How reduction temperature affects the properties of carbon nanotubes growing over the Fe–MgO/Al2O3 catalyst

Abstract

Fe₂O₃–MgO/Al₂O₃ catalyst precursors were prepared by a co-precipitation method for the growth of carbon nanotubes (CNTs), and the materials were characterized by various means. The effects of reduction temperature on the surface morphology, texture properties and reduction degree of the catalysts were systematically discussed, and the effects of the catalysts on the diameter uniformity, defect degree and carbon yield of carbon nanotubes were further investigated. The results showed that the reduction temperature strongly affected the reduction degree and morphology of Fe-containing species. As the reduction temperature increased from 560 °C to 760 °C, the reduction products obtained were (Fe₂O₃, Fe₃O₄), (Fe₃O₄, Fe_xO), (Fe_xO, Fe), and (Fe_xO, Fe), and the specific surface area tended to decrease while the pore size gradually increased, which would have a great influence on further reduction of the catalyst after C₃H₆ was introduced. The results showed that the best catalyst performance was achieved when the reduction temperature was 660 °C, and carbon nanotubes with a carbon yield of 1800%, a graphitization degree of 0.98, a diameter distribution in the range of 6–20 nm, a specific surface area of 260.55 m² g⁻¹ and a resistivity of 52.6 mΩ cm could be obtained, which was because at this temperature, the composition and structure of the active material in the catalyst were favorable for further diffusion of carbon.