Catalytic onions
16 Aug 2002
In a collaborative effort between the Fritz-Haber Institute in Berlin and the Boreskov Institute of Catalysis in Novosibirsk, Russia, the usefulness of 'onion-shaped' carbon as a catalyst for the synthesis of styrene has been investigated for the first time.
Styrene, an important raw material for the manufacture of plastics, is made from ethylbenzene. Industrial styrene is mainly produced at high temperature by the endothermic catalytic dehydrogenation (by which two hydrogen atoms are removed from the starting material) of ethylbenzene (EB) over promoted iron oxide-based catalysts in the presence of a large excess of steam. However, thermodynamic limitations, problems of coke deposition, and a large amount of wasted energy has led to the development of alternative routes.
Among them, the exothermic catalytic oxidative dehydrogenation (ODH) of EB has received lots of interest, due to the absence of any equilibrium limitations and the fact that the process can be conducted at a lower temperature.
Recent reports proposed that carbon species are the active phase for the ODH, and the investigators at the Fritz-Haber Institute have studied the usefulness of several kinds of carbon nanostructures over the years, including carbon nanotubes and nanofibres.
But this is the first time that onion-shaped carbon has been studied. Onion-shaped carbon itself is built up from individual closed shells of carbon atoms, and, just as with a real onion, the shells are wrapped around each other.
The researchers reported that, with a styrene yield of 62%, the carbon onion structure produced significantly better results than the industrial catalysts currently in use, as well as all the other carbon forms they have examined thus far.
'Future practical application (of the technology) is possible,' reports Robert Schloegl, a key reseacher at the Fritz-Haber Institute.
