Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

New materials hold the key to fundamental advances in energy conversion and storage, both of which are vital in order to meet the challenge of global warming and the finite nature of fossil fuels. Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. This review describes some recent developments in the discovery of nanoelectrolytes and nanoelectrodes for lithium batteries, fuel cells and supercapacitors. The advantages and disadvantages of the nanoscale in materials design for such devices are highlighted.

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Nanostructured materials for advanced energy conversion and storage devices

Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

Metal–Organic Frameworks for Separations

Kenji Sumida, David L. Rogow, Jarad A. Mason, Thomas M. McDonald, Eric D. Bloch, Zoey R. Herm, Tae-Hyun Bae, Jeffrey R. Long

Carbon Dioxide Capture in Metal–Organic Frameworks

Chemical liquid deposition (CLD) modified 4A zeolite is developed as a size selective sorbent at 0.01 nm resolution for gas separation. The silica layer formed by CLD modification is located on the...

Chemical Liquid Deposition Modified 4A Zeolite as a Size-Selective Adsorbent for Methane Upgrading, CO2 Capture and Air Separation

Prediction of cross-term coefficients in binary diffusion: Diffusion in zeolite

Hydrogen adsorption properties of a superactived carbon (AX-21) doped with Pt nanoparticles by using plasma reduction were studied and were compared with that by using traditional H2 reduction. The hydrogen storage capacity was significantly increased by plasma reduction. The H2 storage capacity on Pt-doped AX-21 at 298 K and 10 MPa was increased from 1.19 wt % (by H2 reduction) to 1.46 wt % on the sample obtained by plasma reduction. The plasma-reduced sample produced 1.5−3 nm Pt particles that were highly dispersed on carbon, and most interestingly, the metal particles were recessed into the carbon substrate. Both isosteric heats of adsorption and the activation energies for spillover were decreased by plasma reduction, which was evidence that the energy barrier for H spillover was lowered by plasma treatment, resulting in faster rates as well as higher spillover capacities. Mechanisms for plasma reduction and for edge recession of the metal particles into carbon are proposed.

Enhanced Hydrogen Storage on Pt-Doped Carbon by Plasma Reduction

Over the past several years, selective catalytic reduction of NOx with hydrogen (H2-SCR) has been regarded as a promising technology for NOx abatement under lean-burn conditions. In this review, we discuss the recent progress in the development and understanding of H2-SCR catalysts. The various mechanisms that have been proposed in the literature are reviewed first. The influence of the catalyst chemical components (noble metals, supports, promoters, and perovskites) and their roles in H2-SCR are then analyzed. Non-noble metal catalysts and the new strategy of alloying Pt with transition metals (Ni, Fe, Co, and Cu) are of particular interest and discussed. From a practical viewpoint, the effects of exhaust gas composition on H2-SCR is also addressed. Finally, we propose potential opportunities and challenges in the area of H2-SCR.

Ralph T. Yang

Papers

Chemical Liquid Deposition Modified 4A Zeolite as a Size-Selective Adsorbent for Methane Upgrading, CO2 Capture and Air Separation

Prediction of cross-term coefficients in binary diffusion: Diffusion in zeolite

Enhanced Hydrogen Storage on Pt-Doped Carbon by Plasma Reduction

110th Anniversary: Recent Progress and Future Challenges in Selective Catalytic Reduction of NO by H2 in the Presence of O2

Kinetics and mechanism of gas-carbon reactions: Conformation of etch pits, hydrogen inhibition and anisotropy in reactivity