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Photocatalytic CO2 conversion to hydrocarbon products is an appealing strategy for solving the escalating problem of energy scarcity and global warming. Although there has been much research to date, most of it has been aimed at increasing yields rather than product selectivity. However, regulating product selectivity is vital to achieve controlled hydrocarbon products. Particularly, the C2+ products have a higher added value than C1 products (e.g., methane, carbon monoxide, methanol), so it makes more economic sense to increase the selectivity of C2+ products. This review provides a concise overview of the latest developments in the photocatalytic conversion of CO2 into multi-carbon compounds. The available literature has been organized according to the primary factors that determine the selectivity of C2+ products, including vacancy engineering, co-catalyst loading, doping engineering, and surface plasmon resonance effect. Plausible conjectures concerning methods to enhance the selectivity of C2+ products have been presented, with a focus on synthesizing the existing empirical knowledge derived from theoretical and experimental data. [ABSTRACT FROM AUTHOR]

Effectively harnessing solar energy for the conversion of CO2 into valuable chemical energy presents a viable solution to address energy scarcity and climate change concerns. Nonetheless, the limited light absorption and sluggish charge kinetics significantly hinder the photoreduction of CO2. In this study, we employed a facile sol–gel method combined with wetness impregnation to synthesize Cu-doped TiO2 coated with NiOx nanoparticles. Various characterizations verified the successful incorporation of Cu ions into the TiO2 crystal lattice and the formation of NiOx co-catalysts within the composites. The optimal performance attained with CTN-0.5 demonstrates an output of 11.85 μmol h−1 g−1 for CO and 9.51 μmol h−1 g−1 for CH4, which represent a 4.4-fold and 15.6-fold increase, respectively, compared to those achieved with pure TiO2. The induced Cu defect band broadens the light absorption by decreasing the conduction band edge of TiO2, while NiOx upshifts the valence band of TiO2 because of the interaction of valence orbitals. Light irradiation EPR and FTIR tests suggest that the collaboration of CuOx and NiOx promotes the formation of oxygen vacancies/defects and a rapid charge transfer pathway, thereby provides numerous active sites and electrons to enhance CO2 photoreduction performance. [ABSTRACT FROM AUTHOR]

In this research, a ternary Cu-CuTCPP/Cu2O/CoAl-LDH composite with a dual Z-scheme heterostructure was fabricated based on a Cu2O photocatalyst and applied in photocatalytic CO2 reduction. The physicochemical properties of the prepared catalysts and the possible reaction mechanism in CO2 reduction were analyzed and studied by various characterization methods. The activity of CO2 reduction significantly increased, especially forming C2 products. The optimal yield of C2H4 and C2H6 reached 1.56 and 1.92 μmol g−1 h−1 respectively, which was 14.45 and 17.45 times that from using the Cu2O monomer. In addition, the selectivity of C2 products reached 37.4%. The satisfactory C2 yield was mainly due to the fact that Cu1+δ2(COO)3 nodes in Cu-CuTCPP contained adjacent Cu sites, which effectively promoted the C–C coupling reaction. Moreover, the dual Z-scheme heterojunction stimulated the separation of photogenerated electron–hole pairs and diminished the recombination rate. This work contributes to the development of novel photocatalysts with a dual Z-scheme heterojunction and facilitates the generation of valuable C2 products. [ABSTRACT FROM AUTHOR]

The photocatalytic reduction of CO2 to hydrocarbons is expected to simultaneously alleviate the energy crisis and greenhouse effect. Herein, the ternary BiOCl/C/Cu2O catalysts with different mass ratios were compounded using a simple hydrothermal method, revealing better photocatalytic activity than the monomer. In the absence of sacrificial agents and photosensitizers, 25% BiOCl/C/Cu2O showed optimal photocatalytic performance. The CO and CH4 yields over 25% BiOCl/C/Cu2O reached 26.77 and 9.86 μmol g−1 h−1, which is 2.9 and 8.7 times higher than that of the pristine Cu2O, respectively. The ameliorative activity can be attributed to the construction of the Z-scheme heterostructure and carbon layer, which are conducive to the transfer and separation of photogenerated carriers. This study offers valuable references for the design and investigation of a Z-scheme heterojunction using a carbon layer as an electron transfer medium. [ABSTRACT FROM AUTHOR]

