Ceria based novel nanocomposites catalysts MnxCe1−xO2/α-Al2O3 for low-temperature combustion of methanol
•The reverse nanoemulsion method proved to be effective for obtaining MnOx–CeO2 and MnOx–CeO2/Al2O3 nanocatalysts.•The crystal structure as well as pore distribution of these nanocatalysts has been determined.•The high catalytic activity in the low temperature combustion of methanol was revealed for both non-supported and supported catalysts.•The model of supported MnxCe1−xO2/α-Al2O3 catalysts was proposed and active assembles of Mn–Ce–O moieties were suggested.
A modified nanoemulsion method allowed obtaining nanoparticles (NPs) of the MnOx–CeO2 system within the whole range of the Mn:Ce atomic ratio. The NPs with excess of Ce consisted solely of MnxCe1−xO2 nanocrystallites (NCs) (fluorite structure) while the catalysts with excess of Mn were nanocomposite of MnxCe1−xO2 and of 3–4 times larger Mn3O4 (hausmannite) NCs. The obtained nanomaterials were mesoporous but the composite materials consisted thin slit-shaped pores of size close to the micropore range. The NPs of Mn3O4 were much more active in catalytic combustion of methanol than NPs of CeO2 obtained by the same nanoemulsion method. Nevertheless, incorporation of Mn into CeO2 lattice can improve these NPs to be more active than Mn3O4. The NPs of MnxCe1−xO2 deposited on α-Al2O3 micrograins via the nanoemulsion method preserved activity of the equivalent non-supported NPs. The comparable high activity of Mn0.25Ce0.75O2 monophasic NPs with the nanocomposite of the Mn:Ce = 3:1 ratio suggests joint catalytic action of Mn- and Ce-assembles. Complementary XPS measurements showed a surface Mn-enrichment of the monophasic NPs associated with Mn4+ to Mn2+/3+ reduction and increase of the O2− share in O 1s signal. Such active assemblies have been postulated.
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Journal: Catalysis Today - Volume 257, Part 1, 15 November 2015, Pages 104–110