Peculiar and full debromination of tetrabromodiphenyl ether on Pd/TiO2: A competing route through hydro-debromination and coupling-debromination

The use of palladium deposited TiO 2 (Pd/TiO 2 ) as catalysts yielded complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) in isopropanol solution containing NaOH at 40 °C within 60 min. The final organic products were diphenyl ether and dibenzofuran. It was disclosed that two competing reduction paths (hydro-debromination and coupling-debromination) occurred over Pd nanoparticles . The hydro-debromination was dependent on the participation of active H atom species generated by catalytic transfer hydrogenation on metallic Pd. The coupling-debromination proceeded via the oxidative addition of Pd(0) to B r 2 C 12 H 8 OB r 2 ′ $\text{B}{\text{r}}^2{\text{C}}_{12}{\text{H}}_8\text{OB}{\text{r}}^{2\prime }$ , leading to an transition state of B r 2 Pd II C 12 H 8 OB r 2 ′ $\text{B}{\text{r}}^2\text{Pd}\left(\text{II}\right){\text{C}}_{12}{\text{H}}_8\text{OB}{\text{r}}^{2\prime }$ , the reductive dissociation of which resulted in the elimination of Br − ions, producing a new transition state Pd 0 C 12 H 8 OB r 2 ′ − ${\left[\text{Pd}\left(0\right){\text{C}}_{12}{\text{H}}_8\text{OB}{\text{r}}^{2\prime }\right]}^{-}$ . A further oxidative addition of Pd 0 C 12 H 8 OB r 2 ′ − ${\left[\text{Pd}\left(0\right){\text{C}}_{12}{\text{H}}_8\text{OB}{\text{r}}^{2\prime }\right]}^{-}$ generated B r 2 ′ Pd II C 12 H 8 O − ${\left[\text{B}{\text{r}}^{2\prime }\text{Pd}\left(\text{II}\right){\text{C}}_{12}{\text{H}}_8\text{O}\right]}^{-}$ , and its final reductive elimination provided dibenzofuran, leading to the regeneration of Pd(0). The integration of the catalytic coupling and hydrogenation reaction on Pd nanoparticles greatly accelerated the removal of the halogenated organic pollutants.