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Preparation of carbon nanotubes using cvd CVD method

Pełech I.

Polish Journal of Chemical Technology

2010

Vol. 12, nr 3

45-49

In this work preparation and characteristic of modified nanocarbons is described. These materials were obtained using nanocrystalline iron as a catalyst and ethylene as a carbon source at 700°C. The influence of argon or hydrogen addition to reaction mixture was investigated. After ethylene decomposition samples were hydrogenated at 500°C. As a results iron carbide (Fe3C) in the carbon matrix in the form of multi walled carbon nanotubes was obtained. After a treatment under hydrogen atmosphere iron carbide decomposed to iron and carbon and small iron particles agglomerated into larger ones.

On the reduction of iron catalyst for ammonia synthesis

Arabczyk W., Moszyński D., Jasińska I.

Polish Journal of Chemical Technology

2002

Vol. 4, nr 4

1-5

The influence of the potassium concentration change on the surface area and active surface of an iron catalyst for ammonia synthesis was studied. The removal of potassium leads to the increase of the surface area, while potassium addition gives rise to the decrease of the surface area which is accompanied by the fourfold increase of the active area. The mechanism of the reduction of iron catalyst was proposed. A special attention was paid to the role of promoters. First, the reduction of iron oxides leads to the formation of porous structure with a well-developed surface area. It is due to the formation of aluminium and calcium oxides film on the iron surface. This structure thanks to high oxygen content balances the iron surface tension which results in a high surface area. This process is followed by potassium diffusion from the grain boundaries to the crystallite surface. Potassium atoms are more favoured to form stable structure on the iron surface than aluminium and calcium. It leads to the formation of K+O film on the iron surface. Because K+O structure requires less oxygen atoms part of the iron surface is freed. The balance between chemical bonds and surface energy is disturbed and the surface area is lowered. At the same time some number of free adsorption sites are formed giving rise to the increase of active surface and the activation of a catalyst.