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| 2. |
- Poulsen, R. D., et al.
(författare)
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Effects of Weak Intermolecular Interactions on the Molecular Isomerism of Tricobalt Metal Chains
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:22, s. 7580-7591
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Tidskriftsartikel (refereegranskat)abstract
- Depending on the number of interstitial solvent molecules, n, crystals of the linear chain compound Co-3(dipyridylamide)(4)Cl-2 center dot nCH(2)Cl(2) adopt either symmetrical or unsymmetrical metal chain structures. We explore here the possible reasons for such behavior using Hirshfeld surface analysis of intermolecular interactions as well as the charge density determined from 100(1) K X-ray diffraction data on the unsymmetrical complex Co-3(dipyridylamide)(4)Cl-2 center dot 2.11CH(2)Cl(2), u-1, and crystal structures of u-1 determined from single crystal synchrotron X-ray diffraction data at 20, 150, and 300 K. The new crystal structures are compared with previous structural results on a crystal with slightly different solvent content. This change in solvent content only affects the bond distances to atom Co(3), which are also strongly affected by temperature changes due to a spin crossover transition. Large differences in intermolecular interactions are revealed by the Hirshfeld surface analysis between symmetrical (s-1) and unsymmetrical (u-1) crystal solvates, suggesting that the molecular isomerism is strongly influenced by crystal packing effects. Topological analysis of the static electron density of u-1 suggests that there is direct metal-metal bonding for both the shorter Co(1)-Co(2) and the longer Co(2)-Co(3) contact. The approximate description of the system as a (Co2)(2+)-dimer and an isolated Co2+-ion is reflected in the character of the metal-ligand interactions, which are more ionic for the isolated Co(3) atom, and the topological charges Co(1)(+0.50), Co(2)(+0.77), and Co(3)(+1.36). The two termini of u-1 are found to be very different, both in terms of structural surroundings as well as topology. The central Co(2) atom is similar to a cobalt atom in a tetragonally distorted octahedral environment resulting in preferred occupancy in the t(2g) orbitals. The Co(1) atom has significant deformation in the xz and yz planes (z along the chain axis, x and y toward ligands) reflecting covalent interactions with the terminal chlorine atom Cl(1). The Co(3) atom has a relatively high occupancy of the d(x2-y2) orbital and a relatively low occupancy of the d(xy) orbital confirming that these orbitals are involved in the spin crossover process and predominantly responsible for the observed variation in bond lengths with temperature.
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- Shulman, Alexander, 1978, et al.
(författare)
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Chemical - Looping with oxygen uncoupling using Mn/Mg-based oxygen carriers - Oxygen release and reactivity with methane
- 2011
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 90:3, s. 941-950
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion with oxygen uncoupling (CLOU) is a method for combustion of solid and gaseous fossil fuels, which enables easy separation of carbon dioxide from the gaseous product mixture. In contrast to the related chemical-looping combustion (CLC) technology where gaseous or gasified fuels react directly with oxygen carriers, CLOU processes require oxygen carrier materials to be able to release oxygen in the fuel reactor and to regenerate by re-oxidation in oxygen-rich atmosphere in the air reactor at elevated temperature. Oxygen uncoupling properties and reactivities for methane combustion of 12 oxygen carrier particles, produced from mixtures of manganese and magnesium oxides with optional addition of titanium dioxide or calcium hydroxide, are investigated in a quartz batch reactor at 810 degrees C, 850 degrees C, 900 degrees C and 950 degrees C. All investigated oxygen carriers have oxygen release characteristics. The addition of calcium hydroxide facilitates oxygen release and combustion of methane, whereas addition of titanium dioxide does not have a pronounced effect on either oxygen uncoupling or reactivity of the oxygen carrier. In general, particles with greater extent of oxygen release have superior methane combustion properties. (C) 2010 Elsevier Ltd. All rights reserved.
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- Shulman, Alexander, 1978, et al.
