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Faraday Discussions

Tracey van Heerden, Eric van Steen
It is challenging to isolate the effect of metal-support interactions on catalyst reaction performance. In order to overcome this problem, inverse catalysts can be prepared in the laboratory and characterized and tested at relevant conditions. Inverse catalysts are catalysts where the precursor to the catalytically active phase is bonded to a support-like ligand. We can then view the metal-support interaction as a ligand interaction with the support acting as a supra-molecular ligand. Importantly, laboratory studies have shown that these ligands are still present after reduction of the catalyst...
February 16, 2017: Faraday Discussions
Moritz Wolf, Hendrik Kotzé, Nico Fischer, Michael Claeys
Highly monodisperse cobalt crystallites, supported on Stöber silica spheres, as model catalysts for the Fischer-Tropsch synthesis were exposed to simulated high conversion environments in the presence and absence of CO utilising an in house developed in situ magnetometer. The catalyst comprising the smallest crystallites in the metallic state (average diameter of 3.2 nm) experienced pronounced oxidation whilst the ratio of H2O to H2 was increased stepwise to simulate CO conversions from 26% up to complete conversion...
February 15, 2017: Faraday Discussions
Simon A Kondrat, Paul J Smith, James H Carter, James S Hayward, Geoffrey J Pudge, Greg Shaw, Michael S Spencer, Jonathan K Bartley, Stuart H Taylor, Graham J Hutchings
The effect of sodium species on the physical and catalytic properties of Cu/ZnO catalysts derived from zincian georgeite has been investigated. Catalysts prepared with <100 ppm to 2.1 wt% Na(+), using a supercritical CO2 antisolvent technique, were characterised and tested for the low temperature water-gas shift reaction and also CO2 hydrogenation to methanol. It was found that zincian georgeite catalyst precursor stability was dependent on the Na(+) concentration, with the 2.1 wt% Na(+)-containing sample uncontrollably ageing to malachite and sodium zinc carbonate...
February 15, 2017: Faraday Discussions
Thulani M Nyathi, Nico Fischer, Andy P E York, Michael Claeys
The preferential oxidation of carbon monoxide has been identified as an effective route to remove trace amounts of CO (approx. 0.5-1.0 vol%) in the H2-rich reformate gas stream after the low-temperature water-gas shift. Instead of noble metal-based catalysts, Co3O4-based catalysts were investigated in this study as cheaper and more readily available alternatives. This study aimed at investigating the effect of crystallite size on the mass- and surface area-specific CO oxidation activity as well as on the reduction behaviour of Co3O4...
February 15, 2017: Faraday Discussions
Suwardiyanto, Russell F Howe, Emma K Gibson, C Richard A Catlow, Ali Hameed, James McGregor, Paul Collier, Stewart F Parker, David Lennon
A ZSM-5 catalyst is examined in relation to the methanol-to-hydrocarbon (MTH) reaction as a function of reaction temperature and time-on-stream. The reaction profile is characterised using in-line mass spectrometry. Furthermore, the material contained within a catch-pot downstream from the reactor is analysed using gas chromatography-mass spectrometry. For a fixed methanol feed, reaction conditions are selected to define various stages of the reaction coordinate: (i) initial methanol adsorption at a sub-optimum reaction temperature (1 h at 200 °C); (ii) initial stages of reaction at an optimised reaction temperature (1 h at 350 °C); (iii) steady-state operation at an optimised reaction temperature (3 days at 350 °C); and (iv) accelerated ageing (3 days at 400 °C)...
February 14, 2017: Faraday Discussions
Tim A Wezendonk, Quirinus S E Warringa, Vera P Santos, Adam Chojecki, Matthijs Ruitenbeek, Garry Meima, Michiel Makkee, Freek Kapteijn, Jorge Gascon
The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N2 atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state...
February 14, 2017: Faraday Discussions
D E Sparks, S Vallee, Zhijun Jia, W D Shafer, B H Davis
Fischer-Tropsch synthesis was conducted in a small channel compact heat exchange reactor that was constructed of aluminum. While limited to lower temperature-pressure regions of the Fischer-Tropsch synthesis, the reactor could be operated in an isothermal mode with nearly a constant temperature along the length of the channel. The results obtained with the compact heat exchange reactor were similar to those obtained in the isothermal continuous stirred tank reactor, with respect to both activity and selectivity...
