Heterogeneous catalysis plays a pivotal role in the current chemical and energy vectors production. Notably, to fully utilize the intrinsic activity and selectivity of a catalyst, the chemical reactor has to be designed and operated optimally to achieve enhanced heat/mass transfer, well-defined contact time of reactants, uniform flow pattern, and high permeability. Structured catalysts are a promising strategy to overcome the major drawbacks encountered in the traditional packed-bed reactor technology due to the improved hydrodynamics in combination with enhanced heat/mass transfer. Newly emerged fiber/foam-substrates, with an entirely open 3D network structure, bring distinct advantages over the honeycomb and micro-channel contacting methods, including free radial diffusion, eddy-mixing driven heat/mass transfer, large area-to-volume ratio, and high contacting efficiency. However, how to place the nanocatalysts onto the fiber/foam-substrates is a challenging problem because the commercial washcoating method has great limitations such as the nonuniformity and easy exfoliation of coatings. This review discusses the newly developed non-dip-coating methods for the fiber/foam-structured catalysts and their promising applications in the strongly exo-/endo-thermic and/or high throughput reaction processes.

Metal–organic frameworks (MOFs) are superior sorbents for water adsorption-based applications. The unique step-like water isotherm at a MOF-specific relative pressure allows easy loading and regeneration over a small range of temperature and pressure conditions. With good hydrothermal stability and cyclic durability, it stands out over classical sorbents used in applications for humidity control, water harvesting, and adsorption-based heating and cooling. These are easily regenerated at moderate temperatures using “waste” heat or solar heating. The isotherm thermodynamics and adsorption mechanisms are described, and the presence of MOFs in the water–air system is explained. Based on six selection criteria ≈40 reported MOFs and one COF are identified for potential application. Trends and approaches in further synthesis optimization and production scale-up are highlighted. No-MOF-fits-all, each MOF has its own specific step location matching only with a certain application type. Most applications are technically feasible and demonstrated on the bench-scale or small pilot. Their maturity is benchmarked by their technology readiness level. Retrofitting existing applications with MOFs replacing classical desiccants may lead to rapid demonstration. Studies on techno-economic analysis and life cycle analysis are required for a rational evaluation of the feasibility of promising applications.

High performance and commercially attractive mixed-matrix membranes were developed for H₂/CO₂ separation via a scalable hollow fiber spinning process. Thin (~300 nm) and defect-free selective layers were successfully created with a uniform distribution of the nanosized (~60 nm) zeolitic-imidazole framework (ZIF-8) filler within the polymer (polybenzimidazole, PBI) matrix. These membranes were able to operate at high temperature (150 °C) and pressure (up to 30 bar) process conditions required in treatment of pre-combustion and syngas process gas streams. Compared with neat PBI hollow fibers, filler incorporation into the polymer matrix leads to a strong increase in H₂ permeance from 65 GPU to 107 GPU at 150 °C and 7 bar, while the ideal H₂/CO₂ selectivity remained constant at 18. For mixed gas permeation, there is competition between H₂ and CO₂ transport inside ZIF-8 structure. Adsorption of CO₂ in the nanocavities of the filler suppresses the transport of the faster permeating H₂ and consequently decreases the H₂ permeance with total feed pressure down to values equal to the pure PBI hollow fibers for the end pressure of 30 bar. Therefore, the improvement of fiber performance for gas separation with filler addition is compromised at high operating feed pressures, which emphasizes the importance of membrane evaluation under relevant process conditions.

The electrochemical reduction of CO₂ holds great promise for lowering the concentration of CO₂ in the Earth′s atmosphere. However, several challenges have hindered the commercialization of this technology, including energy efficiency, the solubility of CO₂ in the aqueous phase, and electrode stability. In this Minireview, we highlight and summarize the main advantages and limitations that metal–organic frameworks (MOFs) may offer in this field of research, either when used directly as electrocatalysts or when used as catalyst precursors.

