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Temperature maps of the quartz DBD reactor upon conventional heating acquired by an IR temperature sensor: (a) side view and (b) top view.
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Plasma-enhanced heterogeneous catalysis offers a promising alternative to thermal catalysis for many industrially relevant processes. There is only limited mechanistic understanding about the relation between the interactions of highly energetic electrons and excited molecules with heterogeneous catalysts in a plasma and their catalytic performance...
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Cascade processes are gaining momentum in heterogeneous catalysis. The combination of several catalytic solids within one reactor has shown great promise for the one-step valorization of C1-feedstocks. The combination of metal-based catalysts and zeolites in the gas phase hydrogenation of CO2 leads to a large degree of product selectivity control,...
This study investigated immobilization (without binders and high-temperature heating) of highly active CO2 methanation catalyst particles, prepared by the polygonal barrel-sputtering method, onto porous Al2O3 plates. The catalyst particles were fixed uniformly and firmly on the plates and retained their high CO2 methanation performance.
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... Researchers have been endeavouring to unravel the reaction mechanisms of plasma-assisted methanation using advanced in-situ characterisation tools, including optical emission spectroscopy (OES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). These methods complement each other and help to determine the intermediate species [120,121]. Computational modelling can assist with determining and validating the reaction pathways. However, because plasma CO 2 methanation is an emerging and complex process, limited research has been performed on its mechanisms. ...
... The real-time measurement of the temperature of the catalyst bed in a DBD plasma is very challenging due to electromagnetic interference and plasma luminescence [142,143]. Therefore, most of the reported temperatures for plasma catalytic reactions are based on outer wall temperatures of the reactor [80] or temperatures measured by thermocouples after the plasma is turned off or located at the exit of the gas outlet [80,120,142]. Heat transfer modelling [144] and measurements using a shielded probe inserted in the highvoltage electrode [145] indicate that the wall temperature is significantly lower than the catalyst bed temperature, although by significantly different amounts. ...
In recent years, enormous efforts have been devoted to alleviating global energy demand and the climate crisis. This has instigated the search for alternative energy sources with a reduced carbon footprint. Catalytic hydrogenation of CO2 to CH4, known as the methanation reaction, is a pathway to utilise CO2 and renewable hydrogen simultaneously. However, owing to the high stability of CO2 and thermodynamic limitations at higher temperatures, the methanation process is energy intensive. Non-thermal plasma technology has recently emerged as a promising approach to lowering the activation temperature of CO2. The application of a plasma coupled with catalytic materials allows the methanation reaction to occur at or near ambient conditions, with dielectric barrier discharges providing superior performance. The review considers the various catalytic materials applied for plasma-assisted catalytic CO2 methanation and assesses CO2 conversion, CH4 yield and fuel production efficiency obtained. The importance of reactor designs and process parameters are discussed in detail. The possible reaction pathways are considered based on in-situ and other diagnostics and modelling studies. Finally, a perspective on current barriers and opportunities for advances in non-thermal plasma technology for CO2 methanation is presented.
... Therefore, the as-prepared ruthenium and copper-incorporated mesoporous materials could be a potential catalyst for ammonia synthesis and methanation reactions. 29,30 Figures 8−12 show the gas chromatography−mass spectrometry (GC−MS) results of bulk (pristine) RHS silica catalyst and Ag−Cu-modified catalytic activity for the acetylation of glycerol. Metal ion-modified RHS shows good conversion for glycerol, and it is more selective toward the formation of monoacetin. ...
... Article by protonation in the carbonyl oxygen atom is more stable. 30 Hence, the optimized loading of Ru−Cu in RHS silica and Ag−Cu-Silica RHS catalysts are highly promising catalysts for complete conversion of glycerol and pure selectivity toward diacetin and triacetin formation. ...
The present study compares the surface, textural, and catalytic properties of porous silica doped with bimetallic metal ions that was made from rice husk (RH) biomass. Due to the use of a surfactant during the synthesis process, porous RH-silica (RHS) was derived. In situ doping of silver/copper and ruthenium/copper has been achieved via the xerogel and hydrogel formation methods. The prepared catalysts have been analyzed by various methods, such as surface area and narrow pore size distribution, to confirm their porosity. Powder X-ray diffraction, Fourier transform infrared, and electron microscopy examination were further performed for physicochemical characterization of the synthesized materials. Transmission electron microscopy images showed that ruthenium and copper ions were incorporated perfectly, forming a hexagonal mesoporous (MCM-41) texture due to hydrogel formation and the method of preparation. Copper oxide nanoparticles with silver incorporation in RHS form cube-shaped particles for CuO formation on the surface of the silica matrix instead due to the method of preparation. In this case, ruthenium/copper-doped porous silica forms hexagon-shaped particles of RuO formation in the mesoporous matrix. Finally, the acetylation of glycerol using acetic acid on as-prepared catalysts has been studied. The catalytic activity increases with an increase in temperature and optimization of the molar ratio of glycerol and acetic acid. Increases in temperature result in higher selectivity toward triacetin formation instead of the conventional formation of monoacetin. Hence, we compared the surface physicochemical properties, catalytic conversion, and selectivity nature of bimetallic metal (Ru/Cu and Ag/Cu) ions incorporated in RHS prepared by different synthetic routes.
