Abstract
Ambient sunlight-driven CO
2
methanation cannot be realized due to the temperature being less than 80 °C upon irradiation with dispersed solar energy. In this work, a selective light ...absorber was used to construct a photothermal system to generate a high temperature (up to 288 °C) under weak solar irradiation (1 kW m
−2
), and this temperature is three times higher than that in traditional photothermal catalysis systems. Moreover, ultrathin amorphous Y
2
O
3
nanosheets with confined single nickel atoms (SA Ni/Y
2
O
3
) were synthesized, and they exhibited superior CO
2
methanation activity. As a result, 80% CO
2
conversion efficiency and a CH
4
production rate of 7.5 L m
−2
h
−1
were achieved through SA Ni/Y
2
O
3
under solar irradiation (from 0.52 to 0.7 kW m
−2
) when assisted by a selective light absorber, demonstrating that this system can serve as a platform for directly harnessing dispersed solar energy to convert CO
2
to valuable chemicals.
Nanometal materials play very important roles in solar‐to‐chemical energy conversion due to their unique catalytic and optical characteristics. They have found wide applications from semiconductor ...photocatalysis to rapidly growing surface plasmon‐mediated heterogeneous catalysis. The recent research achievements of nanometals are reviewed here, with regard to applications in semiconductor photocatalysis, plasmonic photocatalysis, and plasmonic photo‐thermocatalysis. As the first important topic discussed here, the latest progress in the design of nanometal cocatalysts and their applications in semiconductor photocatalysis are introduced. Then, plasmonic photocatalysis and plasmonic photo‐thermocatalysis are discussed. A better understanding of electron‐driven and temperature‐driven catalytic behaviors over plasmonic nanometals is helpful to bridge the present gap between the communities of photocatalysis and conventional catalysis controlled by temperature. The objective here is to provide instructive information on how to take the advantages of the unique functions of nanometals in different types of catalytic processes to improve the efficiency of solar‐energy utilization for more practical artificial photosynthesis.
Nanometal materials play very important roles in solar‐to‐chemical energy conversion due to their unique catalytic and optical characteristics. Recent research achievements of nanometals regarding applications in semiconductor photocatalysis, plasmonic photocatalysis, and plasmonic photo‐thermocatalysis are presented. Instructive information on how to take the advantage of nanometals in these catalytic processes for efficient artificial photosynthesis is provided.
Solar‐driven reduction of dinitrogen (N2) to ammonia (NH3) is severely hampered by the kinetically complex and energetically challenging multielectron reaction. Oxygen vacancies (OVs) with abundant ...localized electrons on the surface of bismuth oxybromide‐based semiconductors are demonstrated to have the ability to capture and activate N2, providing an alternative pathway to overcome such limitations. However, bismuth oxybromide materials are susceptible to photocorrosion, and the surface OVs are easily oxidized and therefore lose their activities. For realistic photocatalytic N2 fixation, fabricating and enhancing the stability of sustainable OVs on semiconductors is indispensable. This study shows the first synthesis of self‐assembled 5 nm diameter Bi5O7Br nanotubes with strong nanotube structure, suitable absorption edge, and many exposed surface sites, which are favorable for furnishing sufficient visible light‐induced OVs to realize excellent and stable photoreduction of atmospheric N2 into NH3 in pure water. The NH3 generation rate is as high as 1.38 mmol h−1 g−1, accompanied by an apparent quantum efficiency over 2.3% at 420 nm. The results presented herein provide new insights into rational design and engineering for the creation of highly active catalysts with light‐switchable OVs toward efficient, stable, and sustainable visible light N2 fixation in mild conditions.
A facile wet chemical method for water‐assisted self‐assembly of 5 nm diameter Bi5O7Br nanotubes is reported. The obtained 5 nm Bi5O7Br‐NT is characterized with large surface area (>96 m2 g−1), suitable absorption edge, and sufficient surface oxygen vacancies of light switch. As a result, 5 nm Bi5O7Br‐NT delivers an excellent visible light driven photocatalytic N2 fixation performance with a NH3 generation rate of 1.38 mmol h−1 g−1 in pure water.
