Ruthenium hydrogenation catalysts are of fundamental importance concer
ning of their application in cycloolefin preparation by partial hydrog
enation of aromatic substrates. The performance of the catalysts, espe
cially their activity and selectivity, strongly depends on the prepara
tion procedure and the properties of the active component precursor an
d support. In addition to the conventional impregnation, incipient-wet
ness method, sol-gel technique. and preparation of the metallic ruthen
ium black are also discussed. Special attention is paid to the presenc
e of impurities, because of their substantial effect on the desired ca
talytic properties.