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22 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Identification of C2-C5 products from CO2 hydrogenation over PdZn/TiO2-ZSM-5 hybrid catalysts Jonathan Ruiz Esquius , Hasliza Bahruji , Michael Bowker , Graham Hutchings Faraday Discussions DOI: 10.1039/D0FD00135J Diamond Proposal Number(s): [19850] Open Access Show Abstract ▼ Abstract: The combination of a methanol synthesis catalyst and a solid acid catalyst opens the possibility to obtain olefins or paraffins directly from CO2 and H2 in one step. In this work several PdZn/TiO2-ZSM-5 hybrid catalysts were employed under CO2 hydrogenation conditions (240-360 °C, 20 bar, CO2/N2/H2 = 1/1/3) for the synthesis of CH3OH, consecutive dehydration to dimethyl ether and further oxygenate conversion to hydrocarbons. No significant changes after 36 h reaction on the methanol synthesis catalyst (PdZn/TiO2) were observed by XRD, XAS or XPS. No olefins were observed, indicating that light olefins undergo further hydrogenation under reaction conditions, yielding the corresponding alkanes. Increasing the aluminium sites in the zeolites (Si:Al ratio 80:1, 50:1 and 23:1) lead to a higher concentration of mild Brønstead acid sites promoting hydrocarbon chain growth.	Feb 2021
B18-Core EXAFS	The role of surface oxidation and Fe-Ni synergy in Fe-Ni-S catalysts for CO2 hydrogenation Claire E. Mitchell , David Santos-Carballal , Andrew M. Beale , Wilm Jones , David J. Morgan , Meenakshisundaram Sankar , Nora Henriette De Leeuw Faraday Discussions DOI: 10.1039/D0FD00137F Diamond Proposal Number(s): [19850] Open Access Show Abstract ▼ Abstract: Increasing carbon dioxide (CO2) emissions, resulting in climate change, have driven the motivation to achieve the effective and sustainable conversion of CO2 into useful chemicals and fuels. Taking inspiration from biological processes, synthetic iron-nickel-sulfides have been proposed as suitable catalysts for the hydrogenation of CO2. In order to experimentally validate this hypothesis, here we report violarite (Fe,Ni)3S4 as a cheap and economically viable catalyst for the hydrogenation of CO2 into formate under mild, alkaline conditions at 125 oC and 20 bar (CO2:H2 = 1:1). Calcination of violarite at 200 oC resulted in excellent catalytic activity, far superior to Fe-only and Ni-only sulfides. We further report first principles simulations of the CO2 conversion on the partially oxidised (001) and (111) surfaces of stoichiometric violarite (FeNi2S4) and polydymite (Ni3S4) to rationalise the experimentally observed trends. We have obtained the thermodynamic and kinetic profiles for the reaction of carbon dioxide (CO2) and water (H2O) on the catalyst surfaces via substitution and dissociation mechanisms. We report that the partially oxidised (111) surface of FeNi2S4 is the best catalyst in the series and that the dissociation mechanism is the most favourable. Our study reveals that the partial oxidation of the FeNi2S4 surface, as well as the synergy of the Fe and Ni ions, are important in the catalytic activity of the material for the effective hydrogenation of CO2 to formate.	Jan 2021
I11-High Resolution Powder Diffraction I19-Small Molecule Single Crystal Diffraction	Multi-stimulus linear negative expansion of a breathing M(O2CR)4-node MOF Daniel Watkins , Thomas M. Roseveare , Mark R. Warren , Stephen P. Thompson , Ashleigh J. Fletcher , Lee Brammer Faraday Discussions 49 DOI: 10.1039/D0FD00089B Open Access Show Abstract ▼ Abstract: The metal–organic framework (Me2NH2)2[Cd(NO2BDC)2] (SHF-81) comprises flattened tetrahedral Cd(O2CR)42− nodes, in which Cd(II) centres are linked via NO2BDC2− ligands (2-nitrobenzene-1,4-dicarboxylate) to give a doubly interpenetrated anionic network, with charge balanced by two Me2NH2+ cations per Cd centre resident in the pores. The study establishes that this is a twinned α-quartz-type structure (trigonal, space group P3x21, x = 1 or 2), although very close to the higher symmetry β-quartz arrangement (hexagonal, P6x22, x = 2 or 4) in its as-synthesised