Controlled reduction of LaFe xMn yMo zO3/Al2O3 composites to produce highly dispersed and stable Fe0 catalysts: a Mössbauer investigation

Abstract

were prepared and characterized by XRD, BET, TPR, SEM and Mössbauer spectroscopy. XRD for unsupported perovskite showed the formation of a single phase perovskite structure. The Mössbauer spectra of the perovskites were fitted with hyperfine field distribution model for the perovskite. Supported perovskites on Al 2 O 3 showed a decrease of the hyperfine field in respect to unsupported perovskite, due to decrease of particle size and dispersion of the Fe 3+ specimens on the support. Also showed broaden lines and relaxation effects due to the small particle size. To produce the Fe 0 catalyst, the composite perovskite(25%)/Al 2 O 3 was reduced with H 2 at 900, 1000 and 1100 °C for 1 hour. XRD (Figure 1). This catalyst has been recently investigated for the synthesis of single wall carbon nanotube showing promising results 14. This preparation method shows several potential advantages: i) should allow a good control of the metallic particle size distribution, ii) should improve the thermal stability to the catalyst due to a strong matrix insulation effect (La 2 O 3 and Al 2 O 3 should keep Fe o particles well separated), iii) the precursor elements and stoichiometry can be adjusted to produce catalysts with different metals and different ratios, iv) the metals present in the precursor, e.g. Fe and Mo, should be homogeneously distributed throughout the oxide and produce welldefined metallic particles, and v) the dispersion of the metal particle can be further controlled by the reduction conditions. ) was used. The perovskites were prepared by the reaction of 0.5 mol of citric acid (CA) dissolved in 2 mol of water at 60 °C, followed by the addition of 1 mmol of La(NO 3 ) 3 .6H 2 O and different proportions of the other metals such as Fe(NO 3 ) 3 .9H 2 O, Mn(NO 3 ) 2 .4H 2 O and Mo(acac) 2 O 2 (acac acethylacetonate) in order to produce the desired stoichiometry. The mixture was stirred for about 2 hours, until a clear orange solution of the stable metal-CA complexes is obtained. After the complete dissolution, 400 mmol of ethylene glycol (EG) followed by the addition of the Al 2 O 3 nanopowder in amounts to obtain composites with 25, 33 and 50 wt (%) of perovskite on alumina. The suspension was continuously stirred while the temperature was slowly increased to 90 °C. This step removes the excess of water and allows the polyesterification reaction between CA and EG to be further activated. The prolonged heating at 90 °C occurs for 7 hours and resulted in a viscous orange mass 15 . This resin was then treated at 400-450 °C in air for 2 hours for the charring. The final product, a dark brown powder was ground and then calcined at 800 °C in air for 6 hours. Experimental ProceduresThe powder XRD data were obtained in a Rigaku model Geigerflex equipment using Co Kα radiation scanning from 10 to 80° (2θ) at a scan rate of 4° min -1. Silicon was used as an external standard.

Role of [FeOx(OH)y] surface sites on the adsorption of β-lactamic antibiotics on Al2O3 supported Fe oxide

“…At higher temperatures such as 450 • C, there is an extensive conversion of the amorphous Fe oxy/hydroxide into the oxide phase. It can also be observed at 450 • C the formation of small amounts of a phase attributed to Fe aluminate [28][29][30].…”

Nickel-based Catalyst Precursor Prepared Via Microwave-induced Combustion Method: Thermodynamics of Synthesis and Performance in Dry Reforming of CH4

“…Mixed oxides with the perovskite-type structure have been extensively investigated regarding this purpose [5][6][7] . For example, lanthanum nickelate (LaNiO 3 ) can be easily reduced by hydrogen or other reducing agent, even methane, to form a nickel-supported catalyst (Ni/La 2 O 3 ).…”