Search

Using captured CO2 as a chemical feedstock is widely considered toward establishing low carbon technologies to mitigate climate change. Process systems engineering analyses can help increase the chances of success by identifying attractive targets at early stages. Here, a comparative techno-economic and environmental analysis of three thermocatalytic CO2-based plants individually producing liquid hydrocarbon transportation fuels (LHTF), methanol, and 1-propanol is introduced. While the 1-propanol plant generates a remarkable profit, the LHTF and methanol plants are not economically viable, mainly due to the CO2 and H2 input cost. Sensitivity analysis shows that the feedstock prices need to drop by 80% for these two plants to break even. A tax structure is not a sensible option since it would be more than 4 times the highest carbon tax currently implemented in the country. In terms of the environmental performance, the CO2 utilization efficiencies are 45.5, 60.1, and −33.8% for LHTF, methanol, and 1-propanol syntheses, respectively. The negative utilization efficiency in the 1-propanol plant highlights the need of a greener production of its raw material ethylene. When the entire life cycles of the products are considered, these emerging plants emit 85.9, 77.4, and 35.9% less CO2 than their conventional counterparts for the same output. Our study provides the first evaluation of CO2-based 1-propanol synthesis, highlighting its potential, underscores gaps in the CO2-based LHTF, methanol, and 1-propanol by comparing them on a uniform common basis, and sets future research directions.

ECNS 2015, Zaragoza (Spain), August 30th-September 4th 2015, A particularly interesting aspect of Carbon Nanotubes is their use as nearly one-dimensional nano-containers. Apart of their possibilities for controlled chemistry in nano- fluidics devices new phenomena induced by confinement are also expected, such as liquid like ordered structures or exotic crystalline phases. Here, we present a series of neutron diffraction measurements (instrument D20, ILL, Grenoble) of molecular deuterium confined within Multiple Wall Carbon Nanotubes (MWCTNs). Bulk liquid D2 at its vapour pressure crystallises in an hcp structure at ~18.7 K. At low uptakes we have found a clear depression of the solidification temperature down to ~13.25 K. Interestingly, at the lowest uptake the diffraction pattern is consistent with the minimal fcc lattice compatible with a cylindrical symmetry.

We first focus on the role of the instrumental resolution in Elastic Incoherent Neutron Scattering (EINS) where the connection between the Self Distribution Function (SDF) and the measured EINS intensity profile is highlighted. Second we show how the SDF procedure allows both the total and the partial Mean Square Displacement (MSD) evaluation, through the total and the partial SDFs. Finally, we compare the SDF and the Gaussian procedures, by applying the two approaches to EINS data collected, by the IN13 backscattering spectrometer (ILL, Grenoble), on aqueous mixtures of two homologous disaccharides, i.e. sucrose and trehalose, and on myoglobin. © 2011 Bentham Science Publishers. All rights reserved.

VII Reunión de la Sociedad Española de Técnicas Neutrónicas, Pamplona, 22 - 25 Junio 2014

Ourense, 2 - 4 de Abril de 2014; www.gefenol.es/FisEs/14/

10 págs.; 7 figs.; 1 tab. ; PACS number s : 75.25. z, 75.30.Ds, 75.40.Gb, 75.47.Gk, The spin dynamics of substituted colossal magnetoresistive (CMR) manganites of general formula La0.7 Pb0.3 (Mn1-x Fex) O3, 0≤x≤0.2 is investigated by means of neutron spin-echo measurements. Substitution of Mn by Fe leads to a strong decrease of the temperature of macroscopic magnetic long-range ordering with a concomitant enhancement of the CMR effect. For x=0.2, a long-range-ordered state is not achieved as a result of the increase in antiferromagnetic interactions brought forward by Fe+3 -Mn couplings. The results display two relaxations having well separated decay constants. A fast process with a relaxation time of about 10 ps within the paramagnetic phase is found for all compositions. It shows a remarkably strong dependence with temperature and sample composition as the apparent activation energy for spin diffusion as well as the preexponential term exemplify. The physical origin of such a fast relaxation is assigned to heavily damped or overdamped spin waves (spin diffusion) on the basis of some signatures of excitations having finite frequencies found for the parent compound La0.7 Pb0.3 Mn O3 at temperatures just below Tc, together with preliminary data on the effect of Fe doping on the stiffness constant. A slower relaxation is present for all compositions. Its temperature dependence follows the behavior of the macroscopic magnetization, and its intensity grows within the ordered ferromagnetic state. Its physical origin is ascribed to collective reorientation of nanoscale ferromagnetic domains on the basis of the wave-vector dependence of its relaxation rate and amplitude. © 2007 The American Physical Society., J.G. and J.M.B. thank the Spanish Ministerio de Educacion y Ciencia for financial support under research Grant No. MAT2005-0686-C04-03. F.J.B. and P.R. acknowledge financial support from the European Commission through NMI3 to carry out preliminary measurements at the FZJ facilities.

