Poisoning mechanism of HCl over a Ru-based catalyst for toluene oxidation

It is challenging for catalytic oxidation of volatile organic compounds (VOCs) due to the existence of HCl in municipal solid waste incineration flue gases. A thorough probe into the deactivation mechanism is imperative but still lacking. Herein, the poisoning effect of gaseous HCl on a Ru-based catalyst for toluene catalytic oxidation was investigated. Toluene conversion and CO2 selectivity decreased dramatically from 89.3 % and 93.8 % to 15.0 % and 8.0 %, respectively at 250 °C under HCl atmosphere. HCl led to a reduction of low-temperature redox properties, as well as a decrease of BET surface area, surface oxygen content and mobility, resulting in a loss of catalytic activity. HCl combined with active Ru and Mn, thereby restricting the electron transfer between Ru4+ and Mn2+. Moreover, HCl could be oxidized by active oxygen species to form Cl• radical, which subsequently reacted with toluene oxidation intermediates, resulting in the generation of chlorinated compounds, such as chlorobenzene, dichlorobenzene, carbon tetrachloride, and benzyl chloride. These harmful chlorinated compounds predominantly deposited on catalyst surface. The protective role of H2O against HCl poisoning was mainly attributed to the competitive adsorption between H2O and Cl ions, the washing effect, and the promoting of intermediates oxidation and oxygen activation. It is noteworthy that during toluene oxidation in the presence of HCl + H2O, a detectable level of 0.048 ng I-TEQ/Nm3 PCDD/Fs was observed in the off-gas.