V-Ce/Ti catalysts were prepared for the removal of naphthalene and NOx in the flue gas. The adverse effects of NH3 and NO on the naphthalene degradation were weakened on V-Ce/Ti, resulting in a decrease of only 2.5 % in COx selectivity. The formation of high molecular weight byproducts was also reduced. Besides the acid sites on the catalysts, Ce introduced new Brønsted basic sites, which could also adsorb and degrade naphthalene into naphthol effectively. With the separated active sites for naphthalene degradation and NO removal, the reaction between NH3 and the intermediates during the naphthalene degradation was also inhibited, decreasing the formation and accumulation of phthalimide. The oxidation of the intermediates was promoted by active V5+ introduced by Ce, inhibiting the transformation of the intermediates to higher molecular weight byproducts. Nearly 100 % conversion of naphthalene and NO, as well as 40.1 % of the COx selectivity were obtained on V-Ce/Ti.

Carbon monoxide (CO) has recently been considered an ideal reducing agent to replace NH3 in selective catalytic reduction of NOx (NH3-SCR). This shift is particularly relevant in diesel engines, coal-fired industry, the iron and steel industry, of which generate substantial amounts of CO due to incomplete combustion. Developing high-performance catalysts remain a critical challenge for commercializing this technology. The active sites on catalyst surface play a crucial role in the various microscopic reaction steps of this reaction. This work provides a comprehensive overview and insights into the reaction mechanism of active sites on transition metal- and noble metal-based catalysts, including the types of intermediates and active sites, as well as the conversion mechanism of active molecules or atoms. In addition, the effects of factors such as O2, SO2, and alkali metals, on NO reduction by CO were discussed, and the prospects for catalyst design are proposed. It is hoped to provide theoretical guidance for the rational design of efficient CO selective catalytic denitration materials based on the structure-activity relations.

In response to the stricter EU VII emission standards and the \"150 ℃ challenge\", selective catalytic reduction by ammonia (NH3-SCR) catalysts for motor vehicles are required to achieve high NO conversion below 200 °C. Compounding metal oxides with zeolites is an important strategy to design the low-temperature SCR catalysts. Here, we original prepared Cu-SSZ-13 @ MnGdOx (Cu-Z @ MGO), which achieved over 90% NO conversion and 95% N2 selectivity at 150 ℃. It has been demonstrated that a uniform mesoporous loaded layer of MGO grows on Cu-Z, and a recrystallization zone appears at the MGO-Cu-Z interface. We discover that the excellent low-temperature SCR activity derives from the strong metal oxide-zeolite interaction (SMZI) effects. The SMZI effects cause the anchor and high dispersion of MGO on the surface of Cu-Z. Driven by the SMZI effects, the Mn3+/Mn4+ redox cycle ensures the low and medium temperature-SCR activity and the Cu2+/Cu+ redox cycle guarantees the medium and high temperature-SCR activity. The introduction of MGO improves the reaction activity of -NH2 species adsorbed at Mn sites at 150 ℃, achieving a cycle of reduction and oxidation reactions at low temperatures. This strategy of inducing SMZI effects of metal oxides and zeolites paves a way for development of high-performance catalysts.

TiO2-supported V2O5 catalysts are commonly used in NOx reduction with ammonia due to their robust catalytic performance. Over these catalysts, it is generally considered that the active species are mainly derived from the vanadia species rather than the intrinsic structure of V-O-Ti entities, namely the interface sites. To reveal the role of V-O-Ti entities in NH3-SCR, herein, we prepared TiO2/V2O5 catalysts and demonstrated that V-O-Ti entities were more active for NOx reduction under wet conditions than the V sites (V=O) working alone. On the V-O-Ti entities, kinetic measurements and first principles calculations revealed that NH3 activation exhibited a much lower energy barrier than that on V=O sites. Under wet conditions, the V-O-Ti interface significantly inhibited the transformation of V=O to V-OH sites thus benefiting NH3 activation. Under wet conditions, meanwhile, the migration of NH4+ from Ti site neighboring the V-O-Ti interface to Ti site of the V-O-Ti interface was exothermic; thus, V-O-Ti entities together with neighboring Ti sites could serve as channels linking NH3 pool and active centers for activation of NH4+. This finding reveals that the V-O-Ti interface sites on V-based catalysts play a crucial role in NOx removal under realistic conditions, providing a new perspective on NH3-SCR mechanism.

Accordion-like Ti3C2Tx MXene supplied a possibility to construct two-dimensional composites with novel performance. In this paper, few-layered Ti3C2Tx MXene was created via a chemical etching strategy. The oxidation in-situ using a powerful alkaline solution resulted successfully in TiO2 nanocrystals grown on Ti3C2Tx nanosheets. The alkaline treatment adjusted terminations of the Ti3C2Tx MXene and controlled the oxidation degree by changing temperature. The ratio of Ti3C2Tx and TiO2 was finally optimized. Because of Ti3C2Tx nanosheets with well conductivity and excellent light absorption as well as TiO2 nanocrystal arrays on Ti3C2Tx nanosheets with a high specific surface area and more active sites, TiO2/Ti3C2Tx composites revealed excellent photocatalystic activity, especially for NO removal. The improvement of separation and transfer efficiency of phootogenerated carriers is ascribed to the microstructure of TiO2/Ti3C2Tx composites. The composite sample synthesized at 75 °C revealed the best NO removal efficiency, in which 70% of NO was removed at a concentration of 600 ppb. This study offers a new thought for preparing high performance MXene-based photocatalysts.

