Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

In this study, IR studies of the coadsorption of ethanol and CO on Cu(+) cations evidenced the transfer of electrons from ethanol to Cu(+), which caused the lowering of the frequency of the band attributed to CO bonded to the same Cu(+) cation due to the more effective π back donation of d electrons of Cu to antibonding π* orbitals of CO. The reaction of ethanol with acid sites in zeolite HFAU above 370 K produced water and ethane, polymerizing to polyethylene. Ethanol adsorbed on zeolite Cu(2)HFAU containing acid sites and Cu(+)(exch) also produced ethene, but in this case, the ethene was bonded to Cu(+) and did not polymerize. C=C stretching, which is IR non-active in the free ethene molecule, became IR active, and a weak IR band at 1538 cm(−1) was present. The reaction of ethanol above 370 K in Cu(5)NaFAU zeolite (containing small amounts of Cu(+)(exch) and bigger amounts of Cu(+)(ox), Cu(2+)(exch) and CuO) produced acetaldehyde, which was further oxidized to the acetate species (CH(3)COO(−)). As oxygen was not supplied, the donors of oxygen were the Cu species present in our zeolite. The CO and NO adsorption experiments performed in Cu-zeolite before and after ethanol reaction evidenced that both Cu(+)(ox) and Cu(2+) (Cu(2+)(exch) and CuO) were consumed by the ethanol oxidation reaction. The studies of the considered reaction of bulk CuO and Cu(2)O as well as zeolites, in which the contribution of Cu(+)(ox) species was reduced by various treatments, suggest that ethanol was oxidized to acetaldehyde by Cu(2+)(ox) (the role of Cu(+)(ox) could not be elucidated), but Cu(+)(ox) was the oxygen donor in the acetate formation.