solvated form [Cd(NO2BDC)2]·2DMF·0.5H2O (SHF-81-DMF). The activated MOF exhibits very little N2 uptake at 77 K, but shows significant CO2 uptake at 273–298 K with an isosteric enthalpy of adsorption (ΔHads) at zero coverage of −27.4 kJ mol−1 determined for the MOF directly activated from SHF-81-DMF. A series of in situ diffraction experiments, both single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD), reveal that the MOF is flexible and exhibits breathing behaviour with observed changes as large as 12% in the a- and b-axes (\|Δa\|, \|Δb\| < 1.8 Å) and 5.5% in the c-axis (\|Δc\| < 0.7 Å). Both the solvated SHF-81-DMF and activated/desolvated SHF-81 forms of the MOF exhibit linear negative thermal expansion (NTE), in which pores that run parallel to the c-axis expand in diameter (a- and b-axis) while contracting in length (c-axis) upon increasing temperature. Adsorption of CO2 gas at 298 K also results in linear negative expansion (Δa, Δb > 0; Δc < 0; ΔV > 0). The largest change in dimensions is observed during activation/desolvation from SHF-81-DMF to SHF-81 (Δa, Δb < 0; Δc > 0; ΔV < 0). Collectively the nine in situ diffraction experiments conducted suggest the breathing behaviour is continuous, although individual desolvation and adsorption experiments do not rule out the possibility of a gating or step at intermediate geometries that is coupled with continuous dynamic behaviour towards the extremities of the breathing amplitude.	Nov 2020
I22-Small angle scattering & Diffraction	The persistence of a proxy for cooking emissions in megacities: a kinetic study of the ozonolysis of self-assembled films by simultaneous Small & Wide Angle X-ray Scattering (SAXS/WAXS) and Raman microscopy Adam Milsom , Adam M. Squires , Ben Woden , Nicholas J. Terrill , Andrew D. Ward , Christian Pfrang Faraday Discussions DOI: 10.1039/D0FD00088D Diamond Proposal Number(s): [21663, 23096] Open Access Show Abstract ▼ Abstract: Cooking emissions account for a significant proportion of the organic aerosol emitted into the urban environment and high pollution events have been linked to an increased organic content on urban particulate matter surfaces. We present a kinetic study on surface coatings of self-assembled (semi-solid) oleic acid-sodium oleate cooking aerosol proxies undergoing ozonolysis. We found a clear film thickness-dependent kinetic behaviour and measured the effect of the organic phase on the kinetics for this system. In addition to the thickness-dependent kinetics, we show that significant fractions of unreacted proxy remain at the end of extensive ozone exposure and that this effect scales approximately linearly with film thickness, suggesting that a late-stage inert reaction product may form to inhibit reaction progress – effectively building up an inert crust. We determine this by using a range of simultaneous analytical techniques; most notably Small-Angle X-ray Scattering (SAXS) has been used for the first time to measure reaction kinetics of films of a wide range of thicknesses from ca. 0.59 to 73 µm with films < 10 µm thick being of potential atmospheric relevance. These observations have implications for the evolution of particulate matter in the urban environment, potentially extending the atmospheric lifetimes of harmful aerosol components and affecting the local urban air quality and climate.	Sep 2020
I11-High Resolution Powder Diffraction	Exploring cooperative porosity in organic cage crystals using in situ diffraction and molecular simulations Linjiang Chen , Yu Che , Andrew Cooper , Samantha Y. Chong Faraday Discussions DOI: 10.1039/D0FD00022A Diamond Proposal Number(s): [9282] Show Abstract ▼ Abstract: A porous organic cage crystal, α-CC2, shows unexpected adsorption of sulphur hexafluoride (SF6) in its cage cavities, which are formally occluded even to the smallest diatomic gas, H2, according to a pore analysis of the static crystal structure. In situ powder X-ray diffraction (PXRD) experiments provide unequivocal evidence for the presence of (SF6) inside the ‘occluded’ cage voids, pointing to a mechanism of dynamic flexibility of the system. By combining PXRD results with molecular dynamics simulations, we build a molecular level picture of the cooperative porosity in α-CC2 that facilitates the passage of (SF6) into the cage voids.	Mar 2020
