Unraveling Thermodynamic Stability, Catalytic Activity,and Electronic Structure of [TM x Mg y O z ] +/0/– Clusters at Realistic Conditions: A Hybrid DFT and ab Initio Thermodynamics Study

Aiming toward catalytic applications, a large data set is generated on [TMxMgyOz]+/0/– clusters (TM = Cr, Fe, Co, Ni, x + y ≤ 5) using a massively parallel cascade genetic algorithm (cGA) approach at the hybrid density functional level of theory. The low-energy isomers are further analyzed via ab initio atomistic thermodynamics to estimate their free energy of formation at a realistic temperature T and partial pressure of oxygen pO2. A thermodynamic phase diagram is drawn by minimizing Gibbs free energy of formation to identify the stable phases of neutral and charged [TMxMgyOz]+/0/– clusters. From this analysis, we notice that neutral and negatively charged clusters are stable in the wide range of (T, pO2). The negatively charged clusters are more effective as a catalyst to lower the C–H bond activation barrier for oxidation of methane. We find that the nature of TM atoms toward controlling the activation barrier is less important. However, the TM gives rise to different structural motifs in the cluster,...