Ni-Al bimetallic catalysts for preparation of multiwalled carbon nanotubes from polypropylene: Influence of the ratio of Ni/Al

This study designed a novel Ni-Al bimetallic catalyst for preparation of multiwalled carbon nanotubes (MWCNTs) from polypropylene (PP). The study further investigated the influence of Al content on the catalytic activity of Ni catalyst. A series of bimetallic Ni-Al catalysts were prepared and then characterized by X-ray diffraction, N-2-adsorption-desorption isotherms, transmission electron microcopy and temperature programmed reduction analysis. It was found that bimetallic Ni-Al catalysts had higher surface area, higher reduction temperature, smaller Ni particle size and improved stability. Consequently, the addition of Al not only dramatically enhanced the yield of MWCNTs, but simultaneously improved the morphology and graphitization of MWCNTs. The activities of the bimetallic Ni-Al catalysts were dependent on their composition. Among the different Ni-Albimetallic catalysts, Ni-Al catalyst showed the highest activity when the ratio of Ni/Al was 9/1. Moreover, the obtained MWCNTs presented smooth surface with highest graphitization degree. The improvement of catalytic activity and stability obtained for bimetallic Ni-Al catalysts was attributed to an appropriate interaction and synergy between Ni species and amorphous Al2O3. The combined results indicate that the addition of Al to Ni catalyst with an appropriate amount of Al can give rise to a bimetallic catalyst with excellent properties for synthesis of MWCNTs from PP. With our bimetallic Ni-Al catalyst, it is promising to achieve mass production of MWCNTs by using waste polymers as feedstock. (C) 2015 Elsevier B.V. All rights reserved.