The activation of acetylene by Cu+ ions in zeolites studied by IR spectroscopy

The interaction of acetylene with Cu+ ions in zeolites CuX, CuY, CuZSM-5 and CuMCM-41 was studied by IR spectroscopy. The Ctriple bond; length of mdashC bond was strongly activated, what resulted in a distinct weakening of the triple bond and of triple bond; length of mdashCsingle bondH bond (ΔνCtriple bond; length of mdashC = 156–168 cm−1, Δνtriple bond; length of mdashCsingle bondH = 93–122 cm−1). The ability of Cu+ ions to activate acetylene molecule increases in the order: CuMCM-41 < CuZSM-5 < CuY < CuX. It may be related to increasing amount of AlO4− tetrahedra, and to increasing negative charge of zeolite framework. IR experiments evidenced, that Cu+ in various cationic sites activate acetylene molecule in a different extend. It has been shown, that Cu+ ions are also able to bond two acetylene molecules. The molecules of pyridine when bonded to Cu+ ions increase the electron donor properties of Cu+ ions and their ability to activate acetylene molecule. This effect is however very small. The adsorption of acetylene removes pre-adsorbed CO.