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Catalyseurs nanostructurés pour la méthanisation du CO2 assistée par plasma
No full textWork presented for the double degree of: Doctor por la Universidad de Zaragoza in the framework of the program of Ingeniería Química y del Medio Ambiente Diplôme naDonal de Doctorat de Sorbonne Université, specialité EnergéDque génie des procédés.-- It was read 20/10/2023, Sobresaliente Cum Laude.[EN] Among the different processes for carbon capture and utilisation, CO2 methanation is experiencing a renaissance as a promising technology for the development of Power-to-gas as an energy storage solution and carbon circular economy. The field of plasma catalysis, which considers the association of a catalyst with non-thermal plasma, has been recently developed for boosting CO2 methanation. The challenges of plasma catalysis focus on taking advantage of the activated species and electrons created by the plasma to achieve more favourable reaction pathways and interaction with the active sites of the catalyst and on plasma-catalyst synergy, meaning the enhancement of the catalyst properties by contact with plasma and vice versa. The goal of this work is to explore the effect of morphology and physicochemical properties of nanostructured Ni/CeO2 catalysts on plasma-catalyst synergy and to highlight the key characteristics of the catalysis that control an efficient plasma-assisted CO2 methanation in order to advance in the rational design of materials tailored for applications in plasma catalysis. For the plasma-assisted CO2 methanation tests, a suitable non-thermal plasma type is the dielectric barrier discharge due to mild temperature conditions, which allow the catalyst to be in direct contact with the plasma in a packed bed configuration, and operation at atmospheric pressure, promising for industrial applications. Nickel catalysts supported on Ce-based metal oxides have been proposed in recent publications for plasma-assisted CO2 methanation. Ni is a reliable solution as it is active for CO2 methanation as well as cost-effective. Cerium oxide (CeO2) is an interesting material to be used as support thanks to its redox properties related to the tendency to form oxygen vacancies. Such property can be tuned by enhancing the non-stoichiometric nature of the CeO2 surface, either by doping or, as in this case, by morphology modification, which has been reported for cerium oxide to be controllable via synthesis method. The parameters of the hydrothermal synthesis were varied and CeO2 nanomaterials with different morphology (polyhedra, nanorods, nanocubes), crystallite size, and surface area were produced. The Ni catalysts synthesised with these supports were further characterised by state-of-the-art techniques to examine the most relevant physicochemical properties, e.g., surface area, reducibility and metal-support interaction, surface basicity, and formation of oxygen vacancies. In addition, the electrical behaviour of the catalysts was assessed with focus on how the materials affect the plasma discharge, charge transfer, and the dielectric property of the packed bed. FTIR operando technique was utilised to suggest a possible reaction pathway of the plasma-assisted CO2 methanation on Ni/CeO2. In conclusion, it was found that the physicochemical properties which are relevant in conventional thermal methanation, such as surface area and basicity, are applicable to plasma catalysis but the importance of low dielectric permittivity of the catalyst and charge transfer mechanism was also highlighted for an energy efficient plasma-assisted methanation process. Furthermore, a rod or needle-like CeO2 support allows enhancing the surface defects, the interaction with Ni, and macroposority, which seem to facilitate the methanation reaction in plasma via formate route.