46 research outputs found
Role of Exposed Metal Sites in Hydrogen Storage in MOFs
No full textThe role of exposed metal sites in increasing the H2 storage performances in metal-organic frameworks (MOFs) has been investigated by means of IR spectrometry. Three MOFs have been
considered: MOF-5, with unexposed metal sites, and HKUST-1 and CPO-27-Ni, with exposed Cu2+ and Ni2+, respectively. The onset temperature of spectroscopic features associated with adsorbed H2 correlates with the adsorption enthalpy obtained by the VTIR method and with the shift experienced by the H-H stretching frequency. This relationship can be ascribed to the different nature and accessibility of the metal sites. On the basis of a pure energetic evaluation, it was observed that the best performance was shown by CPO-27-Ni that exhibits also an initial adsorption enthalpy of -13.5 kJ mol-1, the highest yet observed for a MOF. Unfortunately, upon comparison of the hydrogen amounts stored at high pressure, the hydrogen capacities in these conditions are mostly dependent on the surface area and total pore volume of the material. This means that if control of MOF surface area can benefit the total stored amounts, only the presence of a great number of strong adsorption sites can make the (P,T) storage conditions more economically favorable. These observations lead to the prediction that efficient H2 storage by physisorption
can be obtained by increasing the surface density of strong adsorption sites
Upscaling bifunctional materials for Ca-Cu looping: fixed bed reactor tests
No full textPoster presented at the 10th "Trondheim Conference on CO2 Capture, Transport and Storage", June 17 - 19, 2019, in Trondheim - Norway.Calcium-Copper Chemical Looping Technology is a hybrid concept combining Sorption-Enhanced Reforming (SER) and Chemical Looping Combustion (CLC) for hydrogen production from natural gas with integrated CO2 capture.
SER involves reforming, water gas shift and CO2 capture in the same reactor vessel (reformer) making use of a CaO-based high temperature solid sorbent to capture the CO2:
CH4 (g) + 2H2O (g) + CaO → CaCO3 + 4H2(g)
This leads to process intensification due to avoidance of additional water gas shift steps as well as a downstream CO2 separation system, while hydrogen concentrations up to 98 vol% (dry basis) can be obtained at temperatures around 650 °C at 1 bar. To regenerate the sorbent at high temperature (900 °C, 1 bar), heat is provided via indirect heating2 or direct oxy-fuel combustion3.
In the Ca-Cu Looping technology, a second Cu/CuO loop is introduced in the process and the calcination of CaCO3 is coupled and thermally sustained by the exothermic CuO reduction with H2, CO and/or CH4. In this way, expensive Air Separation Unit (ASU) or heat exchange surfaces are avoided, while fixed bed reactors are preferred to fluidized beds allowing the production of pressurized H2 without circulation of solids. Specific Energy Consumption (SPECCA) for the Ca-Cu process have been found to be in the range 1.1-1.5 MJ/kgCO2, which compares well with oxy-SER (1.6-2) and benchmark Fired Tubular Reactor / MDEA system (3.5) 4–6.
The novelty proposed in this work is to combine CaO and CuO phases into one bi-functional material using relatively low-cost raw materials as well as an easy and scalable synthesis method. This configuration has the potential to a) lower the inert fraction in the reactor bed and thus limit the sensible heating requirement in the reactor, and b) to promote close contact between the CaO and CuO phases, improving the heat and mass transfer compared to a segregated particle arrangement.
Mayenite, a suitable phase for increasing the stability of CaO-based synthetic sorbents7, has been used to support the Ca-Cu combined materials. In a previous work, the effect of the CuO precursors (Cu(OH)2, Cu(NO3)2 and CuO mesh powder), and the CuO-CaO loading (at constant weight ration of 2) on the hydrothermal synthesis of combined powder has been investigated in TGA for about 40 carbonation-calcination and oxidation-reduction cycles. This study has shown that 40 wt% CuO
materials are stable for 40 TGA cycles while all investigated 50 wt% CuO materials deactivate, regardless of CuO precursor 8.
Subsequently, the synthesis method has been upscaled to produce 100g of powders which have been agglomerated to particles with 0.5 – 0.8 mm diameter, and subjected to 40 carbonation-oxidation-reduction-calcination cycles in TGA. The agglomerates of the combined Cu(OH)2 prepared powder are stable for 40 TGA cycles, although suffer from an initial 25 wt% capacity reduction in both O2 and CO2 capacities relative to the Cu(OH)2 powder.
