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Photocatalytic CO2reduction (PCO2RR) is regarded as a promising means to mitigate the effects of climate change and current energy shortage. However, photocatalysis is not very effective because of the rapid recombination of photogenerated electron–hole pairs. S-scheme heterojunctions can effectively separate photogenerated carriers and significantly improve the redox ability of photocatalysts. In recent years, S-scheme heterojunction photocatalysts have become a popular topic of research because of their superior photocatalytic performance. This review examines the recent research advancements in S-scheme heterojunction photocatalysts. First, the principle of PCO2RR is briefly introduced. Various types of heterojunctions are introduced, the charge transfer mechanisms and characterization methods of S-scheme heterojunctions are described, and the applications of metal oxides, metal sulfides, and other S-scheme photocatalysts in CO2reduction are discussed and reviewed, respectively. In conclusion, the limitations and prospective directions of S-scheme heterojunction photocatalysts in CO2photoreduction are discussed to provide direction for the design of high-performance S-scheme heterojunction photocatalysts.

Solar-energy-driven CO2hydrogenation is a promising strategy to alleviate the climate crisis. Methane is a desirable derivative of CO2reduction. However, developing a photocatalyst for highly active and selective CH4generation remains challenging. Herein, we report a double Z-scheme Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S photocatalyst for efficient reduction of CO2to CH4. In situ characterization techniques confirmed that the charge migration mechanism in Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S promotes charge separation through double internal electric fields. As a result, the optimized C0.01B0.02C catalyst displayed a formation rate high up to 25.34 μmol g–1h–1and a selectivity of 96.52% of CH4. Moreover, the AQY of CO2conversion on C0.01B0.02C (1.84%) was almost 41 times higher than that of the bare CN. This study provides a novel perspective to develop heterojunction photocatalysts for selective CO2conversion to CH4.

Nd was used as the modifier to improve the NH3-selective catalytic reduction (SCR) performance of MnOxcatalyst used in NOxabatement. The results of the activity test indicated that MnNdOx-0.1 catalyst displayed remarkable catalytic activity and N2selectivity in the temperature range of 50–300 °C. Characterization results proved the enhanced reducibility and the facilitated NH3and NOxadsorption over MnNdOx-0.1 catalyst, accompanied by the existence of more Mn4+and surface adsorbed oxygen species over its surface. The results of the in situ diffuse reflectance infrared Fourier transform study pointed out that the NH3-SCR reaction over the MnNdOx-0.1 catalyst was mainly under the control of the Langmuir–Hinshelwood mechanism (≤100 °C); when the reaction temperature was over 200 °C, the Eley–Rideal mechanism was dominant. More adsorbed NOxand NH3species over the MnNdOx-0.1 catalyst, along with the activation effect of Nd on the adsorbed reactants, had a facilitation impact on the SCR reaction process over the MnNdOx-0.1 catalyst.

There is no time to delay reducing CO2to mitigate the greenhouse effect. For this purpose, electrochemical CO2reduction has rapidly developed and become an essential means of producing CO2derivatives. In recent years, two-dimensional materials have become the preferred choice as catalysts for electrochemical CO2reduction due to their superior properties. In this review, the fundamentals of electrochemical CO2reduction are introduced first. Then we discuss five typical two-dimensional materials, such as TMOs and TMDs, and explain the basic concept of electrochemical CO2reduction and the role of electrolytes. Finally, the development prospects of two-dimensional materials for electrochemical CO2reduction are put forward.

In this work, a ternary BiOCl/g-C3N4/Ag2CrO4composite with a dual Z-scheme heterojunction was prepared based on a g-C3N4photocatalyst and applied in the photocatalytic reduction of CO2. The optimal CH4and CO yields of the ternary composite catalyst could be achieved on BOC/CN/ACO-1% with 81.21 and 30.20 μmol g–1for 6 h, respectively, which was considerably enhanced compared to that for pure g-C3N4. The apparent quantum efficiency was achieved to be 2.68% for the BOC/CN/ACO-1% catalyst in the photoreduction of CO2at 420 nm. This performance enhancement resulted from constructing the dual Z-scheme and the improved light response, which had efficient charge migration and an excellent response to sunlight. This study provides a vital reference for developing dual Z-scheme heterojunction catalysts for the photocatalytic reduction of CO2.

The chemical experiment in this study is specifically created for undergraduate students studying energy and the environment. The target of the experiment is for students to comprehend the deactivation mechanism of the Ce/TiO2catalyst by oxides of phosphorus through practical experiments and enhance their knowledge of environmental technologies. More significantly, experiments can enable students to understand the poisoning mechanism of selective catalytic reduction (SCR) catalysts and understand various equipment for developing SCR catalysts. Fly ash containing oxides of phosphorus can deactivate SCR catalysts. The student group investigates and explains the poisoning effect of oxides of phosphorus on the Ce/TiO2catalyst in this study, using experimental and characterization techniques such as BET, XRD, H2-TPR, NH3-TPD, XPS, and DRIFT to support the findings. Then, the students’ grades in the laboratory experiments are determined by their performance in experimental operations, catalyst preparation, SCR activity, and poisoning effect analysis. It is encouraging that with this experiment, students may link their understanding of chemistry with practical operation, motivating them to carry out more research on SCR catalysts.

In this study, Bi was used as the modifier to elevate the performance of Ce/TiO2catalyst for selective catalytic reduction (SCR) of NOx with NH3. Experimental results indicated that the CeBi/TiO2catalyst with a Bi/Ce molar ratio of 0.15 exhibited excellent low-temperature SCR performance and SO2/H2O resistance compared with the Ce/TiO2catalyst. Characterization results revealed that the introduction of a proper amount of Bi to Ce/TiO2catalyst could generate more Ce3+and chemisorbed oxygen species on its surface, along with the enhanced reducibility and surface acidity. From the results of an in situ DRIFT study, the formation of more adsorbed NH3and NO2species could be detected, as a result, greatly facilitating the low-temperature NH3–SCR reaction over CeBi/TiO2-0.15 catalyst through the Langmuir–Hinshelwood route.