Biporous Metal-Organic Framework with Tunable CO2/CH4 Separation Performance Facilitated by Intrinsic Flexibility.

In this work, we report the synthesis of SION-8, a novel metal-organic framework (MOF) based on Ca(II) and a tetracarboxylate ligand TBAPy4- endowed with two chemically distinct types of pores characterized by their hydrophobic and hydrophilic properties. By altering the activation conditions, we gained access to two bulk materials: the fully activated SION-8F and the partially activated SION-8P with exclusively the hydrophobic pores activated. SION-8P shows high affinity for both CO2 ( Qst = 28.4 kJ/mol) and CH4 ( Qst = 21.4 kJ/mol), while upon full activation, the difference in affinity for CO2 ( Qst = 23.4 kJ/mol) and CH4 ( Qst = 16.0 kJ/mol) is more pronounced. The intrinsic flexibility of both materials results in complex adsorption behavior and greater adsorption of gas molecules than if the materials were rigid. Their CO2/CH4 separation performance was tested in fixed-bed breakthrough experiments using binary gas mixtures of different compositions and rationalized in terms of molecular interactions. SION-8F showed a 40-160% increase (depending on the temperature and the gas mixture composition probed) of the CO2/CH4 dynamic breakthrough selectivity compared to SION-8P, demonstrating the possibility to rationally tune the separation performance of a single MOF by manipulating the stepwise activation made possible by the MOF's biporous nature

A Robust Titanium Isophthalate Metal-Organic Framework for Visible-Light Photocatalytic CO2 Methanation

[EN] Isophthalic acid (IPA) has been considered to build metal-organic frameworks (MOFs), owing to its facile availability, unique connection angle-mode, and a wide range of functional groups attached. Constructing titanium-IPA frameworks that possess photoresponse properties is an alluring characteristic with respect to the challenge of synthesizing new titanium-based MOFs (Ti-MOFs) Here, we report the first Ti-IPA MOF (MIP-208) that efficiently combines the use of preformed Ti-8 oxoclusters and in situ acetylation of the 5-NH2-IPA linker. The mixed solid-solution linkers strategy was successfully applied, resulting in a series of multivariate MIP-208 structures with tunable chemical environments and sizable porosity. MIP-208 shows the best result among the pure MOF catalysts for the photocatalytic methanation of carbon dioxide. To improve the photocatalytic performance, ruthenium oxide nanoparticles were photo-deposited on MIP-208, forming a highly active and selective composite catalyst, MIP-208@RuOx, which features a notable visible-light response coupled with excellent stability and recycling ability.S.W. acknowledges the support from the National Natural Science Foundation of China (22071234) and the Fundamental Research Funds for the Central Universities (WK2480000007). S.N. thanks the Ministerio de Ciencia, Innovacion y Universidades (RTI2018-099482-A-I00 project, the Fundacion Ramon Areces (XVIII Concurso Nacional para la Adjudicacion de Ayudas a la Investigacion en Ciencias de la Vida y de la Materia, 2016), and Generalitat Valenciana grupos de investigacion consolidables (AICO/2019/214 project) and Agencia Valenciana de la Innovacion (INNEST/2020/111 project) for financial support. C.-C.C. acknowledges the support from the Program of China Scholarship Council (201700260093) and PHC Cai YuanPei Project (38893VJ). C.M.-C. is grateful for financial support from the Institut Universitaire de France (IUF) and the Paris Ile-de-France Region -DIM "Respore.'' H.G. thanks the Spanish Ministry of Science and Innovation (Severo Ochoa and RTI2018-098237-CO2-1) and Generalitat Valenciana (Prometeo2017/083) for financial support. The authors thank the staff at Synchrotron SOLEIL and the associated scientists for beamtime and assistance during SCXRD data collections on PROXIMA 2A, as well as Dr. Peng Guo and Dr. Nana Yan from Dalian Institute of Chemical Physics (Chinese Academy of Sciences) for the collection of high-resolution PXRD data for Rietveld refinement.Wang, S.; Cabrero-Antonino, M.; Navalón Oltra, S.; Cao, C.; Tissot, A.; Dovgaliuk, I.; Marrot, J.... (2020). A Robust Titanium Isophthalate Metal-Organic Framework for Visible-Light Photocatalytic CO2 Methanation. 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Energy & Environmental Science, 10(11), 2392-2400. doi:10.1039/c7ee02287eMateo, D., Asiri, A. M., Albero, J., & García, H. (2018). The mechanism of photocatalytic CO2 reduction by graphene-support

