Metallic Phase-Free Zn-Al Mixed Oxide Dual Function Materials Enable High CO Selectivity in Reactive Carbon Capture from Dilute CO2 Streams: Article No. 125305

Reactive carbon capture (RCC), whereby a dual function material (DFM) captures dilute CO2 and subsequently converts it within the same reactor, can address persistent cost concerns in carbon capture and utilization technology advancement. Many DFMs utilize costly precious metals (e.g., Pt or Ru) or oxidation-sensitive transition metals (e.g., Ni and Cu), the latter of which can hinder utilization of CO2 sources containing O2 and/or increase the H2 demand for oxide-metal reduction cycles. We report a precious metal-free, K-modified Zn-Al mixed oxide (ZnAlOx) DFM that exhibited 99?% selectivity to CO at temperatures more than 250 degrees C lower than conventional RCC-to-CO routes. While unmodified ZnAlOx catalysts were effective for RCC, K-modification was found to significantly increase CO2 adsorption capacity, improve retention of adsorbed CO2 through the reactive desorption step, and suppress the formation of unreactive spectator species during reactive desorption. These effects combined to improve CO yield (53?%) far beyond equilibrium-limited predictions for CO2-to-CO under conventional steady state reaction conditions (<1?%). The DFM also exhibited remarkable oxidative stability, with negligible performance loss over 25 RCC cycles using simulated flue gas with 5?% O2, demonstrating its promise as a robust, low-cost material to enable highly selective conversion of CO2 to CO in a single unit operation.