Estudo do desempenho de catalisadores tipo Ni/CexM1-xO2 (M = Zr ou Mn) na reação de oxidação parcial do metano
One of the main applications of methane is in the production of syngas, a mixture of hydrogen and carbon monoxide. Procedures used in this process are steam reforming, CO2 reforming, partial oxidation and autothermal reforming. The present study evaluated and compared the behavior of nickel catalyst...
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| Format: | doctoralThesis |
| Langue: | por |
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Universidade Federal do Rio Grande do Norte
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| Accès en ligne: | https://repositorio.ufrn.br/jspui/handle/123456789/17740 |
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| Résumé: | One of the main applications of methane is in the production of syngas, a
mixture of hydrogen and carbon monoxide. Procedures used in this process are
steam reforming, CO2 reforming, partial oxidation and autothermal reforming. The
present study evaluated and compared the behavior of nickel catalysts supported on
mixed oxides of cerium and manganese in the partial oxidation of methane with that
of nickel catalysts supported on mixed oxides of cerium and zirconium. Mixed oxides
of cerium and zirconium or cerium and manganese were synthesized using two
different preparation methods, the polymeric precursor based on Pechini method and
combustion reaction using a microwave. This was followed by impregnation with
nickel content of 15 %. Samples were calcined at 300, 800 and 900 °C and
characterized by specific surface area (SSA), X-ray fluorescence (XRF), X-ray
diffraction (XRD), scanning electron microscopy (SEM), temperature programmed
reduction (TPR) and the reaction of partial oxidation of methane. The specific areas
of samples decrease with the rise in calcination temperature and after nickel
impregnation. Metal-cerium solid solution was formed and the presence of other
manganese species outside the solid solution structure was confirmed in the
compound with the highest amounts of manganese oxides showed. With regard to
scanning electron microscopy, supports based on cerium and zirconium prepared by
Pechini method exhibited agglomerated particles without uniform geometry or visible
pores on the surface. However, compounds containing manganese presented empty
spaces in its structure. Through synthesis by combustion reaction, morphology
acquired independently of the proposed composition demonstrated greater porosity
in relation to Pechini synthesis. Although catalysts were prepared using different
synthesis methods, the insertion of nickel showed very similar reduction profiles
(TPR). In relation to nickel catalysts supported on mixed oxide of cerium and
zirconium, there is an initial reduction of NiO species that present certain interaction
with the support. This is followed by the reduction of Ce4+ in Ce3+ surface, with
subsequent bulk reduction. For catalysts containing manganese, a reduction of nickel
oxide species occurs, followed by two stages of reduction for species Mn2O3 in
Mn3O4 and Mn3O4 in MnO, with subsequent reduction of bulk. With respect to partial
oxidation reactions, the nickel catalyst supported on mixed oxide of cerium and
zirconium, prepared using the Pechini method, exhibited CH4 conversion of
approximately 80 %, with conversion of 81 % when prepared by combustion. This
behavior continued for 10 hours of reaction. Manganese content was also found to
directly influence catalytic activity of materials; the greater the manganese oxide
content, the faster deactivation and destabilization occurred in the catalyst. In both
synthesis methods, the nickel catalyst supported on mixed oxide of cerium and
zirconium maintained an H2/CO ratio very close to 2 during the 10 hours of partial
oxidation reaction. Samples containing manganese displayed smaller H2/CO ratios
and lower performance in partial oxidation. |
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