MOF-808(Hf) with grafted trialkylphosphines loaded with Pd catalyses Suzuki–Miyaura coupling of functionalised aryl boronic acids with aryl chlorides and demanding cross-couplings of electron-deficient nucleophiles.

The preparation of pure Ar from air requires removal of O2 from a crude Ar stream produced by cryogenic distillation. Whereas their similar boiling points make further separation by distillation expensive, the difference in their molecular sizes makes separation by flexible zeolites an attractive route to kinetic separation. Modifying the cation content of the flexible and cubic zeolite Rho enables precise tuning of a single window size for unprecedented kinetic separation of O2 from Ar. Li-Rho (unit cell Li9.8Al9.8Si38.2O96) is a very selective adsorbent due to its small pore size, but the highly distorted framework results in very slow O2 diffusion. By replacing some of the Li+ with H+, Cs+, or Zn2+, the window can be enlarged and in some cases the window cation occupancy reduced, increasing O2 diffusion rates whilst retaining high O2/Ar selectivity. The optimum unit cell composition among those examined was found to be Li6.2Zn1.8-Rho (O2/Ar selectivity = 813, D/r2(O2) = 0.37 s-1).

Microporous AlPO 4 STA-1 has been synthesised and studied by NMR crystallography; it is an effective catalyst for the Beckmann rearrangement of cyclohexanone oxime.

Mixed matrix membranes (MMMs) combine the high separation performance of porous materials with the processibility of polymers and so possess potential for carbon capture from CO2-containing gas streams. Zeolitic imidazolate frameworks (ZIFs) are promising candidates as molecular-sieve fillers in MMMs due to their tunability and ease of synthesis. We have compared four ZIFs, all as nanoparticles of similar sizes (ca. 400 nm), as MMM fillers, to investigate the effects of ZIF structure and chemistry on MMM performance of pure gas (CO2, N-2) permeation under the same conditions. The chosen ZIFs include two that exhibit strong CO2 adsorption (hybrid ZIF-7/COK-17 and ZIF-94) and two that have higher pore volumes but weaker CO2 interactions (ZIF-8 and a hybrid ZIF-11/ZIF-71). The hybrid ZIF-7/COK-17 and ZIF-94 are structurally related to ZIF-7 (rhombohedral sod topology) and ZIF-8 (cubic sod), respectively, via partial or complete substitution of benzimidazole or 2-methylimidazole by 4,5-dichloroimidazole or 4-methyl-5-imidazolecarboxaldehyde, while the hybrid ZIF-11/ZIF-71 has the rho topology but the same composition as the ZIF-7/COK-17 hybrid. In the first part of the comparative study, MMMs based on two types of commercial polymers, Matrimid (R) 5218 and PEBAX-MH1657, were prepared containing the ZIF-7/COK-17 hybrid and also with ZIF-94. ZIF-94 shows much better compatibility with the polymers, forming homogeneous dispersions at all loadings attempted (<= 35 % wt%) whereas the hybrid shows inhomogeneity above 12 wt% in each case. At 12 wt% loading, both fillers show an increase in CO2 permeability at 1.2 bar and 293 K compared to the pure membrane (in PEBAX, this increases from 49.5 to 60 and 68 Barrer) which is the result of increased solubility compensating for decreased diffusivity, and this improvement in permeability continues to increase at the higher levels of loading possible with ZIF-94. ZIF-7/COK-17 in PEBAX show higher selectivity, achieving a calculated CO2/N-2 selectivity up to 70. Further investigation of CO2 and N-2 permeation on MMMs with the four ZIFs at 12 wt% in PEBAX-MH1657 showed a clear distinction between the ZIF-94 and ZIF-7/COK-17 MMMs (which show higher membrane solubilities but lower diffusivities) compared to ZIF-8 and ZIF-11/ZIF-71 MMMs. At the loading chosen, the CO2 permeability increase achieved by the four ZIFs over PEBAX-MH1657 increases in the order ZIF-11/-71, ZIF-7-COK-17 (ca. 60 Barrer) < ZIF-94 (68) < ZIF-8 (81), reflecting the complex interplay between CO2 solubility (increasing with interaction strength) and diffusivity (increasing with available cage and window size). The calculated CO2/N-2 selectivity is highest for the hybrid ZIF-7/COK-17 membrane (70), which is attributed to molecular sieving effects in the rhombohedral sod structure.

