A desirable catalyst for efficiently controlling NO x emissions often demands excellent SO2 poisoning resistance. Here, we introduced Ce to modify birnessite-MnO2 to obtain a Ce-MnO2 catalyst with excellent activity (T 90 = 85 °C) for the selective catalytic reduction of NO with NH3 (NH3-SCR) at low temperatures. Compared with the MnO2 catalyst that was severely deactivated after poisoning, the Ce-MnO2 catalyst showed a significant improvement in SO2 resistance with the NO conversion slightly decreasing from 100 to 95% at 150 °C. Physicochemical characterizations combined with density functional theory calculations indicated that the sulfates formed on Mn species and Ce species played different roles in the SCR reaction. The SO3 2– adsorbed on the surface of the MnO2 catalyst can react with NH3 to form ammonium sulfites, leading to the deactivation of the catalyst. However, the SO4 2– from Ce2(SO4)3 on the sulfated Ce-MnO2 catalyst existed as new adsorption sites of NH4 +, thus providing this catalyst with more acid sites. In addition, SO2 was preferentially adsorbed and oxidized on Ce species, thereby protecting the Mn active centers from sulfation and deactivation. This work reveals the mechanism of Ce in promoting SO2 resistance over birnessite-MnO2 from the perspective of sulfates.

Birnessite was synthesized by a simple hydrothermal method and used for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR). Physicochemical characterizations showed that the exposure of surface oxygen vacancies on birnessite was affected by heat treatment through the removal of water molecules. The sample heat-treated at a temperature of 150 °C, having the most exposed surface oxygen vacancies, exhibited excellent catalytic activity with 100% NO removal rate at 99 °C. In addition, density functional theory (DFT) calculations were combined with TPD techniques and in situ Fourier transform infrared (FTIR) to disclose the mechanism of NH3-SCR over birnessite. The results indicated that surface oxygen vacancies played a vital role in adsorption and oxidiation of reactant molecules and participated in the formation of acidic sites. This study shows that regulation of the exposure of surface oxygen vacancies of birnessite significantly improves its low-temperature NH3-SCR catalytic activity.

Oxygen reduction reaction (ORR) remains challenging due to its complexity and slow kinetics. In particular, Pt-based catalysts which possess outstanding ORR activity are limited in application with high cost and ease of poisoning. In recent years, nitrogen-doped graphene has been widely studied as a potential ORR catalyst for replacing Pt. However, the vague understanding of the reaction mechanism and active sites limits the potential ORR activity of nitrogen-doped graphene materials. Herein, density functional theory is used to study the reaction mechanism and active sites of nitrogen-doped graphene for ORR at the atomic level, focusing on explaining the important role of nitrogen species on ORR. The results reveal that graphitic N (GrN) doping is beneficial to improve the ORR performance of graphene, and dual-GrN-doped graphene can demonstrate the highest catalytic properties with the lowest barriers of ORR. These results provide a theoretical guide for designing catalysts with ideal ORR property, which puts forward a new approach to conceive brilliant catalysts related to energy conversion and environmental catalysis.

It is highly important to develop efficient and cheap photocatalysts for hydrogen production. Herein, a series of p–n heterojunction Mn 0.5 Cd 0.5 S/CuCo 2 S 4 has been successfully synthesized for the first time by the hydrothermal impregnation method. Mn 0.5 Cd 0.5 S/CuCo 2 S 4 loading with 12 wt % CuCo 2 S 4 shows the highest H 2 evolution rate of 15.74 mmol h –1 g –1 under visible light (λ ≥ 420 nm) irradiation, which is about 3.15 and 15.28 times higher than that of bare Mn 0.5 Cd 0.5 S (4.99 mmol h –1 g –1 ) and CuCo 2 S 4 (1.03 mmol h –1 g –1 ), respectively. In addition, it shows a relatively good stability during the five recycle tests, with about 20% loss of reaction rate compared to that of the first cycle. The superior photocatalytic performance is attributed to the effective separation and transfer of photogenerated charge carriers because of the formation of the p–n junction. The samples are systematically characterized by X-ray diffraction, ultraviolet–visible (UV–vis), diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy, photoluminescence, EIS, and so on. UV–vis and EIS show that CuCo 2 S 4 can effectively improve the visible light response of Mn 0.5 Cd 0.5 S/CuCo 2 S 4 and promote the electron transfer from CuCo 2 S 4 to the conduction band of Mn 0.5 Cd 0.5 S, so as to improve the photocatalytic efficiency. This study reveals that the p–n heterojunction Mn 0.5 Cd 0.5 S/CuCo 2 S 4 is a promising photocatalyst to explore the photocatalysts without noble metals.

To improve the catalytic combustion performance of toluene, a series of Co–CeO x monolith catalysts were synthesized by the citric acid sol–gel method. The results showed that the introduction of Co to CeO2 by the citric acid sol–gel method can effectively improve the catalytic performance in the reaction of toluene oxidation. Co1Ce2O x with the molar ratio of Co to Ce being 1:2 showed optimal activity and reached T 90 at 275 °C. In addition, Co1Ce2O x exhibited excellent adaptability under the various space velocities and concentration conditions, and it also revealed good thermal stability. The physical and chemical properties of the as-prepared catalysts were investigated by various technologies. The results showed that the combination of Co and Ce could induce a strong interaction between Co3O4 nanoparticles and CeO2 nanoparticles, exerting a synergistic promoting effect on the formation of oxygen vacancies, which subsequently enhances the active oxygen mobility and improves the catalytic oxidation performance. The possible mechanism of enhanced catalytic performance of Co1Ce2O x was also proposed.