H2 CO2 Research Articles

Constructing the highly efficient Ni/ZrO2/SiO2 catalyst by a combustion-impregnation method for low-temperature CO2 methanation

CO2 methanation is conducive to the storage of renewable electricity and the utilization of CO2. Exploiting highly efficient Ni-based catalysts with a simple method is of significance for this reaction. To achieve an excellent low-temperature activity, the attention is focused on the small Ni particles and ZrO2 promoter in this work, which can increase the amounts of H2 and CO2 active sites. Firstly, the simple combustion-impregnation method was employed, forming small Ni particles (about 6 nm). More metal-support interface and increased basicity could be generated in the meantime. Hence, the higher H2 dissociation and CO2 adsorption ability were attained. Secondly, ZrO2 serving as a promoter was beneficial to the formation of oxygen vacancies, which played an important role in CO2 activation and CH4 formation. These oxygen vacancies could weaken the CO bonds, improving the CO2 activation. In addition, they might serve as the H reservoir, increasing the H2 adsorption capacity. Because of the H spillover effect from Ni to ZrO2, the activated H atoms on Ni could react with activated CO2 to generate CH4. Therefore, with more active sites for H2 and CO2 activation, the Ni/ZrO2-COM catalyst exhibited the excellent catalytic performance at 300 °C. This work is of great significance in developing highly efficient Ni-based catalysts at low temperatures for CO2 methanation with a facile method.

Pelletized activated carbon-based CO-selective adsorbent with highly oxidation-stable and aggregation-resistant Cu(I) sites

Using Cu(I)-based adsorbent pellets with a high CO selectivity is crucial for efficient CO2 conversion and H2 production. However, their application is hindered by lack of pelletized adsorbents offering high performance and mechanical strength, severe degradation by Cu(I) oxidation under humid conditions, and activity loss due to Cu(I) aggregation at high-temperatures. Herein, these challenges were overcome by developing a Cu(I)-doped pelletized activated carbon (4.26Cu(I)@AC-600A) with highly aggregation-resistant Cu(I) sites that adsorbed 3.06 mmol CO g−1 at 100 kPa (298 K). Its CO adsorption capacity remained 81% after a 12-week exposure to humid air, and was completely recovered by H2 reduction at 473 K. Notably, 4.26Cu(I)@AC-600A had a high CO working capacity of 1.68 mmol g−1 at the pressure swing of 10 to 100 kPa, showing no breakage when tested at 1000 kPa. Breakthrough experiments demonstrated the high performance of 4.26Cu(I)@AC-600A for efficient CO recovery or removal from various H2 sources.

Kinetic-Sieving of Carbon Dioxide from Acetylene through a Novel Sulfonic Ultramicroporous Material.

The engineering and tailoring of porous materials to realize the precise discrimination of CO2 and C2 H2 , with almost identical kinetic diameters, is a challenging task. We herein report the first example of the kinetic-sieving of relatively larger molecule of C2 H2 from CO2 by a novel sulfonic anion-pillared hybrid ultramicroporous materials of ZU-610a. Specifically, ZU-610 constructed from copper(II), isonicotinic acid and 1,2-ethanedisulfonic acid is synthesized and shows the preferential affinity for C2 H2 over CO2 . After the post-synthetic heat treatment of ZU-610, ZU-610a with a contracted aperture is obtained. Interestingly, the C2 H2 -selctive ZU-610 was reversed to the CO2 -selective ZU-610a. High purity C2 H2 (>99.5 %) could be directly obtained from the dynamic breakthrough experiments on an equimolar C2 H2 /CO2 mixture at 298 K. This study provides guidance for the design of adsorbents aimed at separation systems with similar kinetic diameter.