[ES] Entre los diferentes procesos de captura y utilización del carbono, la metanización del CO2 experimenta últimamente un renacimiento como tecnología prometedora para el desarrollo de la conversión de electricidad en gas, del almacenamiento de energía y de la economía circular del carbono. El campo de la catálisis asistida por plasma, que considera la asociación de un catalizador con plasma no térmico, se ha desarrollado recientemente para impulsar la metanización de CO2. Los retos de esta tecnología se centran en aprovechar las especies activadas y los electrones para conseguir vías de reacción e interacción más favorables con los sitios activos del catalizador y en la sinergia plasma-catalizador, es decir, la mejora de las propiedades del catalizador por contacto con el plasma y viceversa. El objetivo de este trabajo es explorar el efecto de la morfología y las propiedades físicoquímicas de los catalizadores de Ni/CeO2 nanoestructurados en la sinergia plasma-catalizador y resaltar las características clave del catalizador que controlan una eficiente metanación de CO2 asistida por plasma con el fin de avanzar en el diseño de materiales para aplicaciones en plasma catálisis. Para los experimentos de metanación de CO2 asistida por plasma, un tipo de plasma no térmico adecuado es la descarga de barrera dieléctrica debido a las condiciones de temperatura suaves, que permiten que el catalizador esté en contacto directo con el plasma en una configuración de lecho fijo, y el funcionamiento a presión atmosférica, prometedor para aplicaciones industriales. En publicaciones recientes se han propuesto catalizadores de níquel soportados sobre óxidos metálicos basados en Ce para la metanación de CO2 asistida por plasma. El niquel es un metal adecuado ya que es activo para la metanación de CO2, además relativamente de bajo costo. El óxido de cerio (CeO2) es un material interesante para ser utilizado como soporte gracias a sus propiedades de redox relacionadas con la tendencia a formar vacantes de oxígeno. Dicha propiedad puede ajustarse potenciando la no estequiometria de la superficie del CeO2, ya sea por dopaje o, como en este caso, por modificación de la morfología, que se ha descrito para el óxido de cerio como controlable a través del método de síntesis. Se variaron los parámetros de la síntesis hidrotermal y se produjeron nanomateriales de CeO2 con diferente morfología (poliedros, nanorods, nanocubos), tamaño de cristalito y área superficial. Los catalizadores de Ni sintetizados con estos soportes se caracterizaron además mediante técnicas avanzadas para examinar las propiedades fisicoquímicas más relevantes, por ejemplo, el área superficial, la reducibilidad y la interacción metal-soporte, la basicidad superficial y la formación de vacantes de oxígeno. Además, se evaluó el comportamiento eléctrico de los catalizadores centrándose en cómo afectan los materiales a la descarga de plasma, la transferencia de carga y la propiedad dieléctrica del lecho fijo. Se utilizó la técnica operando FTIR para sugerir una posible vía de reacción de la metanización de CO2 con Ni/CeO2 asistida por plasma. En conclusión, se encontró que las propiedades fisicoquímicas que son relevantes en la metanación térmica convencional, como el área superficial y la basicidad, no son aplicables a la plasma catálisis, pero también se enfatiza la importancia de la baja permitividad dieléctrica del catalizador y el mecanismo de transferencia de carga para un proceso energéticamente eficiente. Además, un soporte de CeO2 en forma de barra o de aguja permite potenciar los defectos superficiales, la interacción con el Ni y la macroposoridad, que parecen facilitar la reacción de metanación en plasma por vía del formiato.[FR] Parmi les différents procédés de capture et d'utilisation du carbone, la méthanisation du CO2 connaît une renaissance comme une technologie prometteuse pour le développement du Power-to-gas et en tant que solution de stockage de l'énergie et de l'économie circulaire du carbone. Le domaine de la catalyse plasma, qui considère l'association d'un catalyseur avec un plasma non thermique, a été récemment développé pour stimuler la méthanation du CO2. Les défis de la catalyse assistée par plasma consistent à tirer profit des espèces activées et des électrons créés par le plasma pour obtenir des voies de réaction et des interactions plus favorables avec les sites actifs du catalyseur, ainsi que de la synergie plasma-catalyseur, c'est-à-dire de la modification des propriétés du catalyseur par contact avec le plasma et vice-versa. L'objectif de cette thèse est d'explorer l'effet de la morphologie et des propriétés physicochimiques des catalyseurs Ni/CeO2 nanostructurés sur la synergie plasma-catalyseur et de mettre en évidence les caractéristiques clés du catalyseur qui permettent une méthanisation efficace du CO2 assistée par plasma, afin de progresser dans la conception rationnelle de matériaux adaptés aux applications de la plasma-catalyse. Pour les essais de méthanation du CO2 assistée par plasma, les plasmas froids à décharge de barrière diélectrique (DBD) permettent des températures douces, ainsi qu’un contact direct entre