Reaction Enhancement Mechanism of the Nonthermal Discharge and Catalyst Hybrid Reaction for Methane Reforming

Abstract

The reaction enhancement mechanism of methane steam reforming (MSR) in the nonthermal discharge and catalyst hybrid reaction is presented. Coke deposited on Al2O3-supported Ni catalyst was investigated using temperature-programmed oxidation (TPO) analysis and micro-Raman spectroscopy. Although methane conversion in the hybrid reaction is greater than that of normal catalytic reforming, the normal reaction deposited 5 times more coke than the hybrid reaction. Raman spectroscopy revealed that the superposition of the nonthermal discharge on catalysts produced less graphitized coke compared to the normal catalytic reaction, by which it is easily removed by H2O during steam reforming. Excited species produced by nonthermal discharge are so reactive that their reaction is completed only on the pellet surface: coke formation in the catalyst pore was only slightly detectable. In contrast, large amounts of coke were detected from the surface and catalyst pores in the normal reaction. In the hybrid reaction, CH4 and H2O are primarily excited by electron impact. Therefore, methane dehydrogenation followed by coke oxidation is promoted, resulting in a small amount of coke formation with greater methane conversion than in the normal reaction. The results are well-correlated with Arrhenius plot analysis of the overall forward rate constant for MSR in the hybrid reaction.

Non-thermal plasma catalysis of methane: Principles, energy efficiency, and applications

“…These species are responsible for triggering fuel conversion at low temperatures. Steam reforming of methane [10][11][12]25,26], diesel [27], E85 [28,29], gasoline [30] and propane [31] by DBD have been studied. More recently, CO 2 (dry) methane reforming using non-thermal plasma has attracted keen attention [6] as an important part of carbon capture and utilization (CCU) technology.…”

“…Moreover, the energy efficiency of nonoxidative methane conversion in DBD is analyzed experimentally, showing 1% energy efficiency from CH 4 to C 2 hydrocarbons [9]: It is an order of magnitude smaller than theoretical estimations. Finally, non-thermal plasma and catalyst hybrid reaction for lowtemperature SMR are discussed [10][11][12], where energy efficiency increased to 50% and 80%. Plasma-generated reactive species, especially vibrationally excited methane and water (H 2 O), are highly anticipated as reaction promoters at low temperatures.…”

Innovative Methane Conversion Technology Using Atmospheric Pressure Non-thermal Plasma

“…In fact, the reaction order for H2O was more than doubled by applying DBD, which eventually increased the pre-exponential factor of the overall forward rate constant k. The removal of chemisorbed carbon is a vital reaction pathway together with the methane dehydrogenation reaction. Nevertheless, DBD-induced carbon precipitation was uniquely identified on catalyst pellets 21) . Therefore, the carbon to steam (S/C) ratio must be increased to prevent carbon formation as reaction temperature increases.…”

Non-Oxidative Reforming of Methane in a Mini-Gliding Arc Discharge Reactor: Effects of Feed Methane Concentration, Feed Flow Rate, Electrode Gap Distance, Residence Time, and Catalyst Distance

“…A promising way is to use non-thermal plasma for the methane reforming. Numerous investigations have been focused on the direct methane reforming using the non-thermal plasma; these include non-oxidative methane reforming [1][2][3][4][5][6][7][8], oxidative methane reforming [9][10][11][12][13][14][15][16][17][18], and hybrid plasma-catalytic reforming of methane [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. The energetic electrons generated by non-thermal plasma can effectively induce the creation of a huge number of chemically active species via electronic and ionic collision-dissociation-combination mechanisms, and these generated active species can rapidly undergo several chemical reactions under ambient conditions.…”