| 1. |
- Ajpi, Cesario, et al.
(författare)
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Crystal structure and Hirshfeld surface analysis of poly[tris(mu(4)-benzene-1,4-dicarboxylato)tetrakis(di-methylformamide)tr inickel(II)] : a two-dimensional coordination network
- 2019
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Ingår i: Acta Crystallographica Section E. - : International Union of Crystallography. - 2056-9890. ; 75, s. 1839-1843
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the title compound, [Ni-3(C8H4O4)(3)(C3H7NO)(4)], is a two-dimensional coordination network formed by trinuclear linear Ni-3(tp)(3)(DMF)(4) units (tp = terephthalate = benzene-1,4-dicarboxylate and DMF = dimethyl-formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal-organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides interactions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF molecule, which shows positional disorder. Parallel planes are connected mainly through weak C-H center dot center dot center dot O, H center dot center dot center dot H and H center dot center dot center dot C interactions between DMF molecules, as shown by Hirshfeld surface analysis.
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| 2. |
- Ajpi, Cesario, et al.
(författare)
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Crystal structure and Hirshfeld surface analysis of poly[tris-(μ4-benzene-1,4-di-carboxyl-ato)tetra-kis-(di-methyl-formamide)-trinickel(II)] : a two-dimensional coordination network.
- 2019
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Ingår i: Acta Crystallographica Section E. - 2056-9890. ; 75:Pt 12, s. 1839-1843
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the title compound, [Ni3(C8H4O4)3(C3H7NO)4], is a two-dimensional coordination network formed by trinuclear linear Ni3(tp)3(DMF)4 units (tp = terephthalate = benzene-1,4-di-carboxyl-ate and DMF = di-methyl-formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal-organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides inter-actions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF mol-ecule, which shows positional disorder. Parallel planes are connected mainly through weak C-H⋯O, H⋯H and H⋯C inter-actions between DMF mol-ecules, as shown by Hirshfeld surface analysis.
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| 3. |
- Ajpi Condori, Cesario, et al.
(författare)
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Synthesis and Characterization of LiFePO4-PANI Hybrid Material as Cathode for Lithium-Ion Batteries
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the synthesis of LiFePO4-PANI hybrid materials and studies their electrochemical properties (capacity, cyclability and rate capability) for use in lithium ion batteries. PANI synthesis and optimization was carried out by chemical oxidation (self-assembly process), using ammonium persulfate (APS) and H3PO4, obtaining a material with a high degree of crystallinity. For the synthesis of the LiFePO4-PANI hybrid, a thermal treatment of LiFePO(4)particles was carried out in a furnace with polyaniline (PANI) and lithium acetate (AcOLi)-coated particles, using Ar/H(2)atmosphere. The pristine and synthetized powders were characterized by XRD, SEM, IR and TGA. The electrochemical characterizations were carried out by using CV, EIS and galvanostatic methods, obtaining a capacity of 95 mAhg(-1)for PANI, 120 mAhg(-1)for LiFePO(4)and 145 mAhg(-1)for LiFePO4-PANI, at a charge/discharge rate of 0.1 C. At a charge/discharge rate of 2 C, the capacities were 70 mAhg(-1)for LiFePO(4)and 100 mAhg(-1)for LiFePO4-PANI, showing that the PANI also had a favorable effect on the rate capability.
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| 4. |
- Ajpi Condori, Cesario, et al.
