Shedding Light on Solid Sorbents: Evaluation of Supported Potassium Carbonate Particle Size and Its Effect on CO2 Capture from Air

Solid sorbents are essential for developing technologies that directly capture CO₂ from air. In solid sorbents, metal oxides and/or alkali metal carbonates such as potassium carbonate (K₂CO₃) are promising active components owing to their high thermal stability, low cost, and ability to chemisorb the CO₂ present at low concentrations in air. However, this chemisorption process is likely limited by internal diffusion of CO₂ into the bulk of K₂CO₃. Therefore, the size of the K₂CO₃ particles is expected to be an important factor in determining the kinetics of the sorption process during CO₂ capture. To date, the effects of particle size on supported K₂CO₃ sorbents are unknown mainly because particle sizes cannot be unambiguously determined. Here, we show that by using a series of techniques, the size of supported K₂CO₃ particles can be established. We prepared size-tuned carbon-supported K₂CO₃ particles by tuning the K₂CO₃ loading. We further used melting point depression of K₂CO₃ particles to collectively estimate the average K₂CO₃ particle sizes. Using these obtained average particle sizes, we show that the particle size critically affects the efficiency of the sorbent in CO₂ capture from air and directly affects the kinetics of CO₂ sorption as well as the energy input needed for the desorption step. By evaluating the mechanisms involved in the diffusion of CO₂ and H₂O into K₂CO₃ particles, we relate the microscopic characteristics of sorbents to their macroscopic performance, which is of interest for industrial-scale CO₂ capture from air.

Synthesis of functionalized malononitriles via Fe-catalysed hydrogen atom transfers of alkenes

Described herein is a practical and convenient approach that enabled radical-mediated conjugate addition of unreactive alkenes to electron-deficient alkenes leading to a broad range of substituted malononitriles. These reactions are believed to proceed by Fe-catalysed hydrogen atom transfer (HAT) onto the alkenes affording carbon-centered radical intermediates with Markovnikov selectivity, followed by the capture of electron-deficient alkenes. We explored this synthesis approach under mild conditions with high efficiency and broad substrate scope and the utility is highlighted by the further synthetic transformations of the obtained substituted malononitriles.

Total synthesis and stereochemistry establishment of tumescenamide A

Tumescenamide A (1), isolated from Streptomyces tumescens YM23-20, consists of a cyclic depsipeptide and a side-chain 2,4-dimethylheptanoate (Dmh).