Catalytic removal of CO from industrial flue gases has been an increasing concern. One attempt is utilizing the tail part of an SCR unit to oxidize abundant CO and trace “slip NH3” synergistically. Herein, Ru/Cu-SSZ-13 was developed to conduct the oxidation of CO and the selective catalytic oxidation of NH3 (NH3-SCO) simultaneously and showed 10 times higher reaction rates than Ru/SSZ-13 on both oxidations. The RuO2 (110) surface was highly active for CO oxidation and NH3 dehydrogenation but would turn insensitive due to the accumulation of adsorbed NO species (NOcus), which derived from the peroxidation during NH3 dehydrogenation. With the assistance of Cu-SSZ-13, generated NOcus could be consumed in an internal SCR route conducted by the activated Cu2+/Cu+ redox cycle, which made NOcus available for the NH3 preferential oxidation rather than the blocked reactive surface. Also, it promoted NH3 transformation on the Cu-SSZ-13 side and boosted the regeneration of Ru-active sites from occupation by NOcus to enable simultaneous CO oxidation. Therefore, the reactivity of RuO2 was boosted after minimizing the interference between the transformation paths of CO and NH3. Furthermore, due to the high NH3-SCO sensitivity of Ru/Cu-SSZ-13, the trace “slip NH3” can be preferentially removed from CO-rich flue gas.

Slip NH3 is a priority pollutant of concern to be removed in various flue gases with NO x and CO after denitrification using NH3-SCR or NH3-SNCR, and the simultaneous catalytic removal of NH3 and CO has become one of the new topics in the deep treatment of such flue gases. Synergistic catalytic oxidation of CO and NH3 appears to be a promising method but still has many challenges. Due to the competition for active oxidizing species, CO was supposed to hinder the NH3 selective catalytic oxidation (NH3-SCO). However, it is first found that CO could significantly promote NH3-SCO over the CuO x –CeO2 catalyst. The NH3 conversion rates increased linearly with CO concentrations in the range of 180–300 °C. Specifically, it accelerated by 2.8 times with 10,000 ppm CO inflow at 220 °C. Mechanism studies found that the Cu–O–Ce solid solution was more active for CO oxidation, while the CuO x species facilitated the NH3 dehydrogenation and mitigated the competition of NH3 and CO, further stabilizing the promotion effects. Gaseous CO boosted the generation of active isolated oxygen atoms (Oi) by actuating the Cu+/Cu2+ redox cycle. The enriched Oi facilitated oxidation of NH3 to NO and was conducive to the NH3-SCO via the i-SCR approach. This study tapped the potential of CO for promoting simultaneous catalytic oxidation of coexisting pollutants in the flue gas.

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Direct sulfidation using a high concentration of H2S (HC-H2S) has shown potential for heavy metals removal in various acidic effluents. However, the lack of a smooth method for producing HC-H2S is a critical challenge. Herein, a novel short-process hydrolysis method was developed for the on-site production of HC-H2S. Near-perfect 100% efficiency and selectivity were obtained via CS2 hydrolysis over the ZrO2-based catalyst. Meanwhile, no apparent residual sulfur/sulfate poisoning was detected, which guaranteed long-term operation. The coexistence of CO2 in the products had a negligible effect on the complete hydrolysis of CS2. H2S production followed a sequential hydrolysis pathway, with the reactions for CS2 adsorption and dissociation being the rate-determining steps. The energy balance indicated that HC-H2S production was a mildly exothermic reaction, and the heat energy could be maintained at self-balance with approximately 80% heat recovery. The batch sulfidation efficiencies for As­(III), Hg­(II), Pb­(II), and Cd­(II) removal were over 99.9%, following the solubilities (K sp) of the corresponding metal sulfides. CO2 in the mixed gas produced by CS2 hydrolysis did not affect heavy metals sulfidation due to the presence of abundant H+. Finally, a pilot-scale experiment successfully demonstrated the practical effects. Therefore, this novel on-site HC-H2S production method adequately achieved heavy metals removal requirements in acidic effluents.