le plasma et le catalyseur dans une configuration de lit fixe. Au même temps ils permettent l’opération sous pression atmosphérique, conditions idéales pour des applications industrielles. Des catalyseurs à base de nickel supportés par des oxydes métalliques à base de Ce ont été proposés dans des publications récentes pour la méthanisation du CO2 assistée par plasma. Le nickel est une solution fiable, car il est actif dans la méthanisation du CO2 et au même temps économiquement rentable. L'oxyde de cérium (CeO2) est un matériau intéressant à utiliser comme support grâce à ses propriétés d'oxydoréduction liées à sa capacité d’échange d'oxygène. Ces propriétés peuvent être ajustées en améliorant la nature non stœchiométrique de la surface de CeO2, soit par dopage, soit, comme dans le cas présent, par modification de la morphologie, ce qui a été rapporté pour l'oxyde de cérium comme pouvant être contrôlé par la méthode de synthèse. Ainsi, les paramètres de la synthèse hydrothermale ont été modifiés, ce qui a permis d’obtenir des nanomatériaux de CeO2 présentant différentes morphologies (polyèdres, nanorods, nanocubes), tailles de cristallites et surfaces actives. Les catalyseurs Ni synthétisés avec ces supports ont été caractérisés par des techniques de pointe afin d'examiner les propriétés physicochimiques les plus pertinentes, par exemple la surface, la réductibilité et l'interaction métal-support, la basicité de la surface et la formation de lacunes dans l'oxygène. En outre, le comportement électrique des catalyseurs a été évalué en mettant l'accent sur la manière dont les matériaux affectent la décharge du plasma, le transfert de charge et le comportement diélectrique du lit fixe. La technique FTIR operando a été utilisée pour suggérer une voie de réaction possible de la méthanisation du CO2 assistée par plasma sur Ni/CeO2. En conclusion, il a été constaté que les propriétés physicochimiques qui sont pertinentes dans la méthanisation thermique conventionnelle ne sont pas entièrement applicables à la catalyse par plasma, car l'importance d'une faible permittivité diélectrique du catalyseur et d'un mécanisme de transfert de charge est mise en évidence pour un processus de méthanisation efficace sur le plan énergétique. Finalement, un support CeO2 contenant des nanostructures en forme de tige ou d'aiguille permet d'améliorer les défauts de surface, l'interaction avec le Ni et la macroposorité, ce qui semble faciliter la réaction de méthanisation dans le plasma par la voie du formiate.This project has received funding from the European Union’s Horizon H2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement n.º 813393.Peer reviewe
Nanostructured CeO2 as support of Ni-catalysts for plasma-catalytic CO2 methanation: Tailoring support’s nanomorphology towards improved performance
No full textPlasma-assisted CO2 methanation has been recently presented as a highly promising route towards the electrification of power-to-gas processes, a key step in our transition to sustainable energy generation. Interesting results have been obtained via the combination of cold plasmas – such as Dielectric Barrier Discharge – and Ni-catalysts prepared using CeO2-containing oxides as support, well known for they ability towards oxygen exchange. In the present work, the physicochemical and dielectric properties of Ni/CeO2 catalysts were tailored through the modification of the nanostructured morphology of pure CeO2, as an alternative to the use of dopants/promoters. Improved efficiency was observed in the presence of CeO2 nanoneedles and nanorods exposing 〈0 1 1〉 facets, more prompt to oxygen exchange. The lower dielectric permittivity of these materials led to a more efficient management of adsorbed species during on-plasma operation, resulting in improved plasma-catalytic behavior
Catalyseur nanostructuré pour la méthanation du CO2 assistée par plasma