The spin dynamics of substituted colossal magnetoresistive (CMR) manganites of general formula La0.7Pb0.3(Mn1-xFex)O-3, 0

6 págs.; 5 figs.; PACS number s : 61.46. w, 63.22. m, 61.12.Ex, We present a comparative study of the excitations in bulk and liquid D2 confined within the pores of MCM-41. The material (Mobile Crystalline Material-41) is a silicate obtained by means of a template that yields a partially crystalline structure composed by arrays of nonintersecting hexagonal channels of controlled width having walls made of amorphous SiO2. Its porosity was characterized by means of adsorption isotherms and found to be composed by a regular array of pores having a narrow distribution of sizes with a most probable value of 2.45 nm. The assessment of the precise location of the sample within the pores is carried out by means of pressure isotherms. The study was conducted at two pressures which correspond to pore fillings above the capillary condensation regime. Within the range of wave vectors where collective excitations can be followed up (0.3≤Q≤3.0 Å-1), we found confinement brings forward a large shortening of the excitation lifetimes that shifts the characteristic frequencies to higher energies. In addition, the coherent quasielastic scattering shows signatures of reduced diffusivity. © 2006 The American Physical Society., This work was supported in part by Grant No. MAT2002-04178-C04 Spain.

Double exchange (DE)-mediated ferromagnetism in manganites, in which the Zener pair (Mn3+/Mn4+) is a key factor, is marked by the coexistence of the magnetic transition and the metal-insulator transition, thus distinguishing itself from superexchange (SE)-mediated ferromagnetism. Through detailed magnetization, transport and XAS studies, it was proposed by some of us that a unique magnetic pair-making effect occurs in Ru-substituted La0.6Pb0.4Mn1-xRUxO3 by virtue of variable valency of Ru and Mn. Ru ion, exhibiting a variable valency of Ru4+ and Ru5+, governs the DE-mediated coupling by initiating a magnetic pair-making effect with Mn3+ and Mn4+ states. Neutron diffraction measurements carried out on these compounds in the temperature range 4.2-500 K reveal the microscopic nature of magnetic ordering. Data obtained, in conjunction with data from other experimental techniques above, show that (i) Ru participates in the DE interaction with Mn for x 0.4, and (iii) SE ferromagnetic interactions are favored for x > 0.4. (c) 2006 Elsevier B.V. All rights reserved.

The effect of Fe doping on the magnetic properties of La0.7Pb0.3Mn1-xFexO3(0

A study on the effect of Fe doping on the magnetic properties of La0.7Pb0.3Mn1-xFexOx, x = 0 and x = 0.2 perovskites is conducted using muon spectroscopy and macroscopic static magnetization measurements. For x = 0, magnetization curves show a clear ferromagnetic component while a 20% Fe doping leads to the appearance of a kink in zero-field curves at low temperatures, attributed to progressive spin freezing together with a reduction of the ferromagnetic component. On dynamic grounds, we show that this effect translates into the appearance of non-exponential relaxation as T, is crossed from above. (c) 2005 Elsevier B.V. All rights reserved.

Inelastic neutron scattering has been applied to the study of the spin dynamics of Cr-based antiferromagnetic octanuclear rings where a finite total spin of the ground state is obtained by substituting one Cr(III) ion (s = 3/2) with Zn (s = 0), Mn (s = 5/2) or Ni (s = 1) di-cations. Energy and intensity measurements for several intra-multiplet and inter-multiplet magnetic excitations allow us to determine the spin wavefunctions of the investigated clusters. Effects due to the mixing of different spin multiplets have been considered. Such effects proved to be important to correctly reproduce the energy and intensity of magnetic excitations in the neutron spectra. On the contrary to what is observed for the parent homonuclear Cr8 ring, the symmetry of the first excited spin states is such that anticrossing conditions with the ground state can be realized in the presence of an external magnetic field. Heterometallic Cr7M wheels are therefore good candidates for macroscopic observations of quantum effects., Comment: 9 pages, 11 figures, submitted to Phys. Rev. B, corrected typos and added references, one sentence changed

The present neutron-scattering experimental findings concern with a study of fragility of trehalose, maltose, and sucrose/water mixtures. The fragility degree has been characterized by a new definition based on the correlation between viscosity and mean-square displacement as obtained by elastic incoherent neutron scattering. The fragility values obtained for the homologous disaccharides/water mixtures are compared with those obtained for other glass-forming systems of different "strength". The less-fragile character of the trehalose/H2O mixture in respect to maltose and sucrose/H2O mixtures is finally linked to the better bioprotective capability.

