Correlation Between Periodicity and Catalytic Growth Activity of Bimetallic Co-group VI/MgO Catalysts for Production of Carbon Nanotubes by Acetylene Using Chemical Vapor Deposition

Abstract

This work aims to discover a relationship between the periodicity and catalytic growth activity of carbon nanotubes by acetylene chemical vapor deposition. Hence, the effect of addition of group VI metals (25% of Cr, Mo, or W) of the periodic table to 25 wt% Co supported on MgO has been investigated. The fresh catalysts and carbon nanomaterials were characterized by XRD, TPR, TEM, Raman spectroscopy, BET surface measurements, and TG analysis. The results revealed that the addition of group VI metals induces a strong interaction with the structural MgO crystals associated with an enhancement in surface properties. XRD data shows that the appearance of group VI metal oxides in the diffraction patterns primarily dependent on the corresponding atomic weights. TGA data shows that the Co–W/MgO catalyst exhibited higher carbon nanotubes (CNTs) yield compared to the Co–Cr or Co–Mo containing catalysts. The yield of CNTs increases gradually with increasing the atomic weight of group VI metals (W > Mo > Cr). This finding can be attributed to the higher surface coverage of Co-W/MgO and consequently the larger amount of metal sites which are responsible for the higher yield of MWCNTs compared to the other bimetallic catalysts. The higher metallic surface permits decomposing a larger amount of C2H2 molecules more efficiently. XRD, TEM, and Raman spectroscopic data revealed that highly graphitized MWCNTs were produced over all catalysts under study.