(författare)
-
Synthesis and spectroscopic characterization of NiII coordination network : Poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)] as material for lithium ion batteries
- 2022
-
Ingår i: Journal of Molecular Structure. - : Elsevier B.V.. - 0022-2860 .- 1872-8014. ; 1265
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Tidskriftsartikel (refereegranskat)abstract
- The compound Ni3(C8H4O4)3(C3H7NO)3, poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)], was synthesized by the solvothermal method prepared via reaction between NiCl2•6H2O and terephthalic acid using N,N-dimethylformamide (DMF) as solvent. The structure was characterized by powder X-ray diffraction and infrared spectroscopy analyses. The electrochemical properties as a potential active material in lithium-ion batteries were characterized by electrochemical impedance spectroscopy and galvanostatic charge-discharge curves in a battery half-cell. The characterization results show that the coordination network contains one independent structure in the asymmetric unit. It is constructed from Ni2+ ions, terephthalate bridges and in-situ-generated DMF ligands, forming two similar two-dimensional (2D) layer structures. These similar 2D layers are in an alternating arrangement and are linked with each other by dense H—H interactions (45%) to generate a three-dimensional (3D) supramolecular framework with ordered and disordered DMF molecules. The electrochemical measurements, conducted in the potential range of 0.5–3.5 V vs Li/Li+, show that Ni3(C8H4O4)3(C3H7NO)4 has good electrochemical properties and can work as anode in lithium-ion batteries. The material presents an initial specific capacity of ∼420 mAh g−1, which drops during consecutive scans but stabilizes at ∼50 mAh g−1. However, due to the wide potential range there are indications of a gradual collapse of the structure. The electrochemical impedance spectroscopy shows an increase of charge transfer resistance from 24 to 1190 Ohms after cycling likely due to this collapse.
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| 5. |
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| 6. |
- Benavente Araoz, Fabian Andres, 1985-, et al.
(författare)
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Effect of Partial Cycling of NCA/Graphite Cylindrical Cells in Different SOC Intervals
- 2020
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Ingår i: Journal of the Electrochemical Society. - : Institute of Physics Publishing. - 0013-4651 .- 1945-7111. ; 167:4
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Tidskriftsartikel (refereegranskat)abstract
- A quasi-realistic aging test of NCA/graphite lithium-ion 18650 cylindrical cells is performed during a long-term low c-rate cycling and using a new protocol for testing and studying the aging. This to emulate a characteristic charge/discharge profile of off-grid PV-battery systems. The cells were partially cycled at four different cut-off voltages and two state of charge ranges (ΔSOC) for 1000 and 700 cycles over 24 months. Differential voltage analysis shows that a combination of loss of active material (LAM) and loss of lithium inventory (LLI) are the causes of capacity loss. Cells cycled with high cut-off voltages and wide ΔSOC (20% to 95%) were severely affected by material degradation and electrode shift. High cut-off voltage and narrow ΔSOC (65% to 95%) caused greater electrode degradation but negligible cell unbalance. Cell impedance is observed to increase in both cells. Cells cycled with middle to low cut-off voltages and narrow ΔSOC (35%-65% and 20% to 50%) had comparable degradation rates to calendar-aged cells. Cycling NCA/graphite cells with low c-rate and high cut-off voltages will degrade the electrode in the same way high c-rate would do. However, low c-rate at low and middle cut-off voltages greatly decrease cell degradation compared to similar conditions at middle to high c-rate, therefore increasing battery lifetime. © 2020 The Author(s).
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| 7. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
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Photovoltaic/battery system sizing for rural electrification in Bolivia : Considering the suppressed demand effect
- 2019
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 235, s. 519-528
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Tidskriftsartikel (refereegranskat)abstract
- Rural electrification programs usually do not consider the impact that the increment of demand has on the reliability of off-grid photovoltaic (PV)/battery systems. Based on meteorological data and electricity consumption profiles from the highlands of Bolivian Altiplano, this paper presents a modelling and simulation framework for analysing the performance and reliability of such systems. Reliability, as loss of power supply probability (LPSP), and cost were calculated using simulated PV power output and battery state of charge profiles. The effect of increasing the suppressed demand (SD) by 20% and 50% was studied to determine how reliable and resilient the system designs are. Simulations were performed for three rural application scenarios: a household, a school, and a health centre. Results for the household and school scenarios indicate that, to overcome the SD effect, it is more cost-effective to increase the PV power rather than to increase the battery capacity. However, with an increased PV-size, the battery ageing rate would be higher since the cycles are performed at high state of charge (SOC). For the health centre application, on the other hand, an increase in battery capacity prevents the risk of electricity blackouts while increasing the energy reliability of the system. These results provide important insights for the application design of off-grid PV-battery systems in rural electrification projects, enabling a more efficient and reliable source of electricity.
