Nanoporous carbons with high surface area are achieved through direct carbonization of a commercially available zeolitic imidazolate framework (ZIF-8) without any additional carbon sources. The resultant nanoporous carbons exhibit high electrochemical capacitances in an acidic aqueous electrolyte.

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Carbon management by a means of CO2 capture from large stationary sources such as coal-fired power plants or from ambient air is a significant global issue. In the context of steam-stripping as a regeneration process for solid CO2 adsorbents, new adsorbent materials robust enough for direct contact with low temperature steam are needed. Here, mesoporous γ-alumina-supported poly(ethyleneimine) composite materials are prepared and evaluated as effective CO2 adsorbents, using dilute CO2 streams such as simulated flue gas (10% CO2) and ultradilute streams such as simulated ambient air (400 ppm CO2). In comparison to the silica-supported amine adsorbents typically utilized for CO2 capture applications, the alumina-supported amine adsorbents give better performance in terms of both capture capacity and amine efficiency, in particular, at ambient air conditions. In addition, the alumina-supported amines are stable over short multicycle temperature swing tests and, more importantly, appear to be more robust than the silica-based counterparts upon direct contact with steam. Thus, the resulting alumina-supported amines are suggested to be promising new materials for CO2 capture processes equipped with steam-stripping regeneration, especially from ultradilute gas streams.

Oxide supports functionalized with amine moieties have been used for decades as catalysts and chromatographic media. Owing to the recognized impact of atmospheric CO2 on global climate change, the study of the use of amine-oxide hybrid materials as CO2 sorbents has exploded in the past decade. While the majority of the work has concerned separation of CO2 from dilute mixtures such as flue gas from coal-fired power plants, it has been recognized by us and others that such supported amine materials are also perhaps uniquely suited to extract CO2 from ultradilute gas mixtures, such as ambient air. As unique, low temperature chemisorbents, they can operate under ambient conditions, spontaneously extracting CO2 from ambient air, while being regenerated under mild conditions using heat or the combination of heat and vacuum. This Account describes the evolution of our activities on the design of amine-functionalized silica materials for catalysis to the design, characterization, and utilization of these materials in CO2 separations. New materials developed in our laboratory, such as hyperbranched aminosilica materials, and previously known amine-oxide hybrid compositions, have been extensively studied for CO2 extraction from simulated ambient air (400 ppm of CO2). The role of amine type and structure (molecular, polymeric), support type and structure, the stability of the various compositions under simulated operating conditions, and the nature of the adsorbed CO2 have been investigated in detail. The requirements for an effective, practical air capture process have been outlined and the ability of amine-oxide hybrid materials to meet these needs has been discussed. Ultimately, the practicality of such a "direct air capture" process is predicated not only on the physicochemical properties of the sorbent, but also how the sorbent operates in a practical process that offers a scalable gas-solid contacting strategy. In this regard, the utility of low pressure drop monolith contactors is suggested to offer a practical mode of amine sorbent/air contacting for direct air capture.

Organic structure-directing agent (OSDA)-free synthesis of zeolite beta is a subject of both scientific and industrial interest. Herein, we report a comprehensive investigation into the effects of various parameters on the seed-assisted crystallization of zeolite beta in the absence of OSDA. The crystallization behavior of "OSDA-free beta" is strongly governed by the chemical composition of the starting Na(+)-aluminosilicate gel as well as by the Si/Al ratios of the calcined beta seed crystals, which are prepared using tetraethylammonium hydroxide (TEAOH). Furthermore, OSDA-free beta seed crystals can be used to form zeolite beta, termed "green beta". XRD, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and ²⁷Al magic angle spinning NMR analyses showed that the OSDA-free beta and green beta were of high purity and crystallinity. The nitrogen adsorption-desorption of OSDA-free beta and green beta revealed higher surface areas and larger volumes in the micropore region than those of the beta seeds synthesized with OSDA after calcination. These results provide a robust and reliable process for the environmentally friendly production of high-quality zeolite beta in a completely OSDA-free Na(+)-aluminosilicate system.

