Imperial College London

Prof Klaus Hellgardt

Faculty of EngineeringDepartment of Chemical Engineering

Professor of Chemical Engineering
 
 
 
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Contact

 

k.hellgardt

 
 
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Location

 

208Bone BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

165 results found

Kojo G, Wei X, Matsuzaki Y, Matsuo H, Hellgardt K, Otomo Jet al., 2019, Fabrication and electrochemical performance of anode-supported solid oxide fuel cells based on proton-conducting lanthanum tungstate thin electrolyte, Solid State Ionics, Vol: 337, Pages: 132-139, ISSN: 0167-2738

© 2019 Elsevier B.V. The performance of an anode-supported proton-conducting solid oxide fuel cell (p-SOFC)was investigated by controlling transport properties of thin electrolyte membranes. Hole conductivity in electrolyte, which induces to degrade the cell performance, was sufficiently suppressed by using lanthanum tungstate La 28-x W 4+x O 54+3x/2 v 2-3x/2 (LWO)with high proton conductivity and low hole conductivity. SrFe 0.95 Nb 0.05 O 3-δ (SFN)and Ni-Ce 0.9 Gd 0.1 O 2-δ (Ni-GDC10)cermet were used as the cathode and anode, respectively. GDC10 was also used as an interlayer to prevent chemical reactions between the electrolyte and electrodes. SEM images and electrochemical impedance spectroscopy showed that the boundaries between the electrolyte and electrodes were stable because GDC10 blocked chemical reactions and cation diffusion at the electrolyte-electrode interfaces. Fuel cell tests were also performed with SFN/GDC10/LWO/GDC10/Ni-GDC anode-supported single cells. The thickness of the LWO thin electrolyte was approximately 3 μm. The OCV values were measured to be 0.88 V and 0.94 V at 800 °C and 600 °C, respectively. Moreover, the evaluation of the leakage current indicated that thin LWO could achieve the low leakage current due to transport properties such as high proton conductivity and low hole and electron conductivities.

Journal article

Antunes MM, Lima S, Fernandes A, Ribeiro MF, Chadwick D, Hellgardt K, Pillinger M, Valente AAet al., 2019, One-pot hydrogen production and cascade reaction of furfural to bioproducts over bimetallic Pd-Ni TUD-1 type mesoporous catalysts (vol 237, pg 521, 2018), APPLIED CATALYSIS B-ENVIRONMENTAL, Vol: 243, Pages: 801-801, ISSN: 0926-3373

Journal article

del Rio-Chanona EA, Wagner JL, Ali H, Fiorelli F, Zhang D, Hellgardt Ket al., 2019, Deep learning-based surrogate modeling and optimization for microalgal biofuel production and photobioreactor design, AICHE JOURNAL, Vol: 65, Pages: 915-923, ISSN: 0001-1541

Journal article

Holmes-Gentle I, Bedoya-Lora F, Alhersh F, Hellgardt Ket al., 2019, Optical Losses at Gas Evolving Photoelectrodes: Implications for Photoelectrochemical Water Splitting, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 17-28, ISSN: 1932-7447

Journal article

Parkinson B, Balcombe P, Speirs JF, Hawkes AD, Hellgardt Ket al., 2019, Levelized cost of CO2 mitigation from hydrogen production routes, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 12, Pages: 19-40, ISSN: 1754-5692

Journal article

Wagner JL, Lee-Lane D, Monaghan M, Sharifzadeh M, Hellgardt Ket al., 2019, Recovery of excreted n-butanol from genetically engineered cyanobacteria cultures: Process modelling to quantify energy and economic costs of different separation technologies, ALGAL RESEARCH-BIOMASS BIOFUELS AND BIOPRODUCTS, Vol: 37, Pages: 92-102, ISSN: 2211-9264

Journal article

Antunes MM, Lima S, Fernandes A, Ribeiro MF, Chadwick D, Hellgardt K, Pillinger M, Valente AAet al., 2018, One-pot hydrogen production and cascade reaction of furfural to bioproducts over bimetallic Pd-Ni TUD-1 type mesoporous catalysts, APPLIED CATALYSIS B-ENVIRONMENTAL, Vol: 237, Pages: 521-537, ISSN: 0926-3373

