Direct conversion of carbon dioxide into light olefins over ZnZrO_x/ZSM-5@n-ZrO₂ tandem catalyst

The hydrogenation of carbon dioxide to light olefins is a direct and effective approach for achieving carbon neutrality. However, developing a tandem catalytic process involving methanol as an intermediate to achieve efficient directional conversion under mild conditions remains a challenge. Thus, we designed and constructed a bifunctional tandem catalyst, ZnZrOx/ZSM-5@n-ZrO2, where n represents the amorphous (am), monoclinic (m), and tetragonal (t) phases of ZrO2. The catalyst was prepared by coating an n-ZrO2 layer on the surface of ZSM-5 zeolite to form ZSM-5@n-ZrO2 with a coating structure, which was then ground and mixed with ZnZrOx to obtain the ZnZrOx/ZSM-5@n-ZrO2 tandem catalyst. At 340 degrees C and 2 MPa, the selectivity of the ZnZrOx/ZSM-5@t-ZrO2 catalyst toward light olefins reached 81.1%, with the carbon monoxide (CO) byproduct constituting only 34.3%. In contrast, the selectivity of ZnZrOx/ZSM-5 catalyst toward light olefins reached only 40.5% and a CO selectivity of 56.8%. Various characterizations and experimental results indicate that the ZSM-5@t-ZrO2 coating structure in the designed bifunctional catalyst effectively regulates the acid density and pore distribution of zeolite while inhibiting excessive hydrogenation of light olefins, ultimately achieving the desired mild transformation.