Development of optimized Cu–ZSM-5 deNOx catalytic materials both for HC-SCR applications and as FCC catalytic additives

Abstract

Cu-exchanged ZSM-5 zeolites finely coated with CeO 2 nanoparticles were tested in this work as catalysts for the selective catalytic reduction (SCR) of NO with C 3 H 6 . The CeO 2 coated Cu/ZSM-5 shows lower maximum NO conversion activity compared to the non-coated Cu/ZSM-5 catalyst at relatively high temperatures (ca. 450 °C) but the former catalyst is significantly more active at lower temperatures (ca. 350 °C), especially at lower space velocities, both under dry and wet feed conditions. Under simultaneous addition of both SO 2 and water in the feed, the beneficial effect of the CeO 2 coating at lower reaction temperatures was retained only at low space velocities. The same Cu/ZSM-5 based samples were evaluated as fluid catalytic cracking (FCC) catalytic additives for the in situ reduction of NOx formed during regeneration of the coked FCC catalyst. The amounts of NO and CO emitted during regeneration of the spent FCC catalyst at 700 °C in the presence of Cu/ZSM-5 based additives were compared with those obtained when a commercial CO promoter was used in the FCC catalyst inventory. All Cu/ZSM-5 additives exhibited significant NO reduction ability, which was further enhanced by increasing the Cu loading or the amount of additive in the FCC catalyst. The CeO 2 -coated sample reached the highest deNOx performance (up to 78% NO reduction); however, all additives presented insufficient activity for CO oxidation. Simultaneous NO reduction and CO oxidation was achieved only when the CeO 2 -Cu/ZSM-5 additive was promoted with Rh or when the non-promoted additives were combined with a commercial CO promoter. Preliminary studies suggested that the Rh-promoted CeO 2 -Cu/ZSM-5 additives can be very effective for both NO reduction by CO and CO oxidation at certain O 2 concentrations, such as in the O 2 -deficient zones of the FCC regenerator. Further studies are in progress in order to elucidate the reaction mechanism and optimize the additive's formulation.