CAJ | 학술논문

Wiistite-based catalyst for ammonia synthesis exhibits extremely high activity and easy to reductionunder a wide range of conditions. The reaction kinetics of ammonia synthesis can be illustrated perfectly by boththe classical Temkin-Pyzhev and modified Temkin equations with optimized α of 0.5. The pre-exponent factors andactivation energies at the pressures of 8.0 and 15.0MPa are respectively ko = 1.09 × 1015, 7.35 × 1014 Pa0.5.s-1,and E = 156.6, 155.5kJ@mol-1 derived from the classical Temkin-Phyzhev equation, as well as ko = 2.45 × 1014,1.83 × 1014pa0.5.s-1, and E = 147.7, 147.2kJ.mol-1 derived from the modified Temkin equation. Although thedegree of reduction under isothermal condition is primarily dependent upon temperature, low pressure seems to beimperative for reduction under high temperature and low space velocity to be considered as a high activity catalyst.The reduction behavior with dry feed gas can be illustrated perfectly by the shrinking-sphere-particle model, bywhich the reduction-rate constants of 4248exp (-71680/RT) and 644exp (-87260/RT) were obtained for the powder(0.045-0.054 mm) and irregular shape (nominal diameter 3.17 mm) catalysts respectively. The significant effect ofparticle size on reduction rate was observed, therefore, it is important to take into account the influence of particlesize on reduction for the optimization of reduction process in industry.