Abstract
Photoreduction of CO
2
to fuels offers a promising strategy for managing the global carbon balance using renewable solar energy. But the decisive process of oriented photogenerated electron ...delivery presents a considerable challenge. Here, we report the construction of intermolecular cascaded π-conjugation channels for powering CO
2
photoreduction by modifying both intramolecular and intermolecular conjugation of conjugated polymers (CPs). This coordination of dual conjugation is firstly proved by theoretical calculations and transient spectroscopies, showcasing alkynyl-removed CPs blocking the delocalization of electrons and in turn delivering the localized electrons through the intermolecular cascaded channels to active sites. Therefore, the optimized CPs (N-CP-D) exhibiting CO evolution activity of 2247 μmol g
−1
h
−1
and revealing a remarkable enhancement of 138-times compared to unmodified CPs (N-CP-A).
Direct conversion of earth-abundant methane into value-added chemicals under mild conditions is an attractive technology in response to the increasing industrial demand of feedstocks and worldwide ...appeal of energy conservation. Exploring advanced low-temperature C–H activation catalysts and reaction systems is the key to converting methane in a direct and mild manner. The recently developed reaction processes operated at low-temperature thermocatalysis systems or driven in electro- and photocatalysis systems shine light on the way to achieve efficient methane conversion with much economical energy input. In this review, we summarize the typical catalytic processes employed in these reaction systems and in particular highlight the potential heterogeneous catalysts with noteworthy C–H activation performance. We also present the progress along with our perspectives on catalyst design, theoretical simulations, the choice of reaction condition, and the method of reaction product analysis to encourage more viable technology for low-temperature methane conversion in the future.
Display omitted
Direct low-temperature methane conversion is a promising route for the chemical industry to access various basic feedstocks in the future. Developing such technology to displace the traditional energy-intensive syngas pathway has attracted increasing interest. A key for this technology is to seek advanced catalytic systems that enable efficient C–H activation along with a controllable reaction kinetics process. Therefore, it is important to take advantage of the various types of catalytic materials to effectively transform thermal, electric, and photonic energies into the driving forces for C–H activation. In this review, we present recent experimental and theoretical progress in the design of direct low-temperature methane conversion catalysts as well as the C–H activation mechanism in thermocatalysis, electrocatalysis, and photocatalysis systems to encourage more viable technologies for this challenging subject.
Direct methane conversion into value-added products at low temperature is an attractive technology for the chemical industry. However, because of the stable molecular structure and high C–H bond energy, methane conversion is a very tough process and is regarded as the “holy grail” in catalysis. Through the rational design of catalysts and the involvement of electro- and photoactivation processes, low-temperature C–H activation and methane conversion can be realized.
Electrocatalytic CO2 reduction to CO emerges as a potential route of utilizing emitted CO2. Metal‐N‐C hybrid structures have shown unique activities, however, the active centers and reaction ...mechanisms remain unclear because of the ambiguity in true atomic structures for the prepared catalysts. Herein, combining density‐functional theory calculations and experimental studies, the reaction mechanisms for well‐defined metal–N4 sites were explored using metal phthalocyanines as model catalysts. The theoretical calculations reveal that cobalt phthalocyanine exhibits the optimum activity for CO2 reduction to CO because of the moderate *CO binding energy at the Co site, which accommodates the *COOH formation and the *CO desorption. It is further confirmed by experimental studies, where cobalt phthalocyanine delivers the best performance, with a maximal CO Faradaic efficiency reaching 99 %, and maintains stable performance for over 60 hours.
To the “CO2RR”: Metal phthalocyanines (MePcs) with well‐defined metal–N4 structures were used as model catalysts to study the active centers and reaction mechanisms for the electrocatalytic CO2 reduction reaction (CO2RR). Theoretical and experimental studies identify CoPc as the optimum catalyst for the selective electrocatalytic CO2RR to deliver CO. The Co site serves as the active center for achieving a Faradaic efficiency (FE) of up to 99 % with long‐term stability.