This article reviews recent work undertaken at the beamline B22 of the Diamond Light Source using infrared (IR) microspectroscopy to characterise zeolite catalysts and to study their reactivity in real time. The advantage of vibrational microspectroscopic analysis when linked to the brightness and spectral bandwidth of synchrotron IR light are illustrated. The high spatial resolution means that the uniformity of acid site concentrations within individual large crystals of zeolites and between different crystals can be readily checked and changes to acid site concentrations within crystals resulting from steam treatment mapped. When an in situ reaction cell is coupled with mass spectrometric analysis of evolved gases the rapid time response of the method has provided new insight into the initial stages of the conversion of methanol to hydrocarbons over ZSM-5 and SAPO-34 single crystals. Future prospects for applying the method to other types of zeolite catalysed reactions with improved reaction cell design are also discussed.

CALF-20, [Zn2(1,2,4-triazolate)2(oxalate)] shows remarkable performance in post-combustion carbon capture, even under humid conditions1 but its reported crystal morphology hinders its applicability in mixed matrix membranes (MMMs). Here, a route to its preparation as platelets a few tens of nm thick is reported. These were incorporated into a PEBAX MH1567 polymer matrix and the resultant MMMs display improvement in CO2 permeability and CO2/N2 selectivity.

This article reviews recent work undertaken at the beamline B22 of the Diamond Light Source using infrared (IR) microspectroscopy to characterise zeolite catalysts and to study their reactivity in real time. The advantage of vibrational microspectroscopic analysis when linked to the brightness and spectral bandwidth of synchrotron IR light are illustrated. The high spatial resolution means that the uniformity of acid site concentrations within individual large crystals of zeolites and between different crystals can be readily checked and changes to acid site concentrations within crystals resulting from steam treatment mapped. When an in situ reaction cell is coupled with mass spectrometric analysis of evolved gases the rapid time response of the method has provided new insight into the initial stages of the conversion of methanol to hydrocarbons over ZSM-5 and SAPO-34 single crystals. Future prospects for applying the method to other types of zeolite catalysed reactions with improved reaction cell design are also discussed.

An understanding of the CO 2 adsorption mechanisms on small-pore zeolites is of practical importance in the development of more efficient adsorbents for the separation of CO 2 from N 2 or CH 4 . Here we report that the CO 2 isotherms at 25–75 °C on cesium-exchanged phillipsite zeolite with a Si/Al ratio of 2.5 (Cs-PHI-2.5) are characterized by a rectilinear step shape: limited uptake at low CO 2 pressure (P CO2 ) is followed by highly cooperative uptake at a critical pressure, above which adsorption rapidly approaches capacity (2.0 mmol g −1 ). Structural analysis reveals that this isotherm behavior is attributed to the high concentration and large size of Cs + ions in dehydrated Cs-PHI-2.5. This results in Cs + cation crowding and subsequent dispersal at a critical loading of CO 2 , which allows the PHI framework to relax to its wide pore form and enables its pores to fill with CO 2 over a very narrow range of P CO2 . Such a highly cooperative phenomenon has not been observed for other zeolites.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTThe Complex Interplay of Separations, Reactions and Storage in Pursuit of Carbon Neutrality: A Central Role for NanomaterialsChristopher W. Jones*Christopher W. JonesGeorgia Institute of TechnologyMore by Christopher W. Joneshttps://orcid.org/0000-0003-3255-5791, Ah-Hyung Alissa ParkAh-Hyung Alissa ParkColumbia UniversityMore by Ah-Hyung Alissa Parkhttps://orcid.org/0000-0002-6482-3589, and Paul WrightPaul WrightUniversity of St. AndrewsMore by Paul Wrighthttps://orcid.org/0000-0002-4243-9957Cite this: Acc. Chem. Res. 2023, 56, 24, 3545–3546Publication Date (Web):December 19, 2023Publication History Received15 November 2023Published online19 December 2023Published inissue 19 December 2023https://pubs.acs.org/doi/10.1021/acs.accounts.3c00720https://doi.org/10.1021/acs.accounts.3c00720editorialACS PublicationsCopyright © Published 2023 by American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views835Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (1002 KB) Get e-AlertscloseSUBJECTS:Carbon capture and storage,Energy,Materials,Nanomaterials,Separation science Get e-Alerts

