Nanocrystalline Mixed Oxides Containing Magnesium Prepared by a Combined Sol-Gel and Self-Combustion Method for Catalyst Applications

Nicolae Rezlescu,Liliana Sachelarie,Elena Rezlescu,Maria Ignat,Paul Dorin Popa,Corneliu Doroftei

doi:10.4236/msa.2013.48054

Abstract

MgFe2O4 spinel ferrite and La0.6Pb0.2Mg0.2MnO3 perovskite nanopowders were synthesized by a combined sol-gel and self-combustion method and heat treatment. The morphological and structural characterization of the obtained powders has been performed with various techniques: X-ray diffraction (XRD), SEM observations, EDAX spectroscopy and BET analysis. The samples have been catalytically tested in flameless combustion reaction of acetone, benzene, propane and Pb free gasoline at atmospheric pressure. The results revealed a higher catalytic activity of La0.6Pb0.2Mg0.2 MnO3 perovskite than that of MgFe2O4 ferrite. This higher catalytic activity can be ascribed to smaller crystallite size (27 nm), larger surface area (8.5 m2/g) and the presence of manganese cations with variable valence (Mn3+ - Mn4+). The current results suggest that La0.6Pb0.2Mg0.2MnO3 perovskite is preferable to the Mg ferrite and that it can be a promising catalyst for acetone and propane combustion at low temperatures.

Highlights

The aim of the present work is to comparatively estimate the physical and catalytic properties of two magnesium containing oxide compounds prepared by sol-gel-selfcombustion: MgFe2O4 spinel ferrite and La0.6Pb0.2Mg0.2 MnO3 perovskite
The current results suggest that La0.6Pb0.2Mg0.2MnO3 perovskite is preferable to the Mg ferrite and that it can be a promising catalyst for acetone and propane combustion at low temperatures
In this work the combined sol-gel and self-combustion method has been employed to prepare MgFe2O4 spinel and La0.6Pb0.2Mg0.2MnO3 perovskite for catalyst applications. It is an inexpensive method and the obtained prodand Self-Combustion Method for Catalyst Applications ucts were pure and presented nanosized crystallinity. Both samples have been tested in the catalytic combustion of acetone, propane, benzene and Pb free gasoline

Summary

Introduction

The aim of the present work is to comparatively estimate the physical and catalytic properties of two magnesium containing oxide compounds prepared by sol-gel-selfcombustion: MgFe2O4 spinel ferrite and La0.6Pb0.2Mg0.2 MnO3 perovskite. The use of perovskite or spinel type oxide compounds as catalyst has been widely investigated in order to find a catalyst with high thermal stability [1] and low temperature activity [2]. The partial substitution of La3+ ions by lower valence ions (such as Pb2+, Mg2+, Ca2+) produces the partial oxidation of Mn3+ to Mn4+ ions and the increase in oxygen vacancies which enhance the catalytic activity of the perovskite. The stability of Mn4+ ions seems to be the most important factor in the catalytic activity of perovskite manganites [3]. Saracco et al [4] reported the positive effect of the Mg substitution in the basic LaMnO3 perovskite on the catalytic activity of the resulting perovskite

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