B18-Core EXAFS	Hard X-ray spectroscopy: An exhaustive toolbox for mechanistic studies (?) Anke Schoch , Lukas Burkhardt , Roland Schoch , Kai Stuehrenberg , Matthias Bauer Faraday Discussions DOI: 10.1039/C9FD00070D Show Abstract ▼ Abstract: Established and recent hard X-ray spectroscopic methods in form of conventional X-ray absorption near edge structure spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS), and the photon-in/photon-out techniques high energy resolution fluorescence detected XANES and valence-to-core X-ray emission spectroscopy (VtC-XES) provide unique opportunities to study mechanisms in metal-organic reactions. The combination of these techniques allows the determination of the local geometric and electronic structure in form of the numbers of nearest neighbours, their types and distances around an X-ray absorbing atom and the highest occupied and lowest unoccupied molecular levels. Different sample cells for this purpose, which allow high pressure, electrochemical or multi-spectroscopic measurements under inert conditions, are presented and discussed. The potential of HERFD-XANES and VtC-XES to eliminate limitations of conventional EXAFS spectroscopy is established with case studies on the Hieber anion [Fe(CO)3(NO)]- and the iron hydride complex [Fe(CO)H(NO)(PPh3)2]. With VtC-XES the formation of an allyl complex by reaction of [Fe(CO)3(NO)]- in a catalytic nucleophilic substitution reaction can be followed. Combination of HERFD-XANES and VtC-XES allows the identification and investigation of hydride species, as well as their fate in chemical reaction. On the other hand, in order to investigate the active species formation in iron-catalysed cross coupling reactions, conventional XANES and EXAFS are the method of choice for the moment. For all examples, the advantages and limitations of the hard X-ray toolbox are commented and the value of the individual methods are compared.	Jun 2019
B18-Core EXAFS	Effects of heat treatment atmosphere on the structure and activity of Pt 3 Sn nanoparticle electrocatalysts: a characterisation case study Haoliang Huang , Abu Bakr Ahmed Amine Nassr , Veronica Celorrio , S. F. Rebecca Taylor , Vinod Kumar Puthiyapura , Christopher Hardacre , Dan J. L. Brett , Andrea E. Russell Faraday Discussions DOI: 10.1039/C7FD00221A Diamond Proposal Number(s): [10306] Open Access Show Abstract ▼ Abstract: Comprehensive identification of the phases and atomic configurations of bimetallic nanoparticle catalysts are critical in understanding structure-properties relationships in catalysis. However, control of the structure, whilst retaining the same composition, is challenging. Here, the same carbon supported Pt3Sn catalyst is annealed under air, Ar and H2 resulting in variation of the extent of alloying of the two components. The atmosphere-induced extent of alloying is characterised using a variety of methods including TEM, XRD, XPS, XANES, and EXAFS and is defined as the fraction of Sn present as Sn0 (XPS and XANES) or the ratio of the calculated composition of the bimetallic particle to the nominal composition according to the stoichiometric ratio of the preparation (TEM, XRD, and EXAFS) . The values obtained depend on the structural method used, but the trend air < Ar < H2 annealed samples is consistent. These results are then used to provide insights regarding the electrocatalytic activity of Pt3Sn catalysts for CO, methanol, ethanol, and 1-butanol oxidation and the roles of alloyed Sn and SnO2.	Apr 2018
