Evaluation of Catalytic Activity of Acid Activated Multiwalled Carbon Nanotubes in an Esterification Reaction

Abstract

Multiwalled carbon nanotubes (MWCNTs) synthesized earlier by catalytic chemical vapor deposition of acetylene, were used to develop heterogeneous supported acid catalysts by sonicating with 50% aqueous solutions of H2SO4, H3BO3 and H3PO4. The effect of acid treatment of MWCNTs, on their textural properties such as crystallinity, surface area, nature of the surface functional groups and elemental composition was investigated by appropriate instrumental methods of analysis such as BET surface area, Powder XRD, FT-IR, SEM-EDS, TEM and XPS. Acidity of the materials was estimated by n-butyl amine back titration method and the catalytic activity was evaluated in an acid catalyzed esterification reaction between benzyl alcohol and acetic acid. Further, the effect of duration and temperature of the reaction on the conversion of benzyl alcohol to benzyl acetate was studied. The product analysis was made by GC, LC-MS and 1HNMR techniques. The characterization techniques indicated that, the textural properties of the acid activated MWCNTs were distinctly different from those of the pristine MWCNTs inferring a possible incorporation of oxoacids into the mesoporous structure of MWCNTs. All the materials showed catalytic activity in the esterification of benzyl alcohol with acetic acid resulting benzyl acetate with 100% selectivity and 10-88% yield depending on the experimental conditions. Sulphuric acid activated MWCNTs exhibited highest surface acidity and catalytic activity. These catalysts were also found to be recyclable up to 5 times without any significant loss in its catalytic activity. Keywords: Acid activation, benzyl acetate, carbon nanotubes, catalytic activity, esterification, surface acidity.