Supported Pd-perovskite catalyst for CNG engines' exhaust gas treatment

Abstract

Perovskite-type oxides of the series La 1− x A x Mn 1− y B y O 3 (A = Sr; B = Fe or Co) were prepared by solution combustion synthesis and characterized by X-ray diffraction, specific surface analysis, transmission electron microscopy and field emission scanning electron microscopy techniques. Their activity towards the combustion of methane was evaluated in a temperature programmed combustion microreactor. The LaMn 0.9 Fe 0.1 O 3 catalyst was found to provide the best performance. The half-conversion temperature of methane over the LaMn 0.9 Fe 0.1 O 3 catalyst was 398 °C with a W / F = 0.12 g s/cm 3 and a methane feed concentration of 0.4 vol% under oxygen excess. Via temperature programmed oxygen desorption (TPD) analysis as well as catalytic combustion runs, the prevalent activity of the LaMn 0.9 Fe 0.1 O 3 catalyst could be explained by its higher and increased capability to desorb suprafacial, weakly chemisorbed oxygen species. Further catalyst development allowed to maximise the catalytic activity of this compound by promoting it with CeO 2 (1:1 molar ratio) and with 1 wt% Pd. This promoted catalyst was lined on cordierite monoliths in a γ-Al 2 O 3 -supported form (catalyst weight percentage: 15 wt%) and then tested in a lab-scale test rig under realistic conditions for compressed natural gas-vehicles' exhaust gas treatment. Half methane conversion was achieved at 340 °C (gas high space velocity = 10 000 h −1 ), nearly the same but with a fourfold lower amount of the expensive noble metal than that used in commercial 4wt%Pd–γ-Al 2 O 3 catalysts.