Catalytic Activities of Perovskite-type LaBO3(B = Fe, Co, Ni) Oxides for Partial Oxidation of Methane

Abstract

Direct conversion of methane to C2-hydrocarbons via oxidative coupling reaction has received a great deal of attention for the last twenty five years because the reaction has been recognized as a promising route for the production of ethylene from natural gas. However, the process is considered to be economically unfeasible because the yield of ethylene produced in the reaction is less than 25%. In recent, it has been proposed that the disadvantage may be overcome by integrating with processes involving endothermic reactions such as cracking of ethane to ethylene and steam reforming of methane to synthesis gas and the heat of the exothermic coupling reaction can be alternatively used to generate electricity. An interesting potential application of perovskites as catalysts is their use for redox reactions. Lanthanum-transition metal perovskite oxides (LaBO3) are proved to be effective catalysts for the catalytic oxidations of hydrocarbons, CO, and ammonia and considered to be promising materials for application as electrode materials in solid oxide fuel cells. There are few reports on the application of LaBO3 oxides to the catalytic partial oxidation of methane. Tagawa et al. found that the LaAlO3 catalyst prepared by the mist decomposition method is highly active and selective for the oxidative coupling of methane and proposed that an amorphous phase of LaAlO3 is responsible for the catalytic activity. Spinicci et al. found that both catalytic activity and C2-selectivity are largely enhanced when Al ion in the LaAlO3 perovskite is substituted with Li or Mg. In the oxidative methane coupling reaction catalyzed by metal oxide, the transfer of oxygen to the surface from bulk or gas phase is very important on its catalytic activity because the abstraction of a hydrogen from methane is caused by an oxygen ion present on the surface of metal oxide catalyst. LaBO3 perovskite oxides may be suitable catalysts for the methane coupling reaction because they are characterized by high mobility of oxygen ions. Actually, the perovskite oxides have received increasing interest in the mixed-conducting ceramic membrane reactor technology for partial oxidation of methane. In this work, we prepared LaFeO3, LaCoO3, and LaNiO3 perovskite oxides by using a sol-gel method and examined them as catalysts for the oxidative coupling of methane in the temperature range of 650 to 800 C at atmospheric pressure. Experimental Section