Activity of iron pyrite towards low-temperature ammonia production

© 2016 In this work we report the characteristics of iron pyrite toward the production of ammonia at low temperatures under ultra-high vacuum conditions. We review (with additional unpublished details) our previous systematic study of nitrogen and hydrogen adsorption on single-crystal iron pyrite (FeS 2 ) and summarise our earlier findings regarding the possibility of ammonia synthesis on this material. We also present new results concerning the adsorption of nitrogen and hydrogen on two related materials, namely molybdenum-treated iron pyrite surfaces and iron pyrite nanostructures deposited on a gold single-crystal. On the bare iron pyrite samples, ammonia is produced upon hydrogenation of preadsorbed N species at 230 K, demonstrating that all hydrogenation steps are possible at low pressures and temperatures. Nitrogen adsorbs molecularly on FeS 2 {100} at low temperatures, desorbing at 130 K, but does not adsorb dissociatively even at pressures up to 1 bar. Adsorbed nitrogen species can, however, be obtained through exposure to excited nitrogen species. Hydrogen adsorbs on FeS 2 {100}, but only in the presence of an incandescent Ta filament. Recombinative desorption of H 2 occurs at 225 K and is accompanied by desorption of H 2 S at 260 K. On the molybdenum-treated iron-pyrite, no appreciable N ads species were detected under the experimental conditions studied, and the same is true for iron pyrite nanostructures on Au{111}. We also provide further details of our efficient and reproducible method for preparing well-ordered stoichiometrically pure FeS 2 {100} suitable for surface science studies

Spontaneous local symmetry breaking: A conformational study of glycine on Cu{311}

[Image] Understanding the interplay between intrinsic molecular chirality and chirality of the bonding footprint is crucial in exploiting enantioselectivity at surfaces. As such, achiral glycine and chiral alanine are the most obvious candidates if one is to study this interplay on different surfaces. Here, we have investigated the adsorption of glycine on Cu{311} using reflection–absorption infrared spectroscopy, low-energy electron diffraction, temperature-programmed desorption, and first-principles density-functional theory. This combination of techniques has allowed us to accurately identify the molecular conformations present under different conditions and discuss the overlayer structure in the context of the possible bonding footprints. We have observed coverage-dependent local symmetry breaking, with three-point bonded glycinate moieties forming an achiral arrangement at low coverages, and chirality developing with the presence of two-point bonded moieties at high coverages. Comparison with previous work on the self-assembly of simple amino acids on Cu{311} and the structurally similar Cu{110} surface has allowed us to rationalize the different conditions necessary for the formation of ordered chiral overlayers.We acknowledge financial support from the Engineering and Physical Sciences Research Council.This is the final version of the manuscript. It first appeared from ACS via http://dx.doi.org/10.1021/acs.jpcc.5b0234

Proline-derived structural phases on Cu{311}

Structural phases formed by adsorption of L-proline onto a Cu{311} surface in ultra-high vacuum were investigated using reflection-absorption infrared spectroscopy, low-energy electron diffraction and scanning tunnelling microscopy. An ordered structural phase formed by self-assembly of L-prolinate with (2,1;1,2) periodicity, and a transition from pure l3 bonding to a mixture of l3 and l2 bonding with increasing exposure at 300 K, were observed. This behaviour has broad parallels with that previously seen with alaninate and glycinate on Cu{311}, but the detailed correlation between structure and bonding, and their evolution during subsequent annealing, are markedly different for prolinate as compared to alaninate and glycinate. At annealing temperatures around 480–490 K, a new structural phase with (5,3;4,6) periodicity emerges. We tentatively attribute this to pyrrole-2-carboxylate, formed by dehydrogenation and aromatization of the pyrrolidine ring of prolinate. The observation of equal areas of the two possible mirror domains associated with the two possible adsorbate–substrate bonding enantiomers implies a prochiral intermediate.The Engineering and Physical Sciences Research Council is acknowledged for financial support.This is the final published version. It first appeared at http://link.springer.com/article/10.1007/s11244-015-0400-2

Epitaxial growth of few-layer MoS2(0001) on FeS2{100}.

Physical vapour deposition of Mo on an FeS2{100} surface was performed at 170 K. Near-epitaxial growth of MoS2(0001) overlayers of the order of 1 nm thickness was observed when the Mo-covered substrate was subsequently heated to 600 K.The authors thank the EPSRC (grant ref. EP/E039782/1) for funding.This is the final published version. It first appeared at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CC/c4cc06628f#!divAbstract

Increased thermal stability of activated N2 adsorbed on K-promoted Ni{110}

Industrial synthesis of ammonia takes place at high temperatures and pressures via the dissociative adsorption of molecular nitrogen on a transition metal catalyst. In contrast, biological ammonia synthesis occurs under ambient conditions via the hydrogenation of intact molecular nitrogen at the active site of an enzyme. We hypothesise that the latter process may be mimicked within an inorganic system if the intact nitrogen molecule can be polarised, rendering it particularly susceptible to attack by hydrogen. Furthermore, by analogy with the surface chemistry of carbon monoxide at alkali-modified nickel and cobalt surfaces, we consider whether such a polarisation may be achieved by coadsorption with potassium on the same or similar transition metals. Here, we report on reflection absorption infrared spectroscopy results, interpreted with the aid of first-principles density functional calculations, which reveal both similarities and differences between the behaviour of carbon monoxide and nitrogen. Importantly, our calculations suggest that the surface-induced dipole of molecular nitrogen can indeed be enhanced by the coadsorbed alkali metal

