The Chemistry of Metal-Organic Frameworks for Carbon Dioxide
Capture, Regeneration, and Conversion
Christopher A. Trickett, Aasif Helal, Bassem A. Al‑Maythalony, Zain H. Yamani, Kyle E. Cordova and Omar M. Yaghi
Nature Rev. Mater., 2017, 2, 17045.
The carbon dioxide challenge is one of the most pressing problems facing our planet. Each stage in the carbon cycle: capture, regeneration, and conversion presents its own materials requirements. Recent work on metal-organic frameworks (MOFs) demonstrated their potential and effectiveness in progressing towards addressing this challenge. In this Review, we correlate specific MOF structural and chemical properties that have led to the highest capture capacity, most efficient separations and regeneration processes, and the most catalytically active conversions.
This Review discussed the post-combustion CO2 capture by MOF and the precision with which the interior of MOFs is designed. The flexibility with which one can tailor a given MOF allows for the optimization and enhancement of CO2 capture properties. The majority of research on developing MOFs for CO2 capture has focused on reversible adsorption - a process that significantly lowers the need for energy input during regeneration and overcomes a key challenge of using traditional sorbents like monoethanolamine solutions. As a result, the structures of MOFs have since been systematically developed, fine-tuned and studied in detail to have: (i) coordinatively unsaturated metal sites, (ii) incorporation of specific heteroatoms within the backbone or as part of a covalently bound functionality, (iii) covalent functionalization by incorporation or grafting of dialkylamines within a MOF, (iv) building unit interactions such as SBU-based interactions, (v) hydrophobic frameworks are an alternative for the capture of CO2 by simple exclusion of water from the pores, and (vi) hybrid functionalities that have the goal to maximize the density of strong binding sites that promote strong interactions with CO2 to increase the CO2 uptake. Furthermore, we also elaborated on the application of MOFs in the atmospheric carbon capture from air, and also carbon capture for natural gas upgrading. The separation of CO2 from methane is an important process for natural gas sweetening as the CO2 in the presence of moisture is corrosive and lowers energy efficiency.
Additionally, we covered the area of: (a) MOFs for short-term storage and transport of carbon dioxide (b) practical consideration in carbon dioxide regeneration involving technologies as (i) pressure swing adsorption (PSA); (ii) vacuum swing adsorption (VSA); (iii) temperature swing adsorption (TSA); and (iv) carbon dioxide separation by MOF membranes.
Finally, we reviewed the utilization of CO2 by MOFs. This section was divided into two main categories: (i) reduction and hydrogenation of carbon dioxide in MOFs and (ii) carbon dioxide conversion by MOFs for fine chemicals. The first part was subdivided into three parts: (a) photocatalytic reduction of carbon dioxide; (b) electrocatalytic reduction; and (c) hydrogenation of CO2 using MOF-nanoparticle composites. The second part consists of three categories: (a) defect-driven catalysis; (b) linker promoted catalysis; and (c) inorganic secondary building unit-driven catalysis.
The potential of MOFs for satisfying the demands in every aspect of the carbon dioxide cycle has captured the imagination of scientists, with exponential progress being made in the field. With the early phase of discovery and proof-of-concept for CO2-related applications now well established, this progress is shifting from fundamental aspects to practical considerations. The field is now moving toward testing materials under conditions applicable to commercial and real-world use, including separation from multiple component mixtures at low concentration and in the presence of water, and developing means to recover CO2 and recycle the MOFs for long-term use.
The Saudi Aramco support to KFUPM through the Strategic Research Partnership has enabled KFUPM to establish world class research programs on campus, and develop state of the art technologies in fields pertaining to the core business areas of the world leading oil company.
The KFUPM-UC Berkeley collaborative Review article featured on Nature Reviews Materials cover page.
Prof. Omar M. Yaghi with the Saudi Aramco funded Carbon Capture Chair group at KFUPM.