Decomposition of Saccharides and Alcohols in Solution Plasma for Hydrogen Production

Solution plasma or in-liquid plasma, which is generated by gas-phase discharge within bubbles in a solution, is an exciting reaction field for biomass conversion. However, it is not fully elucidated how the solution plasma works to degrade biomass or how biomass is degraded in it. In this study, various saccharides and alcohols, mainly sucrose, were treated in solution plasma using a high-voltage pulse power supply to study the degradation mechanisms. Hydrolysis and gasification were observed in the solution-plasma treatment of sucrose. The former was mainly influenced by the water temperature, and the latter was mainly influenced by the discharge power. Therefore, it was inferred that hydrolysis occurred in the hot-compressed water region around the plasma, and gasification occurred at the interface between the plasma and water. Gasification of saccharides and alcohols produced H2-rich gases, but gasification was faster for high-volatility alcohols and slower for non-volatile saccharides. The formation of H2-rich gas can be attributed to H2 formation by the water–gas shift reaction of CO and direct H2 formation from water, in addition to H2 from the sample.

Does CO2 Oxidize Ni Catalysts? A Quick X-ray Absorption Spectroscopy Answer.

MgAl2O4-supported Ni materials are highly active and cost-effective CO2 conversion catalysts, yet their oxidation by CO2 remains dubious. Herein, NiO/MgAl2O4, prepared via colloidal synthesis (10 wt % Ni) to limit size distribution, or wet impregnation (5, 10, 20, and 40 wt % Ni), and bare, i.e., unsupported, NiO are examined in H2 reduction and CO2 oxidation, using thermal conductivity detector-based measurements and in situ quick X-ray absorption spectroscopy, analyzed via multivariate curve resolution-alternating least-squares. Ni reoxidation does not occur for bare Ni but is observed solely on supported materials. Only samples with the smallest particle sizes get fully reoxidized. The Ni-MgAl2O4 interface, exhibiting metal-support interactions, activates CO2 and channels oxygen into the reduced lattice. Oxygen diffuses inward, away from the interface, oxidizing Ni entirely or partially, depending on the particle size in the applied oxidation time frame. This work provides evidence for Ni oxidation by CO2 and explores the conditions of its occurrence and the importance of metal-support effects.

Plasmonic Hybrid Nanostructures in Photocatalysis: Structures, Mechanisms, and Applications.

(Sun)Light is an abundantly available sustainable source of energy that has been used in catalyzing chemical reactions for several decades now. In particular, studies related to the interaction of light with plasmonic nanostructures have been receiving increased attention. These structures display the unique property of localized surface plasmon resonance, which converts light of a specific wavelength range into hot charge carriers, along with strong local electromagnetic fields, and/or heat, which may all enhance the reaction efficiency in their own way. These unique properties of plasmonic nanoparticles can be conveniently tuned by varying the metal type, size, shape, and dielectric environment, thus prompting a research focus on rationally designed plasmonic hybrid nanostructures. In this review, the term "hybrid" implies nanomaterials that consist of multiple plasmonic or non-plasmonic materials, forming complex configurations in the geometry and/or at the atomic level. We discuss the synthetic techniques and evolution of such hybrid plasmonic nanostructures giving rise to a wide variety of material and geometric configurations. Bimetallic alloys, which result in a new set of opto-physical parameters, are compared with core-shell configurations. For the latter, the use of metal, semiconductor, and polymer shells is reviewed. Also, more complex structures such as Janus and antenna reactor composites are discussed. This review further summarizes the studies exploiting plasmonic hybrids to elucidate the plasmonic-photocatalytic mechanism. Finally, we review the implementation of these plasmonic hybrids in different photocatalytic application domains such as H2 generation, CO2 reduction, water purification, air purification, and disinfection.

Visible-light-driven CO2 reduction and H2 evolution boosted by 1D Cu2O/CuO heterostructures

