Hani M. El-Kaderi

Metallic and bimetallic nanocatalysts incorporated into highly porous coordination polymer MIL-101

This paper reports the development of a facile, general and effective approach, based on microwave irradiation (MWI), for the incorporation of a variety of metallic and bimetallic nanoparticle catalysts within the highly porous coordination polymer MIL-101. The current approach is based on the simultaneous activation of the pores of MIL-101 and the rapid chemical reduction of metal precursors using MWI in the presence of a reducing agent. Small Pd, Cu and Pd–Cu nanoparticles of 2–3 nm are incorporated within the pores and larger particles of 4–6 nm are supported on the surface of the MIL-101 crystals. TEM images reveal that the loading of the particles using MWI is uniform across the MIL crystals. The observed catalytic activities toward CO oxidation of the Pd nanocatalysts supported on the highly porous MIL-101 polymer are significantly higher than any other reported metal clusters supported on metal–organic frameworks. The observed high activity is attributed to the small metal nanoparticles imbedded within the pores of the MIL crystals. The activity of the small embedded particles is higher than those supported on the surface. This allows the use of small metal loadings for efficient low temperature CO oxidation. These results should allow optimization of a new class of nanocatalysts incorporated within the highly porous MIL-101. These materials are promising environmentally relevant catalyst systems.

A 2D Mesoporous Imine‐Linked Covalent Organic Framework for High Pressure Gas Storage Applications

Hole-some mixture: A 2D mesoporous covalent organic framework (see figure) featuring expanded pyrene cores and linked by imine linkages has a high surface area (SA(BET) = 2723 m(2)  g(-1)) and exhibits significant gas storage capacities under high pressure, which make this class of material very promising for gas storage applications.

Pyrene-directed growth of nanoporous benzimidazole-linked nanofibers and their application to selective CO2 capture and separation

A pyrene-based benzimidazole-linked polymer (BILP-10) has been synthesized by the co-condensation of 1,3,6,8-tetrakis(4-formylphenyl)pyrene and 1,2,4,5-benzenetetramine tetrahydrochloride in dimethylformamide. The use of pyrene as a molecular building unit leads to the formation of self-assembled nanofibers that have moderate surface area (SABET = 787 m2 g−1) and very high CO2/N2 (128) and CO2/CH4 (18) selectivities at 273 K. Furthermore, results from gas uptake measurements indicate that BILP-10 can store significant amounts of CO2 (4.0 mmol at 273 K/1.0 bar) and H2 (1.6 wt% at 77 K/1.0 bar) with respective isosteric heats of adsorption of 38.2 and 9.3 kJ mol−1 which exceed all of the previously reported values for BILPs and are among the highest values reported to date for unmodified porous organic polymers. Under high pressure settings, BILP-10 displays moderate uptakes of H2 (27.3 g L−1, 77 K/40 bar), CH4 (72 L L−1, 298 K/40 bar), and CO2 (13.3 mmol g−1, 298 K/40 bar). The unusually high CO2 and H2 binding affinities of BILP-10 are presumably facilitated by the amphoteric pore walls of the polymer that contain imidazole moieties and the predominant microporous nature.

Highly selective CO2/CH4 gas uptake by a halogen-decorated borazine-linked polymer

A new borazine-linked polymer featuring chlorine-decorated cavities, BLP-10(Cl), has been prepared by the thermal decomposition of benzidine–boron trichloride in toluene under refluxing conditions. BLP-10(Cl) exhibits a moderate Langmuir surface area (1308 m2 g−1) and one of the highest CO2/CH4 selectivities (28.3) by porous materials at 1.0 bar and 273 K. Computational studies revealed that H2, CO2, and CH4 interact more favorably with the borazine unit with isosteric heats of adsorption of 7.46, 28.3, and 20.2 kJ mol−1, respectively. These values are in good agreement with experimental data collected by using the virial method. Results from this study suggest that including highly polarizable and halogenated building units into the framework of porous architectures can significantly enhance their performance in gas separation applications.

Impact of post-synthesis modification of nanoporous organic frameworks on small gas uptake and selective CO2 capture

Porous organic polymers containing nitrogen-rich building units are among the most promising materials for selective CO2 capture and separation applications that impact the environment and the quality of methane and hydrogen fuels. In this study, we report on post-synthesis modification of nanoporous organic frameworks (NPOFs) and its impact on gas storage (H2, CH4, CO2) and selective CO2 binding over N2 and CH4 under ambient conditions. The synthesis of NPOF-4 was accomplished via acid catalyzed cyclotrimerization reaction of 1,3,5,7-tetrakis(4-acetylphenyl)adamantane in ethanol/xylenes. NPOF-4 is microporous and has high surface area (SABET = 1249 m2 g−1). Post-synthesis modification of NPOF-4 by nitration afforded NPOF-4-NO2 and its subsequent reduction resulted in an amine-functionalized framework NPOF-4-NH2 that exhibits improved gas storage capacities and very high CO2/N2 (139) and CO2/CH4 (15) selectivities compared to NPOF-4.