No full textParmi les différents procédés de capture et d'utilisation du carbone, la méthanisation du CO2 connaît une renaissance comme une technologie prometteuse pour le développement du Power-to-gas et en tant que solution de stockage de l'énergie et de l'économie circulaire du carbone. Le domaine de la catalyse plasma, qui considère l'association d'un catalyseur avec un plasma non thermique, a été récemment développé pour stimuler la méthanation du CO2. Les défis de la catalyse assistée par plasma consistent à tirer profit des espèces activées et des électrons créés par le plasma pour obtenir des voies de réaction et des interactions plus favorables avec les sites actifs du catalyseur, ainsi que de la synergie plasma-catalyseur, c'est-à-dire de la modification des propriétés du catalyseur par contact avec le plasma et vice-versa. L'objectif de cette thèse est d'explorer l'effet de la morphologie et des propriétés physicochimiques des catalyseurs Ni/CeO2 nanostructurés sur la synergie plasma-catalyseur et de mettre en évidence les caractéristiques clés du catalyseur qui permettent une méthanisation efficace du CO2 assistée par plasma, afin de progresser dans la conception rationnelle de matériaux adaptés aux applications de la plasma-catalyse. Pour les essais de méthanation du CO2 assistée par plasma, les plasmas froids à décharge de barrière diélectrique (DBD) permettent des températures douces, ainsi qu’un contact direct entre le plasma et le catalyseur dans une configuration de lit fixe. Au même temps ils permettent l’opération sous pression atmosphérique, conditions idéales pour des applications industrielles. Des catalyseurs à base de nickel supportés par des oxydes métalliques à base de Ce ont été proposés dans des publications récentes pour la méthanisation du CO2 assistée par plasma. Le nickel est une solution fiable, car il est actif dans la méthanisation du CO2 et au même temps économiquement rentable. L'oxyde de cérium (CeO2) est un matériau intéressant à utiliser comme support grâce à ses propriétés d'oxydoréduction liées à sa capacité d’échange d'oxygène. Ces propriétés peuvent être ajustées en améliorant la nature non stœchiométrique de la surface de CeO2, soit par dopage, soit, comme dans le cas présent, par modification de la morphologie, ce qui a été rapporté pour l'oxyde de cérium comme pouvant être contrôlé par la méthode de synthèse. Ainsi, les paramètres de la synthèse hydrothermale ont été modifiés, ce qui a permis d’obtenir des nanomatériaux de CeO2 présentant différentes morphologies (polyèdres, nanorods, nanocubes), tailles de cristallites et surfaces actives. Les catalyseurs Ni synthétisés avec ces supports ont été caractérisés par des techniques de pointe afin d'examiner les propriétés physicochimiques les plus pertinentes, par exemple la surface, la réductibilité et l'interaction métal-support, la basicité de la surface et la formation de lacunes dans l'oxygène. En outre, le comportement électrique des catalyseurs a été évalué en mettant l'accent sur la manière dont les matériaux affectent la décharge du plasma, le transfert de charge et le comportement diélectrique du lit fixe. La technique FTIR operando a été utilisée pour suggérer une voie de réaction possible de la méthanisation du CO2 assistée par plasma sur Ni/CeO2. En conclusion, il a été constaté que les propriétés physicochimiques qui sont pertinentes dans la méthanisation thermique conventionnelle ne sont pas entièrement applicables à la catalyse par plasma, car l'importance d'une faible permittivité diélectrique du catalyseur et d'un mécanisme de transfert de charge est mise en évidence pour un processus de méthanisation efficace sur le plan énergétique. Finalement, un support CeO2 contenant des nanostructures en forme de tige ou d'aiguille permet d'améliorer les défauts de surface, l'interaction avec le Ni et la macroposorité, ce qui semble faciliter la réaction de méthanisation dans le plasma par la voie du formiate.Among the different processes for carbon capture and utilisation, CO2 methanation is experiencing a renaissance as a promising technology for the development of Power-to-gas as an energy storage solution and carbon circular economy. The field of plasma catalysis, which considers the association of a catalyst with non-thermal plasma, has been recently developed for boosting CO2 methanation. The challenges of plasma catalysis focus on taking advantage of the activated species and electrons created by the plasma to achieve more favourable reaction pathways and interaction with the active sites of the catalyst and on plasma-catalyst synergy, meaning the enhancement of the catalyst properties by contact with plasma and vice versa. The goal of this work is to explore the effect of morphology and physicochemical properties of nanostructured Ni/CeO2 catalysts on plasma-catalyst synergy and to highlight the key characteristics of the catalysis that control an efficient plasma-assisted CO2 methanation in order to advance in the rational design of materials tailored for applications in plasma catalysis. For the plasma-assisted CO2 methanation tests, a