Direct Conversion of CO to Olefins over a CrO/ZSM-5@CaO Cooperative and Bifunctional Material Under Isothermal Conditions.

Direct conversion of point-source CO into fine chemicals over cooperative and bifunctional materials (BFMs) - composed of adsorbents and catalysts - has emerged as a promising approach to improve the energy efficiency of the carbon capture and conversion processes. In this study, a bifunctional material consisting of CrO/ZSM-5 catalyst and CaO adsorbent was developed and tested in the CO-oxidative dehydrogenation of propane (CO-ODHP) for reactive capture of CO in a fixed bed reactor. First, CaO was prepared using two distinct methods: solid-state and citrate sol-gel. The citrate sol-gel method resulted in small and finely-distributed CaO particles, allowing more accessible sites for CO adsorption. Consequently, a high CO adsorption capacity of ∼14 mmol/g was achieved with fast adsorption kinetics compared to CaO prepared by the solid-state method. The CaO adsorbent was then combined with the CrO/ZSM-5 catalyst for BFM synthesis and tested in the CO-ODHP process, targeting propylene production. The BFM was extensively characterized to provide insights into the BFM's surface chemistry, morphology, and reaction mechanism in the reactive capture process of CO-ODHP. The results revealed that under isothermal adsorption-reaction conditions at 600 °C, a propane conversion of 22.5%, a propylene selectivity of 55.3%, and an olefin selectivity of 67.3% were achieved. The excellent propylene selectivity was attributed to the catalyst acidity and redox property of the CrO/ZSM-5 catalyst, which facilitated the reaction pathway of propane dehydrogenation in the process of CO-ODHP. Overall, this study renders CrO/ZSM-5@CaO as promising BFMs with high CO capture capacity and catalytic activity for integrated CO capture and conversion in the ODHP reaction.