Organic structure-directing agents (OSDAs) have been widely used for the synthesis of zeolites. In most cases, OSDAs are occluded in zeolites as an isolated cation or molecule geometrically fitted within the zeolite cavities. This is not the case for zeolite beta synthesized by using tetraethylammonium (TEA(+)) cation as an OSDA, in which a cluster/aggregate of ca. six TEA(+) cations is occluded intact in the cavity (i.e., the channel intersection) of zeolite beta. The structure direction of TEA(+) in such a nontypical, clustered mode has remained elusive. Here, zeolite beta was hydrothermally synthesized using TEA(+) in the absence of other alkali metal cations in order to focus on the structure-directing behaviors of TEA(+) alone. The solid products formed throughout the hydrothermal synthesis were analyzed by an array of characterization techniques including argon adsorption-desorption, high-energy X-ray total scattering, Raman and solid-state NMR spectroscopy, and high-resolution transmission electron microscopy. It was revealed that the formation of amorphous TEA(+)-aluminosilicate composites and their structural, chemical, and textural evolution toward the amorphous zeolite beta-like structure during the induction period is vital for the formation of zeolite beta. A comprehensive scheme of the formation of zeolite beta is proposed paying attention to the clustered behavior of TEA(+) as follows: (i) the formation of the TEA(+)-aluminosilicate composites after heating, (ii) the reorganization of aluminosilicates together with the conformational rearrangement of TEA(+), yielding the formation of the amorphous TEA(+)-aluminosilicate composites with the zeolite beta-like structure, (iii) the formation of zeolite beta nuclei by solid-state reorganization of such zeolite beta-like, TEA(+)-aluminosilicate composites, and (iv) the subsequent crystal growth. It is anticipated that these findings can provide a basis for broadening the utilization of OSDAs in the clustered mode of structure direction in more effective ways.

Amine/oxide hybrid carbon dioxide adsorbents prepared via impregnation of low molecular weight polymeric amines into porous oxide supports are among the most promising solid adsorbents developed for postcombustion CO 2 capture or CO 2 extraction from ambient air. The oxidative stability of adsorbents prepared by impregnation of poly(ethylenimine) (PEI) or poly(allylamine) (PAA) into mesoporous γ-alumina under humid oxidation conditions is evaluated in this work. The PEIbased adsorbents, which contain primary, secondary, and tertiary amines, are shown to degrade drastically at elevated temperatures (110 °C) and in high oxygen concentrations (21%, akin to air), with these effects reduced by both reductions in temperature (70 °C) and oxygen concentration (5%, akin to flue gas). The oxidation behavior of PEI-based adsorbents supported on alumina is qualitatively similar to past work on silica-supported PEI adsorbents. In contrast, the alumina-supported PAA adsorbents that contain only primary amines show significantly improved oxidative stability, losing only 10% or less of their original CO 2 capacity after prolonged oxidative treatment under a variety of conditions. Analysis of the fresh and thermally treated samples by Fourier transform (FT) IR, FT-Raman, and 13 C NMR spectroscopies demonstrates the clear formation of carbonyl functionalities over the oxidized PEI-based adsorbents, whereas no significant changes in the spectra for PAA samples are observed after oxidative treatments. The collected data demonstrate that secondary-amine-free, primary-amine-rich polymers such as PAA may be used to formulate supported amine adsorbents with improved oxidative stability compared to adsorbents based on PEI, which is used ubiquitously in the field today.

Low-molecular-weight poly(allylamine) is prepared via free-radical polymerization, and the resulting polymer is impregnated into mesocellular silica foams at different amine loadings. The resulting poly(allylamine)–silica composites are demonstrated as effective adsorbents for the extraction of carbon dioxide from dilute (simulated flue gas) and ultradilute (simulated ambient air) gas streams. The composite adsorbents are shown to have comparable adsorption capacities to more-conventional poly(ethyleneimine)–silica adsorbents. Potential advantages of poly(allylamine)-derived adsorbents are discussed.