Spanish adaptation of the Stroke and Aphasia Quality of Life Scale-39 (SAQOL-39)

[Abstract] Aim. The stroke and aphasia quality of life scale-39 is an interviewer administered questionnaire that has been developed and validated in the United Kingdom to be applied to patients with chronic aphasia as a consequence of a stroke. The objective of this article was to translate the Stroke and Aphasia Quality of Life-39 Scale (SAQOL-39) into Spanish language, and evaluate its acceptability and reliability. Methods. The cross-cultural adaptation of the SAQOL- 39 into Spanish was carried out by following the translation and back-translation method. Twenty three patients with long-term aphasia due to stroke were tested. The patients were interviewed twice in a period from 2 to 12 days. The acceptability of the Spanish SAQOL- 39 was evaluated by examining the floor/ceiling effects and the missing data. The reliability was assessed by Cronbach’s alpha (internal consistence) and intraclass correlation coefficients (test-retest reliability) for the overall scale and its subdomains. Results. There were no difficulties to translate the original version into Spanish. There was good acceptability demonstrated by minimal missing data and floor/ceiling effects. Test-retest reliability for the overall score, and the subscales scores was 0.949 (0.854-0.944). Internal consistency analysis by Cronbach’s α was 0.950 (0.851-0.900). Conclusion. This small scale study provided preliminary evidence for the acceptability and reliability of the Spanish version of the SAQOL-39. Further testing in larger samples is needed to evaluate the validity of the scale, its sensitivity to change and to confirm its reliability

On the Solvation of Redox Mediators and Implications for their Reactivity in Li-Air Batteries

Lithium-air batteries are a promising energy storage technology for transport applications, given their exceptionally high energy density. However, their development is significantly hampered by high overpotentials, which lead to poor efficiency and short lifetimes. Redox mediators provide a solution to this problem by shuttling electrons from the electrode to the active species at just above the redox potential of the mediator. Thus, knowing the redox potential and having the ability to tune it are critical to electrochemical performance. We focus on LiI as a model mediator—given its additional role in controlling LiOH vs Li2O2 chemistry—and use cyclic voltammetry (CV), NMR, UV/Vis spectrometry, and molecular dynamics (MD) simulations to monitor the effects of electrolyte composition on solvation. Li+ and I– solvation in common Li-air solvents, the electrochemical implications, and the applicability of each technique to probe the nature of the solvation shell and its effect on the electrochemical properties are explored. Starting with a simple thermodynamic model, we then used UV/Vis spectrometry to probe I– solvation, 1H NMR spectroscopy to study water solvation and 31P of the probe molecule triethylphosphine oxide (TEPO) to explore Li+ solvation; we find that no single descriptor can provide an accurate description of the solvation environment. Instead, we use all these methods in combination with the MD results to help rationalise the CV data. We find that the I– solvation improves significantly in tetraglyme (G4), with increasing salt and water concentration, but minimal effects on changing salt/water concentrations are seen in DMSO. In contrast, increasing salt concentration increases the Li+ activity in DMSO but not in G4. Furthermore, a simple model considering the equilibria between the different species was used to explain the 1H NMR data.</jats:p

On the Solvation of Redox Mediators and Implications for their Reactivity in Li-Air Batteries

Lithium-air batteries are a promising energy storage technology for transport applications, given their exceptionally high energy density. However, their development is significantly hampered by high overpotentials, which lead to poor efficiency and short lifetimes. Redox mediators provide a solution to this problem by shuttling electrons from the electrode to the active species at just above the redox potential of the mediator. Thus, knowing the redox potential and having the ability to tune it are critical to electrochemical performance. We focus on LiI as a model mediator—given its additional role in controlling LiOH vs Li2O2 chemistry—and use cyclic voltammetry (CV), NMR, UV/Vis spectrometry, and molecular dynamics (MD) simulations to monitor the effects of electrolyte composition on solvation. Li+ and I– solvation in common Li-air solvents, the electrochemical implications, and the applicability of each technique to probe the nature of the solvation shell and its effect on the electrochemical properties are explored. Starting with a simple thermodynamic model, we then used UV/Vis spectrometry to probe I– solvation, 1H NMR spectroscopy to study water solvation and 31P of the probe molecule triethylphosphine oxide (TEPO) to explore Li+ solvation; we find that no single descriptor can provide an accurate description of the solvation environment. Instead, we use all these methods in combination with the MD results to help rationalise the CV data. We find that the I– solvation improves significantly in tetraglyme (G4), with increasing salt and water concentration, but minimal effects on changing salt/water concentrations are seen in DMSO. In contrast, increasing salt concentration increases the Li+ activity in DMSO but not in G4. Furthermore, a simple model considering the equilibria between the different species was used to explain the 1H NMR data.</jats:p