In this study, Bi was used as the modifier to elevate the performance of Ce/TiO2 catalyst for selective catalytic reduction (SCR) of NOx with NH3. Experimental results indicated that the CeBi/TiO2 ...catalyst with a Bi/Ce molar ratio of 0.15 exhibited excellent low-temperature SCR performance and SO2/H2O resistance compared with the Ce/TiO2 catalyst. Characterization results revealed that the introduction of a proper amount of Bi to Ce/TiO2 catalyst 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 NH3 and NO2 species 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.
Photoreduction carbon dioxide to hydrocarbons has been recognized as one of the most promising and sustainable solutions to realize solar-to-chemical energy conversion and alleviate environmental ...pollution. Herein, we prepared g-C3N4 photocatalyst modified by NiS2 quantum dots as co-catalyst based on a seed-mediated hydrothermal process. The composite showed superior activity and stability in photocatalytic CO2 reduction. The highest CO evolution rate of 10.68 μmol h−1 g−1 was obtained on NSQD/CN-25 catalyst, which was 3.88-fold as high as unadulterated g-C3N4, and its apparent quantum efficiency (AQE) was 2.03% at 420 nm. During the photoconversion process, the possible intermediate products (such as COO-, CO2- and HCO3-) were detected by in situ FTIR analysis. Notably, the electron transfer from g-C3N4 to NiS2 QDs could effectively accelerate the separation of photoexcited electron–hole pairs. This work paves a new strategy toward designing cost-effective photocatalyst with high performance for photocatalytic CO2 reduction.
Lead salts poisoning was a great challenge for the catalysts application in selective catalytic reduction (SCR) reaction of NOx with NH3 in stationary sources. Herein, several typical transition ...metal (Cu, Co and Zr) oxides modified Mn-Ce/AC catalysts were prepared by impregnation method, and the effects of Cu, Co and Zr doping on resistance PbCl2 poisoning for the catalyst were investigated. The addition of three transition metal oxides improved the PbCl2 resistance of Mn-Ce/AC catalyst and maintained excellent low-temperature denitrification activity of the catalyst. The lead resistance performance of the three metal oxides followed: Cu > Co > Zr oxides. The NO conversion of Cu-doping catalyst after PbCl2 poisoning was only ca. 10% lower than that of fresh Mn-Ce/AC catalyst at 225 °C. Cu, Co and Zr doping could decrease the loss of specific surface area caused by poisoning, while Cu-doped catalyst showed lowest crystallinity of active components. Meanwhile, the contents of Mn4+ and chemisorbed oxygen in Cu-doped catalyst were higher than those in Co- or Zr-doped catalysts. Cu, Co and Zr doping improved the surface acidity and redox performance of the poisoned catalysts, with Cu-doped poisoned catalyst exhibiting nearly the same surface acidity and redox performance as the fresh Mn-Ce/AC catalyst. Furthermore, Cu doping could also improve NO adsorption and was in favor to the SCR process. Besides, in situ DRIFTS results showed that the catalytic reaction pathways of all the poisoned or modified catalysts were in accordance with both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Finally, a possible anti-PbCl2 poisoning mechanistic model of (Cu, Co and Zr) oxides modified on Mn-Ce/AC catalyst was proposed.
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•Cu-modified MC/AC catalyst showed best resistance to PbCl2 poisoning.•Transition metal oxides alleviated damage of PbCl2 to MC/AC structure.•Redox ability and acidity of PbCl2-poisoned catalyst were promoted by modifying.•NH3-SCR reaction on PbCl2-poisoned catalyst followed L-H and E-R mechanism.
