A used acidic ionic liquid catalyst, which has been deactivated by conjunct polymers, is regenerated by combining the used catalyst, a metal and a Broensted acid to hydrogenate the conjunct polymer. Regenerating a used acidic ionic liquid catalyst, which has been deactivated by conjunct polymers, includes: combining the used ionic liquid catalyst, a metal and HCI in a reaction zone under hydrogenation conditions to hydrogenate a portion of the conjunct polymer; removing reaction product from the reaction zone; mixing the removed reaction product with a hydrocarbon solvent in which the hydrogenated conjunct polymers are soluble; allowing the mixture to separate into a lighter phase which contains the hydrogenated conjunct polymers, and a heavier phase which contains a regenerated ionic liquid catalyst; and recovering at least a portion of the heavier phase is also disclosed.