February 10, 2017: Faraday Discussions
Daniel Rojo-Gama, Samaneh Etemadi, Eliot Kirby, Karl Petter Lillerud, Pablo Beato, Stian Svelle, Unni Olsbye
Zeolites representing seven different topologies were subjected to life-time assessment studies as methanol to hydrocarbons (MTH) catalysts at 400 °C, P(MeOH) = 13 kPa and P(tot) = 100 kPa. The following topologies were studied: ZSM-22 (TON), ZSM-23 (MTT), IM-5 (IMF), ITQ-13 (ITH), ZSM-5 (MFI), mordenite (MOR) and beta (BEA). Two experimental approaches were used. In the first approach, each catalyst was tested at three different contact times, all giving 100% initial conversion. The life-time before conversion decreased to 50% at each contact time was measured and used to calculate critical contact times (i...
February 10, 2017: Faraday Discussions
Pieter van Helden, Jan-Albert van den Berg, Melissa A Petersen, Werner Janse van Rensburg, Ionel M Ciobîcă, Jan van de Loosdrecht
A multi-site microkinetic model for the Fischer-Tropsch synthesis (FTS) reaction up to C2 products on a FCC cobalt catalyst surface is presented. This model utilizes a multi-faceted cobalt nanoparticle model for the catalyst, consisting of the two dominant cobalt surface facets Co(111) and Co(100), and a step site represented by the Co(211) surface. The kinetic parameters for the intermediates and transition states on these sites were obtained using plane-wave, periodic boundary condition density functional theory...
February 10, 2017: Faraday Discussions
Peng Zhai, Pei-Pei Chen, Jinglin Xie, Jin-Xun Liu, Huabo Zhao, Lili Lin, Bo Zhao, Hai-Yan Su, Qingjun Zhu, Wei-Xue Li, Ding Ma
Various carbonaceous species were controllably deposited on Co/Al2O3 catalysts using ethylene as carbon source during the activation process for Fischer-Tropsch synthesis (FTS). Atomic, polymeric and graphitic carbon were distinguished by Raman spectroscopy, thermoanalysis and temperature programmed hydrogenation. Significant changes occurred in both the catalytic activity and selectivity toward hydrocarbon products after ethylene treatment. The activity decreased along with an increase in CH4 selectivity, at the expense of a remarkable decrease of heavy hydrocarbon production, resulting in enhanced selectivity for the gasoline fraction...
February 10, 2017: Faraday Discussions
G Marien Bremmer, Eirini Zacharaki, Anja O Sjåstad, Violeta Navarro, Joost W M Frenken, Patricia J Kooyman
Using a MEMS nanoreactor in combination with a specially designed in situ Transmission Electron Microscope (TEM) holder and gas supply system, we imaged the formation of multiple layers of graphene encapsulating a cobalt nanoparticle, at 1 bar CO : N2 (1 : 1) and 500 °C. The cobalt nanoparticle was imaged live in a TEM during the Boudouard reaction. The in situ/operando TEM studies give insight into the behaviour of the catalyst at the nanometer-scale, under industrially relevant conditions. When switching from Fischer-Tropsch syngas conditions (CO : H2 : N2 1 : 2 : 3 at 1 bar) to CO-rich conditions (CO : N2 1 : 1 at 1 bar), we observed the formation of multi-layered graphene on Co nanoparticles at 500 °C...
February 9, 2017: Faraday Discussions
Alberto Roldan, Nora H de Leeuw
Fischer-Tropsch (FT) synthesis has been a recursive method to form valuable molecules from syngas. Metal surfaces have been extensively studied as FT catalysts; among them, iron presents several phases under reaction conditions, oxides and carbides, as active sites for the FT and reverse water gas shift reaction. We present CO reduction on an iron sulfide phase with spinel structure, Fe3S4, also considering the pathways where C-O dissociates leaving CHx species on the surface, which may feed longer aliphatic chains via the FT process...
February 9, 2017: Faraday Discussions
Saeedeh S Tafreshi, Alberto Roldan, Nora H de Leeuw
Hydrazine (N2H4) is produced at industrial scale from the partial oxidation of ammonia or urea. The hydrogen content (12.5 wt%) and price of hydrazine make it a good source of hydrogen fuel, which is also easily transportable in the hydrate form, thus enabling the production of H2in situ. N2H4 is currently used as a monopropellant thruster to control and adjust the orbits and altitudes of spacecrafts and satellites; with similar procedures applicable in new carbon-free technologies for power generators, e.g...
February 9, 2017: Faraday Discussions
H Bahruji, M Bowker, W Jones, J Hayward, J Ruiz Esquius, D J Morgan, G J Hutchings
The formation of PdZn bimetallic alloys on ZnO, TiO2 and Al2O3 supports was investigated, together with the effect of alloy formation on the CO2 hydrogenation reaction. The chemical vapour impregnation (CVI) method produced PdZn nanoparticles with diameters of 3-6 nm. X-ray photoelectron spectroscopy and X-ray diffraction revealed the changes in the structure of the PdZn alloy that help stabilise formate intermediates during methanol synthesis. PdZn supported on TiO2 exhibits high methanol productivity of 1730 mmol kgcat(-1) h(-1) that is associated with the high dispersion of the supported PdZn alloy...
