Structure and Catalytic Activity of Perovskites La-Ni-O Supported on Alumina and Zirconia

 
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Structure and Catalytic Activity of Perovskites La-Ni-O Supported on Alumina and Zirconia (EN)

Ladavos, A. K. (EN)

Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας (EL)
Ladavos, A. K. (EN)

Lanthanum nickelate binary oxidic species supported on alumina and zirconia were tested for their catalytic activity for the NO + CO reaction. The support took place by impregnation of Al2O3 or ZrO2 without any pretreatment or after addition of lanthana on the support surface. The zirconia based solids show a surface area (BET) of 5-7 m2 g-1, one order of magnitude smaller than those based on alumina (40-60 m2 g-1). The crystal phase developed on ZrO2 was only La2NiO4 while on Al2O3 the phases found by X-rays were LaNiO3 and LaAlO3. The solids La2NiO4/ZrO2 containing nickel in 2+ state, were more active than LaNiO3/Al2O3 containing Ni3+. The smaller activity of the La-Ni-O solids supported on Al2O3 is attributed to the stronger adsorption of oxygen, or oxygenated species, on Ni3+ as compared to the weaker adsorption on Ni2+ existed in the La-Ni-O solids supported on ZrO2. Especially the stronger adsorption of nitric oxide in the first case results in a reaction route where an excess of nitric oxide as large as 25-30% is eliminated as compared to the reacting carbon monoxide. The excess of eliminated nitric oxide undergoes disproportionation towards nitrous oxide and nitrogen, the former undergoing further decomposition towards nitrogen and oxygen. In the second case of ZrO2/La-Ni-O the weaker adsorption of nitric oxide results in a nearly equimolecular elimination of the two reactants and the excess of nitric oxide reacting does not exceed a 12-14% of carbon monoxide. The Arrhenius plots for the nitric oxide reduction on the alumina-based solids show a unique behaviour for the whole temperature range examined while similar plots for the zirconia-based solids show a two stage behaviour corresponding to different surface mechanism. The activation energies of nitric oxide elimination with carbon monoxide on the above solids are appreciably smaller than activation energies of nitrous oxide decomposition on the same materials, in accordance with previous observations. Finally the activity of La2NiO4/ZrO2 solids calculated per mass of perovskite is nearly five times that of La2NiO4 pure perovskites prepared through the nitrate or citrate routes although their surface areas are equal for the citrate and only double for the nitrate solids. (EN)

alumina (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Applied Catalysis B-Environmental (EN)

Αγγλική γλώσσα

1993

<Go to ISI>://A1993KU22300004

Elsevier (EN)



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