The Unique CO Activation Effects for Boosting NH₃ Selective Catalytic Oxidation over CuO_x–CeO₂

Abstract

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.

Highly Efficient RuOx/NbOx-ZrOx Catalysts for Ammonia Removal via Tuning Acidic Active Species

“…This illustrated that for R/Z, the ammonia adsorption on the Lewis acid site was more stable than on the Bro̷nsted acid site. Note that a new peak of amide (−NH 2 ) appeared at 1568 cm –1 starting from 100 °C. , At the same time, the peak at 1265 cm –1 was red-shifted and a peak associated with −NH 2 also appeared at 1250 cm –1 . , The intensity of these peaks progressively increased in 100–200 °C and subsequently decreased after 200 °C. This might be due to the activation of NH 3 species adsorbed on Lewis and Bro̷nsted acid sites below 200 °C, which dissociates H and thus generated −NH 2 intermediate species (eq ).…”

Highly Selective Activation of C–H Bond and Inhibition of C–C Bond Cleavage by Tuning Strong Oxidative Pd Sites

“…The fitting accuracy could be testified by the R factor (0.0103). The Cu 2p XPS spectra (Figure S4b) indicated that the Cu species on the surface of the PdCu 1.2 /Al 2 O 3 catalyst all existed in the Cu 2+ state, considering that the binding energy centered at 953.8 and 933.7 eV attributed to the 2p 1/2 and 2p 3/2 of Cu 2+ species and the characteristic satellite peak at 939–946 eV. ,− From the Cu K-edge XANES spectra (Figure d), the absorption edge of PdCu 1.2 /Al 2 O 3 was very close to that of CuO. The Cu–O and Cu–Cu bonds were quite similar to those in the CuO standard sample in Figure e (the curve fit is demonstrated in Figure S6, and EXAFS fitting parameters are shown in Table S4), further proving the existence of CuO in PdCu 1.2 /Al 2 O 3 .…”

Ammonia Abatement via Selective Oxidation over Electron-Deficient Copper Catalysts

“…The activity of Cu/NCNT also outperformed those Cu catalysts (with the same nominal Cu loading of ca. 2 wt %) supported on other types of carbons, namely, pristine CNTs (p-CNT) and AC, or non-carbon materials (ZSM-5 and Al 2 O 3 ) at temperatures in the 160–220 °C range (Figure b), and it is among the most active Cu-based NH 3 -SCO catalysts reported in the open literature (Table S2) in terms of T 50 , i.e., the temperature to achieve 50% conversion of NH 3 . ,− Notably, Cu/CNT catalysts (even the relatively low-performance Cu/p-CNT sample) demonstrated clearly lower T 50 values than those Cu catalysts on non-CNTs materials, highlighting the superiority of CNT supports in NH 3 -SCO catalysis. In addition, the NH 3 -SCO activity of Cu/NCNT can be sustained without noticeable degradation even after degreening treatment at high reaction temperatures, i.e., at 220 °C for 8 h and then 300 °C for 8 h (Figure S2a).…”