Theoretical Exploration\nof the Mechanisms for Methane-to-Methanol\nConversion Using Bare and ZSM-5-Supported Pd<sub>4</sub> Clusters

This paper presents a comprehensive mechanistic investigation\ninto\nthe partial oxidation of methane to methanol on bare and ZSM-5-supported\nPd<sub>4</sub> clusters utilizing N<sub>2</sub>O as an oxidant. The\nstudy employs density functional theory (DFT) with ONIOM2 (QM: MM)\n(B3PW91/LANL2DZ/6-31G(d,p):UFF) with dispersion correction calculations\nto explore potential energy surfaces (PESs) associated with the methane-to-methanol\nconversion process in a ZSM-5-supported Pd<sub>4</sub> cluster. Two\nspin multiplicities (SM = 1, 3) were considered for the overall reaction\npathway. The investigation reveals that C–H activation of methane\ntakes place subsequent to the formation of Pd<sub>4</sub>O from the\nN<sub>2</sub>O decomposition step, which ultimately leads to methanol\nformation. The study indicates that in terms of activation barrier,\nthe N–O and C–H activation steps exhibit a lower energy\nbarrier in the singlet state, while the recombination step of CH<sub>3</sub> and OH moieties is preferable in the triplet spin state.\nHowever, the reaction process does not involve any spin crossover,\nas the triplet spin state consistently maintains the lowest energy\npathway throughout the reaction. From the overall analysis of the\nreaction mechanisms for methane to methanol, it is evident that zeolite\nsupport and spin multiplicity play a significant role in lowering\nthe activation barriers.