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The effect of nickel content on the structure and activity of co-precipitated Ni-Al layered double hydroxides (LDHs) as catalyst precursors for CO 2 removal by methanation was studied by variation of the Ni 2? /Al 3? molar ratio (Ni 2? /Al 3? = 3.0, 1.5 and 0.5), and of the reduction and reaction temperatures as well as of the space velocities. Powder X-ray diffraction (PXRD), H 2 chemisorption, and temperature programmed reduction (TPR) techniques were applied for physicochemical characterization of the samples. It was specified that the nanoscaled dimensions of the as-synthesized samples also generate nano-metrical metallic nickel particles (PXRD). The existence of readily and hardly reducible Ni 2? -O species in the studied samples (TPR), affects catalytic performance. The studied catalysts hydrogenate CO 2 effectively to residual concentrations of the latter in the range of 0-10 ppm at reaction temperatures from 400 to 220°C and space velocities between 22,000 and 3000 h -1 . The variation of the CO 2 methanation activity with the changes of space velocities depends on the nickel content, and reduction and reaction temperatures. After reduction at 400 and 450°C, a sample of Ni 2? /Al 3? = 3.0 has demonstrated the highest conversion degree at all the reaction temperatures and space velocities, while a catalyst of Ni 2? /Al 3? = 0.5 dominated in the methanation activity after reduction within 530-600°C. The Ni 2? /Al 3? = 1.5

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© Versita Sp. z o.o. Received 29 June 2012; Accepted 2 October 2012 Keywords: Biogenic iron oxide materials • Sphaerotilus-Leptothrix group bacteria • Mossbauer spectroscopy • X-ray diffraction • IR spectroscopyMaterials based on biogenic iron oxides, which are a product of the metabolic activities of the neutrophilic iron-oxidizing bacteria (NIOB) from Sphaerotilus-Leptothrix group, were investigated. Natural microbial probes were collected from freshwater flow from Vitosha Mountain (Bulgaria) and cultivated under laboratory conditions in respect to select suitable cultures and conditions (nutrition media) for biomaterial accumulation of biogenic oxides. Samples were studied by physicochemical methods: X-ray diffraction, Mossbauer spectroscopy and IR spectroscopy. Their phase composition and physicochemical properties were obtained. Presence of both amorphous and crystal phase (ultra-and highly dispersed particles) was proved. Iron-containing compound in the natural biomass consists of α-FeOOH. The cultivated materials have more complex composition with iron-containing ingredients as α-FeOOH, γ-FeOOH, γ-Fe 2 O 3 and Fe 3 O 4 . The sample of natural biomass was tested in reaction of CO oxidation and it showed potential to be used as catalyst support.

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