CNG engines exhaust gas treatment via Pd-Spinel-type-oxide catalysts

Four spinel-type catalysts AB2O4 (CoCr2O4, MnCr2O4, MgFe2O4 and CoFe2O4) were prepared and characterized by XRD, BET, TEM and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a temperature-programmed combustion (TPC) apparatus. Spinel-type-oxides containing Cr at the B site were found to provide the best results. The half-conversion temperature of methane over the CoCr2O4 catalyst was 376 °C with a W/F = 0.12 g s/cm−3. On the basis of temperature-programmed oxygen desorption (TPD) analysis as well as of catalytic combustion runs, the prevalent activity of the CoCr2O4 catalyst could be explained by its higher capability to deliver suprafacial, weakly chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of palladium deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and CoCr2O4 catalysts enables half methane conversion at 330 °C (GHSV = 10,000 h−1), a performance similar to that of conventional 4 wt% Pd-γ-Al2O3 catalysts but enabled with just a four-fold lower amount of noble metal.