The CO2 reduction reaction (CO2RR) offers an efficient path to the neutral carbon cycle and clean energy storage. For this reaction, 1D copper oxides (CuxO) are promising photocatalyst since promote an efficient charge transfer, suppress the photocorrosion, and provide active sites for CO2 adsorption. Therefore, in this work, 1D Cu2O/CuO heterostructures were manufactured by thermal oxidation of a copper mesh. This method works at atmospheric pressure, it is scalable, and it has a high yield, in a view of large-scale production. The copper mesh, a 3D metal skeleton, was selected as the substrate due to good light diffusion, low cost, and easy application. The characterization carried out made it possible to identify a homogeneous growth of the 1D Cu2O/CuO nanoneedles, which presented adequate band gaps for their activation with visible light and a stable photocurrent. These properties favored the CO2RR to solar fuels: HCOOH, CH3OH, HCOH, CH4, and CH3CH2OH. Furthermore, the samples exhibited activity for H2 evolution from H2O splitting. In this reaction, the heterostructures suffer photocorrosion of CuO to Cu2O, which competes for the electrons photogenerated during the reaction. However, this phenomenon was effectively suppressed by the addition of the CO2RR products and seawater as sacrificial agents. In general, the productions obtained from both reactions were up to 45% higher than the reference, which was attributed to the efficient transport of charges in the 1D architectures, the affinity for CO2, and its homogeneous exposure.

Defect engineering in polymeric carbon nitride with accordion structure for efficient photocatalytic CO2 reduction and H2 production

Herein, simultaneously adjustable N-vacancy defect containing and C-doped graphitic carbon-nitride nanosheets (g-CN-X) in accordion-like architectural structures have been synthesized through ethanol containing steam process for the first time. The band-gap energy of the g-CN-X could be precisely tuned enhancing visible light absorption up to the whole visible spectrum region. Henceforth, the optimized catalyst (g-CN-10) has demonstrated an impressive hydrogen evolution rate of 27.6 mmol h−1 g−1 which is 16.2 times higher than the bulk-g-CN, with an apparent quantum yield of 9.1 % at 420 nm wavelength. Furthermore, the g-CN-10 has showed CO2 photoreduction yield to CO production rate of 226.1 μmol h-1g−1, about 28.6 times higher than bulk g-CN (7.9 μmol h−1 g−1). Both the performances are distinctly higher than all other previous reports. Theoretical calculations show that the defect sites lead to a more localized charge density distribution and promote photocatalytic active spots, which uplift the light absorption efficiency and improve the transport of charge carriers involved in the photocatalysis, demonstrating the importance of defect engineering to achieve highly efficient and multifunctional photocatalysis.

Collision-Induced infrared absorption and Raman scattering of H2 in supercritical CO2

• The solvation of H 2 in supercritical CO 2 is investigated. • Co-localized infrared/Raman spectroscopic experiments are reported. • A collision induced infrared spectrum of H 2 in supercritical CO 2 is clearly put in evidence. • The effect of the local density fluctuations on the IR and Raman spectra are discussed. In this study, the solvation of H 2 in supercritical CO 2 was investigated by co-localized infrared absorption/Raman scattering spectroscopies. The Fermi dyad and combinations of vibrational modes of CO 2 were detected by Raman and infrared spectroscopy respectively, with increasing intensities according to CO 2 concentrations varying from 1 to 15 mol.L -1 . H 2 rotational bands and vibrons with almost constant intensities were detected by Raman spectroscopy according to a constant H 2 pressure of 3 MPa. In contrast, a collision-induced infrared band of H 2 was reported for the first time in supercritical CO 2 and its intensity was found to be directly proportional to the intensity of the CO 2 bands. In addition, the intensities of the H 2 and CO 2 contributions were found to be sensitive to the local density fluctuations existing near the critical temperature of CO 2 (Tc = 31 °C, Pc = 7.4 MPa).

Ensemble process for producing high-purity H2 via simultaneous in situ H2 extraction and CO2 capture

