Transformations of Formaldehyde Molecules in Cu−ZSM-5 Zeolites

Abstract

The activation of CO bond in formaldehyde molecule was followed by IR spectroscopy. IR studies showed that the interaction of formaldehyde with Cu+ weakens of the CO bond and results in a red shift of the CO IR band (Δν = 56 cm-1). The activation of the CO bond is the result of π back-donation of d electrons of Cu+ to π* antibonding orbitals of the molecule. Experiments on coadsorption of formaldehyde and CO on the same Cu* showed that formaldehyde acts as electron donor to the Cu+−CO system, resulting in stronger π back-donation to antibonding orbitals of CO. IR studies showed that formaldehyde molecules sorbed in zeolite Cu−ZSM-5 are oxidized to formate ions. Cu2+ ions, which survived the self-reduction to Cu+ during the pretreatment of zeolite under vacuum, were oxidant. Such Cu2+ ions are reduced to Cu+ during the reaction with formaldehyde molecules.