... When a temperature value is given, it is important to be precise in specifying which temperature it is (external surface temperature, catalyst bed surface temperature, reactor exit gas temperature, plasma gas temperature etc.). Recent work with materials having a thermo-sensitive spectral response has shown that the surface temperature of the catalyst is not even necessarily thermalised with the plasma temperature [119,120]. Any available information on one of these temperatures is always important to know, but it is essential to be specific about its meaning. In particular, when the conversion performance is compared with and without plasma for different temperatures imposed with an external furnace, it is essential to take into account in this comparison the heating of the catalyst bed induced by the plasma itself. ...
This paper brings the comparison of performances of CO2 conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field, organised in an open access online database. This tool is open to all users to carry out their own analyses, but also to contributors who wish to add their data to the database in order to improve the relevance of the comparisons made, and ultimately to improve the efficiency of CO2 conversion by plasma-catalysis. The creation of this database and database user interface is motivated by the fact that plasma-catalysis is a fast-growing field for all CO2 conversion processes, be it methanation, dry reforming of methane, methanolisation, or others. As a result of this rapid increase, there is a need for a set of standard procedures to rigorously compare performances of different systems. However, this is currently not possible because the fundamental mechanisms of plasma-catalysis are still too poorly understood to define these standard procedures. Fortunately however, the accumulated data within the CO2 plasma-catalysis community has become large enough to warrant so-called “big data” studies more familiar in the fields of medicine and the social sciences. To enable comparisons between multiple data sets and make future research more effective, this work proposes the first database on CO2 conversion performances by plasma-catalysis open to the whole community. This database has been initiated in the framework of a H2020 European project and is called the “PIONEER DataBase”. The database gathers a large amount of CO2 conversion performance data such as conversion rate, energy efficiency, and selectivity for numerous plasma sources coupled with or without a catalyst. Each data set is associated with metadata describing the gas mixture, the plasma source, the nature of the catalyst, and the form of coupling with the plasma. Beyond the database itself, a data extraction tool with direct visualisation features or advanced filtering functionalities has been developed and is available online to the public. The simple and fast visualisation of the state of the art puts new results into context, identifies literal gaps in data, and consequently points towards promising research routes. More advanced data extraction illustrates the impact that the database can have in the understanding of plasma-catalyst coupling. Lessons learned from the review of a large amount of literature during the setup of the database lead to best practice advice to increase comparability between future CO2 plasma-catalytic studies. Finally, the community is strongly encouraged to contribute to the database not only to increase the visibility of their data but also the relevance of the comparisons allowed by this tool.
... Most work is done with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) [118][119][120][121][122], which is also commonly applied in thermal catalysis. Transmission IR can be used and has some advantages, such as easier quantitative studies, less temperature dependence, no grain size dependence and smaller temperature gradients in the catalyst material [123]. ...
... Furthermore, X-rays-based methods are also gaining interest for in-situ structural analysis of catalysts because of the brightness of synchrotron radiation (e.g., [130]). Finally, in-situ measurement of the catalyst surface temperature in a DBD plasma provides valuable insights, although such measurements are also quite challenging [122,126,130]. ...
... Thus, it is possible to conclude that the mechanism for the thermo-and plasma-catalytic CO 2 methanation reaction are somehow similar, probably because of the mild conditions of the studied DBD plasma. To this day, the few publications that exist on the topic seem to propose a mechanism concordant to the one proposed in this work, i.e., progressive hydrogenation of formates and carbonyls to methane, with the formation of adsorbed carbonates, although it was deduced for different catalytic materials and setups and using different techniques [23,[44][45][46]. ...
CO2 methanation is an attractive reaction to convert CO2 into a widespread fuel such as methane, being the combination of catalysts and a dielectric barrier discharge (DBD) plasma responsible for synergistic effects on the catalyst’s performances. In this work, a Ru-based zeolite catalyst, 3Ru/CsUSY, was synthesized by incipient wetness impregnation and characterized by TGA, XRD, H2-TPR, N2 sorption and CO2-TPD. Catalysts were tested under thermal and plasma-assisted CO2 methanation conditions using in-situ operando FTIR, with the aim of comparing the mechanism under both types of catalysis. The incorporation of Ru over the CsUSY zeolite used as support induced a decrease of the textural properties and an increase of the basicity and hydrophobicity, while no zeolite structural damage was observed. Under thermal conditions, a maximum CO2 conversion of 72% and CH4 selectivity above 95% were registered. These promising results were ascribed to the presence of small Ru0 nanoparticles over the support (16 nm), catalyst surface hydrophobicity and the presence of medium-strength basic sites in the catalyst. Under plasma-catalytic conditions, barely studied in similar setups in literature, CO2 was found to be excited by the plasma, facilitating its adsorption on the surface of 3Ru/CsUSY in the form of oxidized carbon species such as formates, aldehydes, carbonates, or carbonyls, which are afterwards progressively hydrogenated to methane. Adsorption and surface reaction of key intermediates, namely formate and aldehydic groups, was observed even on the support alone, an occurrence not reported before for thermal catalysis. Overall, similar reaction mechanisms were proposed for both thermal and plasma-catalysis conditions.
