Plasma–catalysis: the known knowns, the known unknowns and the unknown unknowns

Whitehead, J. Christopher

doi:10.1088/0022-3727/49/24/243001

Cited by 380 publications

(368 citation statements)

References 153 publications

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“…16,19,20 Improvement of performance in either partial or fully packed bed DBD is typically attributed to the effective polarization and enhanced electric field strength at the contact points and in some cases to the synergistic effect of plasmacatalysis; however, the exact fundamental mechanisms are still not fully understood. 16,21,22 Several experimental studies have been attempted to investigate the nature of physical and chemical interactions between packing materials and plasma in packed DBDs. [22][23][24] However, experimental studies have their limitations in terms of parameters that can be accurately measured during plasma operation, and the packing itself adds an extra impediment in visibility for optical/laser analysis.…”

mentioning

confidence: 99%

“…16,21,22 Several experimental studies have been attempted to investigate the nature of physical and chemical interactions between packing materials and plasma in packed DBDs. [22][23][24] However, experimental studies have their limitations in terms of parameters that can be accurately measured during plasma operation, and the packing itself adds an extra impediment in visibility for optical/laser analysis. While such experimental diagnostic studies are indispensable, we believe computational modeling can be used as a complementary tool to optimize the system in a directed way, providing more quantitative process-parameter relationships.…”

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confidence: 99%

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Fluid model for a partially packed dielectric barrier discharge plasma reactor

Gadkari

2017

Physics of Plasmas

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In this work, a two-dimensional numerical \ud fluid model is developed for a partially\ud packed dielectric barrier discharge (DBD) in pure helium. In\ud fluence of packing on\ud the discharge characteristics is studied by comparing the results of DBD with partial\ud packing with those obtained for DBD with no packing. In the axial partial packing\ud configuration studied in this work, the electric field strength was shown to be en\ud hanced at the top surface of the spherical packing material and at the contact points\ud between the packing and the dielectric layer. For each value of applied potential,\ud DBD with partial packing showed an increase in the number of pulses in the current\ud profile in the positive half cycle of the applied voltage, as compared to DBD with\ud no packing. Addition of partial packing to the plasma-alone DBD also led to an\ud increase in the electron and ion number densities at the moment of breakdown. The\ud time averaged electron energy profiles showed that a much higher range of electron\ud energy can be achieved with the use of partial packing as compared to no packing\ud in a DBD, at the same applied power. The spatially and time averaged values over\ud one voltage cycle also showed an increase in power density and electron energy on\ud inclusion of partial packing in the DBD. For the applied voltage parameters studied\ud in this work, the discharge was found to be consistently homogeneous and showed\ud the characteristics of atmospheric pressure glow discharge

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confidence: 99%

mentioning

confidence: 99%

Fluid model for a partially packed dielectric barrier discharge plasma reactor

Gadkari

2017

Physics of Plasmas

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“…The temperature of the electrons in such plasmas are typically 10 4 -10 5 K, whilst the heavier species such as the ions and gas molecules remain at temperatures around ambient. This generates radicals, ions and vibrationally and electronically excited species not normally present in thermal equilibrium at room temperature [1,2]. In principle, almost 97% of the plasma discharge power of low temperature plasmas can be converted into vibrational excitation of the gas feed molecules [3,4].…”

Section: Introductionmentioning

confidence: 99%

“…However, progress has been slow, largely because catalyst selection appears to be based on those materials that are active for the analogous thermally-driven processes, and this may be due to the paucity of analytical information on non-thermal plasmas compared to, e.g. gas phase catalysis [1]. There are few analytical studies on the chemistry taking place actually in the glow of non-thermal plasmas, and these largely employ emission spectroscopy [8][9][10] or the detection of a single species [11].…”

Section: Introductionmentioning

confidence: 99%

A Direct Fourier Transform Infrared Spectroscopic Comparison of the Plasma- and Thermally-Driven Reaction of CO2 at Macor

