A. Maltha et al., ROLE OF ALKALI PROMOTERS ON MN3O4 IN THE SELECTIVE REDUCTION OF NITROBENZENE, Applied catalysis. A, General, 115(1), 1994, pp. 85-101
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 block
ing (higher concentrations) effect. Reducibility measurements of the v
arious catalysts (thermogravimetry, temperature-programmed reduction),
adsorption heat experiments (heat-flow microcalorimetry) and determin
ation of the composition of the surface layers (X-ray photoelectron sp
ectroscopy) exclude an influence of the promoter on the reducibility o
f the catalyst, on the heat of adsorption of nitrobenzene and on the o
xidation state of manganese. It can be seen that most of the alkali io
ns are present in the surface layers of the catalyst. The most likely
mechanism is that by which the promoter influences a certain adsorptio
n mode of nitrobenzene existing at the reaction temperature on the sur
face of Mn3O4.