(420b) Fe-Ni Enzyme Inspired Sulfur-Tolerant Catalysts: A Combined Theoretical and Experimental Study

A very promising technique to efficiently control sulfur poisoning of catalysts and to do hydrogenation is to mimic how nature does it.  Excellent examples are naturally occurring iron- or nickel-containing metalloenzymes like Ni-Fe hydrogenase and Fe nitrogenase.  These enzymes have sulfur atoms in their inherent chemical structure and yet, behave as extremely efficient catalysts.  In the quest for biomimetic catalysts, scientists seek to replicate the coordination sphere that surrounds the metal centers, with the expectation that function will follow form.  Hence, in this present work we have attempted to create Ni-Fe-S complexes of various compositions that have chemical structures similar to those of hydrogenases with the expectation that such structures will be efficient sulfur-tolerant hydrogenation catalysts.  We have used density functional theory to predict the stability and viability of such chemical structures.  We have also studied the role of CO and CN- groups in the hydrogenation reactions.  Nickel/iron/sulfur [4Ni-4Fe-7S] clusters were synthesized via a macro-molecular templating technique. A host of characterization techniques like UV-vis absorption spectroscopy, EXAFS were used to establish the structure of the Ni-Fe-S clusters.