Selective adsorption of fluorinated super greenhouse gases within a metal-organic framework with dynamic corrugated ultramicropores.

Perfluorocompound (PFC) gases play vital roles in microelectronics processing. Requirements for ultra-high purities traditionally necessitate use of virgin sources and thereby hinder the capture, purification, and reuse of these costly gases. Most importantly, gaseous PFCs are incredibly potent greenhouse gases with atmospheric lifetimes on the order of 103-104 years, and thus any environmental emissions have an outsized and prolonged impact on our climate. The development of sorbents that can capture PFC gases from industrial waste streams has lagged substantially behind the progress made over the last decade in capturing CO2 from both point emission sources and directly from air. Herein, we show that the metal-organic framework Zn(fba) (fba2- = 4,4'-(hexafluoroisopropylidene)bis-benzoate) displays an equilibrium selectivity for CF4 adsorption over N2 that surpasses those of all water-stable sorbents that have been reported for this separation. Selective adsorption of both CHF3 and CH4 over N2 is also evident, demonstrating a general preference for tetrahedral C1 gases. This selectivity is enabled by adsorption within narrow corrugated channels lined with ligand-based aryl rings, a site within this material that has not previously been realized as being accessible to guests. Analyses of adsorption kinetics and X-ray diffraction data are used to characterize sorption and diffusion of small adsorbates within these channels and strongly implicate rotation of the linker aryl rings as a gate that modulates transport of the C1 gases through a crystallite. Multi-component breakthrough measurements demonstrate that Zn(fba) is able to resolve mixtures of CF4 and N2 under flow-through conditions. Taken together, this work illuminates the dynamic structure of Zn(fba), and also points toward general design principles that can enable large CF4 selectivities in sorbents with more favorable kinetic profiles.

Dual Functional Materials: At the Interface of Catalysis and Separations.

Dual functional materials (DFMs) are a promising approach to increase the energy efficiency of carbon capture and utilization by combining both steps into a single unit operation. In this Perspective, we analyze the challenges and opportunities of integrated carbon capture and utilization (ICCU) via a thermally driven process. We identify three key areas that will facilitate research progress toward industrially viable solutions: (1) selecting appropriate DFM operating conditions; (2) designing and characterizing interfacial site cooperativity for CO2 adsorption and hydrogenation; and (3) establishing standards for rigorous and comprehensive data reporting.

Establishing tungsten carbides as active catalysts for CO2 hydrogenation.

Molybdenum carbides are promising catalysts for the reverse water-gas shift (RWGS) reaction, and we aim to understand if similar performance can be observed across the library of transition metal carbides. Although tungsten and molybdenum carbides exhibit similar catalytic properties for hydrogenation reactions, tungsten carbide has not been thoroughly evaluated for CO2 hydrogenation. We hypothesize that the extreme synthesis conditions necessary for carburizing tungsten can cause sintering, agglomeration, and carbon deposition, leading to difficulty evaluating the intrinsic activity of tungsten carbides. In this work, tungsten is encapsulated in silica to preserve particle size and demonstrate correlations between the active phase composition and RWGS performance.

Potassium-Promoted Molybdenum Carbide as a Highly Active and Selective Catalyst for CO2 Conversion to CO.

The high concentration of CO2 bound in seawater represents a significant opportunity to extract and use this CO2 as a C1 feedstock for synthetic fuels. Using an existing process, CO2 and H2 can be concurrently extracted from seawater and then catalytically reacted to produce synthetic fuel. Hydrogenating CO2 directly into liquid hydrocarbons is exceptionally difficult, but by first identifying a catalyst for selective CO production through the reverse water-gas shift (RWGS) reaction, CO can then be hydrogenated to fuel through Fischer-Tropsch (FT) synthesis. Results of this study demonstrate that potassium-promoted molybdenum carbide supported on γ-Al2 O3 (K-Mo2 C/γ-Al2 O3 ) is a low-cost, stable, and highly selective catalyst for RWGS over a wide range of conversions. These findings are supported by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations.

Identifying Different Types of Catalysts for CO2 Reduction by Ethane through Dry Reforming and Oxidative Dehydrogenation.