Finally, the combined material agglomerates have been mixed with a commercial reforming catalyst and tested in a lab scale fixed bed reactor along the three main reaction stages of a Ca-Cu looping process – SER, Cu oxidation and Cu reduction. Operation conditions chosen for the process stages were representative for the scaling up of the process in terms of pressure, gas spatial velocities and gas composition.
The obtained evolution of product gas composition with time, as well as the temperature profiles within the bed along each reaction stage during three complete cycles (as depicted in Figure 1 for the SER step) has validated the combined materials concept at lab scale, and shows promises in terms of increased amount of active material per reactor volume.This work is funded by the Research Council of Norway in the framework of CLIMIT-prosjekt 254736Ca-Cu CyclesPeer reviewe
The Beat of the Economic Heart: Joseph Schumpeter and Arthur Spiethoff on Business Cycles
No full textThe paper discusses the relationship between Arthur Spiethoff and Joseph A. Schumpeter, the men and their works. Had it not been for Spiethoff Schumpeter would in all probability have forever been lost to scientific work. It was Spiethoff who brought the Austrian back to academia and research after a sequence of serious mishaps in politics and banking. Spiethoff's contribution to an analysis of business cycles is then summarized and important similarities and some differences between it and Schumpeter's are pointed out. The view of Spiethoff and Schumpeter that cycles are endogenous and cannot possibly be eliminated without at the same time eliminating the dynamism of the capitalist economy is then couterposed with views of some of their contemporaries and particularly modern mainstream macroeconomics that this is not so.Schumpeter; Spiethoff; business cycles; innovations; creative destruction
Crystal structure of dimethyl 4,4′-dimethoxybiphenyl-3,3′-dicarboxylate
No full textIn the title compound, C18H18O6, the benzene rings are coplanar due to the centrosymmetric nature of the molecule, with an inversion centre located at the midpoint of the C—C bond between the two rings. Consequently, the methyl carboxylate substituents are oriented in a trans fashion with regards to the bond between the benzene rings. The methyl carboxylate and methoxy substituents are rotated slightly out of plane relative to their parent benzene rings, with dihedral and torsion angles of 18.52 (8) and −5.22 (15)°, respectively. The shortest O...H contact between neighbouring molecules is about 2.5 Å. Although some structure-directing contributions from C—H...O hydrogen-bonding interactions are possible, the crystal packing seems primarily directed by weak van der Waals forces
Dimethyl 3,3′-dimethoxybiphenyl-4,4′-dicarboxylate
No full textIn the title compound, C18H18O6, the biphenyl moiety is twisted with a dihedral angle of 29.11 (10)°. The carbomethoxy groups form C—C—C—O torsion angles of −18.3 (3) and −27.7 (3)° with the attached rings, as a result of steric hindrances from the nearby methoxy groups. In the absence of stacking interactions and with no H...O contacts shorter than 2.7 Å, the packing is dominated by weaker van der Waals interactions
Synthesis and Crystal Structures of Tris‐[3, 5‐bis(trifluoromethyl)phenyl]arsine Oxide at 293 and 100 K and the Localization of the Trifluoromethyl Groups
No full textModification of Network and Pore Dimensionality in Metal–Organic Frameworks Containing a Secondary Phosphine Functionality
No full textThree new metal-organic frameworks containing a triphenylphosphine moiety, namely [Zn3(tpp)2(DMF)2]·nDMF (1), [Zn3(tpp)2(4,4’-bipy)2]·nDMF (2) and [Zn3(tpp)2(3,3’-bipy)]·nDMF (3), were synthesized using 4,4',4''-phosphanetriyltribenzoic acid (H3tpp) as a tritopic tridentate linker. The absence or presence of additional N-donor linker molecules in the reaction mixture directed the formation of (3,6)-c layered, (3,8)-c pillared layered or (3,4,6)-c frameworks. Compound 1 is composed of a trinuclear zinc secondary building unit (SBU) and the tpp3- anion arranged in a layered (3,6)-c network with kgd topology. There are guest DMF molecules coordinated to the terminal Zn atoms of the trinuclear inorganic SBU. The addition of the neutral N-donor molecules 3,3’-bipyridine (3,3’-bipy) and 4,4’-bipyridine (4,4’-bipy) as second organic linker molecule lead to an increase of dimensionality of the networks. Compound 2 is a (3,4,6)-nodal three-dimensional