The elimination of the additional defect healing post‐treatment step in asymmetric hollow fiber manufacturing would result in a significant reduction in membrane production cost. However, obtaining integrally skinned polymeric asymmetric hollow fiber membranes with an ultrathin and defect‐free selective layer is quite challenging. In this study, P84® asymmetric hollow fiber membranes with a highly thin (~56 nm) defect‐free skin were successfully fabricated by fine tuning the dope composition and spinning parameters using volatile additive (tetrahydrofuran, THF) as key parameters. An extensive experimental and theoretical study of the influence of volatile THF addition on the solubility parameter of the N‐methylpyrrolidone/THF solvent mixture was performed. Although THF itself is not a solvent for P84®, in a mixture with a good solvent for the polymer, like N‐Methyl‐2‐pyrrolidone (NMP), it can be dissolved at high THF concentrations (NMP/THF ratio > 0.52). The as‐spun fibers had a reproducible ideal CO2/N2 selectivity of 40, and a CO2 permeance of 23 GPU at 35 °C. The fiber production can be scaled‐up with retention of the selectivity.

Clathrates are well-known compounds whose low thermal stability makes them extremely rare and appreciated. Although their formation mechanism is still surrounded by many uncertainties, these ice-like structures have the potential to be an alternative for transport and storage of different gases, especially methane. For the formation of methane clathrates extreme pressure conditions and a narrow temperature window are needed. Microporous materials have been proposed to provide nucleation sites that, theoretically, promote clathrate formation at milder conditions. While activated carbons and Metal-Organic Frameworks (MOFs) have already been studied, very little is known about the role of zeolites in this field. In this work, we study the formation of methane clathrates in the presence of RHO zeolite. Experimental results based on adsorption and operando synchrotron X-Ray diffraction demonstrate the formation of clathrates at the surface of the zeolite crystals and reveal mechanistic aspects of this formation at mild conditions.

Xe is only produced by cryogenic distillation of air, and its availability is limited by the extremely low abundance. Therefore, Xe recovery after usage is the only way to guarantee sufficient supply and broad application. Herein we demonstrate DD3R zeolite as a benchmark membrane material for CO₂/Xe separation. The CO₂ permeance after an optimized membrane synthesis is one order magnitude higher than for conventional membranes and is less susceptible to water vapour. The overall membrane performance is dominated by diffusivity selectivity of CO₂ over Xe in DD3R zeolite membranes, whereby rigidity of the zeolite structure plays a key role. For relevant anaesthetic composition (<5 % CO₂) and condition (humid), CO₂ permeance and CO₂/Xe selectivity stabilized at 2.0×10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and 67, respectively, during long-term operation (>320 h). This endows DD3R zeolite membranes great potential for on-stream CO₂ removal from the Xe-based closed-circuit anesthesia system. The large cost reduction of up to 4 orders of magnitude by membrane Xe-recycling (>99+%) allows the use of the precious Xe as anaesthetics gas a viable general option in surgery.

Pre-combustion CO₂ capture is regarded as a promising option to mitigate the environmental pollution from coal combustion, due to its relatively low energy duty and prospects for the use of hydrogen in power generation and industrial sectors. Nowadays, research and development efforts are mainly focusing on advanced technologies to separate H₂ and CO₂ from a synthesis gas of a gasification-based power generation system. In this regard, membrane separation processes are attracting an increasing attention, due to their potential for a more cost-effective and environmental friendly CO₂ capture compared to well-established solvent-based processes. A conceptual design and techno-economic analysis is presented of a pre-combustion CO₂ capture process based on H₂-selective polymeric membranes in an integrated gasification combined cycle (IGCC) power plant, including the water-gas-shift (WGS) system. The design approach is based on the selection of the most effective membrane separation process and economic optimization of operating conditions. The capture process is based on a three-stage membrane separation system, producing a hydrogen stream feeding the power generation unit and a liquid CO₂ stream, ready for transport and geological storage. Considering a state-of-the-art polymeric membrane with a H₂ to CO₂ selectivity of 15 and H₂ permeance of 300 GPU, the IGCC efficiency penalty states at around 5% pts when the separation process is operated with a pressure on membrane feed side of 70 bar, corresponding to an estimated cost of CO₂ capture of 16.6 €/t CO₂. A sensitivity analysis of operating pressure and membrane properties revealed that the cost of CO₂ capture can be reduced to less than 15 €/t CO₂ by moderately increasing the H₂ to CO₂ selectivity and adjusting the designed process accordingly. Additionally, a decrease in the feed-side pressure slightly disfavours the economic performance of CO₂ capture for H₂ permeances greater than 300 GPU. The membrane-based capture process compared most favourably in cost-effectiveness with the well-established solvent based Selexol process.

