Selective Gas Admission and Adsorption Enabled by Molecular Trapdoor Mechanism in Channel-Type Porous Crystalline Solids for Gas Separation

The gas separation industry represents a significant portion of global energyconsumption (10-15%). This project aims to develop a new class of adsorbents –channel-type molecular trapdoor adsorbents – that offer exceptional efficiency inmolecular separation. This innovative technology has the potential to greatly reducecosts in various gas separation processes, including fuel gas purification, carbon dioxide capture, air separation, and paraffin/olefin separation.Conventional molecular sieving is highly selective for gas separation but struggles todifferentiate between small molecules of similar sizes. Fortunately, PI Shang’s discoveryof the “molecular trapdoor” effect, a non-size-based sieving mechanism, offers asolution. Molecular trapdoor adsorbents selectively allow target molecules to enter byregulating their interactions with the materials’ pore-keeping groups. This breakthroughhas led to the development of a series of trapdoor (-like) adsorbents that exhibitexceptional selectivity for molecular separation. However, these adsorbents often haveslow adsorption kinetics and low capacity. This is because they all necessitate a highdensityof pore-keeping groups that block multiple pore apertures of every cage of theporous adsorbents to ensure high selectivity. Unfortunately, these pore-keeping groupsalso hinder gas diffusion and reduce the pore void volume.This project aims to address the inherent limitations of cage-type trapdoor adsorbentsby developing a new class of channel-type trapdoor adsorbents. The new concept of“trapdoor in channel-type adsorbents” allows for reducing the density of pore-keepinggroups while maintaining high selectivity. Rather than blocking multiple cage openings,we only need to block the limited channel ends, thus significantly reducing the numberof pore-keeping groups required for a given pore volume in a porous crystal. To achievethis, we will address key questions, including how to prepare model channel-type zeolitesand metal-organic frameworks accommodating various cations or anions as porekeepinggroups, how to adjust the type and density of pore-keeping groups and type ofchannels to tune gas admission and adsorption properties, how to elucidate themechanism of gas admission and adsorption through experimental and computationalmethods, and how to prove the effectiveness (high adsorption selectivity, kinetics, andcapacity) of our novel channel-type adsorbents through gas separation tests.The new knowledge on fundamentals of adsorption and new adsorbent materialsgenerated through this research will advance selective adsorption-based gas separation,and have implications in other gas technologies, including storage, detection, and(catalytic) conversion, which will potentially bring considerable economic, social, andenvironmental benefits.