Using isopropanol as a liquid organic hydrogen carrier (LOHC) for the reduction nitroarenes employing Au/Ag decorated carbon aerogels

Abstract

In this study, multi-walled carbon nanotubes functionalized with carboxylic acid/chitosan aerogel containing Ag/Au nanoparticles (NPs) (CNT/CS@Au/Ag aerogel) were synthesized using carboxylated multi-walled carbon nanotubes, deacetylated chitosan, AgNO₃, HAuCl_4, and their reduction by NaBH₄ using the sol-gel method, followed by freeze-drying. FE-SEM, EDS, XRD, BET, FT-IR, TGA, and Raman analyses confirmed the porous structure, NPs dispersion, pore size, functional groups, and thermal stability of the synthesized aerogel. Four different aerogels with different Au/Ag ratios or different preparation procedure were prepared. Then, the prepared catalysts were employed at different conditions for the mild reduction of nitroarenes by isopropanol, as an available and non-expensive Liquid Organic Hydrogen Carrier (LOHC). The optimal conditions for nitrobenzene reduction were determined as follows: 40 mg of mixed Ag/Au catalyst (containing 2.5 % Ag/2.5 % Au, reduced Ag and Au salts spontaneously), 3 equivalents of sodium hydroxide, and 5 mL of isopropanol as both solvent and reducing agent. The reaction was carried out at reflux temperature for 24 h. UV–Vis spectroscopy analysis revealed 100 % conversion and 78 % aniline yield. The high catalytic stability of the synthesized aerogel after 5 reuses demonstrated its high potential as a recyclable and economical catalyst. It was also used in the reduction of 15 different NB derivatives, and acceptable results were obtained.