The SWY-type aluminosilicate zeolite, STA-30, has been synthesized via different routes to understand its defect chemistry and solid acidity. The synthetic parameters varied were the gel aging, the Al source, and the organic structure directing agent. All syntheses give crystalline materials with similar Si/Al ratios (6-7) that are stable in the activated K,H-form and closely similar by powder X-ray diffraction. However, they exhibit major differences in the crystal morphology and in their intracrystalline porosity and silanol concentrations. The diDABCO-C82+ (1,1'-(octane-1,8-diyl)bis(1,4-diazabicyclo[2.2.2]octan)-1-ium)-templated STA-30 samples (but not those templated by bisquinuclidinium octane, diQuin-C82+) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 Å) that connect with the characteristic swy and gme cages of the SWY structure. This results in pore volumes up to 30% greater than those measured in activated diQuin-C8_STA-30 as well as higher concentrations of silanols and fewer Brønsted acid sites (BASs). The hierarchical porosity is demonstrated by isopentane adsorption and the FTIR of adsorbed pyridine, which shows that up to 77% of the BASs are accessible (remarkable for a zeolite that has a small-pore crystal structure). A structural model of single can/d6r column vacancies is proposed for the extra-large micropores, which is revealed unambiguously by high-resolution scanning transmission electron microscopy. STA-30 can therefore be prepared as a hierarchically porous zeolite via direct synthesis. The additional noncrystallographic porosity and, subsequently, the amount of SiOHs in the zeolites can be enhanced or strongly reduced by the choice of crystallization conditions.

High silica zeolite ZK-5 (framework Si/Al=4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co-templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite framework - alkali metal cation - nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X-ray powder diffraction. Ammonium exchange gives ZK-5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK-5.

In situ synchrotron infrared microspectroscopy on single crystals of SAPO-34 reveals that a carbene insertion mechanism is responsible for the first carbon–carbon bond formation from surface methoxy groups.

Mixed-linker zeolitic imidazolate frameworks (ZIFs) with the sodalite (sod) topology type and based on ZIF-7 have been prepared by direct synthesis from the mixtures of benzimidazole (BzIm) and 4,5-dichloroimidazole (dcIm). Incorporation of dcIm into the ZIF-7 structure gives ZIF-7/COK-17 hybrids with rhombohedral symmetry that do not show the "open-to-closed form" structural transition upon solvent removal exhibited by ZIF-7. They show Type I isotherms for low molecular weight gases and high affinity for CO2 even at low partial pressures. Synthesis under mild conditions gives ZIF nanoparticles (250-400 nm) suitable for incorporation into mixed matrix membranes (MMMs): these were prepared with both glassy (Matrimid) and rubbery (PEBAX 1657) polymers. Permeation tests at 298 K and 1.2 bar reveal that the incorporation of Zn(BzIm0.55dcIm0.45)2 nanoparticles at up to ca. 12 wt % gives defect-free membranes with enhanced CO2 permeability in both polymer matrices, with retention of selectivity (Matrimid) or with an enhancement in selectivity that is most pronounced for the smaller nanoparticles (PEBAX). The membrane with the best performance exhibits a selectivity of ca. 200 for CO2/N2 (a 4-fold increase compared to the pure polymer) and a CO2 permeability of 64 Barrer. At the relatively low loadings investigated, the MMMs' performance obeys the Maxwell model, and the intrinsic property of diffusivity of the ZIFs can be extracted as a result.

