(560e) Transition Metal-Free Dual Function Materials for Highly Selective CO2 Capture and Conversion

Scaling conventional carbon capture and utilization methods can be limited by high costs and underdeveloped infrastructure for transporting captured CO₂ to upgrading sites. Reactive carbon capture (RCC) can eliminate these concerns by unifying the CO₂capture and conversion steps in a single unit operation. In RCC, a single sorbent-catalyst material (known as a dual function material, or DFM) is used to capture CO₂ from the atmosphere or a point source, most often via interactions with basic surface sites. The bound CO₂ is then converted to products on adjacent catalyst sites by changing the reaction conditions to promote reactive desorption alongside a reactive agent (i.e., H₂).

The process intensification approach of RCC implies minimal cleanup of the input gas stream for CO₂ capture and conversion. It is therefore important to design DFMs that tolerate the poisons common to point source and atmospheric emissions. Oxygen is one such poison, which readily oxidizes the transition metals used in conventional CO₂ hydrogenation such as nickel and copper. These metals must be reduced at elevated temperature prior to CO₂ conversion in RCC applications. This increases H₂ consumption, cycle time, and decreases product yield through the desorption of the captured CO₂.

Here, we report transition metal-free DFMs to address the challenges imposed by the oxidation of conventional CO₂ hydrogenation catalysts. Mixed metal oxide catalysts comprised of zinc and aluminum were doped with several alkali species to facilitate CO₂capture. These zinc aluminate spinels (ZnAlO_X) were prepared at various Zn:Al ratios to understand the mechanisms that govern CO₂ and H₂ activation. The ZnAlO_X DFMs were studied in model RCC experiments and demonstrate over 97% selectivity to CO under atmospheric pressure and temperature swing operation. Subsequent RCC cycling with oxygen probes the stability of these transition metal-free DFMs in more realistic CO₂ capture streams.