Selective Hydrogenation of Benzene to Cyclohexene on Ru/Al2O3

Hydrogenation of benzene to cyclohexene has been studied over
Ru/Al2O3 catalysts in the presence of water. Attention has been paid
to the influence of reaction conditions, ruthenium precursors, and
catalyst pretreatment. The reaction was carried out under kinetic
control and under strong mass transfer limitation. In the presence
of water the formation of cyclohexene cannot be simply ascribed to
physical effects. Mass transfer limitations are, however, important
to obtain high selectivities at high conversion. A pretreatment of
the catalyst under hydrogen, in the absence of benzene, increases
the selectivity to cyclohexene. No effect has been observed when
the pretreatment is carried out under nitrogen. Catalysts prepared
from RuCl3 are more selective with respect to samples prepared
from chlorine-free precursors.