A novel route of enhancing oxidative catalytic activity: hydroxylation of MWCNTs induced by sectional defects

Abstract

As metal-free catalysts, the functionalization of multi-walled carbon nanotubes (MWCNTs) can usually provide the activated sites for oxidative dehydrogenation (ODH). In this paper a novel functionalization of MWCNTs has been proposed via an alkali-assisted hydrothermal treatment on the sectional defects produced by ball milling. The as-prepared hydroxylated MWCNTs exhibit twice the catalytic activity of MWCNTs without ball milling, because the ball-milled treatment leads to the production of more sectional defects located on exposed edges or terminals of MWCNTs and these defects can induce the creation of more hydroxyl groups by an alkali-assisted hydroxylation. The research on the reaction mechanism reveals that the ODH of ethylbenzene (EB) in the presence of CO₂ for the hydroxylated MWCNTs takes on a possible mechanism of two-step dehydrogenation by coupling a reverse water–gas shift reaction and CO₂ may oxidize hydroxyl groups into carbonyl groups to maintain the catalytic cycle.