Laser driven structured quantum rings

In this work we study harmonic emission from structured quantum rings (SQRs). In SQRs, electrons trapped in two-dimensional structures are further confined by an external potential composed of N scattering centers arranged on a circle. We build a suitable one-dimensional model Hamiltonian describing this class of systems and analytically solve the associated Schödinger equation. We find that the solution can be expressed in terms of Mathieu functions and focus on the specific case of N = 6. By exactly solving the time-dependent Schödinger equation, we then show how the harmonic response to linearly polarized lasers strongly depends on the ring physical parameters. The results illustrate how the additional degrees of freedom introduced by these parameters provide important handles to control the emitted spectrum that in some cases extends into the XUV region

Tests of prototype PCM 'sails' for office cooling

This is the post-print version of the final paper published in Applied Thermal Engineering. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.PCM modules, constructed from a paraffin/LDPE composite, were tested in an occupied London office, in summer. Design variations tested the effect on heat transfer of a black paint or aluminium surface, the effect of different phase transition zones and the effect of discharging heat inside or outside. The modules’ temperatures were monitored along with airflow rate, air temperature and globe temperature. Their small size meant any effect on room temperature was negligible. Using DSC measurements of the PCMs’ thermophysical properties, in conjunction with the environmental measurements, a semi-empirical model of the modules was constructed in FLUENT using an enthalpy-porosity formulation to model phase change. Good validation was obtained for all modules using the temperature measurements with notable divergence when maximum liquid fraction was reached. The model was validated by the temperature measurements and used to generate mean liquid fraction and surface heat transfer rate profiles for performance comparisons. The broad phase transition zones of the PCMs results in wasted latent heat capacity. Black modules transfer heat and exhaust latent storage capacity significantly quicker than aluminium modules, due to radiant exchange. Discharging heat outside leads to an increase in thermal storage capacity and a higher rate of heat absorption.Buro Happold Engineers and the EPSRC

Development and Optimisation of Phase Change Material-Impregnated Lightweight Aggregates for Geopolymer Composites Made from Aluminosilicate Rich Mud and Milled Glass Powder

Macro-encapsulated aggregates (ME-LWAs) consisting of expanded clay lightweight aggregates (LWAs) impregnated with a paraffin wax phase change material (PCM) was produced. To fully exploit the thermal energy retaining properties of PCM, it is fundamental to retain as much of the PCM as possible within the pores of the LWA. This paper investigates 3 different commercial materials to create a total of 14 different coating regimes to determine the most efficient coating method and material regarding its ability at retaining the PCM. The ME-LWAs are then further used as aggregates in geopolymer binders made from a combination of aluminosilicate rich mud and waste glass. Physical properties such as thermal conductivity and mechanical strength are determined for the geopolymer binder with and without the addition of the ME-LWA. A polyester resin was determined to be the most suitable choice of coating material for the ME-LWA, producing a practically leak-proof coating. The ME-LWA was also determined to be chemically neutral, showed a 42% higher thermal conductivity than the LWA in their raw state and maintained a latent heat of 57.93 J/g before and after being used in the geopolymer binder. Carbon fibres and graphite spray were used to improve the thermal conductivity of the resin coating, however no significant increase was detected. Finally, the compressive strength and thermal conductivity results achieved are acceptable for applications in buildings for enhancement of their energy efficiency.Partial finance support from the European Commission Horizon 2020 MARIE Skłodowska CURIE Research and Innovation Staff Exchange Scheme through the grant 645696 (i.e. REMINE project) is greatly acknowledged

Wacker-oxidation of Ethylene over Pillared Layered Material Catalysts

This paper concerns the Wacker oxidation of ethylene by oxygen in the presence of water over supported Pd/VOx catalysts. High surface area porous supports were obtained from layer-structured materials, such as, montmorillonite (MT), laponite (LT) (smectites), and hydrotalcite (layered double hydroxide, LDH) by pillaring. Before introduction of Pd, supports MT and LDH were pillared by vanadia. The laponite was used in titania-pillared form (TiO2-LAP) as support of Pd/VOx active component. Acetaldehyde (AcH), acetic acid (AcOH) and CO2 were the products with yields and selectivities, depending on the reaction conditions and the properties of the applied catalyst. Under comparable conditions the pillared smectite catalysts gave higher AcH yield than the pillared LDH catalyst. UV vis spectroscopic examination suggested that the pillared smectites contained polymeric chains of VO4, whereas only isolated monomeric VO4 species were present in the pillared LDH. The higher catalytic activity in the Wacker oxidation was attributed to the more favorable redox property of the polymeric than of the monomeric vanadia. The V3+ ions in the polymeric species can reduce O2 to O2- ions, whereas the obtained V5+ ions are ready to pass over O to Pd0 to generate PdO whereon the oxidation of the ethylene proceeds

Dynamics of carbon formation during the catalytic hydrodeoxygenation of raw bio-oil

