Visible-Light-Mediated Methane Activation for Steam Methane Reforming under Mild Conditions: A Case Study of Rh/TiO2 Catalysts

T. Silva GT, Filho JB, Victória HF, Krambrock K, Teixeira IF, Ribeiro C. Investigating the Metal-TiO2 Influence for Highly Selective Photocatalytic Oxidation of Methane to Methanol

Methane conversion to valuable chemicals is a highly challenging and desirable reaction. Photocatalysis is a clean pathway to drive this chemical reaction, avoiding the high temperature and pressure of the syngas process. Titanium dioxide, being the most used photocatalyst, presents challenges in controlling the oxidation process, which is believed to depend on the metal sites on its surface that function as heterojunctions. Herein, we supported different metals on TiO2 and evaluated their activity in methane photooxidation reactions. We showed that Ni-TiO2 is the best photocatalyst for selective methane conversion, producing impressively high amounts of methanol (1.600 μmol·g-1) using H2O2 as an oxidant, with minimal CO2 evolution. This performance is attributed to the high efficiency of nickel species to produce hydroxyl radicals and enhance H2O2 utilization as well as to induce carrier traps (Ti3+ and SETOVs sites) on TiO2, which are crucial for C-H activation. This study sheds light on the role of catalyst structure in the proper control of CH4 photoconversion.

Unusual facet and co-catalyst effects in TiO2-based photocatalytic coupling of methane

Photocatalytic coupling of methane to ethane and ethylene (C2 compounds) offers a promising approach to utilizing the abundant methane resource. However, the state-of-the-art photocatalysts usually suffer from very limited C2 formation rates. Here, we report our discovery that the anatase TiO2 nanocrystals mainly exposing {101} facets, which are generally considered less active in photocatalysis, demonstrate surprisingly better performances than those exposing the high-energy {001} facet. The palladium co-catalyst plays a pivotal role and the Pd2+ site on co-catalyst accounts for the selective C2 formation. We unveil that the anatase {101} facet favors the formation of hydroxyl radicals in aqueous phase near the surface, where they activate methane molecules into methyl radicals, and the Pd2+ site participates in facilitating the adsorption and coupling of methyl radicals. This work provides a strategy to design efficient nanocatalysts for selective photocatalytic methane coupling by reaction-space separation to optimize heterogeneous-homogeneous reactions at solid-liquid interfaces.

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Water-promoted selective photocatalytic methane oxidation for methanol production

Converting relatively inert methane into active chemical fuels such as methanol with high selectivity through an energy-saving strategy has remained a grand challenge. Photocatalytic technology consuming solar energy is an appealing alternative for methane reforming. However, the low efficiency and the undesirable formation of low-value products, such as carbon dioxide and ethane, limit the commercial application of photocatalytic technology. Herein, we find a facile and practical water-promoted pathway for photocatalytic methane reforming into methanol, enabling methanol production from methane and oxygen with a high selectivity (>93%) and production rate (21.4 μmol cm-2 h-1 or 45.5 mmol g-1 h-1) on metallic Ag nanoparticle-loaded InGaN nanowires (Ag/InGaN). The experimental XPS and theoretical PDOS analyses reveal that water molecules adsorbed on Ag nanoparticles (AgNPs) can promote the electron transfer from InGaN to AgNPs, which enables the formation of partial Ag species with a lower oxidation state in AgNPs. Through the in situ IR spectrum and the reaction pathway simulation studies, these newly formed Ag species induced by water adsorption were demonstrated to be responsible for the highly selective methanol production due to the effective formation of a C-O bond and the optimal desorption of the formed methanol from the surface indium site of the InGaN photocatalyst. This unique water promotion effect leads to a 55-fold higher catalytic rate and 9-fold higher selectivity for methanol production compared to photocatalytic methane reforming without water addition. This finding offers a new pathway for achieving clean solar fuels by photocatalysis-based methane reforming.

Molecular Orbital Insights into Plasmon-Induced Methane Photolysis

As a promising way to reduce the temperature for conventional thermolysis, plasmon-induced photocatalysis has been utilized for the dehydrogenation of methane. Here we probe the microscopic dynamic mechanism for plasmon-induced methane dissociation over a tetrahedral Ag20 nanoparticle with molecular orbital insights using time-dependent density functional theory. We ingeniously built the relationship between the chemical bonds and molecular orbitals via Hellmann-Feynman forces. The time- and energy-resolved photocarrier analysis shows that the indirect hot hole transfer from the Ag nanoparticle to methane dominates the photoreaction at low laser intensity, due to the strong hybridization of the Ag nanoparticle and CH4 orbitals, while indirect and direct charge transfer coexist to facilitate methane dissociation in intense laser fields. Our findings can be used to design novel methane photocatalysts and highlight the broad prospects of the molecular orbital approach for adsorbate-substrate systems.