Journal article

Roberts F, Richard C, Zemichael F, Hii KM, Hellgardt K, Brennan C, Sale Det al., 2018, Base-free, tunable, Au-catalyzed oxidative esterification of alcohols in continuous flow, Reaction Chemistry and Engineering, Vol: 3, Pages: 942-948, ISSN: 2058-9883

Under continuous flow conditions, hydrogen peroxide oxidizes primary alcohols (cinnamyl alcohol, decenol, decanol and benzyl alcohol) in methanol over Au/TiO2, without the need for added base. While the allylic alcohols afforded conjugated aldehydes, aliphatic and benzylic alcohols afforded acids or esters. Selectivity for either product can be achieved by adjusting the reaction parameters. Kinetic studies revealed that the formation of the easter is faster than that of the acid, due to a greater pre-organization (larger ln A) attributed to the more favourable formation of the hemiacetal intermediate.

Journal article

Cardoso A, Ramirez Reina T, Suelves I, Pinilla JL, Millan M, Hellgardt Ket al., 2018, Effect of carbon-based materials and CeO<inf>2</inf>on Ni catalysts for Kraft lignin liquefaction in supercritical water, Green Chemistry, Vol: 20, Pages: 4308-4318, ISSN: 1463-9262

© The Royal Society of Chemistry 2018. Kraft lignin (KL) is a by-product from cellulose production typically treated as a waste or used as a low-value fuel in heat and power generation in the pulp and paper industry. This study explores KL upgrading to monoaromatic compounds using supercritical water (SCW) as reaction medium. The effect of Ni-CeO2catalysts supported on carbon nanofibers (CNF) and activated carbon (AC) on the product distribution was investigated. These catalysts were prepared by a wet-impregnation method with acetone, and reduced Ni was observed without the use of H2. CNF presented a high degree of stability in SCW. Ni in its reduced state was still present in all spent catalysts, mainly when CNF were the support. While catalysts supported in AC led to high yields of char and gas, a 56 wt% yield of a light liquid fraction, recovered as dichloromethane (DCM)-soluble product and consisting mainly of (methoxy)phenols (>80 mol%), was obtained in a batch reactor at 400 °C, 230 bar, with Ni-CeO2/CNF as a catalyst. A short reaction time was key to avoid the formation of gas and char. This study demonstrates that high yields of DCM-soluble products from KL and low char formation can be obtained by using only SCW and catalysts, an alternative to widely reported approaches like the addition of organic co-solvents (e.g., phenol) and/or H2.

Journal article

Holmes-Gentle I, Hellgardt K, 2018, A versatile open-source analysis of the limiting efficiency of photo electrochemical water-splitting, Scientific Reports, Vol: 8, ISSN: 2045-2322

Understanding the fundamental thermodynamic limits of photo-electrochemical (PEC) water splitting is of great scientific and practical importance. In this work, a ‘detailed balance’ type model of solar quantum energy converters and non-linear circuit analysis is used to calculate the thermodynamic limiting efficiency of various configurations of PEC design. This model is released as freely accessible open-source (GNU GPL v3) code written in MATLAB with a graphical user interface (GUI). The capabilities of the model are demonstrated by simulating selected permutations of PEC design and results are validated against previous literature. This tool will enable solar fuel researchers to easily compare experimental results to theoretical limits to assess its realised performance using the GUI. Furthermore, the code itself is intended to be extendable and so can be modified to include non-ideal losses such as the over-potential required or complex optical phenomena.

Journal article

Harun I, Del Rio-Chanona EA, Wagner JL, Lauersen KJ, Zhang D, Hellgardt Ket al., 2018, Photocatalytic Production of Bisabolene from Green Microalgae Mutant: Process Analysis and Kinetic Modeling, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 57, Pages: 10336-10344, ISSN: 0888-5885

Journal article

Hii KM, hellgardt, barreiro, Adrio LA, Hao Z, van Ommen JRet al., 2018, Spatial, temporal and quantitative assessment of catalyst leaching in continuous flow, Catalysis Today, Vol: 308, Pages: 64-70, ISSN: 0920-5861

