A new heterogeneous catalyst for the solvent-free efficient oxidation of alcohols has been developed for a sustainable future with a green reaction technology. This work presents the additive and solvent-free catalytic conversions of primary and secondary alcohols as well as diols into their corresponding carbonyl compounds in moderate to excellent yields. The developed catalyst system is green as it oxidises alcohols under solvent-free conditions and uses simple atmospheric oxygen as the oxidising agent. We have experimentally proved that the alcohol oxidation reaction proceeds through an aerobic oxidative pathway. The double perovskite oxide catalyst CaLaScRuO_6+δ was prepared by the conventional solid-state method. The crystal structure was refined and characterized thoroughly to observe the effect of mixed valent Ru⁵⁺/Ru⁴⁺ ions in the oxygen-rich disordered structure. The conversion of diols into four-, five- and six-membered lactones can enhance the novelty of the present catalyst. The catalyst was found to be very selective for the alcohol oxidation and resulted in the oxidised product without affecting the other functional groups present in the aromatic ring. A reaction mechanism has been proposed for understanding the possible role of mixed metals in heterogeneous catalysis.