A semiconducting hybrid of RhOx/GaN@InGaN for simultaneous activation of methane and water toward syngas by photocatalysis

Prior to the eventual arrival of carbon neutrality, solar-driven syngas production from methane steam reforming presents a promising approach to produce transportation fuels and chemicals. Simultaneous activation of the two reactants, i.e. methane and water, with notable geometric and polar discrepancy is at the crux of this important subject yet greatly challenging. This work explores an exceptional semiconducting hybrid of RhOx/GaN@InGaN nanowires for overcoming this critical challenge to achieve efficient syngas generation from methane steam reforming by photocatalysis. By coordinating density functional theoretical calculations and microscopic characterizations, with in situ spectroscopic measurements, it is found that the multifunctional RhOx/GaN interface is effective for simultaneously activating both CH4 and H2O by stretching the C-H and O-H bonds because of its unique Lewis acid/base attribute. With the aid of energetic charge carriers, the stretched C-H and O-H bonds of reactants are favorably cleaved, resulting in the key intermediates, i.e. *CH3, *OH, and *H, to sit on Rh sites, Rh sites, and N sites, respectively. Syngas is subsequently produced via energetically favored pathway without additional energy inputs except for light. As a result, a benchmarking syngas formation rate of 8.1 mol·gcat-1·h-1 is achieved with varied H2/CO ratios from 2.4 to 0.8 under concentrated light illumination of 6.3 W·cm-2, enabling the achievement of a superior turnover number of 10,493 mol syngas per mol Rh species over 300 min of long-term operation. This work presents a promising strategy for green syngas production from methane steam reforming by utilizing unlimited solar energy.

Solar-Driven Reforming of Methane and Nitrogen to Methanol and Ammonium on Iron-Modified Zeolite under Ambient Conditions in Water

Artificial photosynthesis from selective methane oxidation or nitrogen reduction to value-added chemicals provides a promising pathway for the sustainable chemical industry, while still remaining a great challenge due to the extreme difficulty in C-H and N≡N bond cleavage under ambient conditions. Catalysts that can cocatalyze these two reactions simultaneously are rarely reported. Here, Fe-ZSM-5 with highly dispersed extra-framework Fe-oxo species enables efficient and selective photocatalytic conversion of methane and nitrogen to coproduce methanol and ammonia using H2O as the redox reagent under ambient conditions. The optimized Fe-ZSM-5 photocatalyst achieves up to 0.88 mol/molFe·h of methanol products with 97% selectivity. Meanwhile, the productivity of ammonia is 0.61 mol/molFe·h. In situ EPR and DRIFT studies disclose that water serves as a redox reagent to provide hydroxyl radicals for methane oxidation and protons for nitrogen hydrogenation. Quantum chemical calculations revealed that Fe-oxo species play a significant role in the coactivation of methane and nitrogen molecules, which lowers the energy barriers of rate-determining steps for methanol and ammonia generation.

Highly Efficient Solar-Driven Dry Reforming of Methane on a Rh/LaNiO3 Catalyst through a Light-induced Metal-To-Metal Charge Transfer Process

As an energy-saving and green method, solar-driven dry reforming of methane (DRM) is expected to introduce new activation processes and prevent sintering and coking of the catalysts. However, it still lacks an efficient way to coordinate the regulation of activation of reactants and lattice oxygen migration. In this study, Rh/LaNiO3 is designed as a highly efficient photothermal catalyst for solar-driven DRM, which performs production rates of 452.3 mmol h-1  gRh -1 for H2 and 527.6 mmol h-1  gRh -1 for CO2 under a light intensity of 1.5 W cm-2 , with an excellent stability. Moreover, a remarkable light-to-chemical energy efficiency (LTCEE) of 10.72% is achieved under a light intensity of 3.5 W cm-2 . The characterizations of surface electronic and chemical properties and theoretical analysis demonstrate that strong adsorption for CH4 and CO2 , light-induced metal-to-metal charge transfer (MMCT) process and high oxygen mobility together bring Rh/LaNiO3 excellent performance for solar-driven DRM.

