The influence of SO2 on the adsorption of NO-O2 on the surface of NiO/γ-Al2O3 was investigated by use of temperature programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). It was found that there are a large quantity of nitro and nitrites as well as monodentate nitrates formed after NO-O2 adsorption at room temperature, while the bidentate and bridged nitrates are predominant and the desorption of NO2 increases after NO- O2-SO2 adsorption. SO2 is adsorbed in significant amounts as weakly bonded species, which is characterized by an intense and broad band near 1324 cm-1. Small amounts of sulfates are present on the catalyst surface even at room temperature and grow with increasing adsorption temperature and treatment time. The decomposition of nitrates at low temperatuies can account for the release of NO2 during reaction in the presence of SO2. A mechanism is proposed to explain the role of SO2 in NO catalytic oxidation at low temperatures. Several types of multi- molecular intermediate species such as [ NO2 (SO3 ),. ] the composition of which is similar to the chamber crystals are suggested as active species for producing NO2. These species are formed by combining NO in the structure of coordinated nitrates with SO2 adsorbed on either weakly basic O2- sites or the basic OH- groups. Adsorbed O2 species dissociated on neighboring active metal sites such as Ni2 + also participate in the formation of the multi-molecular intermediate and are helpful to the stability of the intermediate structures. The continuous adsoiption of SO2 on the freesites, especially on the Lewis acid sites near the intermediate species finally breaks down the intermediate structures. The decomposition of multi-molecular intermediates, which is responsible for the release of NO2 > however, leads to the sulfation of the catalyst at the same time. As a result, the deactivation of the catalyst occurs.

Key words: SULFUR DIOXIDE, NITROGEN OXIDE, CATALYTIC OXIDATION, NICKEL OXIDE, ALUMINIUM OXIDE, FLUE GAS DESULFURIZATION