The activation of C=C bond in alkenes by Cu+ ions in zeolites IR, TPD-IR studies and DFT calculations

IR studies evidenced that Cu+ ions in zeolites were able to activate C=C bond in but-1-ene. The stretching frequency of C=C- bond decreased by about 100 cm(-1) upon adsorption of but-1-ene on Cu+ in CuX and CuZSM-5. The bands of CH stretching and deformation in =CH2 fragment did also shift upon the adsorption. The adsorption of but-1-ene was so strong, that it removed CO and NO preadsorbed on Cu+ ions. The experiments TPD-IR showed the heterogeneity of Cu+ sites in CuX and the presence of at least two kinds of Cu+ of various energies of but-1-ene bonding. Quantumchemical DFT calculation revealed a distinct weakening of C=C bond and evidenced that it was caused by a pi-back donation of d-electrons of Cu+ to antibonding pi(*) orbitals of C=C- in but-1-ene.