Ranking of Heterogeneous Catalysts Metals by Their Greenness

Catalysis is a very important process in industry and laboratory practices, especially from the point of green chemistry principles. However, the eco-friendly character of heterogeneous catalysts containing transition-metal components has not yet been evaluated. Therefore, we performed a comprehensive assessment of 18 heterogeneous metal catalysts (Pd, Pt, V, Co, Ni, Mo, Ru, Mn, Au, Cu, Cd, Zr, Fe, Rh, Ir, Sn, Zn, Ag) using a multicriteria decision analysis approach. The ranking of alternatives according to relevant criteria, such as the toxicity of pure metals and metal salts toward fish, Daphnia magna, and algae/plants, metal toxicity toward rats via ingestion, carcinogenicity, the endangerment degree of metals, the boiling point and energy for atom detachment (estimated as metal metal bond strength in diatomic transition-metal units), and the classification of elemental impurities according to the International Conference on Harmonization, and their degree of importance are presented. Life cycle assessment (LCA)-related parameters of metals have been also included. The assessment showed ruthenium, iron, and molybdenum as the most favorable alternatives, in contrast to nickel, cobalt, and rhodium. Results of environmental evaluation strictly depend on the chosen scenario of assessment, in terms of toxicity, endangered elements, or LCA. Sensitivity analyses toward variations in input data and applied weights prove that the results are reliable. Multicriteria decision analysis can be successfully applied in metal catalyst evaluation for particular case studies of different reactions.