Christensen

Ali

Mashhadani

et al. 2018

Plasma Chem Plasma Process

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This paper reports the appraisal of two in situ Fourier Transform InfraRed plasma cells with respect to the interrogation of the glow of a non-thermal plasma (using a transmission cell), and the non-thermal plasma/solid (i.e. dielectric/catalyst) interface (with a reflectance cell). The paper also reports, for the first time, a direct comparison of the IR spectroscopy of plasmaand thermally-driven chemistry. The system chosen for study was the reduction of CO 2 as there is a wealth of data in the literature for comparison. The catalyst was Macor, a ceramic material comprising primarily Al, Si and Mg oxides. In both the thermal and plasma experiments, rotationally-excited CO 2 (CO Ã 2 ) was observed: in the plasma system, rotationally-excited CO (CO*) was produced via the reduction of CO 2 . Using the transmission cell, the conversion of CO 2 to CO was estimated and found to be up to 9% at energy efficiencies of ca. 1-2%, in line with the literature. No reaction of CO 2 was observed in the thermal system. The data obtained using the reflectance cell were similar to those obtained with the transmission cell, with the minor differences reflecting the longer residence time and higher specific input energy. Interestingly, two plasma-induced bands were observed in the reflectance experiments which increased in intensity with time and input power: these may be due transverse and longitudinal optical modes of SiO 2 and did not appear to participate in the observed chemistry.

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“…A method of combining a plasma technique with a catalyst includes a one-stage method of generating plasma in a catalyst bed [17][18][19][20], and a two-stage configuration in which a catalytic reactor is installed downstream of the plasma reactor [16,21,22]. Jiang et al [23] and Guan et al [24] were able to effectively remove NO x using a two-stage reactor configuration in NH 3 -SCR.…”

Section: Introductionmentioning

confidence: 99%

Consideration of the Role of Plasma in a Plasma-Coupled Selective Catalytic Reduction of Nitrogen Oxides with a Hydrocarbon Reducing Agent

Lee

Kang

et al. 2017

Catalysts

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Abstract:The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NO x reduction was performed with n-heptane as a reducing agent over Ag/γ-Al 2 O 3 as a catalyst. We found that the plasma decomposes n-heptane into several oxygen-containing products such as acetaldehyde, propionaldehyde and butyraldehyde, which are more reactive than the parent molecule n-heptane in the SCR process. Separate sets of experiments using acetaldehyde, propionaldehyde and butyraldehyde, one by one, as a reductant in the absence of plasma, have clearly shown that the presence of these partially oxidized compounds greatly enhanced the NO x conversion. The higher the discharge voltage, the more the amounts of such partially oxidized products. The oxidative species produced by the plasma easily converted NO into NO 2 , but the increase of the NO 2 fraction was found to decrease the NO x conversion. Consequently, it can be concluded that the main role of plasma in the SCR process is to produce partially oxidized compounds (aldehydes), having better reducing power. The catalyst-alone NO x removal efficiency with n-heptane at 250 • C was measured to be less than 8%, but it increased to 99% in the presence of acetaldehyde at the same temperature. The NO x removal efficiency with the aldehyde reducing agent was higher as the number of carbons in the aldehyde was more; for example, the NO x removal efficiencies at 200 • C with butyraldehyde, propionaldehyde and acetaldehyde were measured to be 83.5%, 58.0% and 61.5%, respectively, which were far above the value (3%) obtained with n-heptane.

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Plasma–catalysis: the known knowns, the known unknowns and the unknown unknowns

Cited by 380 publications

References 153 publications

Fluid model for a partially packed dielectric barrier discharge plasma reactor

Fluid model for a partially packed dielectric barrier discharge plasma reactor

A Direct Fourier Transform Infrared Spectroscopic Comparison of the Plasma- and Thermally-Driven Reaction of CO2 at Macor

Consideration of the Role of Plasma in a Plasma-Coupled Selective Catalytic Reduction of Nitrogen Oxides with a Hydrocarbon Reducing Agent

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