ni atoms were pushed away from Mg.Wealso performed energy calculations to evaluate carbon interactions on different preferential sites of the Ni-slab, and also the effect of Mg atom on these deposition processes. The calculations showed that carbon adsorption on the bare Ni(1 0 0) surface was more favorable than deposition on this surface doped with magnesium. Our results also indicated that Mg could improve the interaction of surface-adsorbed carbon with gas phase oxygen, leading to the formation of a CO precursor species. In this way, magnesium promotes Ni-based catalysts hindering the surface from attaining a high carbon coverage, and thus making difficult the formation of carbon agglomerates and carbon whiskers. We also considered the effect of Ca in the C?O interaction on the metal surface.