Figure 6. The in situ DRIFT spectra of (a)K-ZnFe2O4, (b)K-ZnFe2O4@K-ZSM5 for CO2hydrogenation; (c) H-ZSM5, (d) K-ZSM-5 in C3H6 atmosphere (0.1 MPa, 320 °C, 20 mL min -1).
double-bond telescopic vibration of the olefins C=C. It indicates that the presence of olefins in the products is produced over the surface of K-ZnFe2O4 (Figure 3a ).
When ZSM-5 is introduced, C=C bond of olefins telescopic vibration absorption peak at 1680-1500 cm-1 significantly decreases, replacing by infrared absorption peaks at about 1000 cm-1 wavenumber, which are attributed to the off-plane bending vibrations of aromatic compounds different from olefins (Figure 6b and S15). The infrared absorption spectra of aromatic compounds are more pronounced in the K-ZnFe2O4@Ce-ZSM-5 and K-ZnFe2O4@K-ZSM-5 (Figure S15). Besides, there are many bending vibrations of -CH3 unlike other catalysts, which are multiple methyl groups linked to the same carbon atom. For the K-ZnFe2O4@K-ZSM-5, more bending vibrations of -CH3 appear than the utilization of other zeolite catalysts, which ascribes to multiple methyl groups linked to the same carbon atom in the wavenumbers from 1500 cm-1 to 1000 cm-1. The result is also well consistent with the high content of isoparaffins hydrocarbons in the product over the K-ZnFe2O4@K-ZSM-5 catalyst (Figure 3c).