Effect of the iron catalyst mechanical treatment on the activity in ammonia synthesis reaction

Abstract

The active form of fused iron catalysts for ammonia synthesis is obtained by the reduction of the precatalyst composed mainly of magnetite and small amount of promoters. The industrially applied catalysts are obtained by melting, cooling, and grinding. The catalysts prepared have irregular shape grains. Tableting a prereduced catalyst could be a method for the preparation of regular grains. Trials have been undertaken to obtain catalysts with a regular shape by sintering, pressing, and violent cooling of drops of the fused catalyst lava. Tableting causes the changes of the microstructure of catalyst pores and the deformation of the crystal structure of the α-Fe. The chapter discusses the influence of tableting pressure on the catalyst activity, catalytic thermal resistance, pores' distribution, and crystallite size. In the pressing process of the reduced form of an iron catalyst, a regular shape of grains can be obtained. The activity of these catalysts decreases with an increase in the tableting pressure. The pressing process leads to the reduction of the large pores' fraction and the decrease of the specific area of the catalysts. Because of pressing and overheating of the catalysts, a crystallization process occurs. The formed area has a smaller activity in the ammonia synthesis process.