Abstract
As CuMCM-41 was found to be active in skeletal isomerisation of n-butenes, we followed by IR spectroscopy the interaction of but-1-ene, cis-but-2-ene, and trans-but-2-ene with Cu + sites in CuMCM-41. It has been revealed that Cu + activated strongly C C bond, what resulted in a frequency shift of C C stretching band by about 100 cm −1. Moreover, the vibration of C H bonds in CH 2 and C H groups neighbouring to the double bonds was also perturbed. We suppose that the activation of C C bond is a result of π-back donation of d electrons of Cu + to π * antibonding orbitals of butenes. IR results evidenced also the heterogeneity of Cu + sites in CuMCM-41 and the presence of Cu + sites of various electron donor properties. But-1-ene molecules bonded to Cu + ions are less prone to accept protons from Brønsted acid sites than molecules bonded by hydrogen bonding to non-acidic SiOH groups, even though they are more negative than free or physisorbed molecules. The IR studies of coadsorption of CO and but-1-ene suggest that the interaction of CO with Cu + is much weaker if but-1-ene is present, than without butene.
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