MOF. Its structure consists of two equivalent interpenetrated nets with the point symbol (52·64)(52·6)2(54·66·72·8·92) with solvent filled pockets. The free electron pair of phosphorus atom of the triphenylphosphine moiety is pointing towards the 0-dimensional pores. The structure of 3 can be described as layers of 1 which are connected by additional 3,3’-bipyridine as pillar into a three-dimensional (3,8)-c network with the point symbol (43)2(46·618·84). The non-interpenetrated structure of 3 contains a solvent filled three-dimensional pore system. All three materials exhibit uptake of CO2 at 195 K after removal of the guest DMF molecules. It is particularly surprising for 2, with its 0-dimensional pores in the single crystal structure and absence of N2 adsorption at 77 K. 3 showed a large gate opening effect for CO2 adsorption at 195 K.acceptedVersio
Methyl 5-iodo-2-methoxybenzoate
No full textIn the title compound, C9H9IO3, the molecules are close to planar [maximum deviation from benzene ring plane = 0.229 (5) Å for the methyl carboxylate C atom] with the methyl groups oriented away from each other. In the crystal, molecules form stacked layers parallel to the ab plane, where every layer has either the iodine or methoxy/methyl carboxylate substituents pointing towards each other in an alternating fashion
A Permanently Porous Yttrium–Organic Framework Based on an Extended Tridentate Phosphine Containing Linker
No full textThe metal–organic framework [Y(tbpp)]·nDMF (1) was synthesized from yttrium(III) nitrate and the tritopic linker tris(4′-carboxy[1,1′-biphenyl]-4-yl)phosphine (H3tbpp). The distance between the coordinating atoms of the carboxylate groups of the extended tridentate phosphine linker is more than 1.8 nm, resulting in an average pore dimension of 0.9 nm in the noninterpenetrated metal–organic framework. The material exhibits high thermal stability and permanent porosity after removal of guest molecules from the one-dimensional pore system. The desolvated compound adsorbs nitrogen, argon, hydrogen, and carbon dioxide. Favorable adsorption of CO2 over N2 is predicted using ideal adsorbed solution theory (IAST). The isosteric enthalpies of adsorption of H2 and CO2 of −7 and −22 kJ mol–1, respectively, are representative for metal−organic frameworks with no accessible strong host–guest binding sites, despite the bifunctional nature of the organic ligand. The absence of strong specific adsorption sites was confirmed by in situ powder synchrotron X-ray diffraction of the reversible isobaric CO2 sorption process. Analysis of the diffraction data indicates that the CO2 molecules in the pores are disordered and nonlocalized. Despite this, it was possible to quantify the evolution of the occupation of the pores. CO2 is adsorbed at an approximately constant below 320 K from 10% loading to full capacity at 195 K.acceptedVersio
Variability in the formation and framework polymorphism of metal-organic frameworks based on yttrium(III) and the bifunctional organic linker 2,5-dihydroxyterephthalic acid
No full textDepending on the solvothermal reaction conditions, we obtained three different metal‐organic frameworks with yttrium(III) as metal component and 2,5‐dihdyroxyterepthalic acid (H4dhtp) as bifunctional organic linker: Y2(H2dhtp)3(dmf)4·(dmf)2 (CPO‐29) contains dinuclear, paddle‐wheel like inorganic secondary building units (SBUs) connected by the organic linker to a network with α‐Po topology, while Y2(H2dhtp)(dhtp)(dmf)2 (CPO‐30) and Y2(H2dhtp)(dhtp)(dmf)2(H2O)2·(H2O)4 (CPO‐31) contain one‐dimensional inorganic SBUs that differ in how the half‐ and fully deprotonated ligands are connected to and arranged around them. Only the carboxylic acid groups of the organic linker are deprotonated in CPO‐29, while CPO‐30 and CPO‐31 contain both 2,5‐dihydroxyterephthalate (H2dhtp2–) linkers and fully deprotonated 2,5‐dioxidoterephthalate (dhtp4–) linkers. All three compounds contain large volumes filled with solvent, but we were able to demonstrate permanence of porosity only for CPO‐30. Variable temperature powder X‐ray diffraction reveals that CPO‐29 and CPO‐31 undergo discontinuous phase transitions upon heating, and the flexibility of the framework structure indicated by these might be the reason for the inability to access the pore volume. Desolvated CPO‐30 and CPO‐31 are polymorphs, whose network structures differ in whether the H2dhtp2– and dhtp4– linkers are located in cis or trans arrangement around the inorganic SBU.publishedVersio