... Most work is done with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) [118][119][120][121][122], which is also commonly applied in thermal catalysis. Transmission IR can be used and has some advantages, such as easier quantitative studies, less temperature dependence, no grain size dependence and smaller temperature gradients in the catalyst material [123]. ...
... Furthermore, X-rays-based methods are also gaining interest for in-situ structural analysis of catalysts because of the brightness of synchrotron radiation (e.g., [130]). Finally, in-situ measurement of the catalyst surface temperature in a DBD plasma provides valuable insights, although such measurements are also quite challenging [122,126,130]. ...
... Plasma also enables the recovery of poisoned catalyst via collision of ions or atoms, leading to desorption of strong adsorbed species, such N* or CO [11,33]. Recently, operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and plasma-assisted temperature-programmed surface reaction (TPSR) have been conducted to discover the enhancement induced by NTP in CO 2 hydrogenation using the CeZrO x catalyst [34,35]. Chen et al. studied the effect of Ni dispersion and support structure of Ni/silicate-1 catalyst on CO 2 hydrogenation under non-thermal plasma and found that the accessibility of Ni active sites is important to the reaction [23]. ...
... These studies found that metal sites of cobalt or nickel are responsible for methane or synthetic natural gas (SNG) formation. Active H species generated in the plasma phase react with surface CeO x or LaO x , producing oxygen defects, which consequently adsorbs and activates CO 2 by removing O from CO 2 molecule [32,34,35]. However, catalysts with different components do not share the same mechanism. ...
... This also explains why the selectivity of CH 4 was 72% in the plasma-catalysis reaction, while CO was the only product using plasma alone at the temperature of 398 K. On the other hand, DRIFTS and the surface reaction experiments indicate that the traditional Langmuir-Hinshelwood pathway (R1) for methane formation cannot be excluded in the plasma-catalysis system. Such a plasma-induced pathway (R2) should be regarded as parallel reactions [34,35], as illustrated in Fig. 9. The gas-phase RWGS reaction and the reduction of surface CH x is a fast process [34,43]. ...
Non-thermal plasma can provide an alternative to CO_2 utilization under mild conditions. Understanding the effect of plasma on catalysis is highly desired. Herein, a comparative study was performed on CO_2 hydrogenation under thermal-catalytic and plasma-catalytic conditions using an alumina-supported cobalt catalyst. Significant
plasma-catalyst synergy was attained at the low-temperature range between 423 K and 498 K where the CO_2 conversion increased up to approximately 3.6 times of the sum of that using plasma or catalyst individually. The plasma-catalytic reaction showed a significantly lower activation energy (~40 kJ/mol), which is only half of that
in the thermal catalytic reaction (~80 kJ/mol). Kinetic analysis and DRIFTS results indicate that CO_2 activation is promoted by plasma with the assistance of active H species from gas phase. Furthermore, the total H_2 adsorption capacity and the coverage of irreversible adsorbed H species on the metal surface were decreased under plasma. The promotion effect is very likely due to a new reaction pathway introduced by plasma on the 15Co/Al_2O_3 catalyst under the conditions studied. No obvious difference in the structure and morphology changes was observed between the spent catalysts after thermal and plasma reactions.
... The synergistic effect of plasma catalysis is usually involved and expected, that is, the reaction rate obtained in plasma catalysis is greater than the sum of plasma alone and thermal catalysis. [15][16][17][18][19][20][21] The plasma-derived heat inevitably occurs, especially for atmospheric pressure plasmas, because of the fast energy relaxation of electronic, vibrational, and rotational excitation state molecules. [22] Besides, in DBD, the plasma-derived heat includes the heating of dielectric material packed between electrodes derived from dielectric loss. ...
Due to serious difficulty in the measurement of catalyst‐bed temperature (Tb) for in‐plasma catalysis (IPC), the evaluation of the IPC synergistic effect is still disputed. Herein, we reported a real‐time measurement of axial temperature (Tax), which is much closer to Tb than wall temperature (Tw), using a thermocouple in a catalyst‐packed coaxial dielectric barrier discharge reactor for the first time. In plasma catalytic CO2 reduction, the effects of discharge power and flow rate on Tax, Tw, and CO2 conversion were examined. On the basis of Tax, compared with the thermal catalytic case, the plasma catalytic case only shows a weak synergistic effect. It was confirmed that the synergistic effect is overestimated if based on Tw (except for the heat‐insulated or quasi‐adiabatic reactors). In‐plasma catalysis (IPC) is expected to achieve synergistic effect between plasma and catalyst. However, due to measurement difficulty of catalyst‐bed temperature (Tb) for IPC, the evaluation of synergistic effect is still disputed. We report a real‐time measurement of axial temperature (Tax), being much close to Tb, by a thermocouple in a catalyst‐packed coaxial dielectric barrier discharge reactor. Thereby, the synergistic effect was assessed based on the Tax in CO2 reduction with H2.
