Impact of metal-support interactions on Fe or Ni/metal oxide catalysts for efficient and economical production of carbon nanotubes from benzene

Abstract

This study focuses on carbon nanotube (CNT) production from liquid benzene, which is simply obtained from plastic pyrolysis. Through catalytic chemical vapor deposition (CCVD) process, Fe and Ni catalysts supported on acidic, basic, and neutral alumina (a-Al<inf>2</inf>O<inf>3</inf>, b-Al<inf>2</inf>O<inf>3</inf>, and n-Al<inf>2</inf>O<inf>3</inf>), magnesium oxide (MgO), and silica (SiO<inf>2</inf>), significantly influenced CNT yields and properties due to their different metal-support interactions in CNT production from benzene under different CCVD temperatures (700–900 °C). Fe/b-Al<inf>2</inf>O<inf>3</inf> was superior among the alumina supports and revealed the highest CNT yield of 24.5 wt% with a uniform CNT diameter of ∼30 nm and a high degree of graphitization at the optimum temperature of 800 °C. However, Fe/MgO could synthesize the smallest size of CNTs (∼20 nm) with relatively low yields (∼11 wt%) under the preferable lower temperature of 700 °C. For Ni-based catalysts, the yields of CNTs with smaller size (∼20 nm) obtained at 700 °C were mostly lower (<10 wt%), then further dropped to <3 wt% at higher temperatures due to the sintering of Ni particles. According to a preliminary cost estimation based on raw material costs and yields of as-produced CNTs, Fe-based catalysts, particularly supported on b-Al<inf>2</inf>O<inf>3</inf> and SiO<inf>2</inf>, were more economical than Ni-based catalysts.