Mixed-linker approach in designing porous zirconium-based metal–organic frameworks with high hydrogen storage capacity

YesThree highly porous Zr(IV)-based metal–organic frameworks, UBMOF-8, UBMOF-9, and UBMOF-31, were synthesized by using 2,2′-diamino-4,4′-stilbenedicarboxylic acid, 4,4′-stilbenedicarboxylic acid, and combination of both linkers, respectively. The mixed-linker UBMOF-31 showed excellent hydrogen uptake of 4.9 wt% and high selectivity for adsorption of CO2 over N2 with high thermal stability and moderate water stability with permanent porosity and surface area of 2552 m2 g−1.University of Bath; Royal Society of Chemistry; Engineering and Physical Sciences Research Counci

Modulator-free green synthesis of the calcium-terephthalate metal-organic framework derived from waste eggshells

DATA AVAILABILITY : Data will be made available on request.Please read abstract in the article.The National Research Foundation (NRF) of South Africa and the South African Research Chairs Initiative (SARChI) of the Department of Science and Innovation (DSI).http://www.elsevier.com/locate/polyam2024ChemistrySDG-12:Responsible consumption and productio

The effects of metakaolinization and fused-metakaolinization on zeolites from quartz rich natural clays

A variety of zeolites have been synthesized by performing either metakaolinization or fused-metakaolinization of natural clays prior to the hydrothermal synthesis step. To understand the differences arising from performing fused metakaolinization rather than simple metakaolinization, the calcination conditions, gel composition, gelling and crystallization conditions were kept similar for both methods. The original clay material, a kaolinite group mineral with Si/Al molar ratio of 1, had a high content of quartz as impurity. The two treatment methods gave different zeolites of high crystallinity and relatively similar Si/Al molar ratio. Zeolite Na-A with 98% crystallinity was produced from the metakaolinization method within 8 h, while Na-X with 96% crystallinity was generated from the fused-metakaolinization (fusion) method within 48 h. In the fusion method, sodalite was formed at or beyond 48 h of hydrothermal reaction, while in the metakaolinite method, apart from a slight decrease in intensities of XRD peaks, no phase change was observed even after 168 h of hydrothermal reaction. Modification of the synthesis gel by increasing the Si/Al molar ratio via addition of fumed silica resulted in mixed zeolite products via the metakaolinite method, while Na–Y was the major product for the fusion method. Except for Na-A, all zeolite products had high surface area of up to 600 m2/g and micropore volume of 0.18 cm3/g. Our findings demonstrate the crucial role of the pre-treatment step in the synthesis of zeolites from clay minerals, and that a variety of high quality zeolites are achievable via choice of pre-treatment protocols

Development of an Improved Kinetic Model for CO2 Hydrogenation to Methanol

International audienceThe kinetics of methanol synthesis remains debatable for various reasons, such as the lack of scientifically conclusive agreement about reaction mechanisms. The focus of this paper is on the evaluation of the intrinsic kinetics of the methanol synthesis reaction based on CO 2 hydrogenation and the associated reverse water-gas shift as overall reactions. The industrial methanol synthesis catalyst, Cu/ZnO/Al 2 O 3 /MgO, was used for performing the kinetic studies. An optimal kinetic model was assessed for its ability to predict the experimental data from differential to integral conditions, contrary to the typical fitting of only the integral conditions' data (common practice, as reported in the literature). The catalyst testing and kinetic evaluations were performed at various temperatures (210-260 • C) and pressures (40-77 bar), and for different stoichiometric numbers (0.9-1.9), H 2 /CO 2 ratios (3.0-4.4) and carbon oxide ratios (0.9-1.0), in an isothermal fixed bed reactor, operated in a plug-flow mode. Experiments with CO in the feed were also generated and fitted. Different literature kinetic models with different assumptions on active sites, rate-determining steps, and hence, model formulations were fitted and compared. The original Seidel model appeared to fit the kinetic data very well, but it has twelve parameters. The modified model (MOD) we propose is derived from this Seidel model, but it has fewer (nine) parameters-it excludes CO hydrogenation, but it takes into consideration the morphological changes of active sites and CO adsorption. This MOD model, with three active sites, gave the best fit to all the data sets

Comparative evaluation of the power-to-methanol process configurations and assessment of process flexibility

