Carbon-structure affecting catalytic carbon dioxide reforming of methane reaction over Ni-carbon composites

Abstract

In this research, carbon dioxide utilization through dry reforming of methane was investigated over Ni-carbon composite catalysts. It was found that the deactivation of Ni catalyst by coke deposition could be reduced by the use of Ni catalysts with a unique composite structure of Ni on the tips of carbon nanotubes (Ni-CNTs). Accordingly, the effects of carbon structures of Ni-CNTs composites over mesocellular silica (MS) support on catalytic activity and stability in dry reforming reaction were examined in detail. Ni-CNTs(x)/MS catalysts were synthesized using the catalytic chemical vapor deposition (CCVD) technique at CCVD temperatures of 550, 650, and 750°C to obtain different carbon structures, and were used in dry reforming reaction at temperatures of 650, 700, and 750°C. The lowest and highest amounts of highly stable CNTs were observed with Ni-CNTs(650)/MS and Ni-CNTS(750)/MS composite catalysts, respectively. Turnover frequency (TOF) values of Ni-CNTs(750)/MS composite catalyst were approximately 2.62 and 3.63 times higher than that of the conventional Ni/MS catalyst at reaction temperatures of 650 and 750°C, respectively. In addition, Ni-CNTs(750)/MS catalyst not only gave a stable ratio of H2/CO products but also showed better trends for catalytic stability at all temperatures. During the reaction period, the carbon structure of less stable CNTs was partially refomed to highly stable CNTs, while that of highly stable CNTs (in the used Ni-CNTs(x)/MS catalyst) was not changed. Consequently, the presence of highly stable CNTs structure in the composite catalyst was found to enhance the activity and stability of dry reforming catalysts.