The performance of mixed-matrix membranes (MMMs) based on Matrimid^® and benzimidazole-linked polymers (BILPs) have been investigated for the separation CO₂/N₂ and the dependency on the filler porosity. BILPs with two different porosities (BILP-101 and RT-BILP-101) were synthesized through controlling the initial polymerization rate and further characterized by several techniques (DRIFTs, ¹³C CP/MAS NMR, SEM, TEM, N₂ and CO₂ adsorption). To investigate the influence of porosity, the two types of fillers were incorporated into Matrimid^® to prepare MMMs at varied loadings (8, 16 and 24 wt%). SEM confirmed that both BILP-101 and RT-BILP-101 are well dispered, indicating their good compatibility with the polymeric matrix. The partial pore blockage in the membrane was verified by CO₂ adsorption isotherms on the prepared membranes. In the separation of CO₂ from a 15:85 CO₂:N₂ mixture at 308 K, the incorporation of both BILPs fillers resulted in an enhancement in gas permeability together with constant selectivity owing to the fast transport pathways introduced by the porous network. It was noteworthy that the initial porosity of the filler had a large impact in separation permeability. The best improvement was achieved by 24 wt% RT-BILP-101 MMMs, for which the CO₂ permeability increases up to 2.8-fold (from 9.6 to 27 Barrer) compared to the bare Matrimid^®.

Membrane separation for gas purification is an energy-efficient and environment-friendly technology. However, the development of high performance membranes is still a great challenge. In principle, mixed matrix membranes (MMMs) have the potential to overcome current materials limitations, but in practice there is no straightforward method to match the properties of fillers and polymers (the main components of MMMs) in such a way that the final membrane performance reflects the high performance of the microporous filler and the processability of the continuous polymer phase. This issue is especially important when high flux polymers are utilized. In this work, we demonstrate that the use of small amounts of a glassy polymer in combination with high performance PIM-1 allow for the preparation of metal–organic framework (MOF)-based MMMs with superior separation properties and low aging rates under humid conditions, meeting the commercial target for post-combustion CO₂ capture.

The use of an azine-linked covalent organic framework (ACOF-1) as filler in mixed-matrix membranes (MMMs) has been studied for the separation of CO₂ from N₂. To better understand the mechanisms that govern separation in complex composites, MMMs were prepared with different loadings of ACOF-1 and three different polymers as continuous phase: low flux-mid selectivity Matrimid^®, mid flux-high selectivity Polyactive™ and high flux-low selectivity 6FDA:DAM. The homogeneous distribution of ACOF-1 together with the good adhesion between the ACOF-1 particles and the polymer matrices were confirmed by scanning electron microscopy. In mixed-gas CO₂/N₂ separation a clear influence of the polymer used was observed on the performance of the composite membranes. While for Matrimid^® and 6FDA:DAM an overall enhancement of the polymer's separation properties could be achieved, in case of Polyactive™ penetration of the more flexible polymer into the COF porosity resulted in a decreased membrane permeability. The best improvement was obtained for Matrimid^®-based MMMs, for which a selectivity increase from 29 to 35, together with an enhancement in permeability from 9.5 to 17.7 Barrer for 16 wt% COF loading, was observed. Our results demonstrate that the combination of the filler-polymeric matrix pair chosen is crucial. For a given filler the polymer performance improvement strongly depends on the polymeric matrix selected, where a good match between the discontinuous and continuous phase, both in the terms of compatibility and gas separation properties, is necessary to optimize membrane performance.

A quasi chemical vapor deposition method for the manufacture of well-defined covalent triazine framework (CTF) coatings on cordierite monoliths is reported. The resulting supported porous organic polymer is an excellent support for the immobilization of two different homogeneous catalysts: (1) an Ir^IIICp∗-based catalyst for the hydrogen production from formic acid and (2) a Pt^II-based catalyst for the direct activation of methane via Periana chemistry. The immobilized catalysts display a much higher activity in comparison with the unsupported CTF operated in slurry because of improved mass transport. Our results demonstrate that CTF-based catalysts can be further optimized by engineering at different length scales.

