Katalytické a tepelné chování nanočásticových perovskitů při ozařování mikrovlnami.

Catalytic and Heating Behavior of Nanoscaled Perovskites under Microwave Radiation

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Perovskite powders of the types La-Ca-Al-M-O , M = Fe, Cr, Mn, Co and La-Sr-Mn-Co-O were prepared via a sol-gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1273 K for 6 h. The phase composition of the samples was established by X-ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100 nm in size and formed agglomerates larger than 1.0 lm. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3 g of catalyst in a fixed-bed quartz reactor (i.d. = 18 mm) under thermal-assisted and microwaveassisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M-atom and its number of unpaired d-electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods.

Práškové perovskity typu La-Ca-Al-M-O , M = Fe, Cr, Mn, Co and La-Sr-Mn-Co-O byly připraveny sol-gel metodou podle modifikované pechiniho metody. Polymerní prekurzor byl nejprve spálen a poté slinován při 1273 K/ 6 hodin. Fázové složení vzorků bylo stanoveno XRD analýzou a mřížkové parametry byly vypočteny pomocí Rietveldovy analýzy. Tvar a velikost částic byla určena elektronovou mikroskopií a měrný povrch práškových perovskitů byl stanoven BET metodou. Průměrná velikost základních částic byla kolem 100 nm, zatímco aglomeráty více než 1 mikrometr. Chemické složení bylo určeno EDX analázou. Katalytické testování bylo prováděno pomocí totální oxidace propanu. Katalytická účinnost byla testována v křemenném reaktoru s pevným ložem obsahujícím 3 g katalyzátoru ohřívaném odporově nebo mikrovlnami. Počáteční výsledky ukazují silnou závislost katalytického a tepelného chování na povaze M atomu a počtu jeho nepárových d-elektronů a na velikosti částic a jejich měrném povrchu. Nebyl pozorován žádný významný rozdíl ve výsledcích získaných při odporovém nebo mikrovlném zahřívání.

Perovskite powders of the types La-Ca-Al-M-O , M = Fe, Cr, Mn, Co and La-Sr-Mn-Co-O were prepared via a sol-gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1273 K for 6 h. The phase composition of the samples was established by X-ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100 nm in size and formed agglomerates larger than 1.0 lm. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3 g of catalyst in a fixed-bed quartz reactor (i.d. = 18 mm) under thermal-assisted and microwaveassisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M-atom and its number of unpaired d-electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods.

Heterogenní katalýza, nanočástice, oxidace, perovskity

Heterogeneous catalysis, Nanoparticles, Oxidation, Perovskites

2008

09.07.2008

WILEY-VCH Verlag GmbH & Co. KGaA,

Weinheim

0930-7516

CHEMICAL ENGINEERING & TECHNOLOGY

31

7

1000–1006

6