Metal oxide-based Z-scheme heterojunction photocatalyst can effectually separate electrons and holes and simultaneously ensure that photocatalysts can maintain appropriate conduction band (CB) and ...valence band (VB) positions, thus maintaining a strong redox capacity. This article introduced the mechanism and types of Z-scheme heterojunction photocatalysts. Nevertheless, direct Z-scheme photocatalytic mechanism was gradually replaced by new S-scheme heterojunction mechanism. Thus, this review also briefly discussed the improved Z-scheme mechanism, that is, S-scheme heterojunction, so that the mechanism of the charge transfer process could be understood more intuitively and clearly. Then we emphatically summarized the applications of different types of heterojunctions in the field of photocatalysis, ranging from environmental remediation to energy conversion. In addition, several typical traditional methods and new strategies for preparing Z-scheme heterojunctions were summed up. Finally, the breakthrough and development prospect of Z-scheme heterojunction were discussed.
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•The mechanism and types of Z-scheme heterojunction photocatalysts were introduced.•The applications of different types of heterojunctions in the field of photocatalysis were summarized.•The breakthrough and development prospect of Z-scheme heterojunction were discussed.
•The chemical deactivation mechanisms of Mn-based SCR catalysts are analyzed.•The methods for improving the poisoning resistance of Mn-based SCR catalysts are discussed.•The regeneration of ...manganese-based SCR catalysts are probed.
As a high-performance technology currently developed, selective catalytic reduction (SCR) of NOx with NH3 has been universally employed to remove NOx from stationary sources. The traditional applied V2O5-based catalysts are proverbially applicable for medium-temperature range but unsuitable for NH3-SCR operated in the low-temperature conditions. Through massive research of theory and experiments, low-temperature NH3-SCR has drawn substantial attention due to the extensive demand for industrial furnaces and their energy-saving characteristics. During the past few years, Mn-based catalysts have been extensively investigated in NH3-SCR reaction for their high catalytic activity at low temperatures. In this paper, the deactivation mechanisms of SO2, H2O, alkali/alkaline earth metals (K, Na, Ca), and heavy metals (As, Pb, etc.) over Mn-based catalysts are discussed in detail. This review summarizes the methods to improve the anti poisoning of manganese-based catalysts, such as specific preparation methods, adding active components, doping additions and carrier modification, etc. Finally, different regeneration methods of poisoning caused by various poisons were analyzed and compared The obtained results can help researchers provide insight into the optimization of Mn-based SCR catalysts.
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•30% In2S3/NiAl-LDH exhibited the best photocatalytic performance.•Efficient separation of photogenerated electron-hole pairs.•A perfect band matching and efficient internal charge ...transfer within the n-n junction.
A novel ball-flower In2S3/NiAl-LDH heterojunction photocatalyst was synthesized via a simple one-step hydrothermal approach for the first time and applied for CO2 photocatalytic reduction. The In2S3/LDH composites exhibited excellent photocatalytic performance and stability in CO2 photoreduction in water under the irradiation of simulated solar light. Experimental results indicated that the 30% In2S3/NiAl-LDH heterojunction photocatalyst exhibited the best photocatalytic performance. And the maximum CH4 yields of 36.1 μmol/(h·g-cat) under 7 h visible light irradiation was about 2.5 and 3.5 times of unadulterated LDH and In2S3. The enhanced photocatalytic performance of 30% In2S3/NiAl-LDH catalyst was due to the highly-efficient separation of photogenerated electron-hole pairs, its larger specific surface area and stronger visible-light absorption capacity.
Facilitating the separation of photoexcited electron-hole pairs and enhancing the migration of photogenerated carriers are essential in photocatalytic reaction. CoS/g-C3N4/NiS ternary photocatalyst ...was prepared by hydrothermal and physical stirring methods. The optimized ternary composite achieved a hydrogen yield of 1.93 mmol g−1 h−1, 12.8 times that of bare g-C3N4, with an AQE of 16.4% at 420 nm. The enhanced photocatalytic activity of CoS/g-C3N4/NiS was mainly ascribed to the synergistic interaction between the Z-scheme heterojunction constructed by CoS and g-C3N4 and the NiS co-catalyst featuring a large amount of hydrogen precipitation sites, which realized the efficient separation and migration of photogenerated carriers. In addition, the CoS/g-C3N4/NiS heterojunction-co-catalyst system exhibited excellent photocatalytic stability and recyclability.
