New Catalyst for Environmentally Designed Ammonia
David Tyler, Chemistry
The Haber-Bosch process for the production of ammonia from N2 and H2 was arguably the most important invention of the twentieth century. Approximately 108 tons of industrial ammonia are produced annually, and the fertilizer synthesized from this ammonia is responsible for feeding over 40% of the world’s population. (This amount is predicted to rise to 60% by 2050.) Temperatures of 350-550 °C and pressures in the range of 150-350 atm are required for industrial nitrogen fixation. Such drastic reaction conditions, combined with the energy required to produce H2, account for ~1-2% of the total annual global energy consumption and for the output of greater than 3.3 ´ 108 M tons/yr of CO2 (7.3% of the worldwide total). Due to the high energy input and high CO2 output, finding a more environmentally benign process to fix N2 is one of the grand challenges in green chemistry. We recently reported the first example of the room temperature, atmospheric pressure reduction of N2 to NH3 using H2 as the reductant. The reaction uses water-soluble Fe-phosphine complexes of the type Fe(P2)2Cl2 to assist in the reaction, where P2 represents a water-soluble bidentate phosphine ligand. Our goals are to understand the mechanism of the reaction and to make the process catalytic.
As with many homogeneously catalyzed reactions, tweaking the catalyst will be key to improving the efficiency of the cycle, and an REU student on this project will participate in the search for an improved catalyst. Thus, the student will make modifications of the phosphine ligands and then synthesize the corresponding Fe complexes. The REU student will then test the efficiencies of the new Fe complexes in the ammonia-forming reaction. In addition to learning about ligand synthesis and coordination compound synthesis, the REU student will learn about mechanistic chemistry, spectroscopic techniques such as multinuclear NMR (e.g., 31P, 15N, and 2D), mass spectrometry, and kinetics.