Hydro-purification of crude terephthalic acid using palladium catalyst supported on multi-wall carbon nanotubes

Palladium catalysts supported on functionalized multi-wall carbon nanotubes were synthesized for hydro-purification of crude terephthalic acid containing 2100 ppm 4-carboxybenzaldehyde (4-CBA) as impurity. PdCl2 and Pd(OAc)2 were used as precursors. Palladium loadings were 0.05 to 0.6 wt.% with catalysts reduced at 200 to 400 °C. Catalysts prepared from both precursors with least 0.3 wt.% palladium resulted in 99%+ removal of 4-CBA. The most desired selectivity was obtained for the catalyst with PdCl2 as precursor, reduction temperature of 300 °C, and palladium loading of 0.3 wt.%. This catalyst had slightly better performance than the commercial catalyst (0.5 wt.% of palladium on activated carbon).