Direct Conversion\nof CO<sub>2</sub> to Olefins over\na Cr<sub>2</sub>O<sub>3</sub>/ZSM-5@CaO Cooperative and Bifunctional\nMaterial Under Isothermal Conditions

Direct conversion\nof point-source CO<sub>2</sub> into fine chemicals\nover cooperative and bifunctional materials (BFMs) – composed\nof adsorbents and catalysts – has emerged as a promising approach\nto improve the energy efficiency of the carbon capture and conversion\nprocesses. In this study, a bifunctional material consisting of Cr<sub>2</sub>O<sub>3</sub>/ZSM-5 catalyst and CaO adsorbent was developed\nand tested in the CO<sub>2</sub>-oxidative dehydrogenation of propane\n(CO<sub>2</sub>–ODHP) for reactive capture of CO<sub>2</sub> in a fixed bed reactor. First, CaO was prepared using two distinct\nmethods: solid-state and citrate sol–gel. The citrate sol–gel\nmethod resulted in small and finely-distributed CaO particles, allowing\nmore accessible sites for CO<sub>2</sub> adsorption. Consequently,\na high CO<sub>2</sub> adsorption capacity of ∼14 mmol/g was\nachieved with fast adsorption kinetics compared to CaO prepared by\nthe solid-state method. The CaO adsorbent was then combined with the\nCr<sub>2</sub>O<sub>3</sub>/ZSM-5 catalyst for BFM synthesis and tested\nin the CO<sub>2</sub>–ODHP process, targeting propylene production.\nThe BFM was extensively characterized to provide insights into the\nBFM’s surface chemistry, morphology, and reaction mechanism\nin the reactive capture process of CO<sub>2</sub>–ODHP. The\nresults revealed that under isothermal adsorption–reaction\nconditions at 600 °C, a propane conversion of 22.5%, a propylene\nselectivity of 55.3%, and an olefin selectivity of 67.3% were achieved.\nThe excellent propylene selectivity was attributed to the catalyst\nacidity and redox property of the Cr<sub>2</sub>O<sub>3</sub>/ZSM-5\ncatalyst, which facilitated the reaction pathway of propane dehydrogenation\nin the process of CO<sub>2</sub>–ODHP. Overall, this study\nrenders Cr<sub>2</sub>O<sub>3</sub>/ZSM-5@CaO as promising BFMs with\nhigh CO<sub>2</sub> capture capacity and catalytic activity for integrated\nCO<sub>2</sub> capture and conversion in the ODHP reaction.