Reductive debromination of tetrabromobisphenol A by Pd/Fe bimetallic catalysts

• TBBPA can be rapidly and completely debrominated to BPA by Pd–Fe catalysts.
• The rate constants are functions of dosages, Pd coverage and solution pH.
• The Pd dosage is the major factor in the observed rates of the reaction.

The bimetallic catalysts of micron sizes were synthesized and the rates of tetrabromobisphenol A (TBBPA) transformation were measured under various conditions using a batch reactor system. The results showed that TBBPA was rapidly debrominated to tri-, di- and mono-bromobisphenol A and to bisphenol A (BPA). The pseudo-first-order rate constants normalized to the specific surface area of the catalysts were found to increase as functions of the Pd coverage on the Fe particles and the dosages of the catalysts and the mass of Pd within the reactors. The rate constants were also decreasing as the solution pH increased. At pH 4.2, Pd coverage of 0.022 wt% and catalyst dosage of 4 g L−1, 99% of TBBPA was transformed within 2 min, and tri-, di-, and mono-bromobisphenol A were detected as the major intermediate products. After reaction for 45 min, BPA was the only compound found in this specific system. Meanwhile, the rate constants measured at constant solution pH correlated linearly with the Pd mass introduced to the reactors, regardless of Pd/Fe catalyst dosage or Pd surface coverage. The study suggested that Pd/Fe catalysts could be used for efficiently treating brominated flame retardants extracted from e-wastes.