New Insights into the Formation of PBDD/Fs in the Incineration Flue Gas: The Activity of Typical Metal and Metalloid Species

The catalytic mechanisms underlying the formation of polybrominated dibenzo-<i>p</i>-dioxins and dibenzofurans (PBDD/Fs) have emerged as a critical environmental concern, particularly regarding the roles of metal- and metalloid-based catalysts. Although these catalysts are recognized as crucial agents for the formation of PBDD/Fs, there is still significant knowledge gaps in identifying the active species and quantifying their catalytic activities. This study systematically investigates four key reaction pathways governing PBDD/Fs formation: aromatic bromination, the Deacon reaction, the precursor, and the de novo synthesis process. Through comprehensive analysis of typical bromides and oxides in the municipal solid waste incineration (MSWI) flue gas, we found pronounced catalytic effects of iron, copper, manganese, and antimony species. Notably, their oxides exhibit excellent catalytic properties across all key pathways, with efficacy in facilitating the Deacon reaction, the precursor, and the de novo synthesis process. Comparative analyses with existing studies indicate that particles of Fe, Cu, Mn, and Sb exhibit different catalytic properties in the formation process of PBDD/Fs and polychlorinated dibenzo-<i>p</i>-dioxins and dibenzofurans (PCDD/Fs), which fundamentally distinguish their respective formation mechanisms. Importantly, our results systematically elucidate the specific catalytic functions of metal/metalloid species for the formation of PBDD/Fs.