Nanostructured Fischer-Tropsch catalysts for the synthesis of synthetic fuels from biomass
As consequence of the increasing shortage of petrol, large scale production schemes are of increasing importance to produce synthetic oils as basic chemicals for industry out of sustainable materials. Within the Fischer-Tropsch process, paraffines, alkenes and alcohols can be produced out of carbon monoxide and hydrogen (synthesis gas). Synthesis gas can be gained from carbon or methane; the latter being an important product of biomass processing. As petrol used to be inexpensive, the technology was not forced to be improved within Europe in the past. However, countries like South Africa during the years of the apartheid or very recently China with its vast resources in coal invest in Fischer-Tropsch plants. A very common heterogeneous catalyst used in Fischer-Tropsch synthesis contains iron/cobalt nanoparticles. The draw back of this catalyst is that a vast number of products is formed needing further processing. In order to improve the efficiency and selectivity of the process there is fundamental research going on within CIS on alternative systems. For Pt/Co for example it is believed that it improves the catalytic performance. As the surface composition of an alloy may be dramatically different from the bulk alloy, research work deals with the aspect of the role of availability of reaction sites (geometrical effect) as well as the change of the surface electronic properties (electronic effect) from alloying on the adsorption of components of the synthesis gas. In a joint work of theory (Klüner) and experiment (Al-Shamery, Borchert, Bäumer) using single crystal surfaces it has been demonstrated within CIS that the strength of the interaction of CO with an alloy surface as well as the preferential metal adsorption site can be substantially tuned not only by the composition of the top most layer but also by the composition of the next layers below [1]. Due to surface aggregation the composition of the top most layers changes dramatically with working temperature. Parallel to this work, there are ongoing developments in order to prepare nanostructured surfaces with high nanoparticle loading using a colloidal approach similar to the cluster research project on Pt-colloids described on the page before. In order to obtain a coverage of monodisperse particles with defined distances a plasma etching method under ultra high vacuum conditions has been developed etching organic ligands away from a mesoscopically ordered two dimensional layer of supported colloids under UHV conditions without breaking the vacuum [2].
[1] D. Fenske, W.-L. Yim, St. Neuendorf, D. Hoogestraat, D. Greshnykh, H. Borchert, Th. Klüner, K. Al-Shamery, ChemPhysChem., 8 (2007)
[2] B. Gehl, U. Leist, V. Zielasek, M. Bäumer, P. Nickut, K. Al-Shamery, V. Aleksandrovic, H. Weller, Rev. Sci. Instr., 77 (2006) 083902
Selected for Virtual Journal of Nanoscale Science & Technology, September 2006