A microporous Al trimesate-based metal-organic framework (MOF), denoted MIL-96-(Al), was selected as a porous hybrid filler for the processing of mixed matrix membranes (MMMs) for CO₂/N₂ postcombustion separation. First, the structural model of MIL-96-(Al) initially reported was revisited using a combination of synchrotron-based single-crystal X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and density functional theory (DFT) calculations. In a second step, pure MIL-96-(Al) crystals differing by their size and aspect ratio, including anisotropic hexagonal platelets and nanoparticles of about 70 nm in diameter, were prepared. Then, a combination of in situ IR spectroscopy, single-gas, and CO₂/N₂ coadsorption experiments, calorimetry, and molecular simulations revealed that MIL-96-(Al) nanoparticles show a relatively high CO₂ affinity over N₂ owing to strong interactions between CO₂ molecules and several adsorption sites such as Al³⁺ Lewis centers, coordinated water, and hydroxyl groups. Finally, the high compatibility between MIL-96-(Al) nanoparticles and the 6FDA-DAM polymer allowed the processing of homogeneous and defect-free MMMs with a high MOF loading (up to 25 wt %) that outperform pure polymer membranes for CO₂/N₂ separation.

Mixed-matrix membranes comprising NH₂-MIL-53(Al) and Matrimid or 6FDA-DAM have been investigated. The metal organic framework (MOF) loading has been varied between 5 and 20 wt%, while NH₂-MIL-53(Al) with three different morphologies, nanoparticles, nanorods, and microneedles has been dispersed in Matrimid. The synthesized membranes have been tested in the separation of CO₂ from CH₄ in an equimolar mixture. At 3 bar and 298 K for 8 wt% MOF loading, incorporation of NH₂-MIL-53(Al) nanoparticles leads to the largest improvement compared to nanorods and microneedles. The incorporation of the best performing filler, i.e., NH₂-MIL-53(Al) nanoparticles, into the highly permeable 6FDA-DAM has a larger effect, and the CO₂ permeability increases up to 85% with slightly lower selectivities for 20 wt% MOF loading. Specifically, these membranes have a permeability of 660 Barrer with a CO₂/CH₄ separation factor of 28, leading to a performance very close to the Robeson limit of 2008. Furthermore, a new non-destructive technique based on Raman spectroscopy mapping is introduced to assess the homogeneity of the filler dispersion in the polymer matrix. The MOF contribution can be calculated by modeling the spectra. The determined homogeneity of the MOF filler distribution in the polymer is confirmed by focused ion beam scanning electron microscopy analysis.

A systematic study of the effect of physicochemical properties affecting catalyst deactivation, overall olefin selectivity and ethylene/propylene ratio during the methanol-to-olefins (MTO) reaction is presented for two zeolites with the DDR topology, namely Sigma-1 and ZSM-58. Both catalysts show high selectivity towards light olefins and completely suppress the formation of hydrocarbons bigger than C4, with selectivity to ethane not exceeding 1% and some traces of propane. By applying seeded growth approach, a series of Sigma-1 zeolites with tunable crystal size and acidity was synthesized. For this series the highest methanol throughput at 450 °C before deactivation was found for crystals 0.5 μm in size with an acidity corresponding to 0.5 Al atoms per zeolite cage, and a selectivity to ethylene and propylene reaching 90%. Comparison between ZSM-58 and Sigma-1 catalysts with similar morphologies and acidity under the same reaction conditions revealed a three times higher throughput of methanol in case of ZSM-58. The analysis of functional surface groups, assessed through FT-IR, revealed the presence of silanol defects in Sigma-1 responsible for faster catalyst deactivation. These silanol defects can be selectively removed (confirmed by FT-IR) from the zeolite framework by applying a mild treatment in presence of NaOH/CTAB, leading to an improved catalyst lifetime. Co-feeding experiments with short olefins and water show low reactivity of primary MTO products, which only react at the surface of the catalyst particles. These results demonstrate that migration of the reaction zone in case of DDR catalysts hardly affects catalyst stability, product composition and nature of deactivating species. The nature of these species depends mostly on reaction temperature: at low temperatures deactivation occurs mainly due to the formation of inert adamantane species, while at high temperatures poly-condensed aromatic hydrocarbons play the major role in deactivation.