•CoS/g-C3N4/NiS ternary photocatalyst was prepared by hydrothermal and physical stirring methods.•A large amount of hydrogen precipitation sites are available on CoS/g-C3N4/NiS ternary photocatalyst.•The Z-scheme heterojunction combined with the co-catalyst promoted the separation and migration of photogenerated carriers.
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•Direct Z-scheme FeWO4/NiAl-LDH heterostructure was fabricated.•The 10%FWLDH possessed the optimal photocatalytic CO yield.•The effective separation of the light-induced e-/h+ pairs ...was available on FWLDH composite.
In recent years, photocatalytic reduction of carbon dioxide technology has been considered as an effective approach to moderate the energy crisis. In order to achieve efficient reduction of CO2, direct Z-scheme heterostructure composed of NiAl-LDH flower-like sphere and FeWO4 nanoflakes (FWLDH) were obtained through a facile hydrothermal strategy. The prepared FWLDH photocatalysts revealed outstanding performance for CO2 photoreduction to CO under the irradiation of visible light. The 10%FWLDH possessed the optimal photocatalytic CO yield (5 μmol· g−1·h−1), reaching up to 2.4 folds higher than that of pristine LDH (2.1 μmol·g−1·h−1). In addition, the CO selectivity was more than 93% over hydrogen evolution from the side reaction of water reduction. Finally, EPR characterization indicated that the electron transfer mechanism of FWLDH catalyst conformed to the Z-scheme pattern. The effective separation of the light-induced electron-hole pairs and the enhancement of the photoelectron reduction ability at the NiAl-LDH conduction band were the reasons for the prominent improvement of the photocatalytic performance of NiAl-LDH. This research could provide a novel perspective for designing photocatalyst with high efficiency for CO2 photoreduction.
Bi2O3/g-C3N4 nanoscale composites with a Z-scheme mechanism were successfully synthesized by high temperature calcination combined with a hydrothermal method. These synthesized composites exhibited ...excellent photocatalytic performance, especially the 40 wt% Bi2O3/g-C3N4 composite, which produced about 1.8 times the CO yield of pure g-C3N4. The obtained products were characterized by X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and so on. Characterization results revealed that Bi ions had well covered the surface of g-C3N4, thus restraining the recombination of electron–hole pairs and resulting in a stronger visible-light response and higher CO yield. In addition, the electron transfer process through the Z-scheme mechanism also promoted the photocatalytic activity.
Ammonia selective catalytic reduction (NH3-SCR) of nitrogen oxides is an effective and well-established technology for NOx removal, but current commercial denitrification catalysts based on ...V2O5-WO3/TiO2 have some obvious disadvantages, including narrow operating temperature windows, toxicity, poor hydrothermal stability, and unsatisfied SO2/H2O tolerance. To overcome these drawbacks, it is imperative to investigate new types of highly efficient catalysts. In order to design catalysts with outstanding selectivity, activity, and anti-poisoning ability, core-shell structured materials have been widely applied in the NH3-SCR reaction, which exhibits numerous advantages including the large surface area, the strong synergy interaction of core-shell materials, the confinement effect, and the shielding effect from the shell layer to protect the core. This review summarizes recent developments of core-shell structured catalysts for NH3-SCR, including basic classification, synthesis methods, and a detailed description of the performance and mechanisms of each type of catalyst. It is hoped that the review will stimulate future developments in NH3-SCR technology, leading to novel catalyst designs with improved denitrification performance.
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•Core-shell structured materials have been widely applied in the NH3-SCR reaction.•Core-shell structured SCR catalyst shows high catalytic activity.•Core-shell structure could protect the active components from deactivation.
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