Modular optimization of metal–organic frameworks (MOFs) was realized by incorporation of coordinatively unsaturated single atoms in a MOF matrix. The newly developed MOF can selectively capture and ...photoreduce CO2 with high efficiency under visible‐light irradiation. Mechanistic investigation reveals that the presence of single Co atoms in the MOF can greatly boost the electron–hole separation efficiency in porphyrin units. Directional migration of photogenerated excitons from porphyrin to catalytic Co centers was witnessed, thereby achieving supply of long‐lived electrons for the reduction of CO2 molecules adsorbed on Co centers. As a direct result, porphyrin MOF comprising atomically dispersed catalytic centers exhibits significantly enhanced photocatalytic conversion of CO2, which is equivalent to a 3.13‐fold improvement in CO evolution rate (200.6 μmol g−1 h−1) and a 5.93‐fold enhancement in CH4 generation rate (36.67 μmol g−1 h−1) compared to the parent MOF.
Less is more: A photocatalyst comprising atomically dispersed Co in an extended MOF efficiently reduces CO2. Directional migration of photogenerated excitons from porphyrin to catalytic cobalt centers was witnessed, thereby supplying long‐lived electrons for reduction of CO2 molecules adsorbed on cobalt centers.
Graphitic carbon nitride (g‐C3N4) has recently emerged as an attractive photocatalyst for solar energy conversion. However, the photocatalytic activities of g‐C3N4 remain moderate because of the ...insufficient solar‐light absorption and the fast electron–hole recombination. Here, defect‐modified g‐C3N4 (DCN) photocatalysts, which are easily prepared under mild conditions and show much extended light absorption with band gaps decreased from 2.75 to 2.00 eV, are reported. More importantly, cyano terminal CN groups, acting as electron acceptors, are introduced into the DCN sheet edge, which endows the DCN with both n‐ and p‐type conductivities, consequently giving rise to the generation of p–n homojunctions. This homojunction structure is demonstrated to be highly efficient in charge transfer and separation, and results in a fivefold enhanced photocatalytic H2 evolution activity. The findings deepen the understanding on the defect‐related issues of g‐C3N4‐based materials. Additionally, the ability to build homojunction structures by the defect‐induced self‐functionalization presents a promising strategy to realize precise band engineering of g‐C3N4 and related polymer semiconductors for more efficient solar energy conversion applications.
The p–n homojunction graphitic carbon nitride (g‐C3N4) photocatalysts with extended light absorption are prepared via in situ bond modulation, which is achieved by low‐temperature heating g‐C3N4 with NaBH4. Such a p–n homojunction endows g‐C3N4 with much increased π‐electron delocalization and highly improved carrier separation and transfer. Consequently, the materials exhibit a fivefold enhanced photocatalytic hydrogen evolution activity under visible light irradiation.
Searching for highly active and efficient photocatalysts for photo‐induced/photo‐assisted reactions remains the most challenging task for solar energy utilization. In previous studies, the search for ...such materials has mainly focused on precious plasmonic metals (for example, Au, Ag, and Cu) and semiconductor oxides (for example, TiO2, ZnO, and WO3). Herein, we report the application of hexagonal tantalum mononitride (TaN) as an optical support in photocatalytic reactions, which could harness visible light to assist CO2 conversion and decompose organic pollutants. Theoretical studies indicated that the improved electron‐hole separation in polar TaN under visible‐light illumination was critical for its use in photocatalysis. This study could guide the use of TaN in various photocatalytic reactions and wider optical applications.
TaN was used in a photocatalytic reaction because of its own optical properties. It is shown that the improved electron‐hole separation and transfer over asymmetrical TaN can account for its activity enhancement with visible‐light irradiation.
Inspired by the crucial roles of phosphates in natural photosynthesis, we explored an environmental “phosphorylation” strategy for boosting photocatalytic H2 production over g‐C3N4 nanosheets under ...visible light. As expected, a substantial improvement was observed in the rate of H2 evolution to 947 μmol h−1, and the apparent quantum yield was as high as 26.1 % at 420 nm. The synergy of enhanced proton reduction and improved hole oxidation is proposed to account for the markedly increased activity. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar‐energy conversion.
The right environment for success: A “phosphorylation” strategy inspired by natural photosynthesis was explored to boost photocatalytic H2 production over g‐C3N4 nanosheets. Thus, the addition of a phosphate led to a high apparent quantum yield (AQY). Experimental and theoretical results indicated that the large increase in activity was due to the synergy of enhanced proton reduction and improved hole oxidation (see picture; TEOA=triethanolamine).
PDF