Targeted synthesis of a mesoporous triptycene-derived covalent organic framework

The synthesis and characterization of a highly porous triptycene-derived covalent organic framework (TDCOF-5) and its performance in small gas storage are reported. TDCOF-5 crystallizes into a 2D mesoporous network that contains accessible boron sites, exhibits high surface area (SALang = 3832 m2 g−1), and high gas uptake under low pressure settings.

Application of pyrene-derived benzimidazole-linked polymers to CO2 separation under pressure and vacuum swing adsorption settings

Pyrene-derived benzimidazole-linked polymers (BILPs) have been prepared and evaluated for selective CO2 uptake and separation under pressure and vacuum swing conditions. Condensation of 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) with 2,3,6,7,10,11-hexaaminotriphenylene, 2,3,6,7,14,15 hexaaminotriptycene, and 3,3′-diaminobenzidine afforded BILP-11, BILP-12 and BILP-13, respectively, in good yields. BILP-12 exhibits the highest specific surface area (SABET = 1497 m2 g−1) among all known BILPs and it also has very high CO2 uptake 5.06 mmol g−1 at 273 K and 1.0 bar. Initial slope selectivity calculations indicate that BILP-11 has high selectivity for CO2/N2 (103) and CO2/CH4 (11) at 273 K. IAST selectivity calculations of BILPs at 298 K also showed high CO2/N2 (31–56) and CO2/CH4 (6.6–7.6) selectivity levels. The isosteric heats of adsorption for CO2 fall in the range of 32 to 36 kJ mol−1 and were considerably higher than those of CH4 (16.1–21.7 kJ mol−1). More importantly, the performance of pyrene-based BILPs in CO2 removal from flue gas and methane-rich gases (natural gas and landfill gas) under different industrial conditions was investigated according to evaluation criteria suggested recently by Bae and Snurr. The outcome of this study revealed that BILPs are among the best known porous materials in the field; they exhibit high working capacity, regenerability, and sorbent selection parameters. Collectively, these properties coupled with the remarkable physicochemical stability of BILPs make this class of polymers very promising for CO2 separation applications.

Synthesis of highly porous borazine-linked polymers and their application to H2, CO2, and CH4 storage

The synthesis of highly porous borazine-linked polymers (BLPs) and their gas uptakes are reported. BLPs exhibit high surface areas up to 2866 m2 g−1 and can store significant amounts of H2 (1.93 wt%) and CO2 (12.8 wt%) at 77 K and 273 K, respectively at 1.0 bar with respective isosteric heats of adsorption of 6.0 and 25.2 kJ mol−1.

Synthesis and evaluation of porous azo-linked polymers for carbon dioxide capture and separation

A series of new azo-linked polymers (ALPs) was synthesized via copper(I)-catalyzed oxidative homocoupling of 2D and 3D aniline-like monomers. ALPs have moderate surface areas (SABET = 412–801 m2 g−1), narrow pore sizes (<1 nm), and high physiochemical stability. The potential applications of ALPs for selective CO2 capture from flue gas and landfill gas at ambient temperature were studied. ALPs exhibit high isosteric heats of adsorption for CO2 (28.6–32.5 kJ mol−1) and high CO2 uptake capacities of up to 2.94 mmol g−1 at 298 K and 1 bar. Ideal adsorbed solution theory (IAST) selectivity studies revealed that ALPs have good CO2/N2 (56) and CO2/CH4 (8) selectivities at 298 K. The correlation between the performance of ALPs in selective CO2 capture and their properties such as surface area, pore size, and heat of adsorption was investigated. Moreover, the CO2 separation ability of ALPs from flue gas and landfill gas under pressure-swing adsorption (PSA) and vacuum-swing adsorption (VSA) processes was evaluated. The results show that ALPs have promising working capacity, regenerability, and sorbent selection parameter values for CO2 separation by VSA and PSA processes.

Enhanced Carbon Dioxide Capture from Landfill Gas Using Bifunctionalized Benzimidazole-Linked Polymers

Tuning the binding affinity of small gases and their selective uptake by porous adsorbents are vital for effective CO2 removal from gas mixtures for environmental protection and fuel upgrading. In this study, an amine-functionalized benzimidazole-linked polymer (BILP-6-NH2) was synthesized by a combination of pre- and postsynthetic modification techniques in two steps. Presynthetic incorporation of nitro groups resulted in stoichiometric functionalization (1 nitro/phenyl) in addition to noninvasive functionalization, where more than 80% of the surface area maintained compared to BILP-6. Experimental studies presented enhanced CO2 uptake and CO2/CH4 selectivity in BILP-6-NH2 compared to BILP-6, which are governed by the synergetic effect of benzimidazole and amine moieties. DFT calculations were used to understand the interaction modes of CO2 with BILP-6-NH2 and confirmed the efficacy of amine groups. Encouraged by the enhanced uptake and selectivity in BILP-6-NH2, we have evaluated its performance in landfill gas separation under vacuum swing adsorption (VSA) settings, which resulted in very promising working capacity and sorbent selection parameters outperforming most of the best solid adsorbent in the literature.