OXIDATION OF SO2 TO SO3 OVER HONEYCOMB DENOXING CATALYSTS

A systematic study addressing the effects of the operating conditions (contact time, temperature), of feed composition (O2, SO2, H2O, NH3, N O(x), NH3 + NO(x), concentrations), and of catalyst design parameters (wall thickness, V content) in the oxidation Of SO2 to SO3 over honeyc omb commercial-type DeNoxing catalysts is described. Data are presente d which refer to transient behavior of the catalysts, indicating that long conditioning times are required associated with the buildup of su rface sulfate species. The steady-state reaction rate is of variable o rder in SO2, the order increasing with SO2 concentration as long as th is is below 200 ppm and then decreasing; it is asymptotically independ ent of oxygen, depressed by water, strongly inhibited by ammonia, and slightly enhanced by NO(x). The apparent activation energy changes fro m almost-equal-to 50 to almost-equal-to 20 kcal/mol on increasing the reaction temperature. A redox steady-state kinetic model is presented which accommodates qualitatively all of the observed effects. Once pro perly modified the same model has the potential to explain also transi ent effects during conditioning of the catalyst.