Ruthenium-containing 1-butyl-1-methylpiperidinium thiosalts are synthesized; their decomposition in situ in a hydrocarbon medium makes it possible to form catalysts active in the hydrogenation of naphthalene. It is shown that the modification of thiosalts with nickel leads to the formation of more active catalyst systems. A thermally stable ionic liquid 1-butyl-1-methylpiperidinium trifluoromethanesulfonate is synthesized. It is shown that the hydrogenation catalyst may be prepared by the decomposition of thiosalts in the ionic liquid and that it can be reused in several cycles without any loss in activity.