The photocatalytic reduction of CO2 to hydrocarbons is expected to simultaneously alleviate the energy crisis and greenhouse effect. Herein, the ternary BiOCl/C/Cu2O catalysts with different mass ratios were compounded using a simple hydrothermal method, revealing better photocatalytic activity than the monomer. In the absence of sacrificial agents and photosensitizers, 25% BiOCl/C/Cu2O showed optimal photocatalytic performance. The CO and CH4 yields over 25% BiOCl/C/Cu2O reached 26.77 and 9.86 μmol g−1 h−1, which is 2.9 and 8.7 times higher than that of the pristine Cu2O, respectively. The ameliorative activity can be attributed to the construction of the Z-scheme heterostructure and carbon layer, which are conducive to the transfer and separation of photogenerated carriers. This study offers valuable references for the design and investigation of a Z-scheme heterojunction using a carbon layer as an electron transfer medium. [ABSTRACT FROM AUTHOR]

Herein, the origin and evolution mechanism of N2O formation over the MnFeOx spherical catalyst were investigated in detail, accompanied by a comparison analysis of pristine MnOx and FeOx catalysts. The results showed that the MnFeOx catalyst possessed higher catalytic activity but poorer N2 selectivity than the sole oxide catalysts, and the N2O concentration could even reach 300 ppm over 175 °C. Further activation tests under separate NH3/NO oxidation conditions revealed the N2O accumulation of the MnFeOx catalyst that was primarily derived from the NSCR pathway below 150 °C and then gradually turned to NH3 over-oxidation with temperature. The coupling of Mn and Fe cations induced electron migration and released more Mn4+ and Os, contributing to the upgraded redox capacity, which served as the inherent motivation of high activity but poor N2 selectivity over the MnFeOx catalyst. For the NH3 over-oxidation pathway, both gaseous O and catalyst oxygen acted as the oxidizers, and the double –NH2/NH species with the assistance of O was deemed as the restricted step for N2O generation. For the NSCR pathway, the byproduct N2O was generated through both E–R and L–H mechanisms, and the former contributed to more N2O. In addition, the kinetic analysis further verified the obtained conclusions. Finally, a possible mechanism model of N2O origins over the MnFeOx catalyst was proposed. [ABSTRACT FROM AUTHOR]

In recent years, heterojunction materials bonded by interlayer van der Waals forces have grown into a very large family. These van der Waals heterostructures have promising applications in photocatalysis due to their suitable energy band structures and optical properties. In this paper, the latest research progress on van der Waals heterojunction materials in photocatalytic systems is reviewed, including the photocatalytic theories and the basic principles of heterojunctions in photocatalysis. The construction, design, and photocatalytic properties and applications of van der Waals heterostructures are described in detail. The prospects and challenges of van der Waals heterojunctions in photocatalytic applications in the future are also presented. This review is intended to offer enlightening guidance for the efficient use of solar energy systems, efficient photocatalysis and early industrialization in the future. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction with NH3 (NH3-SCR) was the most efficient approach to mitigate the emission of nitrogen oxides (NOx). Although the conventional manganese oxide-based catalyst had gradually become a kind of principal catalyst for the low-temperature NH3-SCR reaction, there were still numerous defects. The growing demands for extensive operation temperature scope, strong SO2 tolerance, and excellent catalytic activity had boosted the development of novel manganese oxide-based catalysts. In this review, three forms of manganese oxide-based catalysts were introduced in detail, including single manganese oxide catalysts, composite manganese oxide-based catalysts, and supported manganese oxide-based catalysts. The surface acidity and redox properties of manganese oxide-based catalysts could be strengthened by optimizing the preparation methods, exposing specific crystal planes, and constructing multiple active centers and sacrificial sites, which improved the SCR performance and anti-poisoning properties of catalysts. Secondly, we briefly summarized the NH3-SCR reaction mechanism of manganese oxide-based catalysts, including the Eley–Rideal (E–R) mechanism and the Langmuir–Hinshelwood (L–H) mechanism. Finally, several overtures were proposed for the future research directions of manganese oxide-based catalysts for NH3-SCR reaction, hoping to narrow the gap between the novel manganese oxide-based catalysts and the actual demands and realize commercialized application in the nearest future. [ABSTRACT FROM AUTHOR]

