EM study of carbon shell formation on Ni/MgO catalyst

Abstract

Previous HREM studies have treated the creation of filamentous carbon deposits during the steam reforming of n-butane reaction on Ni/MgO catalysts at temperatures 673 K to 953 K. At highest temperatures besides tubular filaments so-called carbon shells are generated enclosing Ni particles. The mechanism of carbon filament growth has extensively been discussed by several authors and seems to be understood. The creation of shells, on the other hand, has rarely been described up to now. The frequent observation of some intermediate forms between carbon tubes and shells attracted our interest in this problem.Common carbon tubes are formed behind Ni particles whereas the intermediate forms under discussion have the following essential appearances :- Tubes containing Ni inclusions along the tube besides Ni particles on both ends of the tube (Fig. 1).- The Ni particles at the ends of the tubes are either both enclosed by shell-like carbon structures, or one of these particles is partly free of carbon such as the tip particles in common tubes.- One part of these forms often looks like a chain of carbon shells always including Ni particles (Fig. 1, 4 ).- The respective Ni particles appear in various shapes (Fig. 1-5) often drop-like (Fig. 3, 4) or elongated (Fig. 1, 4), suggesting proceeding transformations.