Synthesis, structure and properties of Al-based borohydrides for hydrogen storage

This thesis is dedicated to chemistry and hydrogen storage properties of novel complex hydrides. The main efforts were focused on synthesis and characterization of new Al-based borohydrides and amidoboranes. Somewhat different investigation on the hydrolysis of KBH4 in the atmosphere of CO2 was also performed. The series of mixed-cation M[Al(BH4)4] (M = Li+, Na+, K+, NH4+, Rb+, Cs+) were successfully obtained by a reaction of the corresponding MBH4 with Al(BH4)3. This method provides a high theoretical hydrogen capacity and enables to store highly reactive and unstable Al(BH4)3 in a solid-state form. A good quality of the obtained samples allowed to solve their crystal structures using variable temperature synchrotron X-ray powder diffraction (XRPD). The thermal decomposition of M[Al(BH4)4] shows various pathways: Al(BH4)3 is released below 100 °C for M = Li+ and Na+, while heavier derivatives evolve hydrogen and diborane at about 150 °C. Li[Al(BH4)4] firstly decomposes into Li4Al3(BH4)13 at ~60 °C, desorbing Al(BH4)3, and the latter decomposes at ~90 °C releasing the rest of the starting borohydrides. NH4[Al(BH4)4] occupies a special position, as it contains protic and hydridic hydrogens, recombining into hydrogen already at 35 °C. In general, the experimental decomposition temperatures of metal borohydrides linearly correlate with the square root of the ionic potential of metal atoms calculated from dynamical charges on cations. Al(BH4)3 reacts with ammonia borane, NH3BH3, producing mononuclear Al(BH4)3·NH3BH3 complex. It releases at ~70 °C two equivalents of hydrogen, showing considerably lower decomposition temperature, compared to pure NH3BH3. The striking property of this system is an endothermic dehydrogenation on the first decomposition step, compared to the exothermic one for ammonia borane and its other known complexes. This opens a possibility for its direct rehydrogenation. The main drawback of this system is the low stability of the dehydrogenation intermediate, Al(BH4)3·NHBH, decomposition above 100 °C. In order to suppress its decomposition, we investigated N-substituted derivatives of ammonia borane, obtaining a more promising complex, Al(BH4)3·CH3NH2BH3. Al(BH4)3 serves as a template in the potentially reversible ammonia borane dehydrogenation, with Al atom coordinating both the starting and the final products. Aiming to substitute highly reactive Al(BH4)3 by a halide salt, and using N-substituted NH3BH3, we obtained an ionic form of AlCl3·CH3NH2BH3, namely [Al(CH3NH2BH3)2Cl2][AlCl4]. The further analysis of these compounds will help to define a system for the reversible storage of hydrogen in ammonia borane. A different way to obtain hydrogen using new Al-based reactive hydride composite (RHC) was also explored in this work. In particular, NaAlH4–4NH3BH3 system showed fascinating properties of releasing high purity H2 and low hydrogen release temperature of 70 °C and formation of Na[Al(NH2BH3)4]. The properties of the first Al-based amidoborane look promising. This compound decomposes in two steps with the formation of NaBH4, 8 equivalents of pure hydrogen and an amorphous product AlN4B3H(0÷1.8). The latter reversibly reabsorb about 27% of released hydrogen. The example of Na[Al(NH2BH3)4] decomposition to AlN4B3H(0÷1.8) requires further in-depth studies, viz. its chemical structure and an optimization of the rehydrogenation process. The interest in Al-based complex hydrides has been growing during the last years. Any knowledge about new Al-containing complex hydrides is very important for the future solid-state hydrogen storage. Data obtained in this work might be important in the further predictions of potential RHC systems, applying the computational methods. On the practical side, the combination of any of the described compounds with other hydrides may open avenues to new RHCs with enhanced hydrogen storage properties.(SC - Sciences) -- UCL, 201