February 9, 2017: Faraday Discussions
Y Mathieu, L Sauvanaud, L Humphreys, W Rowlands, T Maschmeyer, A Corma
An unconventional crude from biomass (biocrude) has been processed to yield a hydrocarbon stream that is not only fully processable in conventional refineries but is already close to the specification of commercial fuels such as transportation diesel. The upgrading of biocrude was carried out with a combination of hydrotreatment and catalytic cracking, yielding middle distillate as the main product.
February 8, 2017: Faraday Discussions
Liying Wang, Kalyani Gupta, Josephine B M Goodall, Jawwad A Darr, Katherine B Holt
Copper oxide modified electrodes were investigated as a function of applied electrode potential using in situ infrared spectroscopy and ex situ Raman and X-ray photoelectron spectroscopy. In deoxygenated KHCO3 electrolyte bicarbonate and carbonate species were found to adsorb to the electrode during reduction and the CuO was reduced to Cu(i) or Cu(0) species. Carbonate was incorporated into the structure and the CuO starting material was not regenerated on cycling to positive potentials. In contrast, in CO2 saturated KHCO3 solution, surface adsorption of bicarbonate and carbonate was not observed and adsorption of a carbonato-species was observed with in situ infrared spectroscopy...
February 8, 2017: Faraday Discussions
Jenny Schneider, Konstantin Nikitin, Ralf Dillert, Detlef W Bahnemann
Herein, we report the effect of the laser illumination during the diffuse-reflectance laser-flash-photolysis measurements on the morphological and optical properties of TiO2 powders. A grey-blue coloration of the TiO2 nanoparticles has been observed after intense laser illumination. This is explained by the formation of nonreactive trapped electrons accompanied by the release of oxygen atoms from the TiO2 matrix as detected by means of UV-vis and EPR spectroscopy. Moreover, in the case of the pure anatase sample a phase transition of some TiO2 nanoparticles located in the inner region from anatase to rutile occurred...
February 8, 2017: Faraday Discussions
C J Weststrate, J W Niemantsverdriet
Monomeric forms of carbon play a central role in the synthesis of long chain hydrocarbons via the Fischer-Tropsch synthesis (FTS). We explored the chemistry of C1Hxad species on the close-packed surface of cobalt. Our findings on this simple model catalyst highlight the important role of surface hydrogen and vacant sites for product selectivity. We furthermore find that COad affects hydrogen in multiple ways. It limits the adsorption capacity for Had, lowers its adsorption energy and inhibits dissociative H2 adsorption...
February 7, 2017: Faraday Discussions
Nelson Leung, Andrea Pucci, Rongrong Hu, Eleanor E B Campbell, Govindarajan Krishnamoorthy, Ben Zhong Tang, Shuizhu Wu, Feng Zhang, Ju Mei, Wei Bai, Bingshi Li, Xuewen He, Youhong Tang, Bin Liu, Ruoyu Zhang, Zhaoyang Wang, Anjun Qin, Zhen Li, Deqing Zhang, Dario Pasini, Wenjing Tian, Youichi Tsuchiya, Thaksen Jadhav, Yijia Wang, Zujin Zhao, Gang He, Kai Li, Eric Rivard, Ming-Qiang Zhu, Bin Xu, Jing Zhi Sun, Yoshiki Chujo, Jin-Long Hong, Lingwei Kong, Ping Lu, Cheng-Chung Chang, Kun Wang, Ram Adhar Singh
No abstract text is available yet for this article.
February 7, 2017: Faraday Discussions
Qian Wang, Takashi Hisatomi, Masao Katayama, Tsuyoshi Takata, Tsutomu Minegishi, Akihiko Kudo, Taro Yamada, Kazunari Domen
Water splitting using semiconductor photocatalysts has been attracting growing interest as a means of solar energy based conversion of water to hydrogen, a clean and renewable fuel. Z-scheme photocatalytic water splitting based on the two-step excitation of an oxygen evolution photocatalyst (OEP) and a hydrogen evolution photocatalyst (HEP) is a promising approach toward the utilisation of visible light. In particular, a photocatalyst sheet system consisting of HEP and OEP particles embedded in a conductive layer has been recently proposed as a new means of obtaining efficient and scalable redox mediator-free Z-scheme solar water splitting...
February 6, 2017: Faraday Discussions
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