Enhanced three way catalytic activity of NiFe2O4 by physically mixed metal oxides

The NOx reduction activity of NiFe2O4 in automotive three-way catalysis was enhanced by physical mixing with CeO2, MgO, ZrO2, and Al2O3, while the mixing with TiO2 and Nb2O5 did not promoted the catalytic activity. On both pure NiFe2O4 and the physically mixed catalysts, NO was mainly reduced by C3H6 under the NO-C3H6-CO-O-2 reaction conditions, because the temperature dependence of NO conversion in NO-C3H6-CO-O-2 reaction was the same as that in NO-C3H6-O-2 reaction. The in-situ FT/IR measurement revealed that the NO reduction proceeded with (1) partial oxidation of C3H6 to surface carboxylates, i.e., acetate and formate as good reductants for NO, and (2) reduction of NO by surface carboxylates. The metal oxide additives did not have catalytic activity for partial oxidation of C3H6 nor for NO oxidation to NO2, except CeO2. The main promotion effect was attributed to storage and release of surface carboxylates by metal oxide additives.