We present an extensive gallium NMR study of the geometrically frustrated kagome bi-layer compound SrCr_(9p)Ga_(12-9p)O_(19) (Cr^3+, S=3/2) over a broad Cr-concentration range (.72, Comment: 19 pages, 19 figures, revised version resubmitted to PRB Minor modifications: Fig.11 and discussion in Sec.V on the NMR shift

Exchange integrals and single-ion anisotropy parameters of a ring-shaped molecular cluster, comprising eight chromium(III) ions (s=3/2) were determined by inelastic neutron scattering. Effects due to the mixing of different spin multiplets have been considered. Such effects proved to be important to correctly reproduce the relative intensity of magnetic excitations in the neutron spectra. Evidence of decreasing lifetimes with increasing energy of excited spin states was found. The microscopic picture emerging from neutron spectroscopy was confirmed by the temperature dependence of the heat capacity.

7 figures.-- Supplementary data available.-- © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Crystallization under stringent cylindrical confinement leads to novel quasi-one-dimensional materials. Substances with strong cohesive interactions can eventually preserve the symmetries of their bulk phase compatible with the restricted geometry, while those with weak cohesive interactions develop qualitatively different structures. Frozen molecular deuterium (D2), a solid with a strong quantum character, is structurally held by weak dispersive forces. Here, the formation of one-dimensional D2 crystals under carbon nanotube confinement is reported. In contradiction with its weak cohesive interactions, their structures, scrutinized using neutron scattering, correspond to definite cylindrical sections of the hexagonal close-packed bulk crystal. The results are rationalized on the grounds of numerical calculations, which point towards nuclear quantum delocalization as the physical mechanism responsible for the stabilization of such outstanding structures., This work has been partly supported by the Spanish Agencia Estatal de Investigación (AEI), Fondo Europeo de Desarrollo Regional (FEDER, EU), Ministerio de Economía y Competitividad (MINECO), Ministerio de Ciencia, Innovación y Universidades (MCIU), under Grants No. MAT2016-75354-P (AEI/FEDER, EU), FIS2015-64654-P (MINECO/FEDER, EU), MAT2015-68394-R (MINECO/FEDER, EU), PGC2018-097018-B-I00 (MCIU/AEI/FEDER, EU), MAT2012-33633 (MINECO/FEDER, EU), MAT2012-39199-C02-02 (MINECO/FEDER, EU), by EU COST Action CM1405 “Molecules in Motion” (MOLIM), and by Spanish Ministerio de Ciencia e Innovación under Grants No. MAT2007-65711-C04-01, MAT2007-65711-C04-05, MAT2002-04540-C05-02, MAT2002-04540-C05-03, and MAT2002-04540-C05-04.

In the present contribution, a procedure for molecular motion characterization based on the evaluation of the Mean Square Displacement (MSD), through the Self-Distribution Function (SDF), is presented. It is shown how MSD, which represents an important observable for the characterization of dynamical properties, can be decomposed into different partial contributions associated to system dynamical processes within a specific spatial scale. It is also shown how the SDF procedure allows us to evaluate both total MSD and partial MSDs through total and partial SDFs. As a result, total MSD is the weighed sum of partial MSDs in which the weights are obtained by the fitting procedure of measured Elastic Incoherent Neutron Scattering (EINS) intensity. We apply SDF procedure to data collected,by IN13, IN10 and IN4 spectrometers (Institute Laue Langevin), on aqueous mixtures of two homologous disaccharides (sucrose and trehalose) and on dry and hydrated (H2O and D2O) lysozyme with and without disaccharides. It emerges that the hydrogen bond imposed network of the water-trehalose mixture appears to be stronger with respect to that of the water-sucrose mixture. This result can justify the higher bioprotectant effectiveness of trehalose. Furthermore, it emerges that partial MSDs of sucrose and trehalose are equivalent in the low Q domain (0÷1.7) Å−1 whereas they are different in the high Q domain (1.7÷4) Å−1. This suggests that the higher structure sensitivity of sucrose should be related to the small spatial observation windows. Moreover, the role of the instrumental resolution in EINS is considered. The nature of the dynamical transition is highlighted and it is shown that it occurs when the system relaxation time becomes shorter than the instrumental energy time. Finally, the bioprotectants effect on protein dynamics and the amplitude of vibrations in lysozyme are presented.