(författare)
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High reactivity and mechanical durability of NiO/NiAl2O 4 and NiO/NiAl2O4/MgAl2O4 oxygen carrier particles used for more than 1000 h in a 10 kW CLC reactor
- 2009
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 48:15, s. 7400-7405
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a promising technology for CO 2 capture in the process of combustion of gaseous fossil fuels. Oxygen carrier materials based on Ni/NiO on NiAl2O4 and on NiAl2O4/MgAl2O4 support have previously shown high initial activity combined with high conversion of methane and low concentration of outgoing CO. The feasibility of the Ni/NiO system for CLC depends largely on the lifetime of the oxygen carrier particles in the reactor due to the high price of the material. Avoiding chemical and physical degradation of oxygen carriers is essential for long-term industrial-scale chemical-looping combustion operations, and the particles' activity and mechanical durability have to remain high during long operation times. In this study, a series of oxygen carrier samples were collected from a 10 kW CLC combustor operated for a total of 1016 h using oxygen carrier materials based on NiO/NiAl2O4 (N-VITO) for 405 h and a mixture of used NiO/NiAl2O4 with fresh NiO/NiAl2O 4/MgAl2O4(N-VITOMg) for 611 h, respectively. These samples were collected after certain time intervals and analyzed in terms of reactivity with methane in a quartz batch reactor. Also, the structural and mechanical properties of these samples were investigated by means of powder XRD, BET surface area measurements, light and scanning electron microscopy, energy dispersive X-ray spectrometry, and crushing strength evaluation. It was shown that both N-VITO and N-VITO/N-VITOMg demonstrate high reactivity and mechanical durability after having been used for more than 1000 h in the CLC 10 kW reactor, which makes them excellent candidates for applications within the area of chemical-looping combustion.
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- Shulman, Alexander, 1978, et al.
(författare)
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Incidence of end-stage renal disease following bariatric surgery in the Swedish Obese Subjects Study.
- 2018
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Ingår i: International journal of obesity. - : Springer Science and Business Media LLC. - 1476-5497 .- 0307-0565. ; 42, s. 964-973
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is a major public health problem leading to co-morbidities such as diabetes, hypertension and kidney failure. Bariatric surgery results in pronounced and maintained weight loss and prevention of obesity-related diseases and their complications. Most studies of bariatric surgery on kidney disease show improvements after surgery. However, long-term studies analyzing hard end-points are lacking. Here we report on the long-term effects of bariatric surgery compared to usual obesity care on incidence of end-stage renal disease (ESRD) alone and in combination with chronic kidney disease stage 4 (CKD4/ESRD).4047 patients were included in the Swedish Obese Subjects (SOS) study. Inclusion criteria were age 37-60 years and BMI≥34 in men and BMI≥38 in women. Patients in the bariatric surgery group (N=2010) underwent banding (18%), vertical banded gastroplasty (69%), or gastric bypass (13%); controls (N=2037) received usual obesity care. In this analysis, patients were followed up for a median time of 18 years. The incidence of ESRD and CKD4 was obtained by crosschecking the SOS database with the Swedish National Patient Register.During follow-up, ESRD occurred in 13 patients in the surgery group and in 26 patients in the control group (adjusted hazard ratio (HR)=0.27; 95% CI 0.12-0.60; p=0.001). The number of CKD4/ESRD events was 23 in the surgery group and 39 in the control group (adjusted HR=0.33; 95% CI 0.18-0.62; p<0.001). In both analyses, bariatric surgery had a more favorable effect in patients with baseline serum insulin levels above median compared to those with lower insulin levels (interaction p=0.010). Treatment benefit of bariatric surgery was also greater in patients with macroalbuminuria at baseline compared to those without macroalbuminuria (interaction p<0.001).Our study showed for the first time that bariatric surgery is associated with a long-term protection against ESRD and CKD4/ESRD.
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| 8. |
- Shulman, Alexander, 1978, et al.
