Fig. 1. Catalytic CO2 conversion of the catalysts. (a) Catalytic performance, hydrocarbon product selectivity (excluding CO), and C5+ yield of various CZOx-8 with different alkali metals. (b) Catalytic performance, hydrocarbon product selectivity (excluding CO), and C5+ yield of various CZOx-8 catalysts having different Na loadings. (c) Long-term stability of Na1.8-CZOx-8 catalyst. Reaction conditions: 270 °C, 4.0 MPa, a H2/CO2 ratio of 3, and GHSV of 4000 mL g-1 h-1 for 30 h.

Fig. 2. (a) XRD patterns of spent unpromoted and alkali-promoted CZOx-8 catalyst. (b) Enlarged XRD pattern indicating the formation of Li2CO3. Reaction conditions: 270 °C, 4.0 MPa, a H2/CO2 ratio of 3, and GHSV of 4000 mL g-1 h-1 for 30 h.

Fig. 3. XAS analysis of reduced and spent unpromoted and alkali-promoted CZOx-8 catalysts. Normalized Co K-edge XANES spectra of the reduced (a) and spent (c) catalysts. k3-weighted Fourier transforms of normalized Co K-edge EXAFS spectra (κ3 χ(k)) for the reduced (b) and spent (d) catalysts. (e) Linear combination fitting data of reduced and spent catalysts. Reduction conditions: 350 °C for 6 h at a flow of 50 mL min-1 H2 and 4.0 MPa. Reaction conditions: 270 °C, 4.0 MPa, a H2/CO2 ratio of 3, and GHSV of 4000 mL g-1 h-1 for 30 h.

Fig. 4. Raman spectra of the spent unpromoted and alkali-promoted catalysts. Reaction conditions: 270 °C, 4.0 MPa, a H2/CO2 ratio of 3, and GHSV of 4000 mL g-1 h-1 for 30 h.

Fig. 5. XPS profiles of the spent unpromoted and alkali-promoted catalysts in the C 1s (a), O 1s (b), Zr 3d (c), and Co 2p (d) regions. Reaction conditions: 270 °C, 4.0 MPa, a H2/CO2 ratio of 3, and GHSV of 4000 mL g-1 h-1 for 30 h.

Fig. 6. HR-TEM and corresponding EDX images of the calcined (a)-(d), reduced (e)-(h), and spent (i)-(t) unpromoted and alkali-promoted catalysts. Calcination conditions: 330 °C and 100 mL min-1 air flow for 3 h. Reduction conditions: 350 °C and 50 mL min-1 H2 flow for 6 h under 4.0 MPa. Reaction conditions: 270 °C, 4.0 MPa, a H2/CO2 ratio of 3, and GHSV of 4000 mL g-1 h-1 for 30 h.

Fig. 7. H2-TPR (a), H2-TPD (b), and CO2-TPD (c) profiles of the unpromoted and alkali-promoted catalysts. Amount of H2 consumption (d), H2 desorption (e), and CO2 desorption (f) in mmol g-1 of the unpromoted and alkali-promoted catalysts. Calcination conditions: 330 °C and 100 mL min-1 air flow for 3 h. Reduction conditions: 350 °C and 50 mL min-1 H2 flow for 6 h under 4.0 MPa.

Fig. 8. In-situ CO2 hydrogenation DRIFT profiles of BC-CZOx-8 (a), Li1.8-CZOx-8 (b), Na1.8-CZOx-8 (c), and K1.8-CZOx-8 (d). CO2 and H2 were injected into the cell at flow rates of 16.7 and 50 mL min−1, respectively, under the conditions of 3.0 MPa and 270 °C for 2 h. Pretreatment reduction conditions: 350 °C (ramping rate of 2.5 °C min-1), 3.0 MPa, 50 mL min-1 H2 flow for 6 h. (e) Proposed reaction mechanism on unpromoted and alkali-promoted CZOx-8 catalyst.