suitable non-thermal plasma type is the dielectric barrier discharge due to mild temperature conditions, which allow the catalyst to be in direct contact with the plasma in a packed bed configuration, and operation at atmospheric pressure, promising for industrial applications. Nickel catalysts supported on Ce-based metal oxides have been proposed in recent publications for plasma-assisted CO2 methanation. Ni is a reliable solution as it is active for CO2 methanation as well as cost-effective. Cerium oxide (CeO2) is an interesting material to be used as support thanks to its redox properties related to the tendency to form oxygen vacancies. Such property can be tuned by enhancing the non-stoichiometric nature of the CeO2 surface, either by doping or, as in this case, by morphology modification, which has been reported for cerium oxide to be controllable via synthesis method. The parameters of the hydrothermal synthesis were varied and CeO2 nanomaterials with different morphology (polyhedra, nanorods, nanocubes), crystallite size, and surface area were produced. The Ni catalysts synthesised with these supports were further characterised by state-of-the-art techniques to examine the most relevant physicochemical properties, e.g., surface area, reducibility and metal-support interaction, surface basicity, and formation of oxygen vacancies. In addition, the electrical behaviour of the catalysts was assessed with focus on how the materials affect the plasma discharge, charge transfer, and the dielectric property of the packed bed. FTIR operando technique was utilised to suggest a possible reaction pathway of the plasma-assisted CO2 methanation on Ni/CeO2. In conclusion, it was found that the physicochemical properties which are relevant in conventional thermal methanation, such as surface area and basicity, are applicable to plasma catalysis but the importance of low dielectric permittivity of the catalyst and charge transfer mechanism was also highlighted for an energy efficient plasma-assisted methanation process. Furthermore, a rod or needle-like CeO2 support allows enhancing the surface defects, the interaction with Ni, and macroposority, which seem to facilitate the methanation reaction in plasma via formate route
Supplementary information about The PIONEER database
No full textData processing: Computed columns: By parsing the input data it is possible to increase the amount of columns in the database without changing the source format. The following columns are computed (or updated) in the back-end when the database is loaded from disk to memory.-- Assumptions for calculations:
A number of parameters are (re)calculated based on provided metadata for publications: the residence time (1), the SEI in J L-1 (2), energy efficiency of CO2 conv. % (5) but also the frequency range column (section 8.1).
Each of these calculations rely on data that potentially is given as a range of values, see section 1. By convention, the mean of the range is taken for each of the parameters. All entries for which a (re)calculation has been performed on either the x or y data, have the Calculated field set to ‘Calculated’ (rather than ‘Original’).
Filtering the database on only Original data, this calculated data can be replaced with calculations by the
user based on other aggregation, if desired.
As mentioned for equation (2), the calculation that converts power (in W) to SEI (J L-1) simply relies on
the gas flow rate Φ (in sccm or mLmin-1) and therefore does not take into account if Φ is defined w.r.t. standard
conditions or the actual conditions in the discharge regarding pressure and temperature. Since generally in this
case both the power and gas flux are know, the SEI can be calculated (except for batch reactors where there is
no flow), which allows for a comparison between a larger body of experiments.
Contrary to this, the calculations for the residence time (1) and energy efficiency of CO2 conversion both
take into account the discharge conditions. This discrepancy is a conscious one: the SEI (in J L-1) is often
reported as a macroscopic process parameter that is calculated from the power and fluxes put into the reactor.
For τ res taking into account the conditions inside the plasma is paramount, since it can provide the information
on how long a particle is exposed to plasma conditions. Do note that in lieu of the plasma –or active zone–
volume, for some experiments an approximation such as the reactor volume is used, see column relevant
volume in section 4.
