Effects of dielectric particles on non-oxidative coupling of methane in a dielectric barrier discharge plasma reactor.

• The methane conversion shows its maximum in terms of particle size. • The concept of microelectrodes explains the existence of maximum conversion. • By adjusting particle size, selectivity can be controlled without catalyst. • In terms of coke formation, non-porous silica particles are favored. • Coke is more produced when large particles are used. A dielectric barrier discharge (DBD) plasma reactor was employed for non-oxidative coupling of methane. The coupling reaction in the DBD plasma bed was conducted near atmospheric pressure and room temperature. In the bed, dielectric materials such as ordered mesoporous silica (KIT-6), sea sand silica, and α-Al 2 O 3 were employed. This non-catalytic reaction system could successfully activate C H bond to produce methyl radicals and light hydrocarbons without additional thermal energy and oxidant molecules. The gap distance between dielectric particles was determined by their sizes, which was experimentally shown. The effects of gap distance were found significant on the conversion and the selectivity. The existence of maximum conversion at a specific gap distance was experimentally observed and could be described successfully by using a newly developed concept of micro-electrodes. Based on the concept, the minimum threshold electric potential difference between the dielectric particles could be successfully estimated, where the conversion was shown to be maximized. Furthermore, it seemed quite possible to control the compositions of ethane, ethylene, and acetylene by properly adjusting the size or the gap distance of particles. [ABSTRACT FROM AUTHOR]