The global estimate for annual ammonia production from molecular nitrogen and hydrogen via the Haber-Bosch process is 170 million metric tons. This makes the combined biological and abiological production of ammonia from N2 one of the largest scale chemical syntheses on Earth. The reaction of N2 and H2 to make NH3 is exoergic by only 4 kcal/mol, which means that very little of the energy in H2 is lost in NH3 synthesis. Because ammonia liquefies at modest pressures it is a promising carrier for renewable hydrogen, but closing the hydrogen fuel cycle requires efficient conversion NH3 back to N2 and H2. Thermal nitrogen “unfixation” typically requires high temperatures, and oxidations of NH3 at most electrodes have high overpotentials. To date, no molecular species has mediated the electrocatalytic oxidation of ammonia. We have found that complexes of the formula (trpy')(bpy')RuII(NH3) can catalyze the six-electron oxidation of NH3 to N2 in aprotic solvents at modest overpotentials (trpy' and bpy' are substituted terpyridine and bipyridine, respectively). This talk will present recent findings pertinent to the mechanism of this transformation.

Ruthenium homogeneous catalysts for electrocatalytic oxidation of ammonia to dinitrogen at ambient temperatures

255th National Meeting (2018)

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