Adsorption, Electrochemical And Catalytic Properties Of Binary Titanium-manganese Oxides
ADSORPTION, ELECTROCHEMICAL AND CATALYTIC PROPERTIES OF BINARY TITANIUM-MANGANESE OXIDES
O.I. Pendelyuk, T.V. Lesnichaya, N.M. Visloguzova,
S.A. Kirillov, V.V. Strelko
Institute of Sorption and Endoecology Problems, Ukrainian National Academy of Sciences, General Naumov. st. 13, 03680 Kyiv – 164, Ukraine
Transition metal oxides represent a class of materials prospective for sorption and ion exchange processes. Furthermore, they are successfully applied in numerous branches of modern technology as effective catalysts, electrochemically-active and magnetic materials, superconductors, superionic membranes, etc. This is especially true for manganese-dioxide-based materials, which demonstrate selectivity and reasonable exchange capacity towards Sr+2, being known at the same time as cathodic materials used in commercial electrochemical cells, as well as effective catalysts employed in industrial processes of oxidation of organic substances. Enhancement of the properties of manganese-dioxide-based materials is therefore of great value for water management technologies, applied electrochemistry and catalysis.
In this presentation we report about our recent studies directed towards optimal design of composite amorphous manganese-dioxide based materials modified by titania and studies of their adsorption (first of all, towards strontium as one of the most hazardous pollutant), electrochemical and catalytic properties.
Synthesis of amorphous MnO2-TiO2 materials has been performed by means of precipitation from aqueous solutions using hydrogen peroxide as an oxidant. The samples obtained are fine powders; their specific surfaces are of approx. 50-400 m2/g. The carried out weight loss studies enable to find optimal conditions of heat treatment of samples used in adsorption, electrochemical and catalytic studies.
Briefly, adsorption properties of mixed oxides demonstrate the following trends. Probes of adsorption of Sr+2 on manganese-dioxide-based materials have shown that the Kd values can reach 1×105 mL/g depending on
MnO2/TiO2 ratios. It is found that affinities of amorphous samples and their crystalline analogues towards strontium are significantly different.
The increase of the MnO2/TiO2 ratio is found to correlate with the increase of the selectivity of samples towards strontium. Selectivity factors KSr/Ca for mixed oxides are higher than those for MnO2.
Catalytic properties of mixed oxides have been studied using a model reaction of combustion of propane in its lean mixtures. It appears that at concentrations of C3H8 lower than its ignition limit, complete combustion occurs. This observation is highly promising for further use of manganese-oxide based catalysts.
Electrochemical studies have been made in standard cells with non-aqueous solvents and lithium anodes. Electrochemical activity of amorphous MnO2-TiO2 materials has been determined and compared with that of respective crystalline cathodic materials.
Based on the ESCA data, a conclusion has been drawn that adding titania to manganese oxide leads to the decrease of the bond energy of 1s electrons of the oxygen atoms in hydroxyl groups. This may favour its dissociation and therefore explain high adsorption affinity and catalytic activity of the mixed oxides studied.
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