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| 8. |
- Benavente, Fabian, 1985-
(författare)
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Lithium-ion batteries for off-grid PV-systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis provides a comprehensive and detailed analysis on the effect ofthe battery operation strategy on the lifetime of commercial lithium-ionbatteries and on the economics of off-grid photovoltaic (PV)-batterysystems.Lithium-ion batteries play a key role in the transition to a fossil-freesociety. Compared to electric vehicles, stationary energy storage hasdifferent requirements for the performance and lifetime of batteries.Although optimal battery design is critical to achieve high energy densityand longer lifetime, operation plays an important role in preventingpremature performance degradation. Understanding the effects ofsuppressed demand, geographical location, and application on system lifecycle costs also enables optimal system design.Load profiles for three applications were estimated and implemented in asimulation model, along with meteorological data for three locations andthe suppressed demand (SD) effect. Using the hourly state of charge (SOC)profiles, four battery operation strategies were designed using partialcycling with different cut-off voltages and two state of charge windows(ΔSOC). Commercial cells were used for the experimental tests. After over1000 cycles a post-mortem characterization was performed.The experiments revealed the cause of premature degradation at high SOCoperation to be a combination of impedance rise in the positive electrodeand loss of lithium inventory at the negative electrode leading to decreaseof capacity. Studies on the impedance spectra of the cells using physicsbasedmodeling revealed a loss of conductivity between particles in thepositive electrode. At system level, as the SD increases, so does theoperational ΔSOC width, while the reliability of the system decreases. Wedefined the reliability as loss of power supply probability. Finally,optimization of cost and reliability, revealed that an optimal system designfavors a battery operation strategy with wider ΔSOC instead of batterylifetime.
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| 9. |
- Cardenas, Edgar, et al.
(författare)
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Microstructural evolution of condensed aggregates during the crystallization of ZSM-5 from a heterogeneous system
- 2021
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 568–569
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Tidskriftsartikel (refereegranskat)abstract
- The microstructural evolution of precursors of ZSM-5 zeolite crystallized from a heterogeneous system using fumed silica, sodium aluminate and tetrapropylammonium ions as reagents is investigated. Entities previously described by Ren et al. (Chem. Mater. 2012, 24, 10, 1726–1737) as condensed aggregates, were extensively studied using scanning electron microscopy, and energy dispersive spectroscopy. It was observed that the condensed aggregates first comprise a core of nanocrystals that is enveloped by a shell of amorphous gel phase. During crystallization, the amorphous shell surrounding the core is converted into ZSM-5 crystals that grow to a film surrounding the core. The crystals in the film grow competitively with nutrients provided by the liquid phase from the surroundings, while the nanocrystals in the core show little or no signs of growth.
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| 10. |
- Cardenas, Edgar, 1990-
(författare)
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Synthesis of zeolites from economic raw materials
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis methods using economic raw materials, such as kaolin and diatomite have been developed for the production of zeolites in the present work. Zeolite Y and ZSM-5 have been synthetized successfully from diatomite and kaolin, respectively. The synthesis of zeolite Y was extensively studied (Paper I) in order to obtain final products with high crystallinity and an appropriate SiO2/Al2O3 ratio to be suitable for application as catalyst. Then, the influence of the alkalinity (in terms of SiO2/Na2O ratio) on the outcome of the synthesis was studied. Thus, an optimum range of alkalinity that satisfies the requirements stated before was found. Additionally, the results also showed that diatomite produce similar products as colloidal silica, which may be expected since both silica sources are highly polymerized forms of silica.The synthesized zeolite Y crystals were also ion-exchanged with Lanthanum to obtain a Rare Earth zeolite Y (REY) catalyst (Paper V). The REY catalyst was shown to be thermally stable up to 800°C as expected for this catalyst. The REY catalyst was also evaluated in the reaction of Catalytic Cracking of cumene. The results of catalytic tests shown that the REY catalyst synthetized from diatomite holds activity towards the catalytic cracking of cumene.In addition, studies of synthesis of ZSM-5 zeolite from kaolin have been performed to understand the crystal growth and morphology, crystal size, and aluminum distribution. In particular, the influence of the gel on the morphology of the crystals (Paper II) has been studied. It was observed that when the crystal surface is in contact with the gel phase, dendritic features appear at the crystal surface, that become