Promoting the separation of photogenerated electron–hole pairs and enhancing the charge carrier transfer are critical in photocatalysis. In our work, a ball-flower-like NiS/Zn3In2S6/g-C3N4 photocatalyst fabricated by a hydrothermal method exhibited superior performance for photocatalytic water splitting. The optimized 2.0% NiS/Zn3In2S6/g-C3N4 rivaled noble metal based Pt/g-C3N4 and showed an apparent quantum efficiency (AQE) of 24.3% at 420 nm, with a H2 yield of 4.135 mmol g−1 h−1, which was 30.4 and 9.51 times that of pure g-C3N4 and binary Zn3In2S6/g-C3N4 composites, respectively. The experimental and characterization results suggested that the heterojunction formed between Zn3In2S6/g-C3N4 and the decorating NiS co-catalyst cooperatively suppressed the electron–hole recombination and facilitated the charge carrier transfer, thus resulting in significant improvement of the H2 evolution performance. Moreover, the increased specific surface area and the enhanced visible-light absorption also contributed to superior water splitting performance. The prepared ternary catalytic system with the heterojunction and non-noble metal co-catalyst has great potential as an alternative to noble metals for achieving cost-efficient water splitting systems. [ABSTRACT FROM AUTHOR]

Z-Scheme MoS2/g-C3N4 heterojunction photocatalysts were fabricated using a hydrothermal deposition procedure together with a calcination route, and then applied for CO2 photoreduction. Experimental results indicated that the 10% MoS2/g-C3N4 heterojunction displayed the best photocatalytic performance. Furthermore, the maximum CO yields of 58.59 μmol (g-cat)−1 under 7 h-visible light irradiation was up to 2.94 times that of the unadulterated g-C3N4. The enhanced photocatalytic performance of 10% MoS2/g-C3N4 catalyst was due to the favored visible light response, the efficient separation of photogenerated electron–hole pairs as well as its larger specific surface area. [ABSTRACT FROM AUTHOR]

It was well recognized that Pb had a poisoning effect on a SCR catalyst. In this study, the deactivation mechanism of Pb on the Ce/TiO2 catalyst was investigated based on the characterization results of TPD and in situ DRIFT studies. It was found that the addition of Pb on the Ce/TiO2 catalyst not only inhibited the adsorption and activation of NH3 species, but also led to the decrease of the activity of adsorbed NH3 species in the SCR reaction. The adsorption of NOx species and the oxidation of NO by O2 over the Ce/TiO2 catalyst were also suppressed by the addition of Pb, while the reactivity of adsorbed NO2 species did not decrease. Moreover, the results revealed that the NH3-SCR reaction over the Ce/TiO2 catalyst followed both the E–R and L–H mechanisms, while the NH3-SCR reaction over Ce/TiO2-Pb was mainly controlled by the L–H mechanism. The contributions of the L–H mechanism to the SCR reactions over Ce/TiO2 and Ce/TiO2-Pb decreased with increasing reaction temperature. The deactivation of Ce/TiO2-Pb was mainly attributed to the suppressed NH3 adsorption and activation, accompanied by the inhibited NO oxidation and the decrease of Brønsted acid sites. [ABSTRACT FROM AUTHOR]

