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Influence of chemical composition of nanocrystalline iron’s surface on the rates of two parallel reactions: nitriding and catalytic decomposition of ammonia

Rafał Pelka and Walerian Arabczyk

Institute of Chemical and Environment Engineering, West Pomeranian University of Technology in Szczecin, Pułaskiego 10, 70-322 Szczecin, Poland

 

E-mail: rpelka@zut.edu.pl

Abstract: Influence of chemical composition of nanocrystalline iron’s surface on its activity in the nitriding process of iron and catalytic decomposition of ammonia was studied. The rate of the nitriding reaction was measured by the thermogravimetric method using a tubular differential reactor. Hydrogen concentration in the reactor was also measured. The rate of the catalytic decomposition of ammonia was determined using the reactor’s mass balance. Experiments were conducted at different temperatures within the range from 300°C to 525°C. Iron catalyst for ammonia synthesis was studied. Two sorts of samples with a different content of potassium oxide (0.16 mass % and 0.64 mass % of K2O) were used. The composition of samples from the second group was modified by an addition of different amounts of sulfur. At temperatures above 400°C, when the effect of ammonia decomposition on the gas phase composition was experimentally measured, the presence of potassium and sulfur on the iron surface influenced the rate of the iron nitriding process. The ammonia decomposition rate was higher for samples with a greater amount of potassium. The rate of reactions depended also on the sulfur concentration and dropped when the sulfur content increased. The value of apparent activation energy of ammonia decomposition was in the range of 150 kJ mol−1 to 180 kJ mol−1 while the content of sulfur in the samples increased.

Keywords: ammonia synthesis iron catalyst – nanocrystalline iron – nitriding reaction – catalytic ammonia decomposition reaction – kinetics

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-011-0095-1

 

Chemical Papers 66 (1) 18–25 (2012)

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