| 1. |
- Barrientos, Javier, et al.
(författare)
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CO methanation over TiO2-supported nickel catalysts : A carbon formation study
- 2015
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Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 502, s. 276-286
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Tidskriftsartikel (refereegranskat)abstract
- A systematic study on titania-supported nickel catalysts was performed in order to evaluate the effect of different process conditions on catalyst stability. Reaction tests and temperature-programmed-hydrogenation analyses were used in order to evaluate the effect of temperature, feed composition, water and reduction conditions on catalyst deactivation and carbon deposition. It was shown that high H-2/CO ratios and syngas partial pressures decrease the rate of carbon formation. Moreover, increasing temperature enhanced the formation of more stable carbon species and thus catalyst deactivation. The temperature-programmed hydrogenation analyses also revealed that water reduces the rate of carbon deposition. However, water enhanced catalyst deactivation when the catalysts were reduced at high temperatures. This negative effect of water is probably due to a progressive destruction of the strong-metal-support interaction characteristic of titania-supported nickel catalysts reduced at high temperatures. (C) 2015 Elsevier B.V. All rights reserved.
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| 2. |
- Barrientos, Javier
(författare)
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Deactivation of cobalt and nickel catalysts in Fischer-Tropsch synthesis and methanation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A potential route for converting different carbon sources (coal, natural gas and biomass) into synthetic fuels is the transformation of these raw materials into synthesis gas (CO and H2), followed by a catalytic step which converts this gas into the desired fuels. The present thesis has focused on two catalytic steps: Fischer-Tropsch synthesis (FTS) and methanation. The Fischer-Tropsch synthesis serves to convert synthesis gas into liquid hydrocarbon-based fuels. Methanation serves instead to produce synthetic natural gas (SNG). Cobalt catalysts have been used in FTS while nickel catalysts have been used in methanation. The catalyst lifetime is a parameter of critical importance both in FTS and methanation. The aim of this thesis was to investigate the deactivation causes of the cobalt and nickel catalysts in their respective reactions. The resistance to carbonyl-induced sintering of nickel catalysts supported on different carriers (γ-Al2O3, SiO2, TiO2 and α-Al2O3) was studied. TiO2-supported nickel catalysts exhibited lower sintering rates than the other catalysts. The effect of the catalyst pellet size was also evaluated on γ-Al2O3-supported nickel catalysts. The use of large catalyst pellets gave considerably lower sintering rates. The resistance to carbon formation on the above-mentioned supported nickel catalysts was also evaluated. Once again, TiO2-supported nickel catalysts exhibited the lowest carbon formation rates. Finally, the effect of operating conditions on carbon formation and deactivation was studied using Ni/TiO2 catalysts. The use of higher H2/CO ratios and higher pressures reduced the carbon formation rate. Increasing the temperature from 280 °C to 340 °C favored carbon deposition. The addition of steam also reduced the carbon formation rate but accelerated catalyst deactivation. The decline in activity of cobalt catalysts with increasing sulfur concentration was also assessed by ex situ poisoning of a cobalt catalyst. A deactivation model was proposed to predict the decline in activity as function of the sulfur coverage and the sulfur-to-cobalt active site ratio. The results also indicate that sulfur decreases the selectivity to long-chain hydrocarbons and olefins.
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| 3. |
- Barrientos, Javier, et al.
(författare)
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Deactivation of Ni/gamma-Al2O3 Catalysts in CO Methanation : Effect of Zr, Mg, Ba and Ca Oxide Promoters
- 2017
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Ingår i: Topics in catalysis. - : Springer. - 1022-5528 .- 1572-9028. ; 60:17-18, s. 1276-1284
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst deactivation is one of the major concerns in the production of substitute natural gas (SNG) via CO methanation. Catalysts in this application need to be active at low temperatures, resistant to polymeric carbon formation and stable at high temperatures and steam partial pressures. In the present work, a series of alumina-supported nickel catalysts promoted with Zr, Mg, Ba or Ca oxides were investigated. The catalysts were tested under low temperature CO methanation conditions in order to evaluate their resistance to carbon formation. The catalysts were also exposed to accelerated ageing conditions at high temperatures in order to study their thermal stability. The aged catalysts lost most of their activity mainly due to sintering of the support and the nickel crystallites. Apparently, none of these promoters had a satisfactory effect on the thermal resistance of the catalyst. Nevertheless, it was found that the presence of Zr can reduce the rate of polymeric carbon formation.
