Yuji Hayashi

Bio: Yuji Hayashi is an academic researcher from University of Connecticut. The author has contributed to research in topics: Glow discharge & Hydrogen. The author has an hindex of 14, co-authored 43 publications receiving 766 citations. Previous affiliations of Yuji Hayashi include Nagasaki University & Fujitsu.

CO2 Reforming of CH4 by Atmospheric Pressure ac Discharge Plasmas

Abstract: Partial oxidative reactions of methane by carbon dioxide have been studied using atmospheric pressure alternating current plasmas. The reactions were carried out using a Y-type reactor with metal rods as the inner electrodes inside quartz tubes and aluminum foil wrapped around quartz tubes as the outer electrodes. The waveforms, input voltages, and currents of the reactions were monitored with an oscilloscope. Interactions between excited methane and excited carbon dioxide as well as those between one excited species and the other unexcited species were observed. The products of the reactions include carbon monoxide, hydrogen, ethane, ethylene, propane, and acetylene. The effects of many reaction parameters, including input voltage, total flow rate, mole ratio of methane to carbon dioxide, selective excitation of either reactant, and micro-arc formation, on product distribution and energy efficiency have been investigated. With an increase in the carbon dioxide-to-methane ratio the selectivity to carbon monoxide increased, and less coke formed. Micro-arc formation between excited methane and excited carbon dioxide increased the conversions of both methane and carbon dioxide and favored the production of carbon monoxide. The energy efficiency of the reaction reached a maximum at CH4/CO2=1 with micro-arc formation, but it was minimized at CH4/CO2=1 when no micro-arc formed during the reaction. The reaction with micro-arc formation had a higher energy efficiency than that without micro-arc formation.

CO2 Decomposition Using Glow Discharge Plasmas

Abstract: Carbon dioxide decomposition has been studied using ac glow discharge plasmas at atmospheric pressure. A tubular reactor with a metal rod inside a quartz tube was wrapped with aluminum foil. The reaction mixture was analyzed by using a mass spectrometer. No coke deposits or other side reactions were observed. A variety of parameters, such as different metals, CO 2 concentrations, flow rate of the CO 2 containing gas, frequency, and power were investigated. The effects of these parameters on CO 2 conversion, reaction rates, and energy efficiency were examined. The initial excitation voltage to produce the plasma is independent of the metal identity on the surface of the rod and the flow rate of CO 2 containing gas, but dependent on the CO 2 concentration and ac frequency used. The maximum energy efficiency was obtained with relatively high CO 2 concentration, high flow rate of CO 2 containing gas, high frequency, as well as low input voltage at the expense of conversion.

Plasma decomposition of CO2 in the presence of metal catalysts

Abstract: The decomposition of CO 2 in fan-type ac glow discharge plasma reactors coated with gold, copper, platinum, palladium, rhodium, and mixed rotor/stator systems (Au/Rh and Rh/Au) was investigated. A high-voltage ac signal was used to produce a plasma between the fins of a turning rotor and an immobile stator, through which a 2.5% CO 2 in He mixture was passed. The analysis of the product gases was achieved using a mass spectrometer equipped with a partial pressure analyzer, and the decomposition of CO 2 was found to proceed to CO and O 2 with >80% selectivity. The percentage conversion of CO 2 increases with decreasing flow rate and increasing input voltage. The opposite trend is obtained when the energy efficiency is evaluated. Spectroscopic data indicate that the diluent gas plays a role in the dissociation of CO 2 , likely via charge and energy transfer from excited state He species to produce vibrationally excited CO 2 + intermediates. The order of reactivity for the different metal catalyst coatings is Rh > Pt ≈ Cu > Pd > Au/Rh ≈ Rh/Au ≈ Au. With the Rh-coated reactor, conversions as high as 30.5%, reaction rates of 8.07×10 −4 mol/h, and energy efficiencies of 3.55% could be obtained. There is a clear relationship between excitation temperature, T ex , of a pure He plasma and the conversion of CO 2 in a CO 2 /He plasma: decreasing T ex corresponds to increasing conversion.

Efficient catalytic plasma activation of CO2, NO, and H2O

Abstract: The activation of small molecules, such as CO2, NO, and H2O, has been achieved at atmospheric pressure via ac glow discharge methods in the presence of metal catalysts coated onto the electrode surfaces. A fan-type reactor having one rotating and one static electrode has been designed to diminish mass transfer effects. Time lapse photography of the emitting plasma intermediate species and optical emission studies have been used to monitor reaction pathways. Gas chromatography, mass spectrometry, and combined GC−MS methods have been used to monitor product distributions, selectivities, and activities. The effects of flow rate, input voltage, diluent gases, and metal coating have been systematically studied. Additionally, the mechanisms of CO2 decomposition and the role of the metal catalyst in that decomposition have been studied by optical emission spectroscopy.

Profiles of Carbon Dioxide Decomposition in a Dielectric-Barrier Discharge-Plasma System

Abstract: Decomposition of CO2 to CO and O2 in Ar stream has been investigated under atmospheric pressure by the use of a dielectric-barrier discharge plasma reactor. CO2 dissociation was found to proceed in accordance with the stoichiometry of 2 CO2 = 2 CO + O2 at considerable rates, which increased with increasing the input voltage, the CO2 concentration in Ar, and the heat of oxide formation of the corresponding metallic component used as the electrode. From kinetic and spectroscopic measurements, the major pathway of CO2 decomposition was speculated to be promoted by a synergetic effect between plasma excitations in the gas phase and catalytic actions of the electrode surface.

