Fischer Tropsch reactions catalyzed by Fe-Cu particles supported on modified two-dimensional silicon wafers

Introduction Fisher Tropsch (FT) reactions involve the reaction between CO and H2 to generate amongst others aliphatic hydrocarbons; it is catalysed by iron and promoted by copper supported on a solid support. Industrial... [ view full abstract ]

Introduction

Fisher Tropsch (FT) reactions involve the reaction between CO and H₂ to generate amongst others aliphatic hydrocarbons; it is catalysed by iron and promoted by copper supported on a solid support. Industrial three-dimensional supported catalysts suffer in general from characterization problems as it is difficult to characterize catalytic particles inside support pores (Figure 1).  By using two-dimensional supports, accessibility of reactions sites by analytical techniques is easier [1].  We show here how Fe-Cu particles obtained by in-situ calcination and reduction of Fe-Cu ß-diketonato-coated two-dimensional silicon wafers successfully catalyse FT reactions. Niemantsverdriet showed earlier how preformed iron oxide nano particles spincoated onto flat oxidic surfaces support FT reactions [2].    

Methods

Synthetic methods to prepare [Cu(FcCOCHCOR)_n] (R = CH₃ or Fc = ferrocenyl = Fe^II(C₅H₅)(C₅H₄)) and anchoring them on acetylacetonato-capped silicon wafers will be presented.    Characterization techniques of these catalyst precursors include single crystal X-ray diffraction and electrochemical methods, while for the supported catalyst, X-ray photoelectron spectroscopy and ATR-FTIR techniques were used.   FT reaction products were identified by mass spectrometry.

Results

Fe-Cu particles obtained after calcination and reduction of precursors allowed the reaction between CO and H₂ under FT conditions to liberate up to C6 products.   Fe, FeO, Fe₂O₃ and metallic Cu could be identified on the surfaces by XPS measurements.

Discussion 

 FT reactions are normally performed at temperatures >230^oC and high pressures over iron or cobalt catalysts supported on the surface and inside the pores of 3-dimensional supports (e.g. alumina) with large surface areas (e.g. 200 m²/g).   In such systems, reagent access to catalytic particles in the pores is hindered but catalyst loading is high. 

On flat surfaces, access to Fe-Cu centres is unhindered but catalyst loading is low implying catalytic activity should be higher to achieve comparable catalysis.

References

[1]  P.C. Thüne, J.W. Niemantsverdriet, Surf. Sci. 603 (2009) 1756-1762.

[2]  P. Moodley, F.J.E. Scheijen, J.W. Niemantsverdriet, P.C. Thüne, Catalysis Today, 154 (2010) 142-148.