Lean NOx reduction over Rh/ZrP2O7 catalyst under steady-state and perturbation conditions

Catalytic lean NOx reduction performance was studied over Rh supported on ZrP2O7 and ZrO2 under steady-state and perturbation conditions. The ZrP2O7 support significantly enhanced the NOx purification efficiency at the air-to-fuel (A/F) ratio between 14.6 and 15.0 compared with the ZrO2 support, because of the higher activity toward C3H6 oxidation and the higher stability of metallic Rh against reoxidation. The lean NOx purification efficiency was further enhanced by switching two simulated gas feeds with stoichiometric (A/F=14.6) and lean (A/F=14.9) compositions with shorter intervals (similar to 1 s). Considering faster reduction of Rh oxide in contrast to slower reoxidation of Rh on ZrP2O7, the perturbation effect could be rationalized by the stabilization of metallic Rh species, which is more active than Rh oxide for the catalytic NOx reduction. (C) 2016 Elsevier B.V. All rights reserved.