smoother as the reaction proceeds. On the contrary, when only liquid phase is in contact with crystal surface there is no presence of dendritic features and the growth rate is higher.Further studies demonstrated that the ZSM-5 crystals possess a non-homogeneous aluminum distribution, a phenomenon known as Al-zoning. A thorough characterization at distinct stages of the reaction has been performed (Paper III), on the different reaction mixture phases such as solid part, gel phase and liquid phase. The main finding was that the gel phase consists of a nanoparticle skeleton rich in alumina, filled by a silica rich matrix. In the beginning of crystallization, the silica rich matrix is preferentially consumed to form the crystals, leaving behind the alumina rich nanoparticle skeleton that is consumed later, resulting in the non-homogeneous distribution of aluminum in the crystals.Finally, studies of the microstructure of a TPA-ZSM-5 system using fumed silica as silicon source have been performed (paper IV). In this system, three stages of crystallization were observed. Stage I, formation of amorphous gel phase. Stage II formation of XRD amorphous spherical entities denoted as Condensed Agregates (CAs). Stage III, Crystallization of CAs into ZSM-5. This study was focused only in the stage III. Findings showed that ZSM-5 nanocrystals are formed in the core of the CA (beginning of stage III), surrounded by an amorphous shell composed of alumino-silica. As the crystallization proceeds, the amorphous shell crystallizes into ZSM-5 by competitive growth, but the nanocrystals of the core remain intact. Moreover, compositional analysis results showed that the silicon from the liquid phase provided most of the nutrients for growth of the ZSM-5 crystals resulting in polycrystalline ZSM-5 aggregates with an Al rich core - Si rich shell morphology.
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| 11. |
- Cardenas, Edgar, et al.
(författare)
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Zeolite Y from diatomaceous earth as catalytic cracking catalyst
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A zeolite Y cracking catalyst in the lanthanum form was synthetized from Bolivian diatomite. Characterization was conducted through x-ray diffraction, scanning electron microscopy, nitrogen adsorption and energy dispersive spectroscopy. The catalyst was evaluated in the catalytic cracking of cumene and the results were compared with that of a catalyst prepared from commercial zeolite Y powder. It was shown that the catalytic performance of the catalyst prepared from diatomite was comparable to that for the catalyst prepared from commercial zeolite Y powder.
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| 12. |
- Garcia, Gustavo, et al.
(författare)
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Preparation of zeolite A with excellent optical properties from clay
- 2015
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 619, s. 771-777
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Tidskriftsartikel (refereegranskat)abstract
- Discoloration of zeolite A powder is a common problem when natural raw materials such as kaolin clay are used because of the formation of colored iron compounds. In this study, we report on a novel method to produce zeolite A with excellent optical properties, from clays. The brightness is as high as 94.5 and the yellowness is as low as 3.0. The product is comprised of intergrown zeolite A crystals with cubic habit and a length ranging between 0.5 and 2 μm. Good optical properties are obtained when the raw material contains magnesium, as some natural raw materials do, or alternatively, when a magnesium compound is added to the raw material. Magnesium probably forces iron inside colorless extraneous magnesium aluminosilicate compounds. This simple process appears very promising for the preparation of zeolite A with good optical properties from inexpensive natural raw materials.
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| 13. |
- Garcia, Gustavo, et al.
(författare)
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Selective synthesis of FAU-type zeolites
- 2018
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 489, s. 36-41
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, parameters influencing the selectivity of the synthesis of FAU-zeolites from diatomite were studied. The final products after varying synthesis time were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and gas adsorption. It was found that high concentrations of NaCl could completely inhibit the formation of zeolite P, which otherwise usually forms as soon as maximum FAU crystallinity is reached. In the presence of NaCl, the FAU crystals were stable for extended time after completed crystallization of FAU before formation of sodalite. It was also found that addition of NaCl barely changed the crystallization kinetics of FAU zeolite and only reduced the final FAU particle size and SiO2/Al2O3 ratio slightly. Other salts containing either Na or Cl were also investigated. Our results suggest that there is a synergistic effect between Na+ and Cl-. This is attributed to the formation of (Na4Cl)3+ clusters that stabilize the sodalite cages. This new finding may be used to increase the selectivity of syntheses leading to FAU-zeolites and avoid the formation of undesirable by-products, especially if impure natural sources of aluminosilica are used.