Promises of Plasmonic Antenna-Reactor Systems in Gas-Phase CO2 Photocatalysis

Sunlight-driven photocatalytic CO2 reduction provides intriguing opportunities for addressing the energy and environmental crises faced by humans. The rational combination of plasmonic antennas and active transition metal-based catalysts, known as "antenna-reactor" (AR) nanostructures, allows the simultaneous optimization of optical and catalytic performances of photocatalysts, and thus holds great promise for CO2 photocatalysis. Such design combines the favorable absorption, radiative, and photochemical properties of the plasmonic components with the great catalytic potentials and conductivities of the reactor components. In this review, recent developments of photocatalysts based on plasmonic AR systems for various gas-phase CO2 reduction reactions with emphasis on the electronic structure of plasmonic and catalytic metals, plasmon-driven catalytic pathways, and the role of AR complex in photocatalytic processes are summarized. Perspectives in terms of challenges and future research in this area are also highlighted.

High-density frustrated Lewis pairs based on Lamellar Nb2O5 for photocatalytic non-oxidative methane coupling

Photocatalytic methane conversion requires a strong polarization environment composed of abundant activation sites with the robust stretching ability for C-H scissoring. High-density frustrated Lewis pairs consisting of low-valence Lewis acid Nb and Lewis base Nb-OH are fabricated on lamellar Nb₂O₅ through a thermal-reduction promoted phase-transition process. Benefitting from the planar atomic arrangement of lamellar Nb₂O₅, the frustrated Lewis pairs sites are highly exposed and accessible to reactants, which results in a superior methane conversion rate of 1456 μmol g^-1 h^-1 for photocatalytic non-oxidative methane coupling without the assistance of noble metals. The time-dependent DFT calculation demonstrates the photo-induced electron transfer from LA to LB sites enhances their intensities in a concerted way, promoting the C-H cleavage through the coupling of LA and LB. This work provides in-depth insight into designing and constructing a polarization micro-environment for photocatalytic C-H activation of methane without the assistance of noble metals.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

Synthesis of rhodium intermetallic catalysts by enlarging the inter-particle distance on high-surface-area carbon black supports

Here, we report a "critical distance" method for the synthesis of 9 kinds of sub-5 nm rhodium (Rh)-based intermetallic catalysts. Enlarging the distance between intermetallic particles on high-surface-area carbon black supports could significantly suppress the metal sintering in high-temperature annealing. The prepared Rh₂Sn intermetallic catalysts exhibited enhanced activity in catalyzing the hydrogenation of nitrobenzene.

Atomically Dispersed Nickel Anchored on a Nitrogen-Doped Carbon/TiO2 Composite for Efficient and Selective Photocatalytic CH4 Oxidation to Oxygenates

Direct photocatalytic oxidation of methane to liquid oxygenated products is a sustainable strategy for methane valorization at room temperature. However, in this reaction, noble metals are generally needed to function as cocatalysts for obtaining adequate activity and selectivity. Here, we report atomically dispersed nickel anchored on a nitrogen-doped carbon/TiO₂ composite (Ni-NC/TiO₂ ) as a highly active and selective catalyst for photooxidation of CH₄ to C1 oxygenates with O₂ as the only oxidant. Ni-NC/TiO₂ exhibits a yield of C1 oxygenates of 198 μmol for 4 h with a selectivity of 93 %, exceeding that of most reported high-performance photocatalysts. Experimental and theoretical investigations suggest that the single-atom Ni-NC sites not only enhance the transfer of photogenerated electrons from TiO₂ to isolated Ni atoms but also dominantly facilitate the activation of O₂ to form the key intermediate ⋅OOH radicals, which synergistically lead to a substantial enhancement in both activity and selectivity.

