Abstract
The present work addresses the influence of the support on the catalytic behavior of Co3O4-based catalysts in the combustion of lean methane present in the exhaust gases from natural gas vehicular engines. Three different supports were selected, namely γ-alumina, magnesia and ceria and the corresponding catalysts were loaded with a nominal cobalt content of 30 wt. %. The samples were characterized by N2 physisorption, wavelength dispersive X-ray fluorescence (WDXRF), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction with hydrogen and methane. The performance was negatively influenced by a strong cobalt-support interaction, which in turn reduced the amount of active cobalt species as Co3O4. Hence, when alumina or magnesia supports were employed, the formation of CoAl2O4 or Co–Mg mixed oxides, respectively, with a low reducibility was evident, while ceria showed a lower affinity for deposited cobalt and this remained essentially as Co3O4. Furthermore, the observed partial insertion of Ce into the Co3O4 lattice played a beneficial role in promoting the oxygen mobility at low temperatures and consequently the catalytic activity. This catalyst also exhibited a good thermal stability while the presence of water vapor in the feedstream induced a partial inhibition, which was found to be completely reversible.
Highlights
Compressed natural gas is regarded as a suitable alternative to substitute the traditional automotive fuels such as gasoline or diesel that are becoming more expensive and scarce with time
Co3 O4 catalysts supported over γ-alumina, magnesia and ceria were prepared by the same synthesis route, characterized and examined for the oxidation of methane under lean conditions, with the objective of determining the effect that the different supports have on the textural, structural and redox properties and the activity of the cobalt oxide active phase
In line with the results given by Raman spectroscopy, these findings suggested that a the results given by Raman spectroscopy, these findings suggested that a fraction of deposited cobalt fraction of deposited cobalt species strongly interacted with these supports, thereby negatively species strongly interacted with these supports, thereby negatively influencing their redox properties
Summary
Compressed natural gas is regarded as a suitable alternative to substitute the traditional automotive fuels such as gasoline or diesel that are becoming more expensive and scarce with time. Cobalt oxide-based catalysts, and among them spinel-type cobalt oxide (Co3 O4 ), are considered good alternative candidates to noble metals due to their already demonstrated high efficiency for the oxidation of hydrocarbons and a greater availability [5,6,7] The reason for this high activity seems to lie on their good redox properties such as reducibility and mobility of oxygen species at low temperatures, which derives from the easiness that the constituent ions of these materials have to shift between oxidation states. Co3 O4 catalysts supported over γ-alumina, magnesia and ceria were prepared by the same synthesis route, characterized and examined for the oxidation of methane under lean conditions, with the objective of determining the effect that the different supports have on the textural, structural and redox properties and the activity of the cobalt oxide active phase
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