Effectively harnessing solar energy for the conversion of CO 2 into valuable chemical energy presents a viable solution to address energy scarcity and climate change concerns. Nonetheless, the limited light absorption and sluggish charge kinetics significantly hinder the photoreduction of CO 2 . In this study, we employed a facile sol-gel method combined with wetness impregnation to synthesize Cu-doped TiO 2 coated with NiO x nanoparticles. Various characterizations verified the successful incorporation of Cu ions into the TiO 2 crystal lattice and the formation of NiO x co-catalysts within the composites. The optimal performance attained with CTN-0.5 demonstrates an output of 11.85 μmol h -1 g -1 for CO and 9.51 μmol h -1 g -1 for CH 4 , which represent a 4.4-fold and 15.6-fold increase, respectively, compared to those achieved with pure TiO 2 . The induced Cu defect band broadens the light absorption by decreasing the conduction band edge of TiO 2 , while NiO x upshifts the valence band of TiO 2 because of the interaction of valence orbitals. Light irradiation EPR and FTIR tests suggest that the collaboration of CuO x and NiO x promotes the formation of oxygen vacancies/defects and a rapid charge transfer pathway, thereby provides numerous active sites and electrons to enhance CO 2 photoreduction performance.

In this research, a ternary Cu-CuTCPP/Cu 2 O/CoAl-LDH composite with a dual Z-scheme heterostructure was fabricated based on a Cu 2 O photocatalyst and applied in photocatalytic CO 2 reduction. The physicochemical properties of the prepared catalysts and the possible reaction mechanism in CO 2 reduction were analyzed and studied by various characterization methods. The activity of CO 2 reduction significantly increased, especially forming C2 products. The optimal yield of C 2 H 4 and C 2 H 6 reached 1.56 and 1.92 μmol g -1 h -1 respectively, which was 14.45 and 17.45 times that from using the Cu 2 O monomer. In addition, the selectivity of C2 products reached 37.4%. The satisfactory C2 yield was mainly due to the fact that Cu 1+ δ 2 (COO) 3 nodes in Cu-CuTCPP contained adjacent Cu sites, which effectively promoted the C-C coupling reaction. Moreover, the dual Z-scheme heterojunction stimulated the separation of photogenerated electron-hole pairs and diminished the recombination rate. This work contributes to the development of novel photocatalysts with a dual Z-scheme heterojunction and facilitates the generation of valuable C2 products.

The photocatalytic reduction of CO 2 to hydrocarbons is expected to simultaneously alleviate the energy crisis and greenhouse effect. Herein, the ternary BiOCl/C/Cu 2 O catalysts with different mass ratios were compounded using a simple hydrothermal method, revealing better photocatalytic activity than the monomer. In the absence of sacrificial agents and photosensitizers, 25% BiOCl/C/Cu 2 O showed optimal photocatalytic performance. The CO and CH 4 yields over 25% BiOCl/C/Cu 2 O reached 26.77 and 9.86 μmol g -1 h -1 , which is 2.9 and 8.7 times higher than that of the pristine Cu 2 O, respectively. The ameliorative activity can be attributed to the construction of the Z-scheme heterostructure and carbon layer, which are conducive to the transfer and separation of photogenerated carriers. This study offers valuable references for the design and investigation of a Z-scheme heterojunction using a carbon layer as an electron transfer medium.

Selective catalytic reduction with NH 3 (NH 3 -SCR) was the most efficient approach to mitigate the emission of nitrogen oxides (NO x ). Although the conventional manganese oxide-based catalyst had gradually become a kind of principal catalyst for the low-temperature NH 3 -SCR reaction, there were still numerous defects. The growing demands for extensive operation temperature scope, strong SO 2 tolerance, and excellent catalytic activity had boosted the development of novel manganese oxide-based catalysts. In this review, three forms of manganese oxide-based catalysts were introduced in detail, including single manganese oxide catalysts, composite manganese oxide-based catalysts, and supported manganese oxide-based catalysts. The surface acidity and redox properties of manganese oxide-based catalysts could be strengthened by optimizing the preparation methods, exposing specific crystal planes, and constructing multiple active centers and sacrificial sites, which improved the SCR performance and anti-poisoning properties of catalysts. Secondly, we briefly summarized the NH 3 -SCR reaction mechanism of manganese oxide-based catalysts, including the Eley-Rideal (E-R) mechanism and the Langmuir-Hinshelwood (L-H) mechanism. Finally, several overtures were proposed for the future research directions of manganese oxide-based catalysts for NH 3 -SCR reaction, hoping to narrow the gap between the novel manganese oxide-based catalysts and the actual demands and realize commercialized application in the nearest future.