The recent shale gas boom combined with the requirement to reduce atmospheric CO2 have created an opportunity for using both raw materials (shale gas and CO2 ) in a single process. Shale gas is primarily made up of methane, but ethane comprises about 10 % and reserves are underutilized. Two routes have been investigated by combining ethane decomposition with CO2 reduction to produce products of higher value. The first reaction is ethane dry reforming which produces synthesis gas (CO+H2 ). The second route is oxidative dehydrogenation which produces ethylene using CO2 as a soft oxidant. The results of this study indicate that the Pt/CeO2 catalyst shows promise for the production of synthesis gas, while Mo2 C-based materials preserve the CC bond of ethane to produce ethylene. These findings are supported by density functional theory (DFT) calculations and X-ray absorption near-edge spectroscopy (XANES) characterization of the catalysts under in situ reaction conditions.

Identifying trends and descriptors for selective CO2 conversion to CO over transition metal carbides.

Catalytic reduction of CO2 requires active, selective and low-cost catalysts. Results of this study show that transition metal carbides are a class of promising catalysts and their activity is correlated with oxygen binding energy and reducibility as shown by DFT calculations and in situ measurements.

Molybdenum carbide as alternative catalysts to precious metals for highly selective reduction of CO2 to CO.

Rising atmospheric CO2 is expected to have negative effects on the global environment from its role in climate change and ocean acidification. Utilizing CO2 as a feedstock to make valuable chemicals is potentially more desirable than sequestration. A substantial reduction of CO2 levels requires a large-scale CO2 catalytic conversion process, which in turn requires the discovery of low-cost catalysts. Results from the current study demonstrate the feasibility of using the non-precious metal material molybdenum carbide (Mo2C) as an active and selective catalyst for CO2 conversion by H2.

Ex vivo characterization of particle transport in mucus secretions coating freshly excised mucosal tissues.

Sustained drug delivery to mucosal surfaces has the potential to improve the effectiveness of prophylactic and therapeutic treatments for numerous diseases and conditions, including inflammatory bowel disease, sexually transmitted diseases, cystic fibrosis, glaucoma, dry eye, and various cancers. Sustained delivery systems such as nanoparticles can be useful for mucosal delivery, but recent work suggests they must penetrate the rapidly cleared mucus barrier that overlies all mucosal epithelia to achieve uniform distribution on epithelial surfaces and enhanced residence time. Thus, it is important to evaluate the mucus-penetrating ability of nanosized delivery systems in preclinical animal studies, and for administration to humans. We describe a simple ex vivo method to visualize and quantify nanoparticle transport in mucus on fresh mucosal tissues. Using this method in murine models, we observed variations in the mucus mesh at different anatomical locations, as well as cyclical variations that may have implications for mucosal delivery.

ZK-5: a CO2-selective zeolite with high working capacity at ambient temperature and pressure.

The increased carbon dioxide concentration in the atmosphere caused by combustion of fossil fuels has been a leading contributor to global climate change. The adsorption-driven pressure or vacuum swing (PSA/VSA) processes are promising as affordable means for the capture and separation of CO2. Herein, an 8-membered-ring zeolite ZK-5 (Framework Type Code: KFI) exchanged with different cations (H⁺, Li⁺, Na⁺, K⁺, Mg²âº, Ca²âº) was synthesized as novel CO2 adsorbent. The samples were characterized by SEM, energy-dispersive X-ray spectroscopy (EDAX), XRD, and gas adsorption (CO2 and N2). The Toth adsorption model was used to describe the CO2 adsorption isotherms, and the isosteric heats of adsorption were calculated. CO2 capture adsorbent evaluation criteria such as working capacity, regenerability and CO2/N2 selectivity were applied to evaluate the zeolite adsorbents for PSA/VSA applications. The in situ FTIR CO2 adsorption spectra show that physisorption accounts for the largest fraction of the total CO2 adsorbed. The CO2 adsorption analysis shows that Mg-ZK-5 is the most promising adsorbent for PSA applications with the highest working capacity (ΔN(CO2)=2.05 mmol g⁻¹), excellent selectivity (α(CO2/N2)=121), and low isosteric heat. Li-, Na- and K-ZK-5 with good working capacity (ΔN(CO2)=1.55-2.16 mmol g⁻¹) and excellent selectivity (α(CO2/N2)=103-128) are promising CO2 adsorbents for the VSA working region.