Selective Gas Adsorption by Single-atom Extraframework Transition Metal Sites Regularly Arranged Inside Porous Crystalline Matrices

Chemical separation accounts for approximately 15% of the world’s total energy consumption. Most of today’s chemical separation processes utilize volatility differences to induce selectivity, which involve phase change and thus are energy intensive. Adsorbent-based separation, which involves no phase change but exploits differences in polarizability, size, or shape to impart selectivity, has huge potential to reduce the high energy consumption, emissions, and pollution associated with today’s industrial chemical separations. However, adsorptive separation cannot work effectively when such chemical and/or physical distinctions between molecules are not pronounced. Prominent examples include air separation (N2/O2), natural gas purification (N2/CH4), carbon monoxide extraction (CO/CO2), nitric oxide extraction (NO/O2), and olefin-paraffin separation (e.g., C2H4/C2H6 and C3H6/C3H8), where gas molecules in each pair have very similar physical chemistry properties.In this project, we aim to address the challenge of separating gases that lack the common chemical and/or physical distinctions mentioned above by developing π- backbonding adsorbents that can selectively bind inert π-acidic gases (e.g., N2, CO, NO, C2H4, and C3H6). π-backbonding is a chemical bond that can form between reducing transition metals and π-acidic gases. We will achieve it by addressing the following questions: 1) How to design and develop zeolites and metal-organic frameworks (MOFs) adsorbents that accommodate and regulate various transition metal species as singleatom π-backbonding sites, based on the same concept by comparing these two most important categories of porous adsorbent substrates; 2) How to fine-tune the affinity of the adsorption sites to selected π-acidic gases as probes; 3) How to elucidate the gas adsorption mechanism via a combined experimental and molecular simulation study to enable rational design of π-backbonding adsorbents; and 4) How to prove the efficacy of our novel π backbonding adsorbents through selective gas adsorption studies.Research on the fundamentals of gas adsorption serves as the cornerstone of a suite of gas technologies for the handling of inert π-acidic gases, including gas separation, detection, and (catalytic) gas conversion. As the first study on the role of porous anionic frameworks of zeolites and MOFs in modulating extraframework single-atom transition metal ions as π-backbonding sites, this project would unleash the potential of manipulating π-backbonding interactions as a handle for designing next-generation single-atom adsorbents. Thus, the new knowledge and new adsorbent materials generated in this proposal will be invaluable to advance selective adsorption-based gas technologies, which will potentially bring considerable economic and environmental benefits.