Complete catalytic debromination of polybrominated diphenyl ethers over a silica-supported palladium nanoparticle catalyst

Abstract

Polybrominated diphenyl ethers (PBDE) are widely used as brominated flame retardants, and the release of PBDE into the environment is of great concern. Here, the catalytic debromination of PBDE was achieved with a silica-supported Pd nanoparticle catalyst in a solution of 2-propanol/methanol 99/1 v/v containing dissolved NaOH. Results show that decabromodiphenyl ether (deca-BDE) was completely debrominated at 45 °C into two bromine-free products, diphenyl ether (55 %) and dibenzofuran (45 %), according to gas chromatography–mass spectrometry analysis. This finding indicates that the catalytic reaction included not only substitution of a bromine atom by a hydrogen atom but also a cyclization arising from a C–C bond formation at the ortho positions of the diphenyl ether moiety. Results further show that 2,2′,4,4′-tetrabromodiphenyl ether, having two bromines in ortho positions, was converted to diphenyl ether (90 %) and dibenzofuran (10 %). 4,4′-Dibromodiphenyl ether, having no ortho bromines, yielded only diphenyl ether. This study is the first showing the complete catalytic debromination of deca-BDE to bromine-free products under mild conditions.