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Abstract:
The influence of Li+, Na+ and K+ ions on the activity and selectivity of Mn3O4 in the selective reduction of nitrobenzene has been studied. The alkali ions show both a promoting (low concentrations) and a blocking (higher concentrations) effect. Reducibility measurements of the various catalysts (thermogravimetry, temperature-programmed reduction), adsorption heat experiments (heat-flow microcalorimetry) and determination of the composition of the surface layers (X-ray photoelectron spectroscopy) exclude an influence of the promoter on the reducibility of the catalyst, on the heat of adsorption of nitrobenzene and on the oxidation state of manganese. It can be seen that most of the alkali ions are present in the surface layers of the catalyst. The most likely mechanism is that by which the promoter influences a certain adsorption mode of nitrobenzene existing at the reaction temperature on the surface of Mn3O4.