This paper compares different power-to-methanol process configurations encompassing the electrolyser, adiabatic reactor(s) and methanol purification configurations. Twelve different power-to-methanol configurations based on direct CO2 hydrogenation with H2 derived from H2O-electrolysis were modelled, compared, and analysed. A high temperature solid oxide electrolyser is used for hydrogen production. A fixed bed reactor is used for methanol synthesis. The aim of the paper is to give detailed comparison of the process layouts under similar conditions and select the best performing process configuration considering the overall methanol production, carbon conversion, flexibility, and energy efficiency. ASPEN PLUS® V11 is used for flowsheet modelling and the system architectures considered are the open loop systems where methanol is produced at 100 kton per annum and sold to commercial wholesale market as the final purified commodity. Further optimization requirements are established as targets for future work. Three options of power-to-methanol configuration with methanol synthesis from CO2 hydrogenation are proposed and further evaluated considering process flexibility. From the evaluation, the series-series based configuration with three adiabatic reactors in series performed better in most parameters including the flexible load dependent energy efficiency.</p

Polymer-based shaping strategy for zeolite templated carbons (ZTC) and their metal organic framework (MOF) composites for improved hydrogen storage properties

Porous materials such as metal organic frameworks (MOFs), zeolite templated carbons (ZTC), and some porous polymers have endeared the research community for their attractiveness for hydrogen (H2) storage applications. This is due to their remarkable properties, which among others include high surface areas, high porosity, tunability, high thermal, and chemical stability. However, despite their extraordinary properties, their lack of processability due to their inherent powdery nature presents a constraining factor for their full potential for applications in hydrogen storage systems. Additionally, the poor thermal conductivity in some of these materials also contributes to the limitations for their use in this type of application. Therefore, there is a need to develop strategies for producing functional porous composites that are easy-to-handle and with enhanced heat transfer properties while still retaining their high hydrogen adsorption capacities. Herein, we present a simple shaping approach for ZTCs and their MOFs composite using a polymer of intrinsic microporosity (PIM-1). The intrinsic characteristics of the individual porous materials are transferred to the resulting composites leading to improved processability without adversely altering their porous nature. The surface area and hydrogen uptake capacity for the obtained shaped composites were found to be within the range of 1,054–2,433 m2g−1 and 1.22–1.87 H2 wt. %, respectively at 1 bar and 77 K. In summary, the synergistic performance of the obtained materials is comparative to their powder counterparts with additional complementing properties.The Department of Science and Technology (DST) of South Africa toward HySA Infrastructure (Grant No. ENMH01X), National Research Foundation (NRF) for SA/France collaboration funding (Grant No. ENMH20X) and the Royal Society—DFID Africa Capacity Building Initiative Programme Grant (Grant No. AQ150029).http://www.frontiersin.org/Chemistryam2020Chemistr

Experimental Demonstration of Dynamic Temperature-Dependent Behavior of UiO-66 Metal–Organic Framework: Compaction of Hydroxylated and Dehydroxylated Forms of UiO-66 for High-Pressure Hydrogen Storage

High-pressure (700 MPa or ∼100 000 psi) compaction of dehydroxylated and hydroxylated UiO-66 for H2 storage applications is reported. The dehydroxylation reaction was found to occur between 150 and 300 °C. The H2 uptake capacity of powdered hydroxylated UiO-66 reaches 4.6 wt % at 77 K and 100 bar, which is 21% higher than that of dehydroxylated UiO-66 (3.8 wt %). On compaction, the H2 uptake capacity of dehydroxylated UiO-66 pellets reduces by 66% from 3.8 to 1.3 wt %, while for hydroxylated UiO-66 the pellets show only a 9% reduction in capacity from 4.6 to 4.2 wt %. This implies that the H2 uptake capacity of compacted hydroxylated UiO-66 is at least three times higher than that of dehydroxylated UiO-66, and therefore, hydroxylated UiO-66 is more promising for hydrogen storage applications. The H2 uptake capacity is closely related to compaction-induced changes in the porosity of UiO-66. The effect of compaction is greatest in partially dehydroxylated UiO-66 samples that are thermally treated at 200 and 290 °C. These compacted samples exhibit XRD patterns indicative of an amorphous material, low porosity (surface area reduces from between 700 and 1300 m2/g to ca. 200 m2/g and pore volume from between 0.4 and 0.6 cm3/g to 0.1 and 0.15 cm3/g), and very low hydrogen uptake (0.7–0.9 wt % at 77 K and 100 bar). The observed activation-temperature-induced dynamic behavior of UiO-66 is unusual for metal–organic frameworks (MOFs) and has previously only been reported in computational studies. After compaction at 700 MPa, the structural properties and H2 uptake of hydroxylated UiO-66 remain relatively unchanged but are extremely compromised upon compaction of dehydroxylated UiO-66. Therefore, UiO-66 responds in a dynamic manner to changes in activation temperature within the range in which it has hitherto been considered stable

