Catalytic removal of methane over thermal-proof nanostructured catalysts for CNG engines

Abstract

Five spinel-type catalysts AB2O4 (Co0.8Cr2O4, CoCr2O4, MnCr2O4, MgFe2O4 and CoFe2O4) were prepared and characterized by XRD, BET and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a Temperature Programmed Combustion (TPC) apparatus. The half conversion temperature of methane over the Co0.8Cr2O4 catalyst was 369 °C with a W/F = 0.12 g s/cm3. On the basis of Temperature Programmed Desorption (TPD) of oxygen as well as of catalytic combustion runs, the prevalent activity of the Co0.8Cr2O4 catalyst could be explained by its higher capability to deliver suprafacial chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of Pd, deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and Co0.8Cr2O4 catalysts enables half methane conversion at 340 °C (GHSV = 10,000 h−1), a performance similar to that of conventional 4 wt% Pd-γ Al2O3 catalysts but guaranteed with just a four-fold lower amount of noble metal. Both the catalysts in powder and the monolith hosting the Co0.8Cr2O4 + 1 wt% Pd catalyst, submitted to a thermal ageing treatment in air at 700 °C for 12 h, displayed a negligible deactivation.