Magnus Rønning

Process design simulation of H2 production by sorption enhanced steam methane reforming: evaluation of potential CO2 acceptors

A concept for pure H2 production with CO2 capture by sorption enhanced steam methane reforming (SESMR) has been investigated. Conventional steam reforming with CO2 capture has been used as a base case for comparison. SESMR resulted in competitive thermal efficiencies, which were highly dependent on the CO2 acceptor material. Thus, CaO and other more novel solid acceptors such as Li2ZrO3, K-doped Li2ZrO3, Na2ZrO3 and Li4SiO4 were screened in terms of thermodynamics, kinetics and stability. It was concluded that higher H2 yields and efficiencies can be obtained for the acceptors that have good ability for removing CO2 at low partial pressures. The best efficiencies were obtained using CaO as acceptor due to its more favourable thermodynamics and high reaction rates; however, the stability of CaO has to be improved. On the other hand, Na2ZrO3 is a promising alternative due to the good kinetics for CO2 removal and the stability.

Molecular Dynamics Simulations of the Interactions between Platinum Clusters and Carbon Platelets

Molecular dynamics simulations have been performed with two reactive force fields to investigate the structure of a Pt100 cluster adsorbed on the three distinct sides of a carbon platelet. A revised Reax force field for the carbon-platinum system is presented. In the simulations, carbon platelet edges both with and without hydrogen termination have been studied. It is found that the initial mismatch between the atomic structure of the platelet egde and the adsorbed face of the Pt100 cluster leads to a desorption of a few platinum atoms from the cluster and the subsequent restructuring of the cluster. Consequently, the average Pt-Pt bond length is enlarged in agreement with experimental results. This change in the bond length is supposed to play an important role in the enhancement of the catalytic activity, which is demonstrated by studying the changes in the bond order of the platinum atoms. We found an overall shift to lower values as well as a loss of the well-defined peak structure in the bond-order distribution.

Effects of Steam Addition on the Properties of High Temperature Ceramic CO2 Acceptors

The effects of steam addition on the stability and C O2 capture and regeneration properties of Li2 Zr O3 , K-doped Li2 Zr O3 , Na2 Zr O3 , and Li4 Si O4 at relevant sorption enhanced steam methane reforming conditions has been investigated. It has been observed that the presence of water in the form of steam enhances the capture and regeneration rates. However, a large decay in the capacity is observed when compared to the performance of the acceptors in dry conditions. The reasons for the improved kinetics are not clear, but a higher mobility of the alkaline ions is suggested. The losses in capacity could be due to sintering under high pressure of steam, vaporization of alkali metals, and/or phase segregation.

In situ EXAFS study of the bimetallic interaction in a rhenium-promoted alumina-supported cobalt Fischer-Tropsch catalyst

The local environments about the rhenium atoms in a Co–Re/γ-Al2O3 catalyst after different reduction periods have been studied by X-ray absorption spectroscopy (EXAFS). The bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium LIII EXAFS analysis shows that bimetallic particles are formed after reduction at 450 ○C with the average particle size being less than 15 Å. More than 6 h reduction at 450 ○C is required for complete reduction of accessible rhenium.

EXAFS study of zinc coordination in bacitracin A

Bacitracin is a dodecapeptide antibiotic produced by Bacillus sp. The antibacterial activity depends upon the peptide binding a divalent metal. Hitherto, the exact coordination of the cation has not been established. In particular the role played by the sulphur and nitrogen atoms of the thiazoline ring of bacitracin A has not been clear. Here the coordination of Zn2+ by bacitracin A has been studied using extended X-ray absorption fine structure. The experimental data are consistent with a model in which zinc is coordinated by one oxygen and three nitrogen atoms with the sulphur atom of the thiazoline ring not being directly involved in the zinc coordination.

Studies on the pre-edge region of the X-ray absorption spectra of copper(I) oxide and the diamminecopper(I) ion

The distinctive pre-edge feature in the X-ray absorption spectra of copper(I) oxide and the diamminecopper(I) ion at the copper K-edge has been studied using synchrotron radiation. The relative intensities of these features, which are characteristic of copper(I) compounds, have been measured via the peak areas. The intensity of the oxide peak, with regard to the diammine and other two-coordinate copper environments, is anomalous, being reduced by ca. 60%. This is attributed to the macromolecular nature of the oxide, and the formation of intense excitons. Effects due to the small degree of non-stoichiometry may play and additional part in modifying pre-edge intensity by influencing the exciton lifetime.

Coaxial carbon/metal oxide/aligned carbon nanotube arrays as high-performance anodes for lithium ion batteries.

