Deactivated or partially deactivated hydrocarbon conversion catalysts comprising (a) one or more Lewis acids selected from the group consisting of the fluorides, chlorides and bromides of boron(III), titanium(IV), zirconium(IV), hafnium(IV), phosphorus(V), arsenic(V), tantalum(V), niobium(V) and mixtures thereof and (b) a strong Bronsted acid, may be recovered by contacting said catalysts with hydrogen at elevated temperatures and pressures. The preferred Lewis acid is an acidic halide, preferably tantalum pentafluoride, niobium pentafluoride or mixtures thereof. The preferred Bronsted acid is a hydrogen halide, preferably hydrogen fluoride.