Methane Oxidation over Nanocrystalline LaCo_1-XFe_XO₃:  Resistance to SO₂ Poisoning

Abstract

Catalytic activity for CH 4 oxidation and resistance to SO 2 poisoning were tested for three LaCo 1-X Fe X O 3 prepared by reactive grinding. The catalysts prepared by this method showed well-crystallized perovskite structure and various specific surface areas. The activity in CH 4 oxidation correlates well with BET specific surface area. TPDO experiments showed very large quantities of desorbed β-oxygen that could not be correlated to the activity for CH 4 oxidation. Resistance to sulfur poisoning in the same reaction was tested at 500 °C with 25 ppmv SO 2 added to the feed. Two steps were distinguished during the poisoning reaction. The first one followed an exponential decrease of conversion versus time. The time to reach the end of this step was shown to be directly proportional to the specific surface area. In this step, deactivation was found to be reversible. During regeneration, some sulfur species were found to desorb from the catalyst. The second step was found to be a linear diminution of conversion with time. The slopes of these lines were found to be the same for the three catalysts. A total of 860 h is necessary to deactive the catalyst with the higher specific surface area, and the quantity of sulfur accumulated in the catalyst was found to vary linearly with the poisoning time. XRD showed significant conversion of the catalyst into La 2 (SO 4 ) 3 , Co 3 O 4 , and iron oxide. The complex poisoning behavior is discussed and associated to the observed differences in the catalyst morphology.

Combustion activities of the Ru catalysts supported on hexagonal YbFeO3

“…Supported catalysts were prepared by an impregnation method: 1.0 g of a support was added to a solution of Ru(acac) 3 , Rh(acac) 3 or Pd(OAc) 2 in 10 ml of THF or methanol at room temperature, and after the evaporation of the solvent, the resulting powder was calcined at 500°C for 30 min to afford the noble-metal/support catalysts. The molar ratio of noble-metal/Fe was fixed to 0.05.…”

“…supported on h-YbFeO 3 Figure 3 shows the XRD patterns of the Ru catalysts obtained by calcination at 500°C after impregnation of Ru(acac) 3 . The peaks due to Ru species were not observed, and the patterns were essentially identical with those of the as-synthesized h-YbFeO 3 a) Geometric surface area calculated on the assumption that each h-YbFeO 3 particle is spherical with a diameter of 7 nm.…”

“…Mixed oxides of rare earth (RE) and iron having garnet (RE 3 Fe 5 O 12 ), perovskite (REFeO 3 ) and magnetoplumbite (RE 1¹x M x Fe 12 O 19 : M = Ba, Sr, Pb) structures have been applied in various fields such as magnetism, fuel cells (cathode material for SOFC), gas sensors, catalysts, and so on. 1) 5) Orthorhombic REFeO 3 (o-REFeO 3 ) with the perovskite structure has recently received much attention in the catalyst field.…”

“…Since we found that the h-YbFeO 3 could be synthesized by the Pechini method, the effect of preparation method on catalytic activity was also examined. 3 , Dojin] were used without further purification. Yb(OAc) 3 (15 mmol) and Fe(acac) 3 (15 mmol) were suspended with the aid of ultrasonication in 120 ml of 1,4-butanediol (1,4-BG) in a test tube serving as autoclave liner.…”

“…3 , Dojin] were used without further purification. Yb(OAc) 3 (15 mmol) and Fe(acac) 3 (15 mmol) were suspended with the aid of ultrasonication in 120 ml of 1,4-butanediol (1,4-BG) in a test tube serving as autoclave liner. The test tube was placed in a 300 mL autoclave.…”