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| 4. |
- Barrientos, Javier, et al.
(författare)
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Deactivation of supported nickel catalysts during CO methanation
- 2014
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 486, s. 143-149
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Tidskriftsartikel (refereegranskat)abstract
- Deactivation of Ni-based catalysts was investigated during CO methanation over different supported catalysts. X-ray diffraction and temperature-programmed hydrogenation analyses were used to investigate nickel particle sintering and carbon formation during the first 24 h on stream. Titania-supported catalysts presented high resistance towards carbon deposition and nickel particle growth in comparison with the other tested catalysts. Particle size effects on these two deactivation causes were also evaluated. It was shown that carbon formation rates are higher on bigger crystal particles. However, it was found that titania-supported nickel catalysts reduced at high temperatures show the opposite effect. This difference is most probably due to a stronger interaction between nickel and TiOx (x < 2) species on smaller crystals which changes the CO dissociation properties and, in consequence, carbon formation rates.
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| 5. |
- Barrientos, Javier, et al.
(författare)
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Fischer-Tropsch Synthesis Over Zr-Promoted Co/gamma-Al2O3 Catalysts
- 2017
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Ingår i: Topics in catalysis. - : SPRINGER/PLENUM PUBLISHERS. - 1022-5528 .- 1572-9028. ; 60:17-18, s. 1285-1298
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Tidskriftsartikel (refereegranskat)abstract
- Two Zr-modified alumina supports were synthetized containing the same amount of Zr but a different distribution of this modifier over the alumina surface. These supports, together with the unmodified alumina carrier, were used to prepare three cobalt-based catalysts which were characterized and tested under relevant Fischer-Tropsch conditions. The three catalysts presented very similar porosity and cobalt dispersion. The addition of Zr nor its distribution enhanced the catalyst reducibility. The catalyst activity was superior when using a carrier consisting of large ZrO2 islands over the alumina surface. The use of a carrier with a homogeneous Zr distribution had however, a detrimental effect. Moreover, a faster initial deactivation rate was observed for the Zr-promoted catalysts, fact that may explain this contradictory effect of Zr on activity. Finally, the addition of Zr showed a clear enhancement of the selectivity to long chain hydrocarbons and ethylene, especially when Zr was well dispersed.
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| 6. |
- Barrientos, Javier, et al.
(författare)
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Further insights into the effect of sulfur on the activity and selectivity of cobalt-based Fischer–Tropsch catalysts
- 2016
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 275, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- A sulfur poisoning study was performed by ex situ poisoning of a platinum-promoted cobalt/alumina catalyst with different sulfur amounts. The poisoned catalyst samples were tested at relevant Fischer–Tropsch reaction conditions and at the same CO conversion in order to evaluate the effect of sulfur on catalyst activity and product selectivity. It was found that the activity and the selectivity to long-chain hydrocarbons decrease with increasing sulfur content. Moreover, it was found that sulfur has no significant effect on the CO2 selectivity. It was also shown that sulfur significantly enhances olefin hydrogenation. Finally, a deactivation model relating the catalyst activity and the sulfur to cobalt active site ratio was proposed and used to describe the experimental results.
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| 7. |
- Barrientos, Javier, et al.
(författare)
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The effect of catalyst pellet size on nickel carbonyl-induced particle sintering under low temperature CO methanation
- 2016
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Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 514, s. 91-102
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The present work aims to evaluate the effect of catalyst pellet size on deactivation due to nickel carbonyl-induced particle sintering. For that purpose, a γ-Al2O3-supported nickel catalyst was prepared and tested under low temperature and high CO partial pressure. A total of four different pellet sizes were employed in the present study. It was found that the deactivation rate decreases with increasing pellet size. A very severe deactivation was observed when using small pellets. Large pellets exhibited instead a more stable performance. This difference in catalyst stability was explained by X-ray diffraction analyses which revealed that the growth of the nickel particles was very severe when using small pellets. An evaluation of heat and mass transfer phenomena in these four pellets was also conducted. It was found that, under the present low temperature reaction conditions, the temperature at the catalyst external surface can greatly differ from that in the bulk gas when using sufficiently large pellets. It was also shown that, for large pellets, the major part of the interior of the catalyst is exposed to negligible CO partial pressures and high temperatures, fact that can reduce the potential for nickel carbonyl formation.