Likewise for the efficiency, it is important to account for the actual measurement conditions to establish the
number of particles into which energy has been channelled. For in situ versus effluent conditions this can be very different. Overestimating the number density favourably improves efficiency, whilst an underestimation similarly negatively impacts it. While the way in which the PDB is structured and reports metadata is not without caveats (section 4.3 of the paper), the distinction between in- versus post-plasma dissociation measurements can be partially addressed by tailored filtering and aggregation of the data contained within.-- Normalisations:
Several normalisation functions are available in the interface of the database. As described in the main text, the aim to provide a tool for easy calculation of normalised data within the same interface and compare with different data sets. For flexibility sake, a wide set of normalisations are provided, without restriction on whether they are sensible in a given context. The purpose of each normalised function is described briefly and summarised in table 1 along with the equations utilised.-- Under a Creative Commons license CC BY 4.0.The Pioneer database (PDB) is divided into two parts: performance data and metadata. The performance data originate from measurements reported in literature, where they are typically provided in form of plots or
tables. The PDB and its dedicated online tool allow to compare large amounts of performance data to derive
trends leading eventually to process optimisation. Performance data is provided in form of plain text files with
only two comma-separated columns of numbers with a point (.) as decimal separator, without a header (as it
is inferred from the metadata). The first column contains what is henceforth called process parameters. These
are the independent variables of the experiments, i.e. the x-values like power, pressure etc., see section 7.
The second column contains the so-called performance parameters. These are the dependent variables of the
experiment, i.e. the y-values like conversion, selectivity etc., see section 7. The metadata contain additional
information about the measurements that are crucial for their interpretation. Metadata are provided in table
format following the template discussed subsequently.
Before elaborating on the actual data input, the structure of the PDB metadata is discussed. The metadata is
grouped thematically in categories. Within each category, information is entered into fields, i.e. the columns
of the table. Essential and conditional fields are distinguished. Essential fields contain crucial information for
the assessment of the plasma-catalytic process. In the best case scenario, all of them are given in the respective publication. When fields are listed in the description of a category from section 2 onward, essential fields are indicated by a regular bullet point (•). Conditional fields are by no means less important than essential ones, but can rather be left empty depending on other fields. For instance, most fields in the catalyst category are left empty, when no catalyst is used. Thus, conditional fields are meant to save time. Listed in the following,
they are indicated by a plus (+). In conclusion, all fields are strongly recommended as data useful for valuable
comparison with other work from the community. A subgroup of essential as well as conditional fields are those
fields that contain the process parameters defined in the first paragraph of this section. Generally speaking,
process parameters are the experimental settings in the pursuit of highest performance. The user of the PDB
thus encounters process parameters on two occasions: on the one hand as typical x-values in the performance
data and on the other hand as input to fields of the metadata. Hereafter, fields that contain process parameters
and parameters are used synonymously. The total of fields belonging to the same measurement make up what
is hereafter called a data set, corresponding to a row of the table. Note that here the input of data is addressed.
In the back end, a data set is broken up into (x,y)-pairs for more flexibility in data handling. Data is exported
also in that format.
To ensure comparability, a template is used for inputting information into the PDB metadata. With respect
to information entered, fields can be divided in numerical and textual fields. They are filled with numbers or
text, respectively. For example, parameters are usually numerical fields. A numerical field contains either (i)
one number x if the numerical value is known and does not change during the experiment; (ii) a range of values between xmin and xmax –given as array-like notation rxmin; xmaxs– if the numerical value is not exactly known, or when it changes in the course of the measurement; or (iii) NA if the numerical value is not known. For further use, an aggregate function is applied to array-like data to obtain a single number, by convention the mean.
