Partial oxidation of methane over lanthana-supported catalysts derived from perovskites

Abstract

Partial oxidation of methane is the most attractive route to produce syngas, since it produces H2/CO (molar) = 2, suitable for Fischer-Tropsch and methanol synthesis, besides the low energy consumption and low tendency to coke formation. A promising catalyst for the reaction is based on cobalt which has low cost and low tendency to coke formation. However, it tends to oxidize and then deactivates during reaction. With the goal of preparing alternative and more efficient catalysts, lanthana-supported catalysts derived from perovskites containing lanthanum, iron and cobalt were studied in this work, using titania as support. Perovskites were prepared by the amorphous citrate method and then reduced to produce the catalysts. The samples were characterized by X-ray diffraction, Mössbauer spectroscopy, temperature programmed reduction, acidity measurements using ammonia temperature programmed desorption, transmission electron microscopy, specific surface area measurements and isotopic exchange reaction. The catalysts were evaluated at 1 atm and 800 °C in methane partial oxidation and analyzed by temperature programmed oxidation after reaction. Iron-based perovskite (LaFeO3) was not reduced regardless the support while cobalt-based perovskite (LaCoO3) produced cobalt oxides (Co3O4 and CoO), metallic cobalt and lanthanum oxide (La2O3). It was found that both titania and iron are beneficial to make cobalt reduction easier, producing more active and stable catalysts. At the end of reaction, the catalyst derived from cobalt-based perovskite (LaCoO3/TiO2) was the most active and selective, the activity and selectivity increasing during reaction. However, the supported catalyst based on iron and cobalt (LaFe0.5Co0.5O3/TiO2) is the most promising for industrial applications since it is highly active and selective since the beginning of reaction. The catalysts produced a negligible amount of coke during reaction.