Catalyst leaching is a major impediment to the development of commercially-viable processes conducted in a liquid-phase. To date, there is no reliable technique that can accurately identify the extent and dynamics of the leaching process in a quantitative manner. In this work, a tandem flow-reactor system has been developed, which allowed us to distinguish between surface-catalyzed reactions from those occurring in solution by comparing%conversion at the exit of each reactor (S1, S2) corresponding to predominance of heterogeneous/homogeneous reactions (spatial) and two different residence times (temporal). A multiscale model is subsequently established to quantify the two types of reaction rate and simulate the catalyst leaching from a cross-coupling catalyst, PdEncat™ 30; including: (1) a multi-particle sizes model for catalyst scale; and (2) a dispersion model for reactor scale. The results show that catalyst leaching occurs via more than one process, and that the homogeneous Pd-catalyst (leached from the immobilized catalyst and dissolved in the flow) dominates the reaction and possesses a much higher activity than the heterogeneous (immobilized) Pd-catalyst. Additionally, the change of leached Pd stream inside reactors can be predicted along with the axial direction and the reaction time through the reactor-scale dispersion model.

Journal article

Daggash HA, Patzschke CF, Heuberger CF, Zhu L, Hellgardt K, Fennell PS, Bhave AN, Bardow A, Mac Dowell Net al., 2018, Closing the carbon cycle to maximise climate change mitigation: Power-to-Methanol vs Power-to-Direct Air Capture, Sustainable Energy and Fuels, Vol: 2, Pages: 1153-1169, ISSN: 2398-4902

It is broadly recognised that CO2 capture and storage (CCS) and associated negative emissions technologies (NETs) are vital to meeting the Paris agreement target. The hitherto failure to deploy CCS on the required scale has led to the search for options to improve its economic return. CO2 capture and utilisation (CCU) has been proposed as an opportunity to generate value from waste CO2 emissions and improve the economic viability of CCS, with the suggestion of using curtailed renewable energy as a core component of this strategy. This study sets out to quantify (a) the amount of curtailed renewable energy that is likely to be available in the coming decades, (b) the amount of fossil CO2 emissions which can be avoided by using this curtailed energy to convert CO2 to methanol for use as a transport fuel – power-to-fuel, with the counterfactual of using that curtailed energy to directly remove CO2 from the atmosphere via direct air capture (DAC) and subsequent underground storage, power-to-DAC. In 2015, the UK curtailed 1277 GWh of renewable power, or 1.5% of total renewable power generated. Our analysis shows that the level of curtailed energy is unlikely to increase beyond 2.5% until renewable power accounts for more than 50% of total installed capacity. This is unlikely to be the case in the UK before 2035. It was found that: (1) power-to-DAC could achieve 0.23–0.67 tCO2 avoided MWh−1 of curtailed power, and (2) power-to-Fuel could achieve 0.13 tCO2 avoided MWh−1. The power-to-fuel concept was estimated to cost $209 tCO2 avoided−1 in addition to requiring an additional $430–660 tCO2 avoided−1 to finally close the carbon cycle by air capture. The power-to-DAC concept was found to cost only the $430–660 tCO2 avoided−1 for air capture. For power-to-fuel to become profitable, hydrogen prices would need to be less than or equal to $1635 tH2−1 or methanol prices must increase to $960 tMeOH−1. Absent this ch

Journal article

Holmes-Gentle I, Agarwal H, Alhersh F, Hellgardt Ket al., 2018, Assessing the scalability of low conductivity substrates for photo-electrodes via modelling of resistive losses., PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 20, Pages: 12422-12429, ISSN: 1463-9076

When scaling up photo-electrochemical processes to larger areas than conventionally studied in the laboratory, substrate performance must be taken into consideration and in this work, a methodology to assess this via an uncomplicated 2 dimensional model is outlined. It highlights that for F-doped SnO2 (FTO), which is ubiquitously used for metal oxide photoanodes, substrate performance becomes significant for moderately sized electrodes (5 cm) under no solar concentration for state of the art Fe2O3 thin films. It is demonstrated that when the process is intensified via solar concentration, current losses become quickly limiting. Methodologies to reduce the impact of substrate ohmic losses are discussed and a new strategy is proposed. Due to the nature of the photo-electrode current–potential relationship, operation at a higher potential where the photo-current saturates (before the dark current is observed) will lead to a minimum in current loss due to substrate performance. Crucially, this work outlines an additional challenge in scaling up photo-electrodes based on low conductivity substrates, and establishes that such challenges are not insurmountable.

