Atomic and electronic structures of M (=Ni, Fe, NiFe, or FeNi) adlayer-modified alpha-Al2O3(0001) catalyst interface

In this study, density functional theory calculation is applied to examine the interfacial electronic and physical structures between the monometallic (Fe, Ni) or bimetallic (NiFe, FeNi) adlayer-modified alpha-Al2O3(0001) support and its connection with catalytic activity, for example, methane cracking. It is shown that bimetallic interfaces display the key factors for highly catalytic activity as a result of a balance of system stability, favorable d orbital directionality for molecular adsorption, spin quenching, and electron accumulation at the interface. The most stable interfaces promoting the strong metal-support interaction are the monometallic Fe or Ni and bimetallic NiFe interfaces formed with alpha-Al2O3-(0001). Such interfaces are composed of polar/ionic bonds in which bimetallic modification experiences the most significant interfacial M-M (M = Fe or Ni) and Al-O-M bond expansion. In addition to the spin quenching of the metal adlayer, it is identified that interface lattice expansion/distortion upon metal modification can induce two different molecular adsorption environments where the diffusion and strong adsorption of molecules at the interface and top metal adlayer can occur, respectively.