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| 8. |
- Garcilaso, V., et al.
(författare)
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Promoting effect of CeO2, ZrO2 and Ce/Zr mixed oxides on Co/Γ-Al2O3 catalyst for Fischer-Tropsch synthesis
- 2019
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Ingår i: Renewable energy. - : Elsevier Ltd. - 0960-1481 .- 1879-0682. ; 132, s. 1141-1150
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Tidskriftsartikel (refereegranskat)abstract
- A series of cobalt-based catalysts have been synthesized using as support γ-Al2O3 promoted by ceria/zirconia mixed oxides with a variable Ce/Zr molar ratio. The obtained catalysts demonstrated oxide promotion results in the protection of the major textural properties, especially for Zr-rich solids. Reducibility of cobalt species was enhanced by the presence of mixed oxides. The chemical composition of the oxide promoter influenced not only physicochemical properties of final catalysts but also determined their performance during the reaction. In this sense, Zr-rich systems presented a superior catalytic performance both in total conversion and in selectivity towards long chain hydrocarbons. The observed Zr-promotion effect could be explained by two significant contributions: firstly, the partial inhibition of Co–Al spinel compound formation by the presence of Zr-rich phases which enhances the availability of Co actives site and secondly, Zr-associate acidic sites promote higher hydrocarbons selectivity.
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| 9. |
- Javier Egea, Francisco, et al.
(författare)
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Design and Test of a High-Speed Flash ADC Mezzanine Card for High-Resolution and Timing Performance in Nuclear Structure Experiments
- 2013
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 60:5, s. 3526-3531
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Tidskriftsartikel (refereegranskat)abstract
- This work describes new electronics for the EX-OGAM2 (HP-Ge detector array) and NEDA (BC501A-based neutron detector array). A new digitizing card with high resolution has been designed for gamma-ray and neutron spectroscopy experiments. The higher bandwidth requirement of the NEDA signals, together with the necessity for accuracy, require a high sampling rate in order to preserve the shape for real-time Pulse Shape Analysis (PSA). The PSA is of paramount importance for the NEDA to discriminate between neutrons and gamma-ray signals. Both high resolution and high speed parameters are often difficult to achieve in a single electronic unit. These constraints, together with the need to build new digitizing electronics to improve performance and flexibility of signal analysis in nuclear physics experiments, led to the development a new FADC mezzanine card. In this work, the design and development are described, including the characterization procedure and the preliminary measurement results.
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| 10. |
- Kehoe, Laura, et al.
(författare)
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Make EU trade with Brazil sustainable
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 11. |
- Pascual-Valdunciel, Alejandro, et al.
(författare)
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Intramuscular Stimulation of Muscle Afferents Attains Prolonged Tremor Reduction in Essential Tremor Patients
- 2021
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294 .- 1558-2531. ; 68:6, s. 1768-1776
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Tidskriftsartikel (refereegranskat)abstract
- This study proposes and clinically tests intramuscular electrical stimulation below motor threshold to achieve prolonged reduction of wrist flexion/extension tremor in Essential Tremor (ET) patients. The developed system consisted of an intramuscular thin-film electrode structure that included both stimulation and electromyography (EMG) recording electrodes, and a control algorithm for the timing of intramuscular stimulation based on EMG (closed-loop stimulation). Data were recorded from nine ET patients with wrist flexion/extension tremor recruited from the Gregorio Marañón Hospital (Madrid, Spain). Patients participated in two experimental sessions comprising: 1) sensory stimulation of wrist flexors/extensors via thin-film multichannel intramuscular electrodes; and 2) surface stimulation of the nerves innervating the same target muscles. For each session, four of these patients underwent random 60-s trials of two stimulation strategies for each target muscle: 1) selective and adaptive timely stimulation (SATS) - based on EMG of the antagonist muscle; and 2) continuous stimulation (CON) of target muscles. Two patients underwent SATS stimulation trials alone while the other three underwent CON stimulation trials alone in each session. Kinematics of wrist, elbow, and shoulder, together with clinical scales, were used to assess tremor before, right after, and 24 h after each session. Intramuscular SATS achieved, on average, 32% acute (during stimulation) tremor reduction on each trial, while continuous stimulation augmented tremorgenic activity. Furthermore, tremor reduction was significantly higher using intramuscular than surface stimulation. Prolonged reduction of tremor amplitude (24 h after the experiment) was observed in four patients. These results showed acute and prolonged (24 h) tremor reduction using a minimally invasive neurostimulation technology based on SATS of primary sensory afferents of wrist muscles. This strategy might open the possibility of an alternative therapeutic approach for ET patients.