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| 14. |
- Garcia, Gustavo, et al.
(författare)
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Synthesis of zeolite Y from diatomite as silica source
- 2016
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 219, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- Bolivian diatomite was successfully used as a silica source for the synthesis of zeolite Y. Prior to synthesis, the diatomite was leached with sulfuric acid to remove impurities and aluminum sulfate was used as an aluminum source. The raw materials were reacted hydrothermally at 100 °C in water with sodium hydroxide and different Na2O/SiO2 ratios were investigated. The final products were characterized by scanning electron microscopy, X-ray diffraction, gas adsorption and inductively coupled plasma-atomic emission spectroscopy. Diatomites originating from different locations and therefore containing different types and amounts of minerals and clays as impurities were investigated. After optimization of synthesis time, zeolite Y with low SiO2/Al2O3 ratio (3.0–3.9) was obtained at a high yield for high alkalinity conditions (Na2O/SiO2 = 0.85–2.0). Lower Na2O/SiO2 ratios resulted in incomplete dissolution of diatomite and lower yield. Nevertheless, decreasing alkalinity resulted in a steady increase of the SiO2/Al2O3 ratio in zeolite Y. Consequently, it was possible to synthesize almost pure zeolite Y with a SiO2/Al2O3 ratio of 5.3 for a Na2O/SiO2 ratio of 0.6, albeit at a low yield. In this respect, diatomite enables the synthesis of high silica zeolite Y and behaves similarly to colloidal silica in traditional syntheses, with both sources of silica having in common a high degree of polymerization. Interestingly, the presence of minerals and clays in the starting diatomite had marginal effects on the outcome of the synthesis. However, their dissolution resulted in presence of calcium and magnesium in the zeolite Y crystals. Finally, overrun of all investigated compositions resulted in the formation of zeolite P nucleating and growing onto dissolving zeolite Y crystals, which was shown to be triggered when aluminum was completely depleted at high alkalinity
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| 15. |
- Lopez Nina, Luis Gagarin, et al.
(författare)
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Effect of syngas conversion and catalyst reduction temperature in the synthesis of ethanol : concentration of water vapor in mesoporous Rh/MCM-41 catalyst
- 2015
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Ingår i: Catalysis communications. - : Elsevier. - 1566-7367 .- 1873-3905. ; 69, s. 183-187
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Tidskriftsartikel (refereegranskat)abstract
- Rh-based catalysts typically show low selectivity to CO2 in the synthesis of ethanol from syngas. However, a novel mesoporous Rh/MCM-41 catalyst shows high selectivity to CO2 in a large range of syngas conversions; 1% to 68%, regulated by adjusting the operation conditions (270-430 degrees C, 30-90 bar and 6000-40,000 ml(syngas)/gcat h). The same effect is obtained at different catalyst reduction temperatures (200 degrees C and 500 degrees C) as well as on the non-reduced catalyst. A high concentration of water vapor seems to occur in the pores of Rh/MCM-41 which may promote the water-gas-shift-reaction, producing extra CO2 and H-2. (C) 2015 Elsevier B.V. All rights reserved.
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| 16. |
- Lopez Nina, Luis Gagarin, et al.
(författare)
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Synthesis of Ethanol from Syngas over Rh/MCM-41 Catalyst : Effect of Water on Product Selectivity
- 2015
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 5, s. 1737-1755
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Tidskriftsartikel (refereegranskat)abstract
- The thermochemical processing of biomass is an alternative route for the manufacture of fuel-grade ethanol, in which the catalytic conversion of syngas to ethanol is a key step. The search for novel catalyst formulations, active sites and types of support is of current interest. In this work, the catalytic performance of an Rh/MCM-41 catalyst has been evaluated and compared with a typical Rh/SiO2 catalyst. They have been compared at identical reaction conditions (280 degrees C and 20 bar), at low syngas conversion (2.8%) and at same metal dispersion (H/Rh = 22%). Under these conditions, the catalysts showed different product selectivities. The differences have been attributed to the concentration of water vapor in the pores of Rh/MCM-41. The concentration of water vapor could promote the water-gas-shift-reaction generating some extra carbon dioxide and hydrogen, which in turn can induce side reactions and change the product selectivity. The extra hydrogen generated could facilitate the hydrogenation of a C-2-oxygenated intermediate to ethanol, thus resulting in a higher ethanol selectivity over the Rh/MCM-41 catalyst as compared to the typical Rh/SiO2 catalyst; 24% and 8%, respectively. The catalysts have been characterized, before and after reaction, by N-2-physisorption, X-ray photoelectron spectroscopy, X-ray diffraction, H-2-chemisorption, transmission electron microscopy and temperature programmed reduction.
