Promoting Effect of Ball Milling on the Functionalization and Catalytic Performance of Carbon Nanotubes in Glycerol Etherification

Abstract

A facile and eco-friendly approach using in situ-generated 4-benzenediazonium sulfonate (BDS) was applied to prepare highly functionalized carbon nanotubes (CNTs). The effectiveness of this functionalization was additionally enhanced by a green and short-time ball milling process applied beforehand. The obtained BDS-modified CNTs presented significant activity in glycerol etherification, producing tert-butyl glycerol ethers, which are considered promising fuel additives. Excellent results of ~56% glycerol conversion and ~10% yield of higher-substituted tert-butyl glycerol ethers were obtained within just 1 h of reaction at 120 °C using a low catalyst loading of only 2.5 wt.%. Furthermore, the sulfonated CNTs were reusable over several reaction cycles, with only a minor decrease in activity. Additionally, the sample activity could be restored by a simple regeneration approach. Finally, a clear correlation was found between the content of -SO3H groups on the surface of CNTs and the catalytic performances of these materials in glycerol etherification. Improved interaction between functionalized ball-milled CNTs and the reactants was also suggested to positively affect the activity of these catalysts in the tested process.

The role of mechanochemical treatment of carbon nanotubes in promoting glycerol etherification

“…19–21 Interestingly, particularly promising applications of CNTs relate to heterogeneous catalysis, where CNTs can be used as super-efficient catalysts or as support for active phases. 22,23 It is noted that apart from our recently published pioneering work, focussing on carbon nanotubes functionalized with 4-benzene diazonium sulfonate (BDS), 24 there are no reports in the literature dealing with the application of sulfonated CNTs in the etherification of glycerol with tert -butyl alcohol (TBA). Our results showed that the BDS-functionalized CNTs were very active in glycerol etherification at 120 °C, reaching ∼56% glycerol conversion and ∼10% yield of higher-substituted ethers, using a low catalyst loading of only 2.5 wt%.…”