I11-High Resolution Powder Diffraction I19-Small Molecule Single Crystal Diffraction	Computational Modelling of Solvent Effects in a Prolific Solvatomorphic Porous Organic Cage David P. Mcmahon , Andrew Stephenson , Samantha Y. Chong , Marc A. Little , James T. A. Jones , Andrew I. Cooper , Graeme M. Day Faraday Discussions DOI: 10.1039/C8FD00031J Diamond Proposal Number(s): [15777, 12336] Open Access Show Abstract ▼ Abstract: Crystal structure prediction methods can enable the in silico design of functional molecular crystals, but solvent effects can have a major influence on relative lattice energies, sometimes thwarting predictions. This is particularly true for porous solids, where solvent included in the pores can have an important energetic contribution. We present a Monte Carlo solvent insertion procedure for predicting the solvent filling of porous structures from crystal structure prediction landscapes, tested using a highly solvatomorphic porous organic cage molecule, CC1. Using this method, we can understand why the predicted global energy minimum structure for CC1 is never observed from solvent crystallisation. We also explain the formation of three different solvatomorphs of CC1 from three structurally-similar chlorinated solvents. Calculated solvent stabilisation energies are found to correlate with experimental results from thermogravimetric analysis, suggesting a future computational framework for a priori materials design that factors in solvation effects.	Apr 2018
I07-Surface & interface diffraction	CO oxidation over supported gold nanoparticles as revealed by operando grazing incidence X-ray scattering analysis Yaroslav Odarchenko , David J. Martin , Thomas Arnold , Andrew M. Beale Faraday Discussions DOI: 10.1039/C8FD00007G Diamond Proposal Number(s): [10488, 12780] Open Access Show Abstract ▼ Abstract: The mechanism of carbon monoxide oxidation over gold was explored using a model planar catalyst consisting of monodisperse gold nanoparticles periodically arranged on a single crystal SiO2/Si(111) substrates using a combination of Grazing Incidence Small Angle X-ray Scattering and Grazing Incidence X-ray Diffraction (GISAXS/GIXD) under reaction conditions. It is shown that nanoparticle composition, size and shape change when the catalyst is exposed to reactive gases. During CO oxidation, the particle’s submergence depth with respect to the surface decreases due to the removal of gold oxide at the metal-support edge, meanwhile the particle ‘flattens’ to maximise the number of the reaction sites along its perimeter. The effect of the CO concentration on the catalyst structure is also discussed. Our results support the dual catalytic sites mechanism whereby CO is activated on the gold surface whereas molecular oxygen is dissociating at the gold-support interface.	Apr 2018
B18-Core EXAFS	Supported Metal Nanoparticles with Tailored Catalytic Properties through Sol immobilisation: Applications for the Hydrogenation of Nitrophenols Scott M. Rogers , C. Richard A. Catlow , Diego Gianolio , Peter Wells , Nikolaos Dimitratos Faraday Discussions DOI: 10.1039/C7FD00216E Diamond Proposal Number(s): [10306] Show Abstract ▼ Abstract: The use of sol-immobilisation to prepare supported metal nanoparticles is an area of growing importance in heterogeneous catalysis; it affords greater control of nanoparticle properties compared to conventional catalytic routes e.g. impregnation. This work, and other recent studies, demonstrate how the properties of the resultant supported metal nanoparticles can be tailored by adjusting the conditions of colloidal synthesis i.e. temperature and solvent. We further demonstrate the applicability of these methods to the hydrogenation of nitrophenols using a series of tailored Pd/TiO2 catalysts, with low Pd loading 0.2 wt. %. Here, the temperature of colloidal synthesis is directly related to the mean particle diameter and the catalytic activity. Smaller Pd particles (2.2 nm, k = 0.632 min-1, TOF = 560 h-1) perform better than their larger counterparts (2.6 nm, k = 0.350 min-1, TOF = 370 h-1) for the hydrogenation of p-nitrophenol, with the catalyst containing smaller NPs found to have increased stability during recyclability studies, with high activity (> 90% conversion after 5 minutes) maintained across 5 catalytic cycles.	Mar 2018

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