Insight into catalytic performance of chlorobenzene over phosphate-modified MnCeOx catalysts and suppression mechanism of polychlorinated byproducts

Efficient catalytic oxidation of chlorinated volatile organic compounds (CVOCs) with minimal polychlorinated byproducts remains challenging, and the positive effect of water vapor could facilitate it. Based on MnCeOx catalyst, the formation characteristics of polychlorinated benzenes, highly toxic polychlorinated byproducts (PCDD/Fs, PCBs, and PCNs), and PAHs during catalytic oxidation of chlorobenzene (CBCO) were systemically revealed. A phosphate-modified strategy (trimethyl phosphate, CePO 4 , and H 3 PO 4 ) was developed for promoting chlorine desorption and desirable inhibition on the polychlorinated byproducts. The trimethyl phosphate TMP-modified catalyst demonstrated highest CB conversion (T 90 = 205 °C), stability, and water resistance. A series of experiments involving D 2 O-TPD-MS, radical trapping, and DFT calculation provided complete insights into promotion effect of phosphate-modification strategy on the formation of Brønsted acid sites and the hydrolysis effect on H 2 O molecule. H 2 O performed an essential proton-rich environment and highly reactive water-source oxygen species (·OH), thereby improving dechlorination and deep oxidation properties. The generation pathways of polychlorinated byproducts mainly include reaction steps such as free radical coupling, dechlorination, and condensation. TMP-modified MnCeOx catalyst exhibited the strongest suppression effect on the formation of chlorinated and non-chlorinated byproducts, and their concentrations were decreased by 87.7 % (Polychlorinated benzenes), 82.2 %(PCDD/Fs), 8.5 %(PCBs), and 92.0 %(PAHs), respectively. This work demonstrates a valuable phosphate-modified strategy to suppress the generation of polychlorinated byproducts during CVOCs elimination process and improved the application potential of Mn-based catalysts under practical application conditions (containing water vapor). • The optimal P:Ce molar ratio s 0.1, and TMP performs best activity and stability. • Water vapor inhibits CB conversion and CO 2 selectivity but enhences HCl desorption. • TMP-modification notably inhibits the formation of PCDD/Fs (82.2 %), PAHs (92.0 %). • Promoting dechlorination and deep oxidation are major inhibition pathways.