A textual field contains a string of text. There are a few instances where text can be entered freely as long
as some format is followed. However, usually the field is filled by selecting from a pre-defined list of options
in the template. Most of these lists are fixed but some might be extended in the future depending on the
experimental data provided. This paragraph just gives a general overview. In the in-depth discussion of the
fields of each category, it gets more clear what exactly is supposed to be filled in each field. The metadata of the PDB are divided into six categories
• data identification
• gas mixture
• plasma source
• catalyst
• separation unit
• output data1. General
2. Data Identification
3. Gas Mixture
4. Plasma Source
5. Catalyst
5.1 Catalyst Coupling .
5.2 Catalyst Composition
5.3 Catalyst Pre-treatment Before Reaction
5.4 Catalyst Conditions
5.5 Catalyst Characterization
6. Separation Unit
7. Output Data
8. Data processing
8.1 Computed columns
8.2 Assumptions for calculations
8.3 NormalisationsWhen data is reported according to the specified scheme above, the combined data and metadata can be read
from disk and processed with some scripting. Most notably this performs data type coercion and extraction
from a more flexible ‘human-readable’ format to a consistent, ‘machine-usable’ scheme. Some of the computed columns are redundant to some extent –the authyear column for instance is just a concatenation of the first author name and publication year (yyyy) columns– but these are provided for ease of filtering or grouping data, avoiding frequent (re)computation.This project has received funding from the European Unions Horizon 2020 research and
innovation programme under the Marie Skodowska-Curie grant agreement No. 813393Peer reviewe
Catalyseur nanostructuré pour la méthanation du CO2 assistée par plasma
No full textAmong the different processes for carbon capture and utilisation, CO2 methanation is experiencing a renaissance as a promising technology for the development of Power-to-gas as an energy storage solution and carbon circular economy. The field of plasma catalysis, which considers the association of a catalyst with non-thermal plasma, has been recently developed for boosting CO2 methanation. The challenges of plasma catalysis focus on taking advantage of the activated species and electrons created by the plasma to achieve more favourable reaction pathways and interaction with the active sites of the catalyst and on plasma-catalyst synergy, meaning the enhancement of the catalyst properties by contact with plasma and vice versa. The goal of this work is to explore the effect of morphology and physicochemical properties of nanostructured Ni/CeO2 catalysts on plasma-catalyst synergy and to highlight the key characteristics of the catalysis that control an efficient plasma-assisted CO2 methanation in order to advance in the rational design of materials tailored for applications in plasma catalysis. For the plasma-assisted CO2 methanation tests, a suitable non-thermal plasma type is the dielectric barrier discharge due to mild temperature conditions, which allow the catalyst to be in direct contact with the plasma in a packed bed configuration, and operation at atmospheric pressure, promising for industrial applications. Nickel catalysts supported on Ce-based metal oxides have been proposed in recent publications for plasma-assisted CO2 methanation. Ni is a reliable solution as it is active for CO2 methanation as well as cost-effective. Cerium oxide (CeO2) is an interesting material to be used as support thanks to its redox properties related to the tendency to form oxygen vacancies. Such property can be tuned by enhancing the non-stoichiometric nature of the CeO2 surface, either by doping or, as in this case, by morphology modification, which has been reported for cerium oxide to be controllable via synthesis method. The parameters of the hydrothermal synthesis were varied and CeO2 nanomaterials with different morphology (polyhedra, nanorods, nanocubes), crystallite size, and surface area were produced. The Ni catalysts synthesised with these supports were further characterised by state-of-the-art techniques to examine the most relevant physicochemical properties, e.g., surface area, reducibility and metal-support interaction, surface basicity, and formation of oxygen vacancies. In addition, the electrical behaviour of the catalysts was assessed with focus on how the materials affect the plasma discharge, charge transfer, and the dielectric property of the packed bed. FTIR operando technique was utilised to suggest a possible reaction pathway of the plasma-assisted