Paired interacting orbitals (PIO) study of Mo/SiO2 and Mo/HZSM-5 catalysts for olefin metathesis

Mo/SiO2 and Mo/HZSM-5 olefin metathesis catalysts are theoretically studied using cluster models and the paired interacting orbitals (PIO) method based on the extended Hückel theory. The first step of the catalytic cycle of ethene metathesis, i.e., ethene cycloaddition to the surface Mo methylidene species leading to the molybdacyclobutane formation is analysed. The electronic structure of the Mo ethene–methylidene complexes and the transition states is discussed for different models of the catalysts. It is shown that new MoC and CC bonds are formed in an asynchronous manner. The results support the proposal that the total overlap population between the orbitals of the Mo methylidene and C2H4 fragments of the surface ethene complexes can be an approximate reactivity index for supported Mo catalysts of olefin metathesis.