Ammonia energy decomposition

Ni, M. Thermo-electrochemical modelling of ammonia-fueled solid oxide fuel-cells considering ammonia thermal decomposition in the anode. Int. J. Hydrogen Energy 36 (2011), pp. 3153-3166. 

Figure C2.7.1. Schematic potential energy diagram for tire catalytic syntliesis and decomposition of ammonia on iron. The energies are in kJ mol tire subscript ads refers to species adsorbed on iron [i].

The reinforcing fibers are usually CVD SiC or modified aluminum oxide. A common matrix material is SiC deposited by chemical-vapor infiltration (CVI) (see Ch. 5). The CVD reaction is based on the decomposition of methyl-trichlorosilane at 1200°C. Densities approaching 90% are reported.b l Another common matrix material is Si3N4 which is deposited by isothermal CVI using the reaction of ammonia and silicon tetrachloride in hydrogen at 1100-1300°C and a total pressure of 5 torr.l" " ] The energy of fracture of such a composite is considerably higher than that of unreinforced hot-pressed silicon nitride. 

Zirconia cells similar to the ones employed in the present study, have been used i) by Mason et al (18) to electrochemically remove oxygen from Pt and Au catalysts used for NO decomposition. It was shown that electrochemical oxygen pumping causes a dramatic increase in the rate of NO decomposition (18,19), ii) by Farr and Vayenas to electrochemically oxidize ammonia and cogenerate NO and electrical energy (20,21), iii) by Vayenas et al (11,12,22,23) to study the mechanism of several metal catalyzed oxidations under open circuit (potentiometric) conditions. 

Measurements were made of the decomposition of ammonia on quartz at two temperatures (Hinshelwood Burk, J Chem Soc 127 1105, 1925). Find the order of the reaction and the activation energy. 

Due to the high hydrogen storage capacity of the ammonia molecule (17.7 wt% equal to an energy density of 4,318 Wh kg 1), its decomposition is intensely investigated for COx-free hydrogen production for mobile fuel cell applications [146]. However, compared with the well-established Haber Bosch process for ammonia synthesis, its decomposition is underdeveloped and requires substantial improvements before it can be considered as a practical contribution to the energy supply toolbox. 

Nitrogen iodide (NI3.NH3) is a very unstable material and will explode under the action of very weak shocks. Even at liquid air temperatures, initiation occurs at an energy of 0.6g/cm (Ref 4). The stability of nitrogen iodide under normal conditions depends to a great extent on the presence of ammonia which retards the decomposition of the pure NI3 (Ref 8). 

Ammonia decomposes on zeolites (9), and the effect of this decomposition on the chlorobenzene reaction may be important. Thus, the activity of CuY zeolite for ammonia decomposition was studied. Helium was used as a carrier gas, 1 ml of ammonia was injected, and the extent of ammonia decomposition was determined as a function of temperature. The decomposition was 2.4% at 350°C, 7.8% at 450° C, and 24% at 550° C. The apparent activation energy of ammonia decomposition was estimated at 13 kcal/mole. The activation energy of ammonia decomposition is close to that of benzene formation from chlorobenzene and ammonia. Thus, benzene formation results from the reaction of chlorobenzene and hydrogen formed by the decomposition of ammonia. 

Since k is proportional to k, the temperature dependence of k is determined by the apparent activation energy of ammonia decomposition, ... 

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