Simultaneous catalytic removal of SOx and NOx with hydrotalcite-derived mixed oxides containing copper, and their possibilities to be used in FCC units

Hydrotalcite structures containing copper, magnesium, and aluminum have been investigated for their potential as precursors of catalysts in the decomposition and reduction of nitrogen oxides, and in the simultaneous removal of NO and SO2 under conditions similar to those found in the regenerator of a fluid catalytic cracking (FCC) unit. It is shown that these catalysts are active for the decomposition of NO in the presence of low concentrations of air and for the reduction of NO by propane in the presence of up to 2% oxygen, The lower oxidation states of the copper species (0 and +1) are the active centers for the reactions, Under the conditions encountered in the regenerator of the FCC unit, there is a window in the oxygen concentration (from 0 to 1.5%), where the Cu-hydro talcite-based catalyst can simultaneously remove SO2 (by an oxidative and/or reductive reaction) and NO (by a reduction and/or decomposition reaction), When this process takes place at low O-2 concentrations, some copper-sulfur species are formed, These centers are more active for the NO removal than the original copper centers. We have attributed this increment of activity to the stabilization of the active centers in presence of SO2 in the stream. (C) 1997 Academic Press.