Journal article

Bystron T, Horbenko A, Syslova K, Hii KM, Hellgardt K, Kelsall GHet al., 2018, 2-Iodoxybenzoic acid synthesis by oxidation of 2-Iodobenzoic acid at a Boron-doped diamond anode, ChemElectroChem, Vol: 5, Pages: 1002-1005, ISSN: 2196-0216

For the first time, the electrochemical synthesis of 2-iodoxybenzoic acid (IBX), a benign, well-established, popular and highly selective oxidising agent, is described. The objective of the work was to investigate the possibility of generating IBX electrochemically in aqueous solutions by using boron-doped diamond anodes. In 0.2 M H2SO4 aqueous solution, 2-iodobenzoic acid (IBA) was found to be oxidised at potentials >1.6 V vs. SCE, initially to 2-iodosobenzoic acid (IsBA), which was oxidised to IBX at potentials >1.8 V vs. SCE. Reductions of IBX to IsBA and IsBA to IBA occurred at similar potentials of ca. −0.7 V vs. SCE. The voltammetry results were confirmed by performing a series of batch electrolyses at different electrode potentials. Thus, depending on the electrode potential chosen, IBA can be oxidised anodically either to IsBA or IBX with 100 % overall selectivity. The only side-reaction was O2 generation, but charge yields did not decrease below 55 % even at conversions >95 %.

Journal article

Keung Leung AY, Hellgardt K, Leung A, Hii KMet al., 2018, Catalysis in flow: nickel-catalyzed synthesis of primary amines from alcohols and NH3, ACS Sustainable Chemistry and Engineering, Vol: 6, Pages: 5479-5484, ISSN: 2168-0485

A highly selective synthesis of primary amines from alcohols and NH3 was achieved on using a commercially available Ni catalyst, without adding H2. Using a continuous flow reaction platform, the amination of aliphatic alcohols can be achieved in good yields and selectivities, as the accumulation of water byproduct can be removed. Competitive formation of the nitrile side-product was suppressed when the catalyst was prereduced. Modes of catalyst deactivation were also briefly examined.

Journal article

Iruretagoyena Ferrer D, Hellgardt K, Chadwick D, 2018, Towards autothermal hydrogen production by sorption-enhanced water gas shift and methanol reforming: a thermodynamic analysis, International Journal of Hydrogen Energy, Vol: 43, Pages: 4211-4222, ISSN: 0360-3199

Hydrogen production by the water gas shift reaction (WGS) is equilibrium limited. In the current study, we demonstrate that the overall efficiency of the WGS can be improved by co-feeding methanol and removing CO2 in situ. The thermodynamics of the water gas shift and methanol reforming/WGS (methanol-to-shift, MtoS) reactions for H2 production alone and with simultaneous CO2 adsorption (sorption-enhanced, SEWGS and SEMtoS) were studied using a non-stoichiometric approach based on the minimisation of the Gibbs free energy. A typical composition of the effluent from a steam methane reformer was used for the shift section. The effects of temperature (450–750 K), pressure (5–30 barg), steam and methanol addition, fraction of CO2 adsorption (0–95%) and energy efficiency of the shift systems have been investigated. Adding methanol to the feed facilitates autothermal operation of the shift unit, with and without CO2 removal, and enhances significantly the amount of H2 produced. For a set methanol and CO input, the MtoS and SEMtoS systems show a maximum productivity of H2 between 523 and 593 K due to the increasing limitation of the exothermic shift reaction while the endothermic methanol steam reforming is no longer limited above 593 K. The heat of adsorption of CO2 was found to make only a small difference to the H2 production or the autothermal conditions.

Journal article

Arcelus-Arrillaga P, Hellgardt K, Millan M, 2017, Effect of process conditions on the hydrothermal partial oxidation of phenanthrene as a heavy oil model structure, FUEL, Vol: 209, Pages: 434-441, ISSN: 0016-2361

Journal article

Sawa M, Fantuzzi A, Bombelli P, Howe CJ, Hellgardt K, Nixon PJet al., 2017, Electricity generation from digitally printed cyanobacteria, Nature Communications, Vol: 8, ISSN: 2041-1723

Microbial biophotovoltaic cells exploit the ability of cyanobacteria and microalgae to convert light energy into electrical current using water as the source of electrons. Such bioelectrochemical systems have a clear advantage over more conventional microbial fuel cells which require the input of organic carbon for microbial growth. However, innovative approaches are needed to address scale-up issues associated with the fabrication of the inorganic (electrodes) and biological (microbe) parts of the biophotovoltaic device. Here we demonstrate the feasibility of using a simple commercial inkjet printer to fabricate a thin-film paper-based biophotovoltaic cell consisting of a layer of cyanobacterial cells on top of a carbon nanotube conducting surface. We show that these printed cyanobacteria are capable of generating a sustained electrical current both in the dark (as a ‘solar bio-battery’) and in response to light (as a ‘bio-solar-panel’) with potential applications in low-power devices.