To produce fuel-cell-grade hydrogen (H 2 ) via fossil fuel reforming processes, an efficient H 2 purification method with a carbon capture unit is necessary. In this study, a sorption-enhanced water-gas shift membrane reactor (SE-WGS-MR) system combining a state-of-the-art MgO-based catalyst, carbon dioxide sorbent, and Pd/Ta membrane is developed to simultaneously capture carbon dioxide and purify H 2 . With the optimal sorption-enhanced configuration (SE-WGS), the carbon monoxide conversion is significantly enhanced to 86.6%, compared with 68.5% using the commercial catalyst only. Coupling of the Pd/Ta membrane with the WGS catalyst (WGS-MR) enable over 95% H 2 recovery, with the production of high-purity H 2 . Eventually, the ensemble of the three processes (SE-WGS-MR) afford 99.99% of carbon monoxide conversion and the extraction of high-purity H 2 with 99.5% recovery. This study demonstrates the potential of the single process integrating the catalytic reaction, adsorptive separation, and membrane purification for the production of H 2 with ultra-high purity and recovery. • Integration of WGS catalyst and CO 2 sorbent with a Pd/Ta membrane is examined • Coupling of the Pd/Ta membrane with the WGS catalyst enables over 95% H 2 recovery • Simultaneous CO 2 capture and H 2 purification shifts the CO conversion to 99.99% • The ensemble of the processes extracts ultra-pure H 2 with over 99.5% recovery Jin et al. propose an effective ensemble process for producing pure H 2 via simultaneous in situ H 2 extraction and CO 2 capture. Integration of MgO-based catalyst and CO 2 sorbent with a Pd/Ta composite membrane shifts the CO conversion to 99.99%, enabling the extraction of pure H 2 with over 99.5% recovery.

Integrated Photothermal Nanoreactors for Efficient Hydrogenation of CO2

To alleviate the energy crisis and global warming, photothermal catalysis is an attractive way to efficiently convert CO2 and renewable H2 into value-added fuels and chemicals. However, the catalytic performance is usually restricted by the trade-off between the dispersity and light absorption property of metal catalysts. Here we demonstrate a simple SiO2-protected metal–organic framework pyrolysis strategy to fabricate a new type of integrated photothermal nanoreactor with a comparatively high metal loading, dispersity, and stability. The core-satellite structured Co@SiO2 exhibits strong sunlight-absorptive ability and excellent catalytic activity in CO2 hydrogenation, which is ascribed to the functional separation of different sizes of Co nanoparticles. Large-sized plasmonic Co nanoparticles are mainly responsible for the light absorption and conversion to heat (nanoheaters), whereas small-sized Co nanoparticles with high intrinsic activities are responsible for the catalysis (nanoreactors). This study provides a new concept for designing efficient photothermal catalytic materials.

Thermodynamic modeling of hydrogen–water systems with gas impurity at various conditions using cubic and PC-SAFT equations of state

Hydrogen (H2) has emerged as a viable solution for energy storage of renewable sources, supplying off-seasonal demand. Hydrogen contamination due to undesired mixing with other fluids during operations is a significant problem. Water contamination is a regular occurrence; therefore, an accurate prediction of H2-water thermodynamics is crucial for the design of efficient storage and water removal processes. In thermodynamic modeling, the Peng–Robinson (PR) and Soave Redlich–Kwong (SRK) equations of state (EoSs) are widely applied. However, both EoSs fail to predict the vapor-liquid equilibrium (VLE) accurately for H2-blend mixtures with or without fine-tuning binary interaction parameters due to the polarity of the components. This work investigates the accuracy of two advanced EoSs: the Schwartzentruber and Renon modified Redlich–Kwong cubic EoS (SR-RK) and perturbed-chain statistical associating fluid theory (SAFT) in predicting VLE and solubility properties of H2 and water. The SR-RK involves the introduction of polar parameters and a volume translation term. The proposed workflow is based on optimizing the binary interaction coefficients using regression against experimental data that cover a wide range of pressure (0.34 to 101.23 MPa), temperature (273.2 to 588.7 K), and H2 mole fraction (0.0004 to 0.9670) values. A flash liberation model is developed to calculate the H2 solubility and water vaporization at different temperature and pressure conditions. The model captures the influence of H2-gas (CO2) impurity on VLE. The results agreed well with the experimental data, demonstrating the model’s capability of predicting the VLE of hydrogen-water mixtures for a broad range of pressures and temperatures. Optimized coefficients of binary interaction parameters for both EoSs are provided. The sensitivity analysis indicates an increase in H2 solubility with temperature and pressure and a decrease in water vaporization. Moreover, the work demonstrates the capability of SR-RK in modeling the influence of gas impurity (i.e., H2–CO2 mixture) on the H2 solubility and water vaporization, indicating a significant influence over a wide range of H2–CO2 mixtures. Increasing the CO2 ratio from 20% to 80% exhibited almost the opposite behavior of H2 solubility compared to the pure hydrogen feed solubility. Finally, the work emphasizes the critical selection of proper EoSs for calculating thermodynamic properties and the solubility of gaseous H2 and water vaporization for the efficient design of H2 storage and fuel cells.

