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

Abstract

The interaction of acetylene with Cu + ions in zeolites CuX, CuY, CuZSM-5 and CuMCM-41 was studied by IR spectroscopy. The C C bond was strongly activated, what resulted in a distinct weakening of the triple bond and of C H bond (Δν C C = 156–168 cm −1, Δν C H = 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 AlO 4 − 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.