Journal article

Hii KM, Newton MA, Nicholls R, Brazier JB, Nguyen BN, Barreiro, Mulligan C, Hellgardt, Emerich H, Snigireva I, Thompson PBJet al., 2017, Effect of retained chlorine in ENCAT™ 30 catalysts on the development of encapsulated Pd: insights from in situ Pd K, L3 and Cl K-edge XAS, Catalysis, Structure & Reactivity, Vol: 3, Pages: 149-156, ISSN: 2055-074X

In situ X-ray absorption spectroscopy (XAS) and Pd K, LIII, and Cl K-edges shows that Cl can be present in significant amounts in ENCAT™ 30 catalysts and that it can severely retard Pd nanoparticle (NP) development in flowing solvents. We also show that whilst polymeric encapsulation protects the Pd against solvent induced agglomeration of Pd nanoparticles the evidence suggests it does not prevent the formation PdHx through reaction with the aqeous ethanol solvent, and that, as received, ENCAT™ 30 NP catalysts are not, for the most part, comprised of nanoparticulate Pd0 irrespective of the presence of Cl.

Journal article

Antunes MM, Lima S, Fernandes A, Magalhaes AL, Neves P, Silva CM, Ribeiro MF, Chadwick D, Hellgardt K, Pillinger M, Valente AAet al., 2017, MFI Acid Catalysts with Different Crystal Sizes and Porosity for the Conversion of Furanic Compounds in Alcohol Media, CHEMCATCHEM, Vol: 9, Pages: 2747-2759, ISSN: 1867-3880

Journal article

Martins Lima S, Klaus Hellgardt KH, David Chadwick DC, 2017, Towards sustainable hydrogenation of 5-(hydroxymethyl)furfural: a two-stage continuous process in aqueous media over Raney catalysts, RSC Advances, Vol: 7, Pages: 31401-31407, ISSN: 2046-2069

The hydrogenation of 5-(hydroxymethyl)furfural (HMF) to 2,5-bis(hydroxymethyl)tetrahydrofuran (DHMTHF) in aqueous media under relatively mild reaction conditions has been investigated over heterogeneous RANEY® Cu and Ni catalysts using a continuous-flow hydrogenation reactor. These RANEY® catalysts were selected following a screening of several catalysts including precious metals supported on carbon for the hydrogenation of HMF. A single-stage versus a two-stage process for the hydrogenation of HMF into DHMTHF, i.e. via 2,5-dihydroxymethylfuran (DHMF) has been evaluated. The best result with an average selectivity of 98% for DHMTHF was obtained using a two-stage process; RANEY® Cu was used as a catalyst for the highly selective hydrogenation of HMF to DHMF (92 mol%) in the first stage and this product was used without further purification for in a second-stage selective hydrogenation of DHMF into DHMTHF using RANEY® Ni as a catalyst. The influence of the HMF concentration in the feeding solution (1–3 wt%), flow rate (0.05–0.25 mL min−1) and total pressure (20–90 bar) were investigated for the first-stage hydrogenation of HMF into DHMF over RANEY® Cu. HMF was found to exert an inhibiting effect on the conversion due to strong adsorption. The RANEY® Ni catalyst used in the second stage gradually deactivated. A procedure for in situ regeneration of the partially deactivated RANEY® Ni catalyst using acetic acid washing was investigated with limited success.

Journal article

Deadman BJ, Hellgardt K, Hii KM, 2017, A colorimetric method for rapid and selective quantification ofperoxodisulfate, peroxomonosulfate and hydrogen peroxide, Reaction Chemistry and Engineering, Vol: 2, Pages: 462-466, ISSN: 2058-9883

Redox colorimetric tests have been devised for the rapid analysis of the individual components of aqueous mixtures of peroxodisulfate, peroxomonosulfate and hydrogen peroxide; providing a convenient and selective method for the determination of these industrially relevant oxidants, which are known to inter-convert in solution.

