Ronald Michalsky - Solar fuel production via water splitting and protonation of solid-state nitrogen ions forming ammonia

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  Ronald Michalsky, Peter H.   Pfromm: Solar fuel production via water splitting and protonation   of solid-state nitrogen ions forming ammonia, Prep. Pap.-Am.   Chem. Soc., Div. Fuel Chem. 56 (2011) 2, p.   529-530.


  Ammonia is the basis for modern   agriculture and is used widely as base chemical for the chemical   industry1. The U.S. produces about 9% of the over 100   million metric tons of NH3 produced   worldwide per year2.   Recently, NH3  has been proposed as sustainable   transportation fuel and may enable efficient H2 storage3-5. The   U.S. Department of Energy target6 of 9 wt%   H2 capacity for H2-based   transportation fuels in 2015 is reached readily by 18 wt%   H2 in molecular NH3.   Accomplished easily at 25 °C and about 10 bar, liquefaction of   NH3 yields a fuel that contains by volume   approximately 130-fold more H2 as   H2 itself at this temperature and pressure.   Modified diesel engines have been reported to combust   NH3 generating mainly H2O and   N2 as combustion products7. If   H2 is the desired combustion fuel,   NH3 may be cracked catalytically on board a vehicle   to form N2  and H2 for   subsequent combustion3.

  The Haber-Bosch process synthesizes   NH3 catalytically at high pressure and elevated   temperature. This process consumes up to 5% of the natural gas   produced globally and 2% of the world’s total energy   production8, with   significant fossil-based CO2 emissions9. Due to   the significant capital expense the process is generally   implemented in large facilities in the order of 1000 tons   NH3 per day production and in locations near a   natural gas supply10.

  NH3 might be   synthesized sustainably from N2 and   steam via solar thermochemical processing at near atmospheric   pressure. In this study, a thermodynamic rationale for the   reactive synthesis of NH3 is   presented along with experimental work focusing breaking the N-N   triple bond on the surface of transition metals forming nitrides.   Hydrolysis of various ionic, covalent, intermediate and   interstitial nitrides is studied to assess the impact of the   average charge of the N atom in the solid state on the yield of   NH3 synthesis far from thermodynamic equilibrium.   Corrosion kinetics limiting the formation of   NH3 at decreased temperatures is addressed.

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