Ring opening with group VIII metal catalysts supported on modified substrate

A naphthene ring opening catalyst comprising about 0.5 to about 1.0 wt. % Ir and about 0.01 to about 1.0 wt. % Pt, wherein the concentration of Ir is always greater than the concentration of Pt and wherein the concentrations of Ir and Pt are based on the weight of the naphthene ring opening catalyst, the Ir and Pt metals are supported on a refractory inorganic oxide substrate containing about 2 to about 25 wt. %, based on the weight of the naphthene ring opening catalyst, of at least one modifier selected from the group consisting of Cs, Mg, Ca, and Ba effective for improving selectivity to increased linear paraffin functionality from naphthene ring-containing compounds and reduce isomerization of linear paraffins to branched paraffins.