1. π Complexation The empty s-orbital of cationic copper forms a sigma bond with incoming sulfur and d-orbitals donate electron density to anti-bonding orbitals of sulfur rings [REF].
2. Acid Catalysis Although this mechanism is restricted to HY-ZSM5 zeolite, it is essential to note that experiments involving thiophene adsorption have noted saturation uptakes of thiophene to Cu(I) in CuY-zeolite [REF].