The role of phosphorus in metal oxide catalysts is still controversial. The precise tuning of the acidic and redox properties of metal oxide catalysts for the selective catalytic reduction in NOx using NH3 is also a great challenge. Herein, CeO2 catalysts with different degrees of phosphorylation were used to study the balance between the acidity and redox property by promoting and inhibiting effects of phosphorus. CeO2 catalysts phosphorylated with lower phosphorus content (5 wt%) exhibited superior NOx reduction performance with above 90% NOx conversion during 240-420 °C due to the balanced acidity and reducibility derived from the highest content of Brønsted acid sites on PO43- to adsorb NH3 and surface adsorbed oxygen species. Plenty of PO3- over CeO2 catalysts phosphorylated with the higher phosphorus content (≥ 10 wt%) significantly disrupted the balance between the acidity and the redox property due to the reduced acid/redox sites, which resulted in the less active NOx species. The mechanism of different structural phosphorus species (PO43- and PO3-) in promoting or inhibiting the NOx reduction over CeO2 catalysts was revealed. This work provides a novel method for qualitative and quantitative study of the relationship between acidity/redox property and activity of catalysts for NOx reduction.

The low-temperature SCR of NOx by NH3 is restricted in application since the catalysts is easily poisoned by sulfur and water. The Fe modified Mn-Co-Ce/TiO2/SiO2 catalysts synthesized via impregnation method and sulfating were evaluated for low-temperature NH3-SCR in the presence of SO2 and H2O. The calcination temperature and loading amounts of Mn, Fe, Co and Ce were optimized. Adding of Fe into S-MnCoCe/Ti/Si played an important role in resistance to sulfur and water poisoning. The optimal calcination temperature was 380 °C and the optical mass loading of the catalyst was 10% of Mn, 10% of Fe, 1% of Co and 4% of Ce. The optimal S-MnFeCoCe/Ti/Si catalyst maintained high NOx conversion of 93% at reaction temperature of 160 °C in the presence of 50 ppm SO2 and 10 vol% H2O. The catalytic activity did not continue to fall after two times of repeated used in the temperature range of 100-200 °C, indicating its excellent sulfur and water durability and stability in the presence of SO2 and H2O. The interaction between MnOx and FeOx enhanced sulfur and water durability rather than other bi-metal interactions. Furthermore, the mechanism of Fe improving resistance to SO2 and H2O was discussed.

Electrochemical removal of nitrogen oxides (NOx) by perovskite electrodes is a promising method due to its low cost, simple operation and no secondary pollution. In this study, a series of La0.8Sr0.2Mn1-xCuxO3 (x = 0, 0.05, 0.1 and 0.15) perovskites are fabricated as the improved electrodes of solid electrolyte cells (SECs) for NOx removal and the effects of Cu doping are investigated systematacially. Multiple characterization methods are carried out to analyze the physicochemical properties of perovskites firstly. Then the performances of cells based on various perovskites are evaluated by the measurements of electrochemical properties and NOx conversions. The results show that the Cu-doped electrode has more surface oxygen vacancies and a better redox property, thus having a higher NOx conversion and smaller polarization resistance. The electrode based on La0.8Sr0.2Mn0.9Cu0.1O3 has the maximum 70.8% NOx conversion and the lowest 36.3 Ω cm2 Rp value in the atmosphere of 1000 ppm NO at 700 °C. First-principle calculation reveals that the Cu-doped electrode is easier to form surface oxygen vacancy, while the surface oxygen vacancy plays an important role on electron transfer between electrode and NOx molecule. This study not only provides a new strategy to enhance the electrode performance for NOx removal in SECs but reveals the fundamental effect of Cu doping on the properties of La0.8Sr0.2MnO3 perovskites.

It is widely recognized that green infrastructures in urban ecosystems provides important ecosystem services, including air purification. The potential absorption of nitrogen oxides (NOx) by urban trees has not been fully quantified, although it is important for air pollution mitigation and the well-being of urban residents. In this study, four common tree species (Sophora japonica L., Fraxinus chinensis Roxb., Populus tomentosa Carrière, Sabina chinensis (L.)) in Beijing, China, were studied. The dual stable isotopes (15N and 18O) and a Bayesian isotope mixing model were applied to estimate the sources contributions of potential nitrogen sources to the roadside trees based on leaf and soil sampling in urban regions. The following order of sources contributions was determined: soil > dry deposition > traffic-related NOx. The capacity of urban trees for NOx removal in the city was estimated using a remote sensing and GIS approach, and the removal capacity was found to range from 0.79 to 1.11 g m-2 a-1 across administrative regions, indicating that 1304 tons of NOx could be potentially removed by urban trees in 2019. Our finding qualified the potential NOx removal by urban trees in terms of atmospheric pollution mitigation, highlighting the role of green infrastructure in air purification, which should be taken into account by stakeholders to manage green infrastructure as the basis of a nature-based approach.

Electrochemical removal of nitrogen oxides (NOx) by solid electrolyte cells (SECs) is a promising technology due to no required reductant. Herein, a series of La0.8Sr0.2Mn1-xNixO3 (0 ≤ x ≤ 0.5) perovskites were first synthesized and utilized as the electrode materials of SECs. The role of Ni substitution in electrode performance and NOx reduction mechanism were revealed by various experimental characterization and first-principle calculations. The results indicate that the moderate Ni substitution (x ≤ 0.3) increased the NOx conversion of electrodes while reduced the polarization resistance. The further investigation shows that this improvement was attributed to the more surface oxygen vacancies, better reducibility and higher Mn4+ proportion of the Ni-substituted perovskites. The electrochemical impedance spectroscopy (EIS) shows that these changes facilitated the NOx adsorption and dissociation processes on the electrode. According to first-principle calculations, the Ni-substituted perovskite had a lower formation energy of surface oxygen vacancy, while the NO molecule adsorbed on defect surface gained more electrons thus was easier to be reduced and dissociated. Finally, the electrode performance at different operating temperatures and the operational stability were verified.