Highly siliceous ZSM-22 was synthesized under hydrothermal conditions with ZSM-22 seeds. Characterization by FT-IR and ¹H and ²⁹Si NMR spectroscopy confirms that due to the existence of defective sites in the siliceous ZSM-22, acidic silanol groups including vicinal silanol and silanol nests are detected. Acidic silanol groups are considered as the acid sites of siliceous ZSM-22. As a result, siliceous ZSM-22 shows much lower acid site density and lower acid strength than silica–alumina ZSM-22 which contains hydroxyl groups bridging Si and Al as acid sites. In n-dodecane isomerization, Pt/siliceous ZSM-22 shows much higher isomer selectivity than Pt/silica–alumina ZSM-22. Furthermore, a lower loading amount of Pt on siliceous ZSM-22 (about 0.2 wt% Pt) can lead to high isomer selectivity. Owing to the acidic silanol groups and the low acid site density of siliceous ZSM-22, a good balance between metal and acid function in Pt/siliceous ZSM-22 is achieved, which results in a lower allowable Pt loading value and higher isomer selectivity.

DFT calculations, together with microkinetic modeling, have been employed to probe into the preferred mechanism of hydrocarbon C–C chain growth on Co(10−11) surfaces during Fischer–Tropsch synthesis. The results show that both CH and CH₂ are favored CH_x (x = 1–3) monomers, and are much easier to be formed than CH₄ and CH₃OH. CH and CH₂ self-coupling via a carbide mechanism realizes the initial C–C chain formation, rather than via a CO/CHO insertion mechanism. Meanwhile, CH₃CH₂ is the favored C₂ monomer, and is predominantly formed via a carbide mechanism rather than via a CO/CHO insertion mechanism, leading to C₂H₅OH formation. Starting from CH₃CH₂ intermediates, CH₃CH₂ coupling with CH₂ to form CH₃CH₂CH₂ realizes further C–C chain growth from C₂ to C₃ species, instead of a CO/CHO insertion mechanism leading to C₃H₇OH formation. Thus, the proposed mechanism of C–C chain growth is that RCH₂CH₂ coupling with CH₂ to R′CH₂CH₂ (R′ = RCH₂) realizes C–C chain growth. Meanwhile, CHO insertion into RCH₂CH leads to RCH₂CHCHO, followed by its hydrogenation to an alcohol. However, microkinetic modeling shows that the effect of CH₄ formation on the production of C₂₊ hydrocarbons should be considered, whereas alcohols have a negligible effect on the selectivity of C₂₊ hydrocarbons. Our results confirm that Co(10−11) surfaces exhibit a better catalytic activity and selectivity toward C₂₊ hydrocarbon formation.