Efficient debromination of tetrabromobisphenol A in protic solvents by supported nickel catalysts: Effect of metal-support interactions

Toxic and environmentally hazardous brominated flame retardants (BFR) hinder the recycling of plastic waste, which has led to the development of various extraction processes to remove them. These processes can be further advanced by debrominating BFRs into less harmful compounds with potential commercial value, thus supporting the principles of a circular economy. Herein, Ni/Al 2 O 3 was employed for the catalytic debromination of tetrabromobisphenol A flame retardant in mixtures of H 2 O, isopropanol and NaOH at modest reaction temperatures. Activity experiments conducted in an autoclave indicated that studied catalyst exhibits impressive debromination activity and complete selectivity towards C−Br bond scission. The catalyst reduction temperature was found to correlate with debromination activity, with higher temperatures yielding improved performance. Debromination proceeded under H 2 and also under N 2 in protic solvents via transfer hydrogenation. Catalyst characterization, coupled with high-resolution mass-spectrometry product analytics and deuterium labelling, suggested that the enhanced catalytic activity can be attributed to the activation of the metal-support interface and subsequent interactions with adsorbed solvent molecules and associated dissociation products on the alumina support. Used experimental conditions also provided high tolerance against bromine poisoning of the catalyst, in contrast to reference debromination experiments conducted in toluene. The study demonstrates the capability of Ni/Al 2 O 3 as an efficient and affordable debromination catalyst in solvents of low environmental impact. Furthermore, the results provide additional insights into structure-activity relationships of supported nickel catalysts in protic solvents, which can be leveraged for the development of more efficient and sustainable dehalogenation and heteroatom removal processes for environmental applications. • Ni/Al 2 O 3 studied for TBBPA debromination in mixtures of H 2 O, isopropanol, and NaOH • Debromination activity correlated with the catalyst reduction temperature • High reduction temperatures activate the metal-support interface • Promoted activity was explained by solvent-reactant interactions at the interface • Debromination was feasible under both nitrogen and hydrogen atmospheres