No abstract

Interaction between dielectric barrier discharge (DBD) and porous catalyst in dry methane reforming (CH4  +  CO2  =  2H2  +  2CO) was studied. Coke formation behavior and coke morphology, as well as material conversion and selectivity, over the cross-section of porous pellets was investigated comprehensively by SEM analysis, Raman spectroscopy and pulsed reforming diagnosis, showing DBD and porous pellet interaction is possible only in the interfacial region (the external surface of the pellet): neither generation of DBD nor the diffusion of plasma generated reactive species in the internal micropores is possible. Coke formation and gasification mechanism in nonthermal plasma catalysis of DMR were discussed based on the catalyst effectiveness factor: low-temperature plasma catalysis is equivalent to the high-temperature thermal catalysis.

The oxidation behavior of Ni/Al 2 O 3 catalyst in CO 2 plasma was investigated compared with CO 2 thermal oxidation, aiming for providing new insight into oxidationreduction cycle of plasma catalysis of dry methane reforming (DMR). Temperature programmed reaction spectrometry was applied to enable a quantitative analysis of gas consumption which is related to the oxidation and reduction of Ni/Al 2 O 3 catalysts. The nonthermal plasma oxidation mechanism was further analyzed by Raman spectroscopy, showing the crosssectional distribution of NiO over the 3 mm spherical catalyst pellets. Nonthermal plasmaexcited CO 2 oxidizes Ni only near the external surface of spherical pellets with 20 μm depth: both dielectric barrier discharge generation and plasmaexcited species diffusion into the internal pores are inhibited. The partially oxidized Ni catalyst in the external surface would promote plasmaenabled oxidationreduction cycle, which was further correlated with coke formation behavior in plasma catalysis of DMR.

FIGURE 6 Effects of CH 4 /CO 2 ratio on DMR at ca. 550°C: (a) CH 4 conversion rate; (b) CO 2 conversion rate; (c) H 2 yield rate; (d) CO yield rate; (e) coking rate KAMESHIMA ET AL.