FTIR STUDY OF THE INFLUENCE OF SULFATE SPECIES ON THE ADSORPTION OF NO, CO AND NH3 ON CUO AL2O3 CATALYSTS/

CuO/Al2O3 catalysts have been sulfated by oxidation of various amounts of SO2. The surface properties of the samples were studied using prob e molecules. The IR spectra of CO species adsorbed on the non-sulfated sample show a strong band at 2125 cm(-1) with a shoulder at 2160 cm(- 1), which shift to 2165 and 2180 cm(-1), respectively, with a concomit ant decrease in intensity as the amount of sulfate increases. Adsorbed NO species on the non-sulfated catalyst give rise to two weak bands a t 1754 and 1873 cm(-1). On sulfated samples, the first band disappears whereas that at 1873 cm(-1) shifts towards higher wavenumber and reac hes 1917 cm(-1) for large amounts of sulfate. These results show that the copper electronic state is affected by sulfation. The positive cha rge on the copper sites increases with the amount of sulfate. NH3 adso rption is also influenced by sulfation. Sulfate species are adsorbed o n basic sites and high sulfation prevents NH3 dissociative adsorption while it favours coordinated and protonated species on acid-base pair sites.