Mg/Al mixed oxides with molar ratios of 2_6 of Mg to Al used as supports for platinum catalysts were obtained by the thermal decomposition method. The effect of the composition of the mixed oxides on the physicochemical properties was studied by TPD, nitrogen sorption, XRD and TG-DTA characterization methods. The synthesis of o-phenylphenol(OPP) from a dimer(obtained from cyclohexanone condensation) was investigated over Pt/CHT catalysts and compared with those over Pt/MgO and Pt/Al 2O 3 catalysts. These catalysts show a high activity and selectivity for OPP, with a conversion reaching 93.8% and a selectivity reaching 87.9% in some experiments. For Pt/CHTx catalysts, the calcined hydrotalcites exhibited strong base sites, which were necessary to catalyze the synthesis of OPP. The effect of the composition of the mixed oxides on the physicochemical properties was studied by TPD, nitrogen sorption, XRD The synthesis of o-phenylphenol (OPP) from a dimer (obtained from cyclohexanone condensation) was investigated over Pt / CHT catalysts and compared with those over Pt / MgO and Pt / Al 2O 3 catalysts. These catalysts For a high activity and selectivity for OPP, with a conversion reaching 93.8% and a resolution reaching 87.9% in some experiments. For Pt / CHTx catalysts, the calcined hydrotalcite was strong base sites, which were necessary to catalyze the synthesis of OPP.