(645c) Electronic Structure Effects on Adsorption on Bimetallic Surfaces

The binding energy of adsorbates on metal surfaces has been shown to be a good descriptor of the surface catalytic activity. For example, nitrogen adsorption is directly relevant to the catalytic activity of metal surfaces for ammonia synthesis and decomposition. In this study, atomic nitrogen adsorption on various bimetallic (M1-M2) surfaces (complete adlayers, submonolayers and, M1 clusters on M2-slabs) has been investigated using Density Functional Theory (DFT) and is compared with that on single metals. Our results indicate that there exists a linear correlation between the atomic nitrogen binding energy on single metals with that on complete-adlayer and -submonolayer bimetallic surfaces, allowing for the prediction of the nitrogen binding energy on a variety of bimetallic surfaces simply from the nitrogen binding energy on single metals. Analyzing the density of states of the different surfaces, we elucidate electronic structure effects on nitrogen binding on terraces and steps of single metal and bimetallic surfaces. More specifically, the strength of binding of atomic nitrogen at various surface sites is found to correlate with the d-band center shifts. Using microkinetic modeling, we demonstrate how the relative nitrogen adsorption sites on bimetallic surfaces could guide the design of novel bimetallic catalysts for ammonia decomposition and synthesis by tuning the local microstructure and the alloying with different metals.