Effect of the Composition of Mn-, Co- and Ni-Containing Perovskites on their Catalytic Properties in the Oxidative Coupling of Methane

Abstract

The catalytic properties of complex oxide catalysts with ABO 3 perovskite structure (A = Sr, Ba, La; B = Mn, Co, Ni) in the oxidative coupling of methane were studied with separate introduction of methane and oxygen onto the catalyst. The greatest catalytic activity was found for the nickel-containing oxides but these catalysts have much lower operational stability than Mn-and Co-containing catalysts. Modification of the oxide systems studied by partial replacement of the strontium or transition metal ions by alkali metal ions considerably improves their activity and selectivity.The oxidative coupling of methane (OCM) to give ethylene and other light hydrocarbons holds promise in the direct conversion of natural gas into valuable chemical compounds [1,2]. Complex oxides with ABO 3 perovskite structure, where B is a transition metal ion, are efficient catalysts of OCM along with other complex oxide systems [2]. Variation of the composition of the perovskite systems significantly affects their catalytic properties, even leading to change in the direction of the methane conversion. Thus, LaCoO 3 and LaMnO 3 are efficient catalysts for the complete oxidation of methane [3, 4], while selective OCM is possible on SrCoO 3 and SrMnO 3 [5, 6] and methane may be partially oxidized to synthesis gas on LaFeO 3 [7]. The characteristics of this catalysis depend also on the reaction conditions. A periodic mode, in which the reagents are introduced onto the catalyst separately at a given frequency, is most favorable for OCM on perovskite catalysts [5].In the present communication, in a search for promising new OCM catalysts, we compared the catalytic properties of Mn-, Co-and Ni-containing complex oxides with perovskite structure in OCM carried out in the periodic mode. EXPERIMENTALThe manganese and cobalt complex oxides were prepared according to methods described in our previous work [6,8]. A similar method was used for the nickel catalysts, which were prepared using aqueous solutions of analytical-grade Sr(NO 3 ) 3 , analytical-grade Ni(NO 3 ) 2 ·6H 2 O, titration-standard-grade NaHCO 3 , titration-standard-grade K 2 C 2 O 4 , and analytical-grade ammonia as well as pure-grade Li 2 CO 3 dissolved in acetic acid. Solutions of these metal salts were combined in the required 0040-5760/05/4102-0117

Synthesis and characterization of some nanostructured composite oxides for low temperature catalytic combustion of dilute propane

“…(d) The S BET values are smaller for perovskites and ferrites containing only two cations and these results appear to be caused by an effective increase in the degree of crystallinity as a result of the heat treatment. These values are comparable to those reported by other authors, 32 for similar chemical compositions.…”

Synthesis of Na2WO4-Mn Supported YSZ as a Potential Anode Catalyst for Oxidative Coupling of Methane in SOFC Reactor

“…For Na-W-Mn/SiO2 catalyst, 12.0% CO selectivity, 12.9% CO2 selectivity and 69.0% C2 selectivity at 28.5% CH4 conversion are obtained, which are in agreement with several reports [21][22][23][24]. In a comparison among different supports, YSZ shows greater selectivity to partial oxidation than the complete combustion, as the selectivity to CO is much greater than that to CO2.…”

Modification of CeNi0.9Zr0.1O3 Perovskite Catalyst by Partially Substituting Yttrium with Zirconia in Dry Reforming of Methane

“…Peaks at the lower region are almost the same but there is a shoulder peak for un-modified sample in the moderate temperature region in the TPR profile. It has been reported that the reduction becomes easier while the energy of the metal–oxygen bond decreases [ 32 ]. The peaks at moderate temperature regions can be attributed to the reduction of Ni 3+ to Ni 2+ .…”