COMBINED DESOX DENOX REACTIONS ON A COPPER ON ALUMINA SORBENT CATALYST .1. MECHANISM OF SO2 OXIDATION ADSORPTION

The mechanim Of SO2 oxidation-adsorption to form regenerable sulfates on a copper on alumina sorbent-catalyst was analyzed. Studies were carried out both in a flow reactor with mass-quadrupole detection of the reaction products and by using Fourier-transform infrared (FT-IR) characterization of the nature of the sulfate species. Both in-situ in a flow infrared cell and ex-situ FT-IR studies of the evolution of the sulfate species as a function of time on stream and after regeneration of the sorbent-catalyst were carried out. The results indicate that copper catalyzes the oxidation Of SO2 to SO3 in the presence of gaseous oxygen and that SO3, present probably as S-bonded chemisorbed sulfur oxide, further (i) reacts with near-lying sites of the support without desorption in the gas phase through a mechanism of surface transfer to form a sulfate linked to Al or (ii) reacts with copper species to form a sulfate linked to copper. The relative rates of these two reactions of formation of sulfate species are strongly affected by the reaction temperature, which enhances in particular the former reaction. The latter sulfate species, however, is more easily regenerated by reduction.