Fischer-Tropsch Synthesis, Methanation and Steam Reforming

6 Fischer-Tropsch Synthesis, Methanation, and Steam Reforming 

Three ideas give a coherence to recent work on the first two of these topics CO breakdown, the importance of M-C Hy species, and subsurface atoms (which are also noted in Section 7). 

Two short, powerfully argued, papers have made a considerable contribution to this field. The first is by Joyner who begins by pointing out that the mechanism of the Fischer-Tropsch synthesis is by no means settled. For the reaction (4) and the special case of methanation where = 1, many schemes have been CO + (2n + DH2 -------------------------- C H2 +2 + H20 (4) 

Thus effectiveness in breaking down CO becomes a pointer to effectiveness in Fischer-Tropsch catalysis. After considering more evidence in favour of his model, Joyner then considers very thoughtfully possible criticisms. The relationship between heat of adsorption of CO and catalytic conversion for CO and H2 on a wide range of metals is well supported in Vannice s volcano-shaped curves for CO adsorptions on alumina-supported metals. 

Again in a brief paper with considerable impact, van Barneveld and Ponec have considered many aspects of the Fischer-Tropsch reaction. On Ni and Cu/Ni they find that to explain many known features of the reaction they must dismiss polymerization of—CH2— groups on neighbouring sites and repeated CO insertion into M—H bonds. They favour CO dissociation to C + O followed by C + xH CH c and CH c + COads — (CH,CO) then CH,CO + wH- -H20 + CHjcCH 2- The CH ,CH 2 may add further CO, or add hydrogen to give a desorbable hydrocarbon product. The role of adsorbed CHx seems of paramount importance in their mechanism. 

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