CO2 Electroreduction in Organic Aprotic Solvents: A Mini Review

An annual increase of CO2 concentrations in the atmosphere causes global environmental problems, addressed by systematic research to develop effective technologies for capturing and utilizing carbon dioxide. Electrochemical catalytic reduction is one of the effective directions of CO2 conversion into valuable chemicals and fuels. The electrochemical conversion of CO2 at catalytically active electrodes in aqueous solutions is the most studied. However, the problems of low selectivity for target products and hydrogen evolution are unresolved. Literature sources on CO2 reduction at catalytically active cathodes in nonaqueous mediums, particularly in organic aprotic solvents, are analyzed in this article. Two directions of cathodic reduction of CO2 are considered—nonaqueous organic aprotic solvents and organic aprotic solvents containing water. The current interpretation of the cathodic conversion mechanism of carbon (IV) oxide into CO and organic products and the main factors influencing the rate of CO2 reduction, Faradaic efficiency of conversion products, and the ratio of direct cathodic reduction of CO2 are given. The influence of the nature of organic aprotic solvent is analyzed, including the topography of the catalytically active cathode, values of cathode potential, and temperature. Emphasis is placed on the role of water impurities in reducing CO2 electroreduction overpotentials and the formation of new CO2 conversion products, including formate and H2.

Boosting CO2 hydrogenation efficiency for methanol synthesis over Pd/In2O3/ZrO2 catalysts by crystalline phase effect

The crystalline phases of support have great influence on their surface and structure properties. Therefore, adjusting the crystalline structure of heterogeneous catalysts imposes a significant impact on the catalytic performance. Herein, a suite of Pd/In2O3/ZrO2 catalysts with different crystalline phases of ZrO2 were prepared and evaluated for CO2 hydrogenation to CH3OH using the same amount of metal loading. The activity data showed the distinct superior reactivity of Pd/In2O3/ZrO2 catalyst used mixed monoclinic and tetragonal phases ZrO2(Mix-ZrO2) as support as compared to respective single phase of monoclinic ZrO2(m-ZrO2) and tetragonal ZrO2(t-ZrO2). The catalysts are extensively characterized through BET, XRD, HRTEM, UV–vis, H2-TPR, CO2/H2-TPD and XPS. Combining the characterization results and activity data, the superior activity of Pd/In2O3/Mix-ZrO2 catalyst can be correlated with large particle size of Pd nanoparticles, the concentration of oxygen vacancies, and the abundant medium basic sites, which were essential for activation of H2 and inert CO2 and enhancement of catalytic performance. The best-performing Pd/In2O3/Mix-ZrO2 catalyst exhibited a remarkable reactivity with space time yield (STY) of 0.54 gmethanol·h−1·gcat−1 at 573 K and 5 MPa, and stability without noticeable deactivation after 100 h of time on stream, demonstrating its potential as catalyst used in CH3OH synthesis from CO2 hydrogenation.