Guest-mediated pore-shape modification of the metal-organic framework, Sc2BDC3 upon adsorption of n-pentane and isopentane is examined from 50-1200 bar. Rotation of the BDC linker responsible for the change in pore shape occurs at much lower pressures than previously reported, with distinct adsorption behaviour observed between pentane isomers.

Small pore zeolites that show framework flexibility, such as merlinoite (topology type MER), possess a high potential for the selective adsorption of small gas molecules including CO2. The CO2 adsorption properties of Na-, K-, and Cs-exchanged forms of a merlinoite zeolite with Si/Al = 4.2 have been measured at 298 K, and in situ PXRD was used to follow their structural response to dehydration and CO2 uptake. The Na- and Cs-forms convert from a wide-pore to a narrow-pore form upon dehydration, while the K-form remains in the wide-pore form. The Na- and Cs-forms exhibit stepped CO2 adsorption isotherms, consistent with breathing behavior and expansion from narrow- to wide-pore phases, while K-6.2-MER remains in the wide-pore structure throughout. Synchrotron PXRD of the K- and Cs-forms reveals the effects of CO2 adsorption on the cation site distributions and the framework configuration. All cation forms of MER (4.2) show enhanced adsorption kinetics for Ar compared to those with lower Si/Al, and the wide-pore structure of K-6.2-MER (4.2) shows particularly rapid sorption for both Ar and CO2. Breakthrough curves over K-6.2-MER (4.2) demonstrate good separation of CO2 from CH4 in flowing CO2/CH4 mixtures, even in pelletized form with an alumina binder.

Small-pore aluminosilicate zeolites are attractive targets for synthesis because of their activity as catalysts in important reactions, including ammonia-mediated selective catalytic reduction (SCR) of NOx in auto-exhaust emissions. Such a zeolite with SWY framework type, previously observed as a silicoaluminophosphate, has been prepared with high crystallinity via designed syntheses employing organic 1,8-(1,4-diazabicyclo[2.2.2]octane)octyl (diDABCO-C8) and K+ cations as templates. STA-30 (St Andrews microporous material 30) is an ABC-6 structure in the erionite-offretite family of zeolites that exhibits the 12-layer stacking sequence AABAABAACAAC. The framework, which can be prepared with a controllable Si/Al ratio, possesses columns of alternating d6r units and can cages, of which the latter are oriented to give an inter-column pore space comprising gme cages and swy cages connected via 8Rs. DiDABCO-C8 cations fill the swy cages of as-prepared STA-30, while K+ cations display high occupancy in the can cages. Removal of the template by calcination, followed by ammonium ion exchange of K+ cations residing outside the can cages and subsequent deammoniation, gives a highly crystalline zeolite (K3H6Al9Si72O144, P6(3)/ mmc, a = 12.9922(9) angstrom, c = 29.9624(12) angstrom) with solid acidity shown by solid-state H-1 MAS NMR. Upon hydration, a portion of the Al adopts octahedral geometry, as demonstrated by two sharp resonances at -2.0 and -3.1 ppm in the Al-27 MAS NMR. These octahedral species can be converted back to tetrahedral Al by ammonium exchange and are interpreted as distinct hydrated framework Al sites. The activated K,H-STA-30 is a small-pore solid acid with a three-dimensionally connected micropore volume of 0.31 cm(3) g(-1). In the copper-loaded form, it is an active catalyst for the SCR of NO by ammonia.

MIL-142(Sc) is prepared and the limits of the isoreticular substitution of each linker type are explored and characterised by single-crystal XRD.