Journal article

Hii KM, Loponova KN, Deadman BJ, Zhu J, Reilly C, Holdich RG, Hellgardt Ket al., 2017, Controlled multiphase oxidations for continuous manufacturing of fine chemicals, Chemical Engineering Journal, Vol: 329, Pages: 220-230, ISSN: 0300-9467

The feasibility of an integrated continuous biphasic oxidation process was studied, incorporating (i) electrochemical generation of an oxidant, (ii) membrane emulsification and an Oscillatory Flow Reactor (OFR) to facilitate mass-transfer in a biphasic reaction system and (iii) product extraction to enable regeneration of the oxidant. The biphasic, organic solvent-free dihydroxylation of styrene by ammonium peroxodisulfate solutions (including electrochemically generated peroxodisulfate) was investigated as a model reaction, both in batch and in an OFR. Heating of peroxodisulfate in a strongly acidic solution was demonstrated to be essential to generate the active oxidant (Caro’s acid). Membrane emulsification allowed mass-transfer limitations to be overcome, reducing the time scale of styrene oxidation from several hours in a conventional stirred tank reactor to less than 50 min in a dispersion cell. The influence of droplet size on overall reaction rate in emulsions was studied in detail using fast image capturing technology. Generation of unstable emulsions was also demonstrated during the oxidation in OFR and product yields >70% were obtained. However, the high-frequency/high-displacement oscillations necessary for generation of fine droplets violated the plug flow regime. Membrane emulsification was successfully integrated with the OFR to perform biphasic oxidations. It was possible to operate the OFR/cross-flow membrane assembly in plug flow regime at some oscillatory conditions with comparable overall oxidation rates. No mass-transfer limitations were observed for droplets <60 μm. Finally, the continuous post-reaction separation was demonstrated in a single OFR extraction unit to enable continuous regeneration of the oxidant.

Journal article

Deadman BJ, On-demand electrochemical generation of oxidants and their applications in organic synthesis, 254th ACS National Meeting

Conference paper

Holmes-Gentle I, Hoffmann F, Mesa CA, Hellgardt Ket al., 2017, Membrane-less photoelectrochemical cells: product separation by hydrodynamic control, Sustainable Energy and Fuels, Vol: 1, Pages: 1184-1198, ISSN: 2398-4902

A key step in order to realise photo-electrochemical (PEC) water splitting to produce hydrogen sustainably, is reactor design. Good engineering will minimise energy losses (both optical and ohmic) due to reactor construction, whilst ensuring the H2 and O2 produced are separated, and this can subsequently relax the requirements on the photo-absorber material and/or electro-catalysts. In this paper we show that separation of the products through hydrodynamic flow alone would negate the need for the conventionally used membrane, which has an associated ohmic drop and cost. This is demonstrated to be possible using a ‘laminar flow between two parallel plates’ reactor design and AR/Pe and AR are found to be the two key dimensionless numbers that predict product cross-over (where AR, Pe are aspect ratio and Péclet number respectively). Supersaturation was used as an indicator of bubble formation, which disrupts the laminar flow required for separation and it is shown that by increasing the reactor pressure, higher current densities can be tolerated before supersaturation occurs. Removal of the dissolved hydrogen and oxygen from electrolyte is discussed. A multi-physics model, which employs an optical transfer matrix method, is used to validate the previous conclusions. Experimental data for hematite and Pt deposited on FTO was used as the anode and cathode respectively. Parasitic optical losses and efficiency improvement with stacking are shown for the example reactor configuration. Additionally, the concept of stacking this reactor design in order to absorb light in multiple passes is introduced. This approach relaxes a classical constraint on photo-absorber materials: large absorption length compared to small diffusion length of charge carriers in the semiconductor.

