Figure 4. (a) Effects of zeolite shell thickness on K-ZnFe2O4@K-ZSM-5 catalytic performance;(b) Paraffins composition over composite catalysts with different shell thickness; (c) Detailed product distribution over composite catalysts with different shell thickness.
TG analysis of spent ZnFe2O4 and zeolites was shown in Figure S11. The spent K-ZnFe2O4 have more more obvious degree of carbonization than spent Na-ZnFe2O4, and the rising curve is the process by which iron-carbon compounds is converted to ferrites. When K-ZnFe2O4 is coupled with different ZSM-5, there are more iron-carbon compounds on K-ZSM-5 after the reaction, not only carbon deposits in H-ZSM-5. With the introduction of K-ZSM-5, Na-ZnFe2O4has more carbon deposition resulting in reduced activity, and K-ZnFe2O4 is not easily sintered.
Among different zeolite treated by K ion exchange startegy, the K-ZnFe2O4@K-ZSM-5 exhibited an excellent performance of CO2 hydrogenation. The catalytic performances of K-ZnFe2O4 coupled with different kinds of K-modified zeolites were shown in Figure S12 and Table S7. The introduction of K-ZSM-5 in composite system displayed the best C5+ hydrocarbons selectivity, which indicates that ZSM-5 with K ion exchange promoted the secondary reaction of olefins to form gasoline-range products due to its unique acidic and pore structure.