Fe-based perovskites substituted by copper and palladium for NO + CO reaction

Abstract

Nanoscale Fe-based perovskites with nominal formula LaFe 1− x (Cu,Pd) x O 3 were generated by reactive grinding and characterized by N 2 adsorption, X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H 2-TPR), temperature-programmed desorption (TPD) of O 2, NO, and CO, temperature-programmed surface reduction (TPSR) of NO under CO/He flow, and activity test toward NO + CO reaction. The catalytic performance of LaFeO 3 can be considerably improved via 20% Cu substitution, leading to a 74% N 2 yield and 72% CO conversion at 350 °C, under an atmosphere of 3000 ppm NO and 3000 ppm CO in helium at a space velocity of 50,000 h −1. This improvement was ascribed to the facility in generation of anion vacancies after Cu incorporation, which plays a crucial role on NO adsorption and dissociation. In addition, the enhanced reducibility of LaFe 0.8Cu 0.2O 3 after Cu substitution results in the promotion of CO oxidation and anion vacancy regeneration, providing another clue for this improvement. N 2O decomposition (31% N 2 yield at 500 °C) is much easier than NO decomposition (below 5% at T < 500 ° C ) over LaFe 0.8Cu 0.2O 3. Conversion of both NO and N 2O is significantly improved by the presence of the reducing agent. A mechanism was proposed with dissociation of chemisorbed NO, forming N 2 and/or N 2O, and an oxidized perovskite surface, which was continuously reduced by CO with the generation of CO 2. Great performance at low temperature was found over LaFe 0.97Pd 0.03O 3 with a 96% NO conversion and 86% CO conversion at 300 °C, corresponding to the outstanding redox properties of this catalyst. O 2 has a strongly detrimental effect, leading to the consumption of the reducing agent by oxidation.