Preparation of carbon nanofibers/tubes using waste tyres pyrolysis oil and coal fly ash derived catalyst

In this study, two waste materials namely; coal fly ash (CFA) and waste tyres pyrolysis oil, were successfuly utilized in the synthesis of carbon nanofibers/tubes (CNF/Ts). In addition, Fe-rich CFA magnetic fraction (Mag-CFA) and ethylene gas were also used for comparison purposes. The carbons obtained from CFA were found to be anchored on the surface of the cenosphere and consisted of both CNTs and CNFs, whereas those obtained from Mag-CFA consisted of only multi-walled carbon nanotubes (MWCNTs). The study further showed that the type of carbon precursor and support material played an important role in determining the nanocarbon growth mechanism. The findings from this research have demonstrated that it is possible to utilize waste tyres pyrolysis oil vapor as a substitute for some expensive commercial carbonaceous gases.The South African Department of Science and Technology (DST) for the financial support towards HySA Infrastructure (Grant No. HTC004X), the Council for Scientific and Industrial Research (CSIR) for providing facilities and National Research Foundation (NRF) for funding the SA-Poland collaborative project (HTC071X).http://www.tandfonline.com/loi/lesa202019-05-29hj2018Physic

Effect of inclusion of MOF-polymer composite onto a carbon foam material for hydrogen storage application

Despite the extensive studies done on the remarkable characteristics of metal–organic frameworks (MOFs) for gas storage applications, several issues still preclude their widespread commercial lightweight applications. In most cases, MOF materials are produced in powdery form and often require shaping to attain application-specific properties. Fabrication of MOF-polymer composites is considered an attractive approach for shaping MOF powders. In most cases, the final hybrid material retains the intrinsic adsorbing properties of the pristine MOF coupled with other interesting synergistic features which are sometimes superior to their pristine counterparts. In this regard, the use of porous polymers of intrinsic microporosity (such as PIM-1) has proved to be of interest. However, most of these polymers lack some other important properties such as conductivity, which is of paramount importance in a hydrogen storage system. It is on this basis that our study aimed at direct anchoring of a PIM-1/MOF viscous solution onto a carbon foam (CF) substrate. The effects of PIM-1/UiO-66(Zr) inclusion into CF to the resulting thermal properties (thermal conductivity, thermal diffusivity and volumetric heat capacity) as well as hydrogen uptake capacity was investigated. Contrary to our expectations, the incorporation of PIM-1/UiO-66(Zr) into CF only offered better handling but did not lead to the enhancement of thermal conductivity.The Department of Science and Innovation (DSI) of South Africa towards HySA Infrastructure, National Research Foundation (NRF) for SA/France collaboration funding and the Royal Society—DFID Africa Capacity Building Initiative Programme Grant.http://link.springer.com/journal/109042021-08-09hj2020Chemistr

Co-pelletization of a zirconium-based metal-organic framework (UiO-66) with polymer nanofibers for improved useable capacity in hydrogen storage

We report on a concept of co-pelletization using mechanically robust hydroxylated UiO-66 to develop a metal-organic framework (MOF) monolith that contains 5 wt% electrospun polymer nanofibers, and consists of an architecture with alternating layers of MOF and nanofiber mats. The polymers of choice were the microporous Polymer of Intrinsic Microporosity (PIM-1) and non-porous polyacrylonitrile (PAN). Co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths retain no less than 85% of the porosity obtained in pristine powder and pelletized UiO-66. The composition of the pore size distribution in co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths is significantly different to that of pristine UiO-66 forms, with pristine UiO-66 forms showing 90% of the pore apertures in the micropore region and both UiO-66/nanofiber monoliths showing a composite micro-mesoporous pore size distribution. The co-pelletized UiO-66/nanofiber monoliths obtained improved useable H2 capacities in comparison to pristine UiO-66 forms, under isothermal pressure swing conditions. The UiO-66/PIM-1 monolith constitutes the highest gravimetric (and volumetric) useable capacities at 2.3 wt% (32 g L−1) in comparison to 1.8 wt% (12 g L−1) and 1.9 wt% (29 g L−1) obtainable in pristine UiO-66 powder and UiO-66 pellet, respectively