Catalytic preparation of narrow pore size distribution mesoporous carbon

The carbon deposited during the catalytic decomposition of CH4 over Ni, Co or Fe particles, at temperatures between 500 and 780 degrees C, was investigated by N-2 adsorption, TEM and XPS. A much larger amount of carbon was formed on Ni than on Co or Fe. The pore size distribution curves indicate that the carbon deposited on the three metals has most of the pores in the 3-4 nm range. The proportion of pores in that range decreases on Ni, but increases on Co or Fe with reaction time. During the CH4 decomposition over Ni at 500 degrees C, two kinds of carbon were identified: 1) nanotube carbon (with the smallest inner diameter of about 3 nm) and 2) mesoporous carbon. At high temperatures, almost only the mesoporous carbon with a narrow pore size distribution around 3.5 nm could be observed. It is likely that the nanotubes are the precursors of the mesoporous carbon, because the inner diameter of the smaller ones is almost equal to the size of the pores, and the nanotubes are no longer present at high temperatures. (C) 1998 Elsevier Science Ltd. All rights reserved.