(335g) Solar Thermochemical Production of Metal Nitrides and Ammonia Utilizing Transition Metal Reactants

One of the major products of the chemical industry, ammonia is used widely as artificial fertilizer and has been proposed recently as sustainable transportation fuel. Using transition metal-based catalysts the Haber-Bosch process produces ammonia industrially from its elements. Globally, the Haber-Bosch process consumes up to 5% of all natural gas produced and 2% of the total energy production, with significant fossil-based carbon dioxide emissions. The process cannot easily be scaled down or performed in developing countries due to the required temperature, pressure, natural gas, and utilities. Based on previous research employing Al- or Cr-based reactants to produce ammonia by a solar thermochemical reaction cycle at near atmospheric pressure and 1000-2000°C and without the need for natural gas as reactant, the work presented here studies process and reactant modifications that might allow the solar-driven ammonia production from water and air to proceed at below 1500°C, i.e., at temperatures which would not require sophisticated furnace design and construction materials. Utilizing a laboratory scale Fresnel lens-based tubular solar thermochemical reactor, formation of metal nitrides from various transition metal oxides is studied at atmospheric pressure. Liberation of ammonia from the nitrides due to corrosion with steam will be focused. The effect of ammonia formation favored at low temperatures and metal nitride corrosion favored at high temperatures is addressed. Deviation from thermodynamic calculations for bulk materials is discussed.