Iron-pentasil molecular sieves: characterisation and catalytic behaviour in syngas conversion

Exploring Iron‐based Multifunctional Catalysts for Fischer–Tropsch Synthesis: A Review

“…For example, Goldwasser et al discovered that iron-impregnated zeolites (Si/Al = 73) mostly generate hydrocarbons in the gasoline range (53 %), whereas catalysts prepared by introduction of iron into the synthesis gel produces preferentially iso-C 4 's (65 %). [129] This effect is attributed to the different phases present in the catalysts, that is, iron carbide for impregnated catalysts or iron(III) and iron(II) in framework positions of the ferrisilicate catalyst. Similarly, a recent study by Kang et al showed that, although an impregnated catalyst Fe/Cu/K/ZSM-5 had a slightly lower CO conversion with respect to one prepared by physical mixing of the two components, the former exhibited a higher affinity and thus produced more olefins (Figure 3).…”

“…[129] Carburation of Fe/ZSM-5 zeolites led to increased C 5+ selectivity and decreased methane formation. This was ascribed to the formation of iron carbide phases, which were considered to be active in the promotion of chain growth.…”

“…In other cases, the preparation of ferrisilicates with different Si/ Fe ratios (100 and 3200) was accomplished, and the resulting zeolites were subjected to conventional calcination-reduction treatments. [129] Iron retains its ionic nature in these ferrisilicates, which results in the selective formation of iso-C 4 (65 %).…”

“…Various methods have been used to introduce iron, such as the addition of the metal precursor into the synthesis gel, [129,135] ion exchange, [131,136] impregnation, [114,130] vapor phase deposition, [101] or physical mixing of the zeolite with the iron precursor [102][103][104]127] or iron catalyst. [120] The catalytic performance of the resulting catalysts strongly depends on the prep- aration method, resulting in iron species located at considerably different positions in the support.…”

“…Goldwasser et al prepared iron-impregnated H-ZSM-5 catalysts with different Si/Al ratios. [129] In general, an increase in either the density of acid sites or the acid strength increases the possibility of secondary cracking reactions, which give rise to lower molar mass hydrocarbons. Long aliphatic molecules are not stable in the presence of acid sites and can be easily cracked into lighter olefins and paraffins, thus demonstrating a strong effect of the aluminum content in the multifunctional material.…”