Metal-Support Interaction-Promoted Photothermal Catalytic Methane Reforming into Liquid Fuels

Clean and renewable photocatalytic technology for methane reforming into high-value liquid fuels, such as methanol, is a promising strategy for commercial industrial applications. However, poor charge separation, sluggish methane activation, and excessive oxidation collectively inhibit the production of methanol from photocatalytic methane reforming. Herein, we have developed enhanced metal-support interactions between a GaN nanowire photocatalyst and a Cu nanoparticle (CuNP) cocatalyst via p-doping in GaN. CuNP-loaded p-type GaN (Cu/p-GaN) with enhanced metal-support interaction has 3.5-fold higher activity (12.8 mmol g^-1 h^-1, higher than previous reports) for methanol production in photothermal catalytic methane reforming with oxygen as an oxidant and sunlight as the sole energy source than CuNP-loaded intrinsic GaN (Cu/i-GaN) or n-type GaN (Cu/n-GaN). In-situ IR measurements indicate that enhanced metal-support interaction significantly promotes activation of methane and formation of methanol. Combining with X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) simulations demonstrate that this enhanced metal-support interaction in Cu/p-GaN greatly improves electron transfer from p-GaN photocatalysts to the 3d states of CuNP cocatalysts through the interface between them. Catalytic pathway simulations further reveal that the enhanced metal-support interaction in Cu/p-GaN also desirably decreases the reaction energy of rate-determining methanol desorption, which decreases the excessive oxidation of the produced methanol and accelerates the regeneration of surface catalytic sites. These studies and findings offer critical insights into the design and development of metal nanoparticle-loaded photocatalysts for photocatalysis-based methane reforming into methanol.

Accelerating photo-thermal CO2 reduction to CO, CH4 or methanol over metal/oxide semiconductor catalysts

Photo-thermal reduction of atmospheric carbon dioxide into methane, methanol, and carbon monoxide under mild conditions over suitable (photo)catalysts is a feasible pathway for the production of fuels and platform chemicals with minimal involvement of fossil fuels. In this perspective, we showcase transition metal nanoparticles (Ni, Cu, and Ru) dispersed over oxide semiconductors and their ability to act as photo catalysts in reverse water gas shift reaction (RWGS), methane dry reforming, methanol synthesis, and Sabatier reactions. By using a combination of light and thermal energy for activation, reactions can be sustained at much lower temperatures compared to thermally driven reactions and light can be used to leverage reaction selectivity between methanol, methane, and CO. In addition to influencing the reaction mechanism and decreasing the apparent activation energies, accelerating reaction rates and boosting selectivity beyond thermodynamic limitations is possible. We also provide future directions for research to advance the current state of the art in photo-thermal CO₂ conversion.

Thermo-photo catalysis: a whole greater than the sum of its parts

Thermo-photo catalysis, which is the catalysis with the participation of both thermal and photo energies, not only reduces the large energy consumption of thermal catalysis but also addresses the low efficiency of photocatalysis. As a whole greater than the sum of its parts, thermo-photo catalysis has been proven as an effective and promising technology to drive chemical reactions. In this review, we first clarify the definition (beyond photo-thermal catalysis and plasmonic catalysis), classification, and principles of thermo-photo catalysis and then reveal its superiority over individual thermal catalysis and photocatalysis. After elucidating the design principles and strategies toward highly efficient thermo-photo catalytic systems, an ample discussion on the synergetic effects of thermal and photo energies is provided from two perspectives, namely, the promotion of photocatalysis by thermal energy and the promotion of thermal catalysis by photo energy. Subsequently, state-of-the-art techniques applied to explore thermo-photo catalytic mechanisms are reviewed, followed by a summary on the broad applications of thermo-photo catalysis and its energy management toward industrialization. In the end, current challenges and potential research directions related to thermo-photo catalysis are outlined.

Deciphering the reaction mechanisms of photothermal hydrogen production using H/D kinetic isotope effect

Large H/D isotope separation coefficient and its variation with temperature indicates a hole-mediated O–H bond cleavage as the limiting stage of photothermal hydrogen production.

Selective CH4 Partial Photooxidation by Positively Charged Metal Clusters Anchored on Carbon Aerogel under Mild Conditions

Selective partial photooxidation of CH₄ into value-added chemicals under mild conditions still remains a huge bottleneck. Herein, we design positively charged metal clusters anchored on a three-dimensional porous carbon aerogel. With 0.75FeCA800-4 as an example, X-ray photoelectron spectra and Raman spectra disclose that the iron sites are positively charged. In situ electron paramagnetic resonance spectra show that the Fe^δ+ sites could donate electrons to activate CH₄ into CH₄^- by virtue of the excited-state carbon atoms; meanwhile, they could convert H₂O₂ into ^•OH radicals under irradiation. In addition, in situ diffuse Fourier-transform infrared spectra suggest the CH₃OOH obtained is derived from CH₄ oxidation by the hydroxylation of *CH₃ and *CH₃O intermediates. Consequently, 0.75FeCA800-4 displays a CH₃OOH selectivity of near 100% and a CH₃OOH evolution rate of 13.2 mmol g_Fe^-1 h^-1, higher than those of most previously reported supported catalysts under similar conditions.

