ylation of La(OH)3 reacts with SrCO3 to form a mixed oxide according to “Reaction (10)”.
2LaO(OH) + SrCO3 → SrLa2O4 + CO2 + H2O(10)
Samples LaSr15 and LaSr20
Three peaks DTA, represented on the Figures 5(e) and (f), which makes the superposition of three pics, it can be to explain by the two phases shifts of strontium carbonate and by the departure of CO coming from the decomposition of SrCO3 according to the “Reaction (5)”. Nevertheless, the formation of the mixed compound SrLa2O4 Reaction (10) is not excluded. This reaction would be supported by an acid catalysis of the ions La3+. The quantity of this mixed oxide would be weak and equivalent to that obtained during the treatment of LaSr5 and LaSr10.
Lastly, it should be noted that contrary to the samples LaSr5 and LaSr10, quantity of water which is eliminated from the samples LaSr15 and LaSr20 towards 100˚C is relatively more significant. This water accounts for 1.5% (Dm/m) of the treated mass.
A series of samples, LaSrX where X is the atomic percentage in strontium was prepared by hydrolysis of La2O3 and SrCO3 in neutral medium. These samples was calcined under air at 450˚C and 1150˚C, then characterized by BET specific surface area, XRD analysis and SEM microscopy. The reactivity of lanthanum oxide and SrCO3 was followed by TG and DTA.
After calcination at 450˚C, the addition of strontium is without effect on surfaces of lanthanum oxide. The XRD patterns shows data for crystalline phases of La2O3, La(OH)3, LaO(OH) and La2O2CO3 and of strontium carbonate. There are no interaction between lanthanum oxide and strontium carbonate.
After calcinations at 1150˚C, the addition of 5% and 10% of strontium make slightly increase the specific surface of lanthanum oxide, at this temperature the sintering is important, 70% of values of the surfaces are decreases compared to those calcined at 450˚C. The XRD spectra shows that LaSrX samples are formed by two oxides: a mixed compounds with structure of SrLa2O4 and La2O3. This result are confirmed by SEM micrography.
The TG curves of pure La2O3 and SrCO3 indicate that, SrCO3 decompose at 620˚C approximately and the weight losses of La2O3 result for the drainage of water and the partial de-hydroxylation of La(OH)3 with formation of LaO(OH). The reactivity of LaSrX showed three endothermic weight losses; elimination of water, a partial de-hydroxylation of La(OH)3 and formation of La2O2CO3 and La2(CO3)3. In the range of temperature of 500˚C - 580˚C the DTA indicates, a first allotropic transition from the SrO2 and its decomposition on CO and SrO2 for LaSr15 and LaSr20.
- M. C. J. Bradford and M. A. Vannice, “CO2 Reforming of CH4,” Catalysis Reviews: Science and Engineering, Vol. 41, No. 1, 1999, pp. 1-42. doi:10.1081/CR-100101948
- T. Le Van, C. Louis, M. Kermarec, M. Che and J. M. Tatibouët, “Temperature and Conversion Dependence of Selectivities in Oxidative Coupling of Methane on La2O3 Catalysts,” Catalysis Today, Vol. 13, No. 2-3, 1992, pp. 321-328. doi:10.1016/0920-5861(92)80156-H
- A. Trovarelli, C. De Leitenburg and G. Dolcetti, “Design Better Cerium-Based Oxidation Catalysts,” Chemtech, Vol. 27, No. 6, 1997, pp. 32-37.
- S. J. Huang, A. B. Walters and M. A. Vannice, “NO Reduction with H2 or CO over La2O3 and Sr-Promoted La2O3,” Journal of Catalysis, Vol. 173, No. 1, 1998, pp. 229-237. doi:10.1006/jcat.1997.1911
- M. Traykova, N. Davidova, J.-S. Tsaih and A. H. Weiss, “Oxidative Coupling of Methane—The Transition from Reaction to Transport Control over La2O3/MgO Catalyst,” Applied Catalysis A: General, Vol. 169, No. 2, 1998, pp. 237-247.
- M. Ghelamallah, S. Kacimi and R. I. Fertout, “Incorporation of Barium in Titanium Oxide and Lanthanum Oxide,” Materials Letters, Vol. 59, No. 6, 2005, pp. 714-718. doi:10.1016/j.matlet.2004.06.072
- M. D. Mitchell and M. A. Vannice, “Adsorption and Catalytic Behavior of Palladium Dispersed on Rare Earth Oxides,” Industrial and Engineering Chemistry Fundamentals, Vol. 23, No. 1, 1984, pp. 88-96. doi:10.1021/i100013a016
- A. Galenda, M. M. Natile, L. Nodari and A. Glisenti, “La0.8Sr0.2Ga0.8Fe0.2O3−δ: Influence of the Preparation Procedure on Reactivity toward Methanol and Ethanol,” Applied Catalysis B: Environmental, Vol. 97, No. 3-4, 2010, pp. 307-322. doi:10.1016/j.apcatb.2010.04.004
- T. J. Toops, A. B. Walters and M. A. Vannice, “The Effect of CO2 and H2O on the Kinetics of NO Reduction by CH4 over a La2O3/γ-Al2O3 Catalyst,” Journal of Catalysis, Vol. 214, No. 2, 2003, pp. 292-307. doi:10.1016/S0021-9517(02)00092-1
- L. M. Cornaglia, J. Munera, S. Irusta and E. A. Lombardo, “Raman Studies of Rh and Pt on La2O3 Catalysts Used in a Membrane Reactor for Hydrogen Production,” Applied Catalysis A: General, Vol. 263, No. 1, 2004, pp. 91-101. doi:10.1016/j.apcata.2003.12.003
- K. Matsuzawa, T. Mizusaki, S. Mitsushima, N. Kamiya and K. Ota, “The Effect of La Oxide Additive on the Solubility of NiO in Molten Carbonates,” Journal of Power Sources, Vol. 140, No. 2, 2005, pp. 258-263. doi:10.1016/j.jpowsour.2004.08.041
- T. J. Toops, A. B. Walters and M. A. Vannice “The Effect of CO2 and H2O on the Kinetics of NO Reduction by CH4 over Sr-Promoted La2O3,” Catalysis Letters, Vol. 82, No. 1-2, 2002, pp.45-57. doi:10.1023/A:1020583806660
- B. A. A. Balboul, “The Solid State Reaction between Lanthanum Oxide and Strontium Carbonate,” Thermochimica Acta, Vol. 445, No. 1, 2006, pp. 78-81. doi:10.1016/j.tca.2006.03.005
- ICDD Diffraction Databases, 1994-1998. International Center for Diffraction Data (CDRom), Newtown Square.
- R. C Weast, “Handbook of Chemistry and Physics,” 66th Edition, CRC, Boca Raton, 1985-1986, p. B-148.