The formation, growth and transformation of the carbon residue (coke) deposited on the catalyst during the raw bio-oil hydrodeoxygenation have been studied. These deposits have a great impact on the overall process performance, and they have been formed in accelerated deactivation conditions (450 degrees C, 65 bar, space time of 0.09 g(cat) h g(bio-oil)(-1)) using a continuous fixed bed reactor and a FeMoP/HZSM-5 catalyst. Coke deposition causes partial deactivation of the catalyst, which reaches a pseudosteady state of constant activity and also contant yields of interesting chemicals. The evolution of the coke in the transient state has been studied through temperature-programmed oxidation, Raman spectroscopy and elemental analysis. We have identified three different types of coke, whose composition evolves with time on stream towards condensed and stable structures. The assessment of the evolution of the reaction medium composition and the application of the principal component analysis (PCA) methodology have evidenced that the dynamics of coke have three stages: (1) it is controlled by the thermally-induced deposition of thermal lignin; (2) followed by the interconversion into intermediate coke through aging reactions; and (3) it ends up in a pseudosteady state dominated by the formation of catalytic coke species originating from both deoxygenated and carbonized intermediate coke as well as the condensation of aromatics in the reaction medium.This work has been carried out with the financial support of the Ministry of Economy and Competitiveness of the Spanish Government, some co-founded with ERDF funds (CTQ201567425-R, CTQ2016-79646-P), the Basque Government (IT121819), and the European Commission (Horizon H2020-MSCA RISE-2018, Contract No. 823745). Dr Idoia Hita is grateful for her postdoctoral grant awarded by the Department of Education, University and Research of the Basque Government (POS_2015_1_0035)

The Effect of Zeolite Features on Catalytic Performances of Cuznzr/Zeolite Hybrid Catalysts in One-pot CO2-to-DME Hydrogenation

The production of DME from CO2 hydrogenation is a way of recycling CO2 and it requires the use of a hybrid multifunctional catalyst to efficiently catalyze the two consecutive reaction paths of methanol synthesis and methanol dehydration directly in one single step. The aim of this work is to investigate the utilization of zeolite-based catalysts for dimethyl ether synthesis by assessing the role of catalyst features in both methanol dehydration and one-pot CO2 hydrogenation. Obtained results, discussed in terms of turnover frequency reveal that FER-type zeolite prepared with Si/Al=10 exhibits the best performances during vapor-phase methanol dehydration whilst the efficiency of CO2-to-DME process strongly depends on the way in which metallic and acidic materials are coupled. Single grain prepared via gel-oxalate precipitation of CuZnZr over zeolite crystals exhibit the best performances in terms of CO2 conversion and DME productivity

Efficient Catalytic Hydrotreatment of Kraft Lignin to Alkylphenolics using Supported NiW and NiMo Catalysts in Supercritical Methanol

Efficient catalytic hydrotreatment of Kraft lignin to yield aromatic monomers was demonstrated in supercritical methanol using a variety of NiW and NiMo catalysts on acidic, basic and neutral supports. It was found that NiW catalysts on neutral or basic supports are highly suitable for depolymerization of Kraft lignin to methanol soluble organics in high yields at 320 °C and 35 bar H2 pressure. An extensive analysis of the product mixtures was carried out using GC-MS-FID, GC × GC-FID, 2D HSQC NMR, GPC and elemental analysis, and several techniques were used for the characterization of the prepared catalysts in order to determine the acidity and basicity of the support and morphological changes after the catalytic reaction. The best results were obtained with sulphided NiW catalysts supported on activated carbon. Efficient depolymerization of Kraft lignin and a total 28 wt% monomer yield was obtained within 8 h and 76% of the products were alkylphenolics and guaiacolics. Over prolonged reaction times, the total monomer yield reached 35 wt%, containing up to 26 wt% alkylphenolics. During catalytic processing, deoxygenation was the most prevalent reaction and, importantly, no competing aromatic ring hydrogenation or undesired repolymerization to insoluble char was observed. The catalytic system described here represents a highly efficient and selective method for the production of alkylphenolics and guaiacolics from Kraft lignin

Physico-Chemical Modifications Affecting the Activity and Stability of Cu-Based Hybrid Catalysts during the Direct Hydrogenation of Carbon Dioxide into Dimethyl-Ether

The direct hydrogenation of CO2 into dimethyl-ether (DME) has been studied in the presence of ferrierite-based CuZnZr hybrid catalysts. The samples were synthetized with three different techniques and two oxides/zeolite mass ratios. All the samples (calcined and spent) were properly characterized with different physico-chemical techniques for determining the textural and morphological nature of the catalytic surface. The experimental campaign was carried out in a fixed bed reactor at 2.5 MPa and stoichiometric H2/CO2 molar ratio, by varying both the reaction temperature (200–300 °C) and the spatial velocity (6.7–20.0 NL∙gcat−1∙h−1). Activity tests evidenced a superior activity of catalysts at a higher oxides/zeolite weight ratio, with a maximum DME yield as high as 4.5% (58.9 mgDME∙gcat−1∙h−1) exhibited by the sample prepared by gel-oxalate coprecipitation. At lower oxide/zeolite mass ratios, the catalysts prepared by impregnation and coprecipitation exhibited comparable DME productivity, whereas the physically mixed sample showed a high activity in CO2 hydrogenation but a low selectivity toward methanol and DME, ascribed to a minor synergy between the metal-oxide sites and the acid sites of the zeolite. Durability tests highlighted a progressive loss in activity with time on stream, mainly associated to the detrimental modifications under the adopted experimental conditions

Setting the photoelectron clock through molecular alignment

The interaction of strong laser fields with matter intrinsically provides a powerful tool for imaging transient dynamics with an extremely high spatiotemporal resolution. Here, we study strong-field ionisation of laser-aligned molecules, and show a full real-time picture of the photoelectron dynamics in the combined action of the laser field and the molecular interaction. We demonstrate that the molecule has a dramatic impact on the overall strong-field dynamics: it sets the clock for the emission of electrons with a given rescattering kinetic energy. This result represents a benchmark for the seminal statements of molecular-frame strong-field physics and has strong impact on the interpretation of self-diffraction experiments. Furthermore, the resulting encoding of the time-energy relation in molecular-frame photoelectron momentum distributions shows the way of probing the molecular potential in real-time, and accessing a deeper understanding of electron transport during strong-field interactions