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| 17. |
- Pardo-Tarifa, Fatima, et al.
(författare)
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Ce-promoted Co/Al2O3 catalysts for Fischer-Tropsch synthesis
- 2017
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Ingår i: International journal of hydrogen energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0360-3199 .- 1879-3487. ; 42:15, s. 9754-9765
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Tidskriftsartikel (refereegranskat)abstract
- The effect of ceria promotion on the performance of Co/Al2O3 catalyst was evaluated in a high pressure fixed bed reactor for Fischer Tropsch (FT) synthesis at close industrial conditions. Ce-Al2O3 supports with a molar ratio of Al/Ce = 8 were prepared by two different methods: one by co-precipitation of cerium and aluminum precursors in water in-oil microemulsion and the other one by aqueous impregnation of cerium nitrate on commercial alumina. These supports, together with the unmodified alumina carrier, were used to prepare four cobalt-based catalysts. These catalysts were characterized by XRD, SEM, EDX, TEM, N-2 adsorption/desorption, TPR and chemisorption techniques. The results show that the presence of CeO2 on the surface of the support favors the reducibility of cobalt oxides with a shift down in reduction temperature of about 70 degrees C. The catalytic evaluation of the catalysts revealed that cerium addition by impregnation increases the activity and selectivity to C5+ catalyst in FTS. The catalyst synthetized by microemulsion show lower catalytic performance. Nevertheless, the catalytic property of this material can be improved by increasing the crystalline micro-domains size of CeO2. (C) 2017 Hydrogen Energy Publications LLC.
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| 18. |
- Velasco, Jorge A., et al.
(författare)
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Catalytic partial oxidation of methane over nickel and ruthenium based catalysts under low O2/CH4 ratios and with addition of steam
- 2015
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 153, s. 192-201
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Tidskriftsartikel (refereegranskat)abstract
- Catalytic partial oxidation (CPO) of methane to synthesis gas at low O2/CH4 ratios and in the presence of steam was investigated over nickel and ruthenium catalysts supported on hydrotalcite-derived materials. The influence of catalyst properties and composition on activity, temperature profile and deactivation by carbon formation was examined. All catalyst presented high methane conversions, close to the values predicted by thermodynamic equilibrium and such conversions increased in proportion to the metal surface of the catalyst tested. The temperature profiles at O2/CH4 = 0.2 and H2O/CH4 = 0.3 and a constant exit temperature of 700 °C varied depending on the catalyst type; it was possible to examine catalyst deactivation from the change in the shape of the profile of each catalyst. Since the O2/CH4 and H2O/CH4 ratios were low, the risk or potential for carbon formation was thermodynamically favorable along the entire catalytic bed; however, this potential was qualitatively higher when the temperature profile of the catalyst presented a pronounced maximum peak at the inlet of the reactor. During catalytic reaction tests and methane decomposition experiments, the ruthenium catalyst did not formed appreciable amounts of carbon while a bimetallic catalyst (Ni and Ru) form only small amounts (in comparison with the nickel catalysts). For the ruthenium catalyst, a higher O2/CH4 ratio favored conversions closer to the equilibrium value. The observations presented in this work indicate that during the CPO of methane, at low O2/CH4 ratios and in the presence of steam, the catalyst properties and composition will have a substantial influence on the extent of the combustion and reforming reactions along the catalytic bed. This will in turn define the temperature profile, and therefore the risk or potential for carbon formation; this risk might effectively be overcome by the use of ruthenium-containing catalysts.
