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Supplemental Document

The supporting material contains data and theoretical derivations that are not given in the manuscript, and it is a supplement to this work.

Direct conversion hydrogenation of CO2 to hydrocarbons is a highly attractive but challenging method for obtaining value-added lower olefins with low CO selectivity. In this work, composites of SAPO-34 and ZnO-ZrO2 were successfully fabricated via hydrothermal coating and physical blending methods, respectively. Characterization results indicated that the composite phase together with coexisting acidic and basic sites and distinct micro-mesoporous structure was obtained without overly tight contact between the two active compounds in the physically blended composite. As a result the selectivity for lower olefins was 70% among all hydrocarbon products while CO selectivity was around 41%. Then, H2 reduction on ZnO-ZrO2 precursor was performed to explore the electronic properties of the physically blended composite. Interestingly, the CO by-product was significantly suppressed from 41% to 27% by the alterations of the acid and basic sites resulting from electronic property tuning of Zn and Zr sites during H2 reduction at 500 °C. The synergetic effect of composite phase, suitable electronic property tuning, large number of acidic-basic sites and distinct micro-mesoporous structure all made essential contributions to the enhanced catalytic activity for direct CO2 conversion, the superior selectivity for lower olefins and less amount of CO by-product over ZnO-ZrO2/SAPO-34 composite.

An exploration into the influence of interfacial characteristics between ZnZrO2 and SAPO-34 on CO2 hydrogenation to lower olefins was conducted. This was achieved by fabricating ZnZrO2@Al2O3@SAPO-34 tandem catalyst based on a chemical coating strategy. Physically blended ZnZrO2/SAPO-34 and hydrothermally coated ZnZrO2@SAPO-34 were employed as references for exploring the correlation between interfacial characteristic and catalytic performance. The results showed that ZnZrO2@SAPO-34 fabricated via hydrothermal coating method exhibited inferior catalytic performance resulting from the inactivation of ZnZrO2 active components after hydrothermal treatment. However, post pre-coating modification by Al2O3 of ZnZrO2 prevented the deactivation of ZnZrO2 active components, as well as facilitating the formation of chemically interfacial phase between ZnZrO2 and SAPO-34 with encapsulated structure based on micro-mesoporous system and rich acid-base active centers. The collective contributions aroused by the role of Al2O3 are the crucial to enhanced catalytic performance of ZnZrO2@Al2O3@SAPO-34 tandem catalyst. Under 3 MPa, 3500 ml g−1·h−1 and 380 °C reaction conditions, CO2 hydrogenation on ZnZrO2@Al2O3@SAPO-34 tandem catalyst exhibited a high C2–C4 (75% C2=- C4=, 20% C20–C40) selectivity of 95% with the CH4 selectivity of 3% among hydrocarbon products at the CO2 conversion of 21% and 45% selectivity of CO by-product. Compared with ZnZrO2@SAPO-34, the selectivity of C2–C4 over ZnZrO2@Al2O3@SAPO-34 tandem catalyst increased by 55%. In addition, this work also opens a new window for designing the excellent bifunctional tandem catalysts for the other applications.