Simultaneous Catalytic Removal of SOxand NOxwith Hydrotalcite-Derived Mixed Oxides Containing Copper, and Their Possibilities to Be Used in FCC Units

Hydrotalcite structures containing copper, magnesium, and aluminumhave been investigated for their potential as precursors ofcatalysts in the decomposition and reduction of nitrogen oxides,and in the simultaneous removal of NO and SO2under conditionssimilar to those found in the regenerator of a fluid catalyticcracking (FCC) unit. It is shown that these catalysts are activefor the decomposition of NO in the presence of lowconcentrations of air and for the reduction of NO by propane inthe presence of up to 2% oxygen. The lower oxidation states ofthe copper species (0 and +1) are the active centers for thereactions. Under the conditions encountered in the regeneratorof the FCC unit, there is a window in the oxygen concentration(from 0 to 1.5%), where the Cu-hydrotalcite-based catalyst cansimultaneously remove SO2(by an oxidative and/or reductivereaction) and NO (by a reduction and/or decompositionreaction). When this process takes place at low O2concentrations, some copper-sulfur species are formed. Thesecenters are more active for the NO removal than the originalcopper centers. We have attributed this increment of activity tothe stabilization of the active centers in presence of SO2inthe stream.