Dipl. Ing. Matthias Mayerhofer Technische Universität München ...

Results and Discussion 51
7 Results and Discussion
7.1 Iron based Catalyst Characterization
BET surface depends mainly on the amount of the support that is impregnated on the iron based
catalyst. The catalyst in this study contains 16 wt% of Al2O3. Generally, Addition of alumina improves
significantly the surface area, but the WGSR is decreased (Azhar Uddin,2008),(Noichi,2010).
Hence, according to these studies the surface of the catalyst is expected ~
40 m²/g and the obtained results indicated a surface area of 45.1 m²/g. The active surface area of
the catalyst was measured after the tests and the result obtained was 15.6 m²/g. This indicates a
significant decrease of the potential surface for reaction with the tar. According to the results from
(Azhar Uddin,2008),in some cases the active surface area was also decreases more than 50%
after the use of the catalyst.
X-ray diffraction (XRD) patterns were recorded with PHILIPS X’Pert Pro System with a Cu-Karadiation
of λ=0.154056 nm (45kV, 40mA) and step size 0,017° (40 sec/step). The measurements
were acquired both for the fresh and used catalyst in order to determine the influence of the reduction
and the interaction of the hydrocarbons with its crystallites. The measurements indicated that
the Magnetite (Fe3O4) is much more intense in the fresh catalyst. Iron oxide (FeO), aluminum oxide
(Al2O) and hematite (Fe2O3) are the main crystallites of the used catalyst. This is expected as after
the use, the catalyst is more reduced iron state and it is more active.
Scanning Electron Microscope was used to scan the fresh and used iron based catalyst. The used
catalyst was observed to have grey and black particles, so with the microscope analysis, the point
was to investigate whether this difference could be evident. In the following Figure 23: SEM image
of Fresh catalyst Figure 24 and Figure 25 are presented the results from the measurements. From
this measurement, the particle size growth is evident, and this could lead to possible deactivation.
Still in these tests, the growth of the particles didn’t affect the catalyst’s performance.
Figure 23: SEM image of Fresh catalyst