(författare)
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Manganese/iron, manganese/nickel, and manganese/silicon oxides used in chemical-looping with oxygen uncoupling (CLOU) for combustion of methane
- 2009
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 23:10, s. 5269-5275
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping with oxygen uncoupling (CLOU) is a developing technology, which allows for inherent separation of carbon dioxide during combustion of gaseous and solid fuels. In contrast to the related chemical-looping combustion technology (CLC), where gaseous or gasified fuels react directly with oxygen carrier materials, CLOU utilizes oxygen carriers capable of releasing gaseous oxygen, provided appropriate thermal conditions exist in the fuel reactor, whereupon fuel reacts with the released oxygen. The oxygen carriers are thereafter regenerated by oxidation in the air reactor. In this work, a set of oxygen carrier materials synthesized from manganese oxides mixed with iron, nickel, and silicon oxides are evaluated in terms of their ability to release oxygen and to be regenerated with oxygen and in terms of demonstrated methane conversion in a quartz fluidized bed batch reactor at 810, 850, and 900 °C. The results demonstrate that two Mn/Fe oxygen carriers and one Mn/Ni oxygen carrier have both oxygen release characteristics and high reactivities with methane.The Mn/Fe oxygen carrier synthesized at 1100 °Cwas additionally shown to have an increasing methane conversion on a long-term basis, which opens for a possibility to use Mn/Fe oxygen carriers in time-extended large-scale chemical-looping operations.
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- Shulman, Alexander, 1978, et al.
(författare)
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Reversible sorption in the crystalline microporous semiconductor Rb-CTH-1
- 2010
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 183:9, s. 1912-1916
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Tidskriftsartikel (refereegranskat)abstract
- The sorption capacity of the recently reported crystalline microporous semiconductor Rb-CTH-1 was investigated, revealing that the structure demonstrates heat-induced reversible sorption of 3 wt% water and hydrocarbons. The Rb-CTH-1 structure maintains its crystallinity and semiconducting properties when heated to 150 degrees C. The treatment causes desorption induced irreversible rearrangements of the remaining guest species with a response in the semiconductive properties of the material. (C) 2010 Elsevier Inc. All rights reserved.
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| 12. |
- Shulman, Alexander, 1978, et al.
(författare)
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Reversible sorption of water in the crystalline microporous semiconductor K-SBC-1
- 2010
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811. ; 132:1-2, s. 128-131
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Tidskriftsartikel (refereegranskat)abstract
- Microporous semiconducting crystal structures are exceedingly rare and their usefulness for applications typical for microporous semiconductors is largely related to their sorption properties and to their semiconductor response to sorption. The sorption properties of the unique crystalline microporous semiconducting antimony(III) oxide telluride K-SBC-1 were evaluated by means of temperature-resolved diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermogravimetric analysis (TGA/DSC), and X-ray powder diffraction. K-SBC-1 was found to demonstrate heat-induced reversible sorption and desorption-induced rearrangements of guest water molecules. Upon heating to 300 degrees C 66% of the water content of K-SBC-1 desorbed. Desorption of water could be made more facile through activation of K-SBC-1 by heat treatment and then occurred at room temperature in a flow of nitrogen. These are unique properties compared to the few known related structures and thus represent a significant advancement in the field of microporous semiconductors. (C) 2010 Elsevier Inc. All rights reserved.
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| 13. |
- Shulman, Alexander, 1978, et al.
(författare)
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Structural analysis of the microporous semiconductor K-SBC-1 during its reversible sorption of water
- 2009
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 182:8, s. 2118-2121
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Tidskriftsartikel (refereegranskat)abstract
- The reversible sorption of water molecules in the crystalline microporous semiconductor K-SBC-1 was investigated using temperature-resolved single-crystal XRD analysis. Three crystallographic sites of adsorbed water molecules, differing in adsorption strength, were discovered in the pores of K-SBC-1. The least tightly bound is located at the centre of the {Sb12O18} tube and begins to desorb around 50°C. Above 200°C the more strongly bound water molecules rearrange from their potassium-coordinating positions to the centre of the tube, thus obtaining the characteristics of the loosely bound water, and desorb thereafter. At 240°C approximately 10% of the water has desorbed, leaving the host framework of K-SBC-1 intact. Upon re-adsorption of water at room temperature the molecules preferentially adsorb at sites in the centre of the {Sb12O18} tube. This shows that a heat treatment of 240–300°C activates K-SBC-1 for sorption and explains the observed facile desorption of water from activated samples.
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