Plasma technology - a novel solution for CO2 conversion?

Abstract: CO2 conversion into value-added chemicals and fuels is considered as one of the great challenges of the 21st century. Due to the limitations of the traditional thermal approaches, several novel technologies are being developed. One promising approach in this field, which has received little attention to date, is plasma technology. Its advantages include mild operating conditions, easy upscaling, and gas activation by energetic electrons instead of heat. This allows thermodynamically difficult reactions, such as CO2 splitting and the dry reformation of methane, to occur with reasonable energy cost. In this review, after exploring the traditional thermal approaches, we have provided a brief overview of the fierce competition between various novel approaches in a quest to find the most effective and efficient CO2 conversion technology. This is needed to critically assess whether plasma technology can be successful in an already crowded arena. The following questions need to be answered in this regard: are there key advantages to using plasma technology over other novel approaches, and if so, what is the flip side to the use of this technology? Can plasma technology be successful on its own, or can synergies be achieved by combining it with other technologies? To answer these specific questions and to evaluate the potentials and limitations of plasma technology in general, this review presents the current state-of-the-art and a critical assessment of plasma-based CO2 conversion, as well as the future challenges for its practical implementation.

Non-thermal plasmas for non-catalytic and catalytic VOC abatement.

Abstract: This paper reviews recent achievements and the current status of non-thermal plasma (NTP) technology for the abatement of volatile organic compounds (VOCs). Many reactor configurations have been developed to generate a NTP at atmospheric pressure. Therefore in this review article, the principles of generating NTPs are outlined. Further on, this paper is divided in two equally important parts: plasma-alone and plasma–catalytic systems. Combination of NTP with heterogeneous catalysis has attracted increased attention in order to overcome the weaknesses of plasma-alone systems. An overview is given of the present understanding of the mechanisms involved in plasma–catalytic processes. In both parts (plasma-alone systems and plasma–catalysis), literature on the abatement of VOCs is reviewed in close detail. Special attention is given to the influence of critical process parameters on the removal process.

Catalytic Technology for Carbon Dioxide Reforming of Methane to Synthesis Gas

Abstract: The mitigation and utilization of greenhouse gases, such as carbon dioxide and methane, are among the most important challenges in the area of energy research. Dry reforming of CH4 (DRM), which uses both CO2 and CH4 as reactants, is a potential method to utilize the greenhouse gases in the atmosphere. Natural gas containing high concentrations of CO2 and CH4 could therefore be utilized for hydrogen and synthesis gas (syngas) production in the near future, without need for the removal of CO2 from the source gas. Thus, the DRM reaction is a suitable process to convert CH4 and CO2 to syngas, which is a raw material for liquid fuel production, through the Fischer–Tropsch process. Herein, the development of CO2 reforming for syngas production is reviewed, covering process chemistry, catalyst development, and process technologies as well as the potential future direction for this process.

Plasma Catalysis: Synergistic Effects at the Nanoscale

Abstract: Thermal-catalytic gas processing is integral to many current industrial processes. Ever-increasing demands on conversion and energy efficiencies are a strong driving force for the development of alternative approaches. Similarly, synthesis of several functional materials (such as nanowires and nanotubes) demands special processing conditions. Plasma catalysis provides such an alternative, where the catalytic process is complemented by the use of plasmas that activate the source gas. This combination is often observed to result in a synergy between plasma and catalyst. This Review introduces the current state-of-the-art in plasma catalysis, including numerous examples where plasma catalysis has demonstrated its benefits or shows future potential, including CO2 conversion, hydrocarbon reforming, synthesis of nanomaterials, ammonia production, and abatement of toxic waste gases. The underlying mechanisms governing these applications, as resulting from the interaction between the plasma and the catalyst, rend...

Promotional effect of alkaline earth over Ni–La2O3 catalyst for CO2 reforming of CH4: Role of surface oxygen species on H2 production and carbon suppression

Abstract: Alkaline earth elements (Mg, Ca and Sr) on Ni–La 2 O 3 catalyst have been investigated as promoters for syngas production from dry CO 2 reforming of methane (DRM). The catalysis results of DRM performance at 600 °C show that the Sr-doped Ni–La 2 O 3 catalyst not only yields the highest CH 4 and CO 2 conversions (∼78% and ∼60%) and highest H 2 production (∼42% by vol.) but also has the lowest carbon deposition over the catalyst surface. The XPS, O 2 -TPD, H 2 -TPR and FTIR results show that the excellent performance over the Sr-doped Ni–La 2 O 3 catalyst is attributed to the presence of a high amount of lattice oxygen surface species which promotes C–H activation in DRM reaction, resulting in high H 2 production. Moreover, these surface oxygen species on the Ni-SDL catalyst can adsorb CO 2 molecules to form bidentate carbonate species, which can then react with the surface carbon species formed during DRM, resulting in higher CO 2 conversion and lower carbon formation.