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Sulfate adsorption is one of the factors that cause the poisoning of catalyst in the low-temperature NH3selective catalytic reduction reaction (NH3-SCR). In this paper, by controlling the co-adsorption time of SO2and O2at 150 °C, a range of sulfated MnCeOxcatalysts with different contents of metal sulfate species were prepared to reveal the influence of metal sulfate species content on the catalytic performances and reaction mechanisms at low temperature. The catalytic activity below 250 °C rapidly decreases with increasing metal sulfate species content. The results of characterizations shed light on the reduction of specific surface area, Mn4+and Ce3+content, and redox ability of MnCeOxowing to the formation of metal sulfate species. Further experiments reveal that metal sulfate species preferentially absorb on MnOxdomains rather than on CeO2domains, and the adsorbed metal sulfate species can suppress the Eley-Rideal and the Langmuir–Hinshelwood reaction mechanisms over the sulfated MnCeOx. All the above results are detrimental to the activity of sulfated MnCeOxin the low-temperature NH3-SCR reaction.

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Mn-based catalysts preferred in low-temperature selective catalytic reduction (SCR) are susceptible to SO2poisoning. The stubborn sulfates make insufficient O2activation and result in deficient reactive oxygen species (ROS) for activating reaction molecules. H2O has long been regarded as an accomplice to SO2, hastening catalyst deactivation. However, such a negative impression of the SCR reaction was reversed by our recent research. Here, we reported a H2O contribution over Mn-based SCR catalysts to counteract SO2poisoning through accessible O2activation, in which O2was synergistically activated with H2O to generate ROS for less deactivation and more expected regeneration. The resulting ROS benefited from the energetically favorable route supported by water-induced Eareduction and was actively involved in the NH3activation and NO oxidation process. Besides, ROS maintained high stability over the SO2+ H2O-deactivated γ-MnO2catalyst throughout the mild thermal treatment, achieving complete regeneration of its own NO disposal ability. This strategy was proven to be universally applicable to other Mn-based catalysts.

A single-atom Ce-modified α-Fe2O3catalyst (Fe0.93Ce0.07Oxcatalyst with 7% atomic percentage of Ce) was synthesized by a citric acid-assisted sol–gel method, which exhibited excellent performance for selective catalytic reduction of NOxwith NH3(NH3-SCR) over a wide operating temperature window. Remarkably, it maintained ∼93% NO conversion efficiency for 168 h in the presence of 200 ppm SO2and 5 vol % H2O at 250 °C. The structural characterizations suggested that the introduction of Ce leads to the generation of local Fe–O–Ce sites in the FeOxmatrix. Furthermore, it is critical to maintain the atomic dispersion of the Ce species to maximize the amounts of Fe–O–Ce sites in the Ce-doped FeOxcatalyst. The formation of CeO2nanoparticles due to a high doping amount of Ce species leads to a decline in catalytic performance, indicating a size-dependent catalytic behavior. Density functional theory (DFT) calculation results indicate that the formation of oxygen vacancies in the Fe–O–Ce sites is more favorable than that in the Fe–O–Fe sites in the Ce-free α-Fe2O3catalyst. The Fe–O–Ce sites can promote the oxidation of NO to NO2on the Fe0.93Ce0.07Oxcatalyst and further facilitate the reduction of NOxby NH3. In addition, the decomposition of NH4HSO4can occur at lower temperatures on the Fe0.93Ce0.07Oxcatalyst containing atomically dispersed Ce species than on the α-Fe2O3reference catalyst, resulting in the good SO2/H2O resistance ability in the NH3-SCR reaction.

CeO2/TiO2(denoted as CeTi) catalysts obtained by solid-phase impregnation behaved better in low-temperature selective catalytic reduction of NOxwith NH3(NH3-SCR) than that by conventional wet impregnation. To explore the main factors for activity distinction, the texture property, CeO2dispersion and structure changes of TiO2were comprehensively analyzed. It was found that surface changes of TiO2had a significant impact on the improved activity. From results of inductively coupled plasma atomic emission spectrometer (ICP-AES), diffuse reflectance UV–vis spectroscopy (UV–vis-DRS) and Raman, it was inferred that Ce ions were partially incorporated into TiO2lattice, accompanied with the formation of defects and vacancies during solid-phase impregnation. Accordingly, CeTi catalysts from solid-phase impregnation exhibited superiority in adsorption and activation of reactants. Further result from monitoring the preparation process indicated that the evolved NO played an important role in promoting Ce doping through depriving oxygen atoms on TiO2surface. The interaction between Ce and Ti was enhanced. The catalyst performed better in NH3-SCR, especially at low temperature, which testified the solid-phase impregnation could be an effective method to modulate interface structure for designing efficient catalyst.

•Manganese oxide (MnOx) with attractive feature of rich oxygen vacancy was constructed by a surfactant-assisted method.•MnOx-OV owned amorphous structure and large specific surface area (326 m2·g-1).•The NO conversion of MnOx-OV reached 100% at the low temperature window of 100–200 °C under a high space velocity of 120,000 mL·g-1·h-1.•Detailed experimental results proved that MnOx-OV obeyed the mechanism of Langmuir-Hinshelwood (L-H).