Journal article

Arcelus-Arrillaga P, Pinilla JL, Hellgardt K, Millan Met al., 2017, Application of Water in Hydrothermal Conditions for Upgrading Heavy Oils: A Review, ENERGY & FUELS, Vol: 31, Pages: 4571-4587, ISSN: 0887-0624

Journal article

Hii KM, Brazier JB, 2017, Effects of Cl on the reduction of supported PdO in ethanol/water mixtures, Catalysis, Structure & Reactivity, Vol: 3, Pages: 54-62, ISSN: 2055-074X

The reduction of γ-Al2O3-supported PdO in flowing aqueous ethanol was investigated. Quick EXAFS (QEXAFS) performed at the Pd K-edge reveals that the presence of Cl can have a profound effect on the reduction process. At low loadings of Pd (1 wt-%), the size dependency of the process is inverted, compared to Cl-free samples. The extent of reduction was found to be dependent on loading/particles size. It is shown, using in situ QEXAFS at the Cl K- and Pd L3-edges, that residual Cl is not removed by the flowing solvent mixture, even at an elevated temperature of 350 K. The origins of these behaviours are discussed in terms of the differing effects that Cl may have when bonded to oxidic or reduced metal centres and the results were compared to earlier observations made on the effects of Cl on commercial polyurea encapsulated Pd ENCAT™ NP 30 catalysts.

Journal article

Phanopoulos A, Leung AHM, Yow S, Palomas D, White AJP, Hellgardt K, Horton A, Crimmin MRet al., 2017, Binuclear β-diketiminate complexes of copper(I), Dalton Transactions, Vol: 46, Pages: 2081-2090, ISSN: 1477-9226

The reaction of a series of dinucleating bis(β-diketiminate) pro-ligands with mesitylcopper in the presence and absence of mono and diphosphines has allowed the isolation of a new series of dicopper(I) complexes. Inclusion of trans-1,2-cyclohexyl (1), 2,6-pyridyl (2), and 2,2′-oxydiaryl (3) spacers between the β-diketiminate units has been studied. The isolation of three new copper(I) phosphine complexes [1·Cu2(PPh3)2], [2·Cu2(PPh3)2] and [3·Cu2(PPh3)2] is reported. While these compounds display large Cu⋯Cu separations of 5.4–7.9 Å in the solid state, solution data are consistent with a large degree of conformational freedom. Modification of the monophosphine to a diphosphine, DPPE, allowed the isolation of the novel 11-membered bimetallic macrocycle [2·Cu2(DPPE)] containing both a binucleating nitrogen based ligand and a chelating diphosphine. While acetonitrile adducts of this series could also be generated in situ, under forcing conditions reaction of the 2,6-pyridyl bridged ligand with mesityl copper led to the formation [2·Cu2]2. This latter complex is a dimer of dicopper(I) units in which the bis(β-diketiminate) ligand now binds four copper(I) centers through not only the expected κ2-N,N′-chelation but also κ1- and η2-binding of the central pyridine through orthogonal Cu–N and Cu–arene interactions. Reversible coordination of alkenes, pyridine and quinoline to the copper cluster was identified allowing the isolation and structural characterisation of a further series of dinuclear complexes [2·Cu2(pyridine)2], [2·Cu2(cyclopentene)2] and [2·Cu2(norbornene)2]. Solution studies allow quantification of the reversible binding event through a van't Hoff analysis. Both solution and the solid state data suggest a weak anagostic interaction exists in the latter two alkene complexes of copper(I). The new complexes have been characterized by X-ray dif

Journal article

Hii KM, Brazier JB, Hellgardt K, 2017, Catalysis in flow: O2 effect on the catalytic activity of Ru(OH)x/Al2O3 during the aerobic oxidation of an alcohol, Reaction Chemistry and Engineering, Vol: 2, Pages: 60-67, ISSN: 2058-9883

Changes in the turnover frequency (TOF) of Ru(OH)x/γ-Al2O3 during aerobic oxidation of benzyl alcohol in a plug flow differential reactor were monitored online using an inline FTIR instrument over extended periods of time (up to 72 h). A new equation for catalyst deactivation is derived, to account for the different lengths of time the catalyst is exposed to the reactants (benzyl alcohol and O2). Catalyst activity and stability are dependent on the amount of O2 in the system; catalyst deactivation can be attributed to two simultaneous processes: a fast and reversible inhibition by the benzoic acid side product and a slower and irreversible loss of catalytic sites due to reduction of Ru. At steady state, the reaction rate is zero-order in benzyl alcohol and partial positive order in O2. Finally, the suitability of a packed-bed (integral) reactor for the reaction is discussed.

Journal article

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