Two Zn-metalloporphyrins, both containing at least one-pyridyl group, were studied regarding their capacity to complex hexachloroplatinic acid comprised in leaching solutions and resulted after hydrometallurgical processes on spent automotive catalysts. The number of pyridyl groups and the steric and electronic influences from surrounding groups determine a different type of coordination with the hexachloroplatinic acid from solution, and surprisingly, although containing only one group of basic pyridyl, the unsymmetrical Zn(II)- 5-pyridyl-10,15,20-tris-(3,4-di-methoxy-phenyl)-porphyrin had a removal capacity of 98% higher than that of Zn(II)-meso-tetrakis-pyridylporphyrin, substituted with four pyridyl groups, but with only a removal capacity of 84 %