Aluminium complexes of B- and N-based hydrides: synthesis, structures and hydrogen storage properties

The storage of hydrogen in a solid state is one of the main challenges for stationary and mobile applications. Light metal hydrides have attracted significant attention as potential candidates for energy storage. Remarkably, Al-containing hydrides, namely AlH3 and M(AlH4)n, are among the most fascinating classes of materials, able to cycle up to 5.5 wt% of hydrogen at moderate temperatures. This review covers the recent research on the families of Al-based complex hydrides involving other light elements such as B and N. They were classified according to the charge of the Al-based complexes, as anionic, molecular, cationic or “autoionized” where Al is centering both the cation and the anion. The factors influencing the stability and the hydrogen purity of the series of anionic aluminium amides M[Al(NH2)4]n, borohydrides M[Al(BH4)4] and amidoboranes M[Al(NH2BH3)4], as well as molecular [Al(L)(BH4)3] (L ¼ molecular ligands) and cation [Al(NH3)6]3þ-based complexes are discussed. In particular, the ability of the strong Lewis acid Al3þ to coordinate both the initial hydrogenated species as well as their dehydrogenation products makes it a good template for chemical transformations involving light chemical and complex hydrides

Principal Component Analysis (PCA) for Powder Diffraction Data: Towards Unblinded Applications

We analyze the application of Principal Component Analysis (PCA) for untangling the main contributions to changing diffracted intensities upon variation of site occupancy and lattice dimensions induced by external stimuli. The information content of the PCA output consists of certain functions of Bragg angles (loadings) and their evolution characteristics that depend on external variables like pressure or temperature (scores). The physical meaning of the PCA output is to date not well understood. Therefore, in this paper, the intensity contributions are first derived analytically, then compared with the PCA components for model data; finally PCA is applied for the real data on isothermal gas uptake by nanoporous framework γ –Mg(BH 4 ) 2 . We show that, in close agreement with previous analysis of modulation diffraction, the variation of intensity of Bragg lines and the displacements of their positions results in a series of PCA components. Every PCA extracted component may be a mixture of terms carrying information on the average structure, active sub-structure, and their cross-term. The rotational ambiguities, that are an inherently part of PCA extraction, are at the origin of the mixing. For the experimental case considered in the paper, the extraction of the physically meaningful loadings and scores can only be achieved with a rotational correction. Finally, practical recommendations for non-blind applications, i.e., what boundary conditions to apply for the the rotational correction, of PCA for diffraction data are given

CO2-promoted hydrolysis of KBH4 for efficient hydrogen co-generation

Hydrolysis of metal borohydrides in the presence of CO2 has not been studied so far, although carbon dioxide contained in air is known to accelerate hydrogen generation. KBH4 hydrolysis promoted by CO2 gas put through an aqueous solution was studied by timeresolved ATR-FTIR spectroscopy, showing a transformation of BH4 into B4O5(OH)4 2, and a drastically accelerated hydrogen production which can be completed within minutes. This process can be used to produce hydrogen on-board from exhaust gases (CO2 and H2O). We found a new intermediate, K9[B4O5(OH)4]3(CO3)(BH4)$7H2O, forming upon hydrolysis on air via a slow adsorption of the atmospheric CO2. The same intermediate can be crystallized from partly hydrolyzed solutions of KBH4 þ CO2, but not from the fully reacted sample saturated with CO2. This phase was studied by single-crystal and powder X-ray diffraction, DSC, TGA, Raman, IR and elemental analysis, all data are fully consistent with the presence of the three different anions and of the crystallized water molecules. Its crystal structure is hexagonal, space group P-62c, with lattice parameters a ¼ 11.2551(4), c ¼ 17.1508(8) A°. Formation of the intermediate produces 16 mol of H2 per mole of adsorbed CO2 and thus is very efficient both gravimetrically and volumetrically. It allows also for an elimination of carbon dioxide from exhaust gases