Coaxial carbon/metal oxide/aligned carbon nanotube (ACNT) arrays over stainless-steel foil are reported as high-performance binder-free anodes for lithium ion batteries. The coaxial arrays were prepared by growth of ACNTs over stainless-steel foil followed by coating with metal oxide and carbon. The carbon/manganese oxide/ACNT arrays can deliver an initial capacity of 738 mAh g(-1) with 99.9 % capacity retention up to 100 cycles and a capacity of 374 mAh g(-1) at a high current density of 6000 mA g(-1). The external carbon layer was recognized as a key component for high performance, and the mechanism of performance enhancement was investigated by electrochemical impedance spectroscopy, electron microscopy, and X-ray diffraction analysis. The layer increases rate capability by enhancing electrical conductivity and maintaining a low mass-transfer resistance and also improves cyclic stability by avoiding aggregation of metal-oxide particles and stabilizing the solid electrolyte interface. The resultant principle of rational electrode design was applied to an iron oxide-based system, and similar improvements were found. These coaxial nanotube arrays present a promising strategy for the rational design of high-performance binder-free anodes for lithium ion batteries.

Multivariate curve resolution applied to in situ X-ray absorption spectroscopy data: an efficient tool for data processing and analysis.

Large datasets containing many spectra commonly associated with in situ or operando experiments call for new data treatment strategies as conventional scan by scan data analysis methods have become a time-consuming bottleneck. Several convenient automated data processing procedures like least square fitting of reference spectra exist but are based on assumptions. Here we present the application of multivariate curve resolution (MCR) as a blind-source separation method to efficiently process a large data set of an in situ X-ray absorption spectroscopy experiment where the sample undergoes a periodic concentration perturbation. MCR was applied to data from a reversible reduction-oxidation reaction of a rhenium promoted cobalt Fischer-Tropsch synthesis catalyst. The MCR algorithm was capable of extracting in a highly automated manner the component spectra with a different kinetic evolution together with their respective concentration profiles without the use of reference spectra. The modulative nature of our experiments allows for averaging of a number of identical periods and hence an increase in the signal to noise ratio (S/N) which is efficiently exploited by MCR. The practical and added value of the approach in extracting information from large and complex datasets, typical for in situ and operando studies, is highlighted.

One-step electrochemical synthesis of tunable nitrogen-doped graphene

A one-step electrochemical approach for the production of tunable nitrogen-doped graphene has been developed in this work. The simultaneous production and nitrogen incorporation of graphene are realized by electrochemical exfoliation of graphite in an aqueous electrolyte containing (NH4)2SO4 and NH3·H2O, which serve as an exfoliating agent and a nitrogen source, respectively. Both nitrogen contents and nitrogen bonding configurations can be manipulated by tuning the exfoliation conditions. The mechanism of nitrogen doping is proposed, based on analysis of the released gas from the graphite electrode, partially exfoliated graphite and graphene obtained. This green, efficient, low cost and scalable method provides a possible way for the large scale production of high-quality nitrogen-doped graphene. The nitrogen-doped graphene obtained is evaluated as a catalyst for the oxygen reduction reaction. It is demonstrated to be among the best nitrogen-doped graphene-based catalysts for the oxygen reduction reaction, even though the preparation process is extremely facile. Significantly, an Al–air battery is assembled, for the first time, by utilizing nitrogen-doped graphene as the cathode catalyst in this work. It can deliver a high specific capacity of 619 mA h gAl−1, corresponding to a specific energy of 817 W h kgAl−1, which is on a par with or better than that of Al–air batteries based on metal catalysts.

Towards a highly-efficient fuel-cell catalyst: optimization of Pt particle size, supports and surface-oxygen group concentration.

In the present work, methanol oxidation reaction was investigated on Pt particles of various diameters on carbon-nanofibers and carbon-black supports with different surface-oxygen concentrations, aiming for a better understanding of the relationship between the catalyst properties and the electrochemical performance. The pre-synthesized Pt nanoparticles in ethylene glycol, prepared by the polyol method without using any capping agents, were deposited on different carbon supports. Removal of oxygen-groups from the carbon supports had profound positive effects on not only the Pt dispersion but also the specific activity. The edge structures on the stacked graphene sheets in the platelet carbon-nanofibers provided a strong interaction with the Pt particles, significantly reconstructing them in the process. Such reconstruction resulted in the formation of more plated Pt particles on the CNF than on the carbon-black and exposure of more Pt atoms with relatively high co-ordination numbers, and thereby higher specific activity. Owing to the combined advantages of optimum Pt particle diameter, an oxygen-free surface and the unique properties of CNFs, Pt supported on heat-treated CNFs exhibited a higher mass activity twice of that of its commercial counterpart.