In catalyst design, the focus is often on the frontier molecular orbitals, namely the HOMO (Highest Occupied Molecular Orbital) and the LUMO (Lowest Unoccupied Molecular Orbital). These orbitals are most involved in chemical reactions. By aligning the HOMO of the reactant with the LUMO of the catalyst (or vice versa), the overlap is maximized, facilitating electron transfer and stabilizing the transition state. For example, in heterogeneous catalysis involving metal surfaces, the d-orbitals of transition metals often play a significant role in interacting with the molecular orbitals of reactants.
