Catalytic hydrodehalogenation of the flame retardant tetrabromobisphenol A by alumina-supported Pd, Rh and Pt catalysts

Tetrabromobisphenol A (TBBPA) is one of the most used BFRs, being characterized by a strong persistence and leading to negative effects on both the environment and human health. The aim of this work is to evaluate the feasibility of aqueous-phase catalytic hydrodehalogenation (HDH) for the fast and environmentally-friendly degradation of the brominated flame retardant TBBPA. Pd, Rh, and Pt on alumina commercial catalysts (1% wt.) were tested and reactions were performed under ambient operating conditions. TBBPA (1 mg L-1) was completely removed in short reaction times (< 5 min) using the Pd catalyst while longer reaction times were required in the case of Rh and Pt catalysts as active phase. Furthermore, although TBBPA suffered a strong adsorption on the catalyst surface, both adsorbed and free molecules reacted. Bromine balance was closed (> 95%) in 15 min using Pd/Al2O3. Nevertheless, employing Rh and Pt alumina-supported catalysts debromination of TBBPA increased progressively requiring much longer times and only 83% and 78% debromination yields were achieved after 2 h reaction, respectively. Bisphenol A (BPA), a well-known endocrine disruptor, was generated as reaction intermediate but it was further hydrogenated with both Pd and Rh catalysts, whereas it remained as reaction product with the Pt catalyst. A series reaction pathway considering both hydrodebromination and hydrogenation steps was proposed based on the obtained results. The experimental data obtained with the Pd/Al2O3 catalyst were successfully described by a pseudo-first order kinetic model, obtaining an apparent activation energy of 36 kJ mol(-1). Notably, this catalyst showed a reasonable stability after three consecutive HDH runs.