The present invention discloses a method for preparing heterometallic catalysts comprises the steps of providing plurality of metal salts and a ligand whereby said ligand is 2,2’-bipyridine, synthesizing plurality of monometallic and polymetallic complexes from the plurality of metal salts and the ligand, reacting the plurality of monometallic and polymetallic complexes with each other to form heterometallic complexes and thermally decomposing the heterometallic complexes to form the heterometallic catalysts whereby said heterometallic catalysts are nano-sized heterometallic catalysts, characterized by the step of thermally decomposing is performed at a temperature of 600 to 650°C for 6 to 8 hours.