Michalsky, RonaldPfromm, Peter H.2012-11-212012-11-212012-10-17http://hdl.handle.net/2097/14978Ammonia is an important fertilizer component and could be used as a convenient hydrogen carrier. This work studies a solar thermochemical reaction cycle that separates the reductive N[subscript 2] cleavage from the hydrogenation of nitrogen ions to NH[subscript 3] without using electricity or fossil fuel. The hydrolysis of binary metal nitrides of magnesium, aluminum, calcium, chromium, manganese, zinc, or molybdenum at 0.1 MPa and 200-1000°C recovered up to 100 mol% of the lattice nitrogen with up to 69.9 mol% as NH[subscript 3] liberated at rates of up to 1.45 x 10ˉ³ mol NH[subscript 3] (mol metal)ˉ¹ sˉ¹ for ionic nitrides. These rates and recoveries are encouraging when extrapolated to a full scale process. However, nitrides with lower ionicity are attractive due to simplified reduction conditions to recycle the oxidized reactant after NH[subscript 3] formation. For these materials diffusion in the solid limits the rate of NH3 liberation. The nitride ionicity (9.96-68.83% relative to an ideal ionic solid) was found to correlate with the diffusion constants (6.56 x 10[superscript -14] to 4.05 x 10[superscript -7] cm² sˉ¹) suggesting that the reduction of H[subscript 2]O over nitrides yielding NH[subscript 3] is governed by the activity of the lattice nitrogen or ion vacancies, respectively. The ionicity appears to be a useful rationale when developing an atomic-scale understanding of the solid-state reaction mechanism and when designing prospectively optimized ternary nitrides for producing NH[subscript 3] more sustainably and at mild conditions compared to the Haber Bosch process.en-USThis Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).Solar radiationHeterogeneous catalysisTransition metal nitrideTransition metal oxideNitrogen diffusionMulliken population analysisText