Effect of surface properties of Ni-MgO-Al2O3 catalyst for simultaneous H2 production and CO2 utilization using dry reforming of coke oven gas

We designed the customized Ni-MgO-Al2O3 catalyst for the dry reforming of methane (DRM) using coke oven gas (COG). The calcination conditions of the catalysts were systematically controlled to investigate the effect of the surface properties of the catalysts on catalytic performance. The characterization results showed that the physicochemical properties of the catalyst, such as basicity, BET surface area, Ni dispersion, Ni crystallite size, and reducibility varied with the calcination temperature. Considering the gas composition of the COG, the operating conditions were also optimized by calculating thermodynamic equilibrium to maximize the CO yield and minimize carbon deposition. As a result of catalytic evaluations conducted at selected operation conditions, we found that the catalytic activity is strongly affected by the number of Ni active sites correlated with the Ni dispersion and reduction degree. In addition, the basicity of the catalyst played an important role in CO2 adsorption and activation, which is related to coke resistance. Among the prepared catalysts, the Ni-MgO-Al2O3 (calcination temperature = 800 °C) catalyst exhibiting best catalytic performance due to a large number of Ni active sites and relatively good basicity, was selected as the optimal catalyst, and the possibility of commercialization was confirmed through the long-term stability test and start-up/shut-down test.

Selective CO2 deoxygenation to CO in chemically looped reverse water–gas shift using iron-based oxygen carrier

Chemical-looped reverse water–gas shift reaction was investigated using transition metal/metal oxides as oxygen carriers. Iron is identified as the only promising oxygen carrier that shows compelling CO 2 splitting reactivity. A chemically looped reverse water–gas shift reaction was developed using an iron-based oxygen carrier. Compared with conventional catalytic conversion processes, the chemical looping method has the advantage of high selectivity and cheap materials cost due to the separation of CO2 splitting and H2 oxidation half-reactions that are enabled by earth-abundant transition metal oxygen carriers. However, for such process to be economically attractive, the operation temperature should ideally be low enough such that low-grade industrial waste heat can be utilized. In other words, the reactivity of oxygen carriers toward the aforementioned half-reactions is most critical. To address the materials challenge, four transition metal-based oxygen carriers, i.e., iron, nickel, manganese, and copper, are studied using temperature-programmed techniques under H2 and CO2. Iron is identified to be the only oxygen carrier reactive toward CO2 splitting and capable of completing the redox cycle at 450 °C with 100% reverse water–gas shift selectivity. Although the thermal stability of the iron oxygen carriers shows room for improvement, our work demonstrates the great potential of a scalable and economically viable route for CO2 conversion that is compatible with current industrial processes.Graphical abstract

Numerical analysis of turbulent flame enhancement by nanosecond repetitively pulsed plasma discharges

Experimental studies of plasma-assisted combustion have shown that Nanosecond Repetitively Pulsed (NRP) discharges are a very efficient way to improve flame stability in lean regimes. These discharges generate a non-equilibrium plasma that induces a local heating and an important production of active species sufficient to enhance the combustion. The aim of this article is to understand the physical and chemical mechanisms involved in plasma-assisted turbulent combustion. High-performance computations of a lean bluff-body turbulent premixed methane-air flame, experimented at EM2C laboratory, are conducted for that purpose. Simulations are performed by combining a semi-empirical plasma model with an analytical combustion mechanism. Without electrical discharges, only a weak reaction zone behind the bluff body is observed. However, when the flame is assisted with the plasma, the flame power and surface increase significantly. A chemical analysis performed at the flame basis shows that the heat and the radical O produced by NRP discharges induce the dissociation of main burnt gases species H2O and CO2 into radicals OH, H, CO, O and species H2, O2. The species with long lifespan OH, H2 and O2 are convected from the center of the bluff-body recirculation zone to the flame front where they are consumed increasing the chemical reactivity. This causes a local increase of heat release rate that attaches the turbulent flame front which can develop downstream.

Visible-light photocatalytic oxygen production on a high-entropy oxide by multiple-heterojunction introduction

High-entropy oxides (HEOs), as multi-component ceramics with high configurational entropy, have been of recent interest due to their attractive properties including photocatalytic activity for H2 production and CO2 conversion. However, the photocatalytic activity of HEOs is still limited to ultraviolet light. In this study, to achieve visible-light-driven photocatalysis, 10 different heterojunctions were simultaneously introduced in the Ti-Zr-Nb-Ta-W-O system. The oxide, which was synthesized by a high-pressure torsion method and oxidation, successfully produced oxygen from water under visible light without co-catalyst addition. The photocatalytic performance was attributed to high visible-light absorption, low bandgap, appropriate band structure, presence of multiple heterojunctions and accordingly easy electron-hole separation and slow recombination. These results not only show the potential of high-entropy oxides as new visible-light-active photocatalysts, but also introduce the multiple-heterojunction introduction as a strategy to achieve photocatalysis under visible light.