Promoting the separation of photogenerated electron-hole pairs and enhancing the charge carrier transfer are critical in photocatalysis. In our work, a ball-flower-like NiS/Zn 3 In 2 S 6 /g-C 3 N 4 photocatalyst fabricated by a hydrothermal method exhibited superior performance for photocatalytic water splitting. The optimized 2.0% NiS/Zn 3 In 2 S 6 /g-C 3 N 4 rivaled noble metal based Pt/g-C 3 N 4 and showed an apparent quantum efficiency (AQE) of 24.3% at 420 nm, with a H 2 yield of 4.135 mmol g -1 h -1 , which was 30.4 and 9.51 times that of pure g-C 3 N 4 and binary Zn 3 In 2 S 6 /g-C 3 N 4 composites, respectively. The experimental and characterization results suggested that the heterojunction formed between Zn 3 In 2 S 6 /g-C 3 N 4 and the decorating NiS co-catalyst cooperatively suppressed the electron-hole recombination and facilitated the charge carrier transfer, thus resulting in significant improvement of the H 2 evolution performance. Moreover, the increased specific surface area and the enhanced visible-light absorption also contributed to superior water splitting performance. The prepared ternary catalytic system with the heterojunction and non-noble metal co-catalyst has great potential as an alternative to noble metals for achieving cost-efficient water splitting systems.

Bi 2 O 3 /g-C 3 N 4 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% Bi 2 O 3 /g-C 3 N 4 composite, which produced about 1.8 times the CO yield of pure g-C 3 N 4 . 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-C 3 N 4 , 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Z-Scheme MoS2/g-C3N4 heterojunction photocatalysts were fabricated using a hydrothermal deposition procedure together with a calcination route, and then applied for CO2 photoreduction. Experimental results indicated that the 10% MoS2/g-C3N4 heterojunction displayed the best photocatalytic performance. Furthermore, the maximum CO yields of 58.59 μmol (g-cat)-1 under 7 h-visible light irradiation was up to 2.94 times that of the unadulterated g-C3N4. The enhanced photocatalytic performance of 10% MoS2/g-C3N4 catalyst was due to the favored visible light response, the efficient separation of photogenerated electron-hole pairs as well as its larger specific surface area.

It was well recognized that Pb had a poisoning effect on a SCR catalyst. In this study, the deactivation mechanism of Pb on the Ce/TiO 2 catalyst was investigated based on the characterization results of TPD and in situ DRIFT studies. It was found that the addition of Pb on the Ce/TiO 2 catalyst not only inhibited the adsorption and activation of NH 3 species, but also led to the decrease of the activity of adsorbed NH 3 species in the SCR reaction. The adsorption of NOx species and the oxidation of NO by O 2 over the Ce/TiO 2 catalyst were also suppressed by the addition of Pb, while the reactivity of adsorbed NO 2 species did not decrease. Moreover, the results revealed that the NH 3 -SCR reaction over the Ce/TiO 2 catalyst followed both the E-R and L-H mechanisms, while the NH 3 -SCR reaction over Ce/TiO 2 -Pb was mainly controlled by the L-H mechanism. The contributions of the L-H mechanism to the SCR reactions over Ce/TiO 2 and Ce/TiO 2 -Pb decreased with increasing reaction temperature. The deactivation of Ce/TiO 2 -Pb was mainly attributed to the suppressed NH 3 adsorption and activation, accompanied by the inhibited NO oxidation and the decrease of Brønsted acid sites.