CO2 methanation on Ni/CeO2. In conclusion, it was found that the physicochemical properties which are relevant in conventional thermal methanation, such as surface area and basicity, are applicable to plasma catalysis but the importance of low dielectric permittivity of the catalyst and charge transfer mechanism was also highlighted for an energy efficient plasma-assisted methanation process. Furthermore, a rod or needle-like CeO2 support allows enhancing the surface defects, the interaction with Ni, and macroposority, which seem to facilitate the methanation reaction in plasma via formate route.Parmi les différents procédés de capture et d'utilisation du carbone, la méthanisation du CO2 connaît une renaissance comme une technologie prometteuse pour le développement du Power-to-gas et en tant que solution de stockage de l'énergie et de l'économie circulaire du carbone. Le domaine de la catalyse plasma, qui considère l'association d'un catalyseur avec un plasma non thermique, a été récemment développé pour stimuler la méthanation du CO2. Les défis de la catalyse assistée par plasma consistent à tirer profit des espèces activées et des électrons créés par le plasma pour obtenir des voies de réaction et des interactions plus favorables avec les sites actifs du catalyseur, ainsi que de la synergie plasma-catalyseur, c'est-à-dire de la modification des propriétés du catalyseur par contact avec le plasma et vice-versa. L'objectif de cette thèse est d'explorer l'effet de la morphologie et des propriétés physicochimiques des catalyseurs Ni/CeO2 nanostructurés sur la synergie plasma-catalyseur et de mettre en évidence les caractéristiques clés du catalyseur qui permettent une méthanisation efficace du CO2 assistée par plasma, afin de progresser dans la conception rationnelle de matériaux adaptés aux applications de la plasma-catalyse. Pour les essais de méthanation du CO2 assistée par plasma, les plasmas froids à décharge de barrière diélectrique (DBD) permettent des températures douces, ainsi qu’un contact direct entre le plasma et le catalyseur dans une configuration de lit fixe. Au même temps ils permettent l’opération sous pression atmosphérique, conditions idéales pour des applications industrielles. Des catalyseurs à base de nickel supportés par des oxydes métalliques à base de Ce ont été proposés dans des publications récentes pour la méthanisation du CO2 assistée par plasma. Le nickel est une solution fiable, car il est actif dans la méthanisation du CO2 et au même temps économiquement rentable. L'oxyde de cérium (CeO2) est un matériau intéressant à utiliser comme support grâce à ses propriétés d'oxydoréduction liées à sa capacité d’échange d'oxygène. Ces propriétés peuvent être ajustées en améliorant la nature non stœchiométrique de la surface de CeO2, soit par dopage, soit, comme dans le cas présent, par modification de la morphologie, ce qui a été rapporté pour l'oxyde de cérium comme pouvant être contrôlé par la méthode de synthèse. Ainsi, les paramètres de la synthèse hydrothermale ont été modifiés, ce qui a permis d’obtenir des nanomatériaux de CeO2 présentant différentes morphologies (polyèdres, nanorods, nanocubes), tailles de cristallites et surfaces actives. Les catalyseurs Ni synthétisés avec ces supports ont été caractérisés par des techniques de pointe afin d'examiner les propriétés physicochimiques les plus pertinentes, par exemple la surface, la réductibilité et l'interaction métal-support, la basicité de la surface et la formation de lacunes dans l'oxygène. En outre, le comportement électrique des catalyseurs a été évalué en mettant l'accent sur la manière dont les matériaux affectent la décharge du plasma, le transfert de charge et le comportement diélectrique du lit fixe. La technique FTIR operando a été utilisée pour suggérer une voie de réaction possible de la méthanisation du CO2 assistée par plasma sur Ni/CeO2. En conclusion, il a été constaté que les propriétés physicochimiques qui sont pertinentes dans la méthanisation thermique conventionnelle ne sont pas entièrement applicables à la catalyse par plasma, car l'importance d'une faible permittivité diélectrique du catalyseur et d'un mécanisme de transfert de charge est mise en évidence pour un processus de méthanisation efficace sur le plan énergétique. Finalement, un support CeO2 contenant des nanostructures en forme de tige ou d'aiguille permet d'améliorer les défauts de surface, l'interaction avec le Ni et la macroposorité, ce qui semble faciliter la réaction de méthanisation dans le plasma par la voie du formiate
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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