The interaction of acetylene with Cu+ ions in zeolites CuX, CuY, CuZSM-5 and CuMCM-41 was studied by IR spectroscopy. The C&3bond; C bond was strongly activated, what resulted in a distinct weakening of the triple bond and of &3bond; C-H bond (Delta nu(C&3bond; C) = 156-168 cm(-1), Delta nu(&3bond; 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 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. (c) 2005 Elsevier B.V. All rights reserved.