Tailoring Ir-FeOx interactions and catalytic performance in preferential oxidation of CO in H2 via the morphology engineering of anatase TiO2 over Ir-FeOx/TiO2 catalysts

Ir-FeOx/TiO2 catalysts with both Ir and Fe contents of ∼1% wt. employing anatase TiO2 nanocrystals predominantly exposing either {100}, {101}, or {001} facets as the support were prepared and a comprehensive study was conducted on their interactions in pairs that are strongly dependent on the TiO2 morphology. The strongest FeOx-TiO2 interactions occurred over TiO2{001} support while TiO2{101} support contributes to the strongest Ir-TiO2 and Ir-FeOx interactions. Catalytic performance of the Ir-FeOx/TiO2 catalysts in preferential oxidation of CO in H2 is not only affected by the CO reactivity, but also determined by the Ir-FeOx interfaces. Ir-FeOx/TiO2{101} catalyst exhibits the highest CO conversion and best O2 selectivity over the three Ir-FeOx/TiO2 catalysts, which could be ascribed to stronger Ir-FeOx interactions that contribute to the enhancement of a H-spillover effect and subsequently facilitate the transformation of surface carbonaceous intermediates into CO2. These results add the versatility of the morphology engineering strategy in tailoring the structures and catalytic performance of oxide-based catalysts, and broaden the concept of morphology-dependent catalysis of oxide-based nanocrystal catalysts.

Unravelling gas sorption in the aluminum metal‐organic framework CAU‐23: CO2, H2, CH4, SO2 sorption isotherms, enthalpy of adsorption and mixed‐adsorptive calculations

AbstractThe report is the first broader evaluation of the gas sorption properties of CAU‐23 for the adsorptives CO2, H2, CH4, and SO2. CAU‐23 is of intermediate porosity among Al‐MOFs with specific BET surface areas of the order of MIL‐100>MIL‐53>CAU‐23>MIL‐160>MIL‐53‐TDC>Alfum>CAU‐10‐H and total pore volumes of the order of MIL‐100>MIL‐53>CAU‐23>Alfum=MIL‐160>MIL‐53‐TDC>CAU‐10‐H. CO2 uptake (3.97 mmol g−1, 293 K) and H2 uptake (10.25 mmol g−1, 77 K) of CAU‐23 are second in the series and only slightly smaller than for MIL‐160. The CH4 uptake of CAU‐23 (0.89 mmol g−1, 293 K) is unremarkable in comparison with the other Al‐MOFs. The SO2 uptake (8.4 mmol g−1, 293 K) follows the porosity and higher SO2 uptakes were only observed for MIL‐53 and MIL‐100. CAU‐23 is one of the best Al‐MOFs for high‐pressure sorption of CO2, with an uptake of 33 wt.‐% at 20 bar, 293 K. Gas sorption measurements at two different temperatures gave near zero‐coverage enthalpy of adsorptions, ▵Hads0 for CO2 of −22 kJ mol−1 and of SO2 for −38 kJ mol−1 which is at the low end of the other Al‐MOFs (−22 to −39 kJ mol−1 for CO2; −41 to −51 kJ mol−1 for SO2), yet ▵Hads increases for CAU‐23 with CO2 and SO2 to −25 and −57 kJ mol−1, respectively. For CO2/CH4 and SO2/CO2 separation, ideal adsorbed solution theory (IAST) predicted gas selectivities of 5 and 27–50 (depending on molar ratio and model), respectively, in line with 4.5–6.3 and 17–50, respectively, with most of the other Al‐MOFs, where only MIL‐53‐TDC with 83 and MIL‐160 with 126 gave a higher SO2/CO2 selectivity at a molar ratio of 0.5.