Characterization of KNO3/NaX catalyst for sunflower oil transesterification

► The biodiesel obtained at mild conditions met the European norm EN-14214. ► The amount of KNO3 increased the strength and number of basic sites of the zeolite. ► There is a direct influence between catalytic activity and the presence of K2O specie. ► K2O specie was showed in several characterization techniques (XRD, XPS, CO2-TPD).