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| 19. |
- Velasco, Jorge A., et al.
(författare)
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Gas to liquids : A technology for natural gas industrialization in Bolivia
- 2010
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Ingår i: Journal of Natural Gas Science and Engineering. - : Elsevier BV. - 1875-5100 .- 2212-3865. ; 2:5, s. 222-228
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Tidskriftsartikel (refereegranskat)abstract
- Gas-to-Liquids (GTL) technology converts natural gas, through Fischer-Tropsch synthesis, into liquid and ultra-clean hydrocarbons such as light oils, kerosene, naphtha, diesel, and wax. Bolivia has natural gas reserves that reach 48.7 trillion cubic feet and produces nearly 40.0 million cubic meters per day, from which, around 88% are exported to Brazil and Argentina. In spite of these considerable amounts of natural gas reserves and production, the country experiences a shortage of diesel which cannot be solved using conventional refining processes due the light nature of its crude oil. Thus, the GTL process seems to be a promising solution for Bolivia's diesel problems, at the same time that its natural gas reserves could be monetized. Although GTL can be considered as a well proven and developed technology, there are several aspects along the main processing steps (synthesis gas generation, Fischer-Tropsch synthesis, and product upgrading) to be considered at the time of implementing a GTL plant. The aim of this paper is to give an overall view of some relevant issues related to Gas-to-Liquids technology as an option for natural gas industrialization in Bolivia, and also to provide a landscape of Bolivian natural gas industry.
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| 20. |
- Velasco, Jorge A., et al.
(författare)
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Methane partial oxidation and methane decomposition over Ni andNi-Ru supported catalysts for synthesis gas production
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Nickel and nickel-ruthenium based catalysts were compared in the catalytic partial oxidation (CPO) of methane and in the equilibrium of the methane decomposition reaction. A hydrotalcite-derived material as well as α- Al2O3 and γ-Al2O3 were used as catalyst supports. The catalysts were characterized by H2 chemisorption, N2 physisorption, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO) and transmission electron microscopy (TEM). Catalyst properties and composition influenced the catalytic performance during partial oxidation (i.e. activity and temperature profiles). During methane decomposition equilibrium tests, all catalysts presented smaller equilibrium constants than those calculated on the basis of graphite; the deviation from graphite data was mainly associated with maximum nickel particle size (for both Ni and bimetallic Ni-Ru supported catalysts). Among all catalysts, the bimetallic Ni-Ru catalyst supported on hydrotalcite-derived material showed an interesting enhanced behavior; however, resistance towards catalyst deactivation, by mechanisms different than carbon formation, still needs to be improved.
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| 21. |
- Velasco, Jorge A., et al.
(författare)
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Synthesis gas production for GTL applications : Thermodynamic equilibrium approach and potential for carbon formation in a catalytic partial oxidation pre-reformer
- 2014
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Ingår i: Journal of Natural Gas Science and Engineering. - : Elsevier. - 1875-5100 .- 2212-3865. ; 20, s. 175-183
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Tidskriftsartikel (refereegranskat)abstract
- The present work is focused on synthesis gas production for Gas to Liquids (GTL.) applications. A thermodynamic equilibrium approach has been chosen in order to address the methane reforming processes in presence of steam and oxygen (i.e. autothermal reforming "ATR" and catalytic partial oxidation "CPO"). The effect of operational variables on the performance of the reforming units has been analyzed at conditions typical for GTL processes. Also, the performance of a synthesis gas generation unit (SGU) comprising a CPO pre-reformer followed by an ATR reactor has been investigated. The potential for carbon formation in the CPO pre-reformer has been evaluated by applying the "equilibrated gas principle". Our results show that synthesis gas production can be strongly influenced by changes in operating variables such as the steam-to-carbon (S/C) and the oxygen-to-carbon (O-2/C) ratios, recycled gas (tail gas) compositions, and operating pressures and temperatures; however, effective operation of the SGU (CPO + ATR) requires an correct combination of these variables in order to accomplish the synthesis gas requirements of the Fischer-Tropsch synthesis. Likewise, it is shown that the risk of carbon formation in the CPO reactor can be reduced or even eliminated by a proper manipulation and combination of such variables.
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