Tunable Selectivity in CO2 Photo-Thermal Reduction by Perovskite-Supported Pd Nanoparticles

Photo-thermal catalysis has recently emerged as a promising alternative to overcome the limitations of traditional photocatalysis. Despite its potential, most of the photo-thermal systems still lack adequate selectivity patterns and appropriate analysis of the underlying reaction pathways, thus hampering a wide implementation. Herein, a novel photocatalyst based on Pd nanoparticles (NPs) supported on barium titanate (BTO) was prepared for the selective photo-thermal reduction of CO₂ and displayed catalytic rates of up to 8.2 mol_CO  g_Pd ^-1  h^-1 . The photocatalyst allowed for a tailored selectivity towards CO or CH₄ as a function of the metal loading or the light intensity. Mechanistic studies indicated that both thermal and non-thermal contributions of light played a role in the overall reaction pathway, each of them being dominant upon changing reaction conditions.

Nanostructured Photothermal Materials for Environmental and Catalytic Applications

Solar energy is a green and sustainable clean energy source. Its rational use can alleviate the energy crisis and environmental pollution. Directly converting solar energy into heat energy is the most efficient method among all solar conversion strategies. Recently, various environmental and energy applications based on nanostructured photothermal materials stimulated the re-examination of the interfacial solar energy conversion process. The design of photothermal nanomaterials is demonstrated to be critical to promote the solar-to-heat energy conversion and the following physical and chemical processes. This review introduces the latest photothermal nanomaterials and their nanostructure modulation strategies for environmental (seawater evaporation) and catalytic (C1 conversion) applications. We present the research progress of photothermal seawater evaporation based on two-dimensional and three-dimensional porous materials. Then, we describe the progress of photothermal catalysis based on layered double hydroxide derived nanostructures, hydroxylated indium oxide nanostructures, and metal plasmonic nanostructures. Finally, we present our insights concerning the future development of this field.

Triggering Water and Methanol Activation for Solar-Driven H2 Production: Interplay of Dual Active Sites over Plasmonic ZnCu Alloy

Methanol steam reforming (MSR) is a promising reaction that enables efficient production and safe transportation of hydrogen, but it requires a relatively high temperature to achieve high activity, leading to large energy consumption. Here, we report a plasmonic ZnCu alloy catalyst, consisting of plasmonic Cu nanoparticles with surface-deposited Zn atoms, for efficient solar-driven MSR without additional thermal energy input. Experimental results and theoretical calculations suggest that Zn atoms act not only as the catalytic sites for water reduction with lower activation energy but also as the charge transfer channel, pumping hot electrons into water molecules and subsequently resulting in the formation of electron-deficient Cu for methanol activation. These merits together with photothermal heating render the optimal ZnCu catalyst a high H₂ production rate of 328 mmol g_catalyst^-1 h^-1 with a solar energy conversion efficiency of 1.2% under 7.9 Suns irradiation, far exceeding the reported conventional photocatalytic and thermocatalytic MSR. This work provides a potential strategy for efficient solar-driven H₂ production and various other energy-demanding industrial reactions through designing alloy catalysts.

Photocatalytic Conversion of Methane: Recent Advancements and Prospects

Abundant and affordable methane is not only a high-quality fossil fuel, it is also a raw material for the synthesis of value-added chemicals. Solar-energy-driven conversion of methane offers a promising approach to directly transform methane to valuable energy sources under mild conditions, but remains a great challenge at present. In this Review, recent advances in the photocatalytic conversion of methane are systematically summarized. Insights into the construction of effective semiconductor-based photocatalysts from the perspective of light-absorption units and active centers are highlighted and discussed in detail. The performance of various photocatalysts in the conversion of methane is presented, with the photooxidation classified according to the oxidant systems. Lastly, challenges and future perspectives in the photocatalytic oxidation of methane are described.

Active site separation of photocatalytic steam reforming of methane using a gas-phase photoelectrochemical system

Steam reforming of methane (SRM) requires high temperatures to be promoted, and the production of carbon dioxide from the side reaction has also become a problem. In this study, we separated the reaction sites for SRM to