Laminar N-Doped Carbon Materials from a Biopolymer for Use as a Catalytic Support for Hydrodechlorination Catalysts

Nitrogen-doped porous carbons were prepared using a chitosan biopolymer as both a carbon and nitrogen precursor and metallic salts (CaCl₂ and ZnCl₂-KCl) as a templating agent with the aim of evaluating their performance as catalyst supports. Mixtures of chitosan and templating salts were prepared by simple grinding subjected to pyrolysis and finally washed with water to remove the salts. The resulting materials were characterized, showing that homogeneous nitrogen doping of carbon was achieved (7-9% wt.) thanks to the presence of a nitrogen species in the chitosan structure. A lamellar morphology was developed with carbon sheets randomly distributed and folded on themselves, creating slit-shaped pores. Substantial porosity was observed in both the micropore and mesopore range with a higher surface area and microporosity in the case of the materials prepared by ZnCl₂-KCl templating and a larger size of mesopores in the case of ZnCl₂. Catalysts with well-dispersed Pd nanoparticles (around 10 nm in diameter size) were synthesized using the chitosan-based carbons obtained both by salt templating and direct chitosan pyrolysis and tested in the aqueous phase hydrodechlorination of 4-chlorophenol. The fast and total removal of 4-chlorophenol was observed in the case of catalysts based on carbons obtained by templating with CaCl₂ and ZnCl₂-KCl in spite of the low metal content of the catalysts (0.25% Pd, wt.).