Decoloration of azo and triarylmethane dyes in the aqueous phase by catalytic hydrotreatment with Pd supported on pillared clays

Abstract

Catalytic hydrotreatment of synthetic dyes as azo compounds and triarylmethanes has been carried out under ambient-like conditions (25–50 °C, 1 atm) with H₂ using Pd supported on Al-pillared clays and Al₂O₃ as catalysts. The treatment leads to complete decoloration of aqueous solutions of the azo dyes (azobenzene, methyl orange, Congo red and oil red) due to the catalytic hydrogenation of the NN bonds. Under acid pH the color removal was enhanced and a solid residue was formed in the case of Congo red, being completely removed. With aqueous solutions of the triarylmethane dyes crystal violet, fuchsine and malachite green complete decoloration was also achieved upon hydrogenation of the chromophore groups or modification of the chemical structure.