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| 12. |
- Suárez París, Rodrigo, et al.
(författare)
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Catalytic conversion of biomass-derived synthesis gas to fuels
- 2015
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Ingår i: Catalysis. Volume 27. - Cambridge : Royal Society of Chemistry. - 9781782620549 - 9781782622697 ; , s. 62-143
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Bokkapitel (refereegranskat)abstract
- Biomass-derived fuels constitute a promising alternative for diversifying the fuel supply and reducing the consumption of fossil fuels, leading to a reduction in greenhouse gas emissions and thus mitigating global warming. Biomass can be converted to synthesis gas, which can serve as a source for various liquid and gaseous fuels. Although significant progress has been achieved in the overall process, both economic and technical challenges still need to be overcome. Many pilot plants are already in operation and the first demonstration and semi-commercial installations are under construction or starting to operate. Catalysis is a key parameter in the conversion of synthesis gas to fuels. The aim of this work is to present the latest advances in the catalytic conversion of synthesis gas to Fischer-Tropsch gasoline and diesel, synthetic natural gas, ethanol and mixed alcohols. The syntheses of methanol and dimethyl ether are also briefly reviewed.
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| 13. |
- Suárez París, Rodrigo, et al.
(författare)
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Hydroconversion of paraffinic wax over platinum and palladium catalysts supported on silica–alumina
- 2016
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 275, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- Two bifunctional catalysts consisting of platinum or palladium supported on amorphous silica–alumina were prepared and tested in hydrocracking/hydroisomerization of paraffinic wax. The performance of both noble metals was studied at the following reaction conditions: P = 35 bar; T = 300–330 °C; H2/wax = 0.1 wt/wt; WHSV = 1–4 h−1. The platinum sample was more active in hydrocracking of C22+ compounds and more selective to middle distillates. On the other hand, the palladium-based catalyst resulted in a higher isomerization degree of the products and lower amounts of methane and ethane. The higher production of light compounds over platinum is attributed to a monofunctional hydrogenolysis mechanism, in addition to the classical bifunctional route. Characterization studies showed that both catalysts had comparable metal and acid site distributions. These observations would indicate that the different catalyst performance is due to the different nature of platinum and palladium as hydrogenation/dehydrogenation function.
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| 14. |
- Zariquiey, Roberto, et al.
(författare)
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Linking endangerment databases and descriptive linguistics : an assessment of the use of terms relating to language endangerment in grammars
- 2022
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Ingår i: Language Documentation & Conservation. - : University of Hawaii Press. - 1934-5275. ; 16, s. 290-318
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Tidskriftsartikel (refereegranskat)abstract
- The world harbours a diversity of some 6,500 mutually unintelligible languages. As has been increasingly observed by linguists, many minority languages are becoming endangered and will be lost forever if not documented. The increased urgency has led to the development of several global endangerment databases and a more fine-grained understanding of the language endangerment progression as well as its possible reversal. In the present paper, we explore the terminological correlates of this development as found in the descriptive linguistic literature, using a corpus of over 10,000 digitized grammatical descriptions. Comparing this with existing endangerment databases, we find that simply counting terms related to endangerment does signal endangerment, but the degree of endangerment is more difficult to assess from grammatical descriptions. The label endangered seems to be an umbrella term that covers different situations ranging from moribund languages with less than ten speakers to minority languages with several thousand speakers. For many languages considered endangered in existing databases, explicit terms to this effect cannot be found in their descriptions. The discrepancy is due to incompleteness of the searchterm set, gaps in the literature, and projected rather than observed information in the databases. Our explorations illustrate the potential for database curation assisted by computational searches both to maintain accuracy of the databases and to investigate assumed language endangerment. Future work includes a larger cloud of search terms, usage of term frequencies, and prescreening of descriptive literature for the existence of a relevant section. From the perspective of descriptive linguistics, this study calls for a more careful correlation between the language endangerment indexes, as developed in the global endangerment databases, and the treatment of the endangerment status of individual languages in descriptive grammars.
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