Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-IV-12Pd-DOPED PEROVSKITE CATALYSTS FOR CNG ENGINE’SEMISSION CONTROLP. Palmisano, N. Russo, D. Fino, G. Saracco and V. SpecchiaMaterials Science and Chemical Engineering Department, Politecnico di Torino,C.so Duca degli Abruzzi 24, Torino 10129 Italy,phone/fax: +39 011 0904710/4699, e-mail: nunzio.russo@polito.itAdvanced compressed natural gas (CNG) engines entail considerable advantages overconventional gasoline and diesel engines. Natural gas (NG) is a largely available fossil fueland therefore non-renewable. However, NG has some advantages compared to gasoline anddiesel from an environmental perspective. Its emissions are lower. The low flame temperatureof lean operated CNG engines helps to limit the formation of NO x . Furthermore, since NGcontains only 75 wt% carbon versus 86-88 wt% for gasoline or diesel, it produces less CO 2per unit of energy released. Furthermore, soot particulate can hardly be formed from methanecombustion. Other benefits lie in the fact that NG is neither toxic, carcinogenic, nor caustic.However, unconverted methane in CNG flue gases is much harder to oxidize than gasolinederivedunburned hydrocarbons (UHC). The strong greenhouse effect of methane (more thanone order of magnitude higher than that of CO 2 ) forces a higher and higher concern at alegislation level and, as a consequence, the development of new aftertreatment technologies toabate these emissions. Catalytic combustion of methane on honeycomb converters similar tothose used for the treatment of gasoline engine exhaust gases is the way to go. Commercialcatalysts are mostly based on gamma-Al 2 O 3 -supported Pd [1], having a at least three foldhigher noble metal loading compared to that of conventional three-way catalysts (up to300 g/ft 3 against 80 g/ft 3 ). A research line of ours is aimed at developing nanostructured Pdperovskite-type-oxidecatalysts employing an overall noble metal load significantly smallerthan that used in conventional converters, the catalytic performance being the same. Severalperovskite-type oxide catalysts (LaMnO 3 , LaMn 0.9 Pd 0.1 O 3 , LaFeO 3 , LaFe 0.9 Pd 0.1 O 3 , LaCrO 3 ,LaCr 0.9 Pd 0.1 O 3 ) were prepared by Solution Combustion Synthesis (SCS), characterized byB.E.T., SEM (Scanning Electron Microscopy – Fig. 1) and XRD (X-Ray Diffractometer)analyses, and tested as catalysts for methane combustion [2]: a gas mixture (2.5 vol.% CH 4 ;7.5 vol.% O 2 , He = balance) was fed at the constant rate of 0.83 ml·s –1 to a fixed-bed microreactor constituted of 100 mg of catalyst and 900 mg of SiO 2 (W/F = 0.12 g s/cm 3 ). Startingfrom 950 °C, the inlet temperature, measured by a K-type thermocouple placed alongside thequartz tube, was decreased at a 2 °C/min rate and the outlet CO 2 , CO, CH 4 and O 2concentrations were determined by continuous NDIR and paramagnetic analyzers, thusallowing to calculate methane conversion and close the carbon balances.162