Interfacial stability, electronic property, and surface reactivity of alpha-MoO3/gamma-Al2O3 composites: DFT and DFT plus U calculations

The design of alpha-MoO3/gamma-Al2O3 composite is of high interest because such composites are with extraordinary catalytic selectivity for petroleum refining. However, the role of each component in heterogeneous catalyst as well as the essential relationship between interfacial structure and surface reactivity is still ambiguous. To deeply understand these details, we investigated the structure, stability, electronic property, and surface reactivity of alpha-MoO3/gamma-Al2O3 composites by density functional theory DFT and DFT + U. The models of alpha-MoO3/gamma-Al2O3 composites were constructed by combining the alpha-MoO3 (0 1 0) surface with non-spinel and spinel gamma-Al2O3 (1 0 0) and (1 1 0) facets. We found that both the nature of gamma-Al2O3 support and the surface coverage of alpha-MoO3 significantly influenced the interfacial stability and surface catalytic activity. For all composites, the interfaces were stabilized via the formation of different Al-O-Mo bonds between the gamma-Al2O3 slab and the alpha-MoO3 slab. The interaction energy and adhesion work of interface indicated that the spinel gamma-Al2O3 (1 1 0) surface is most favorable for the stabilization of alpha-MoO3 surface. Fermi softness (S-F), a readily obtainable electronic property was used to evaluate the surface reactivity of the composites. The results indicated that the surface reactivity of all composites is clearly higher than pure alpha-MoO3, and the monolayer coverage composites with exposed (1 1 0) surface of gamma-Al2O3 exhibited the highest surface reactivity. By analysis of the charge density difference and density of states, we found that the electrons on the interface are largely redistributed and charges transfer from gamma-Al2O3 to alpha-MoO3, which promoted the delocalization of both interfacial and surface electronic states near the Fermi level, resulting in strengthened the interfacial interaction and surface reactivity. In addition, the adsorption and dissociation of H2S on the surfaces of all ML composites was investigated. The reaction pathway and kinetic barrier were determined. The results shown that ML- Mo/nspAl(1 1 0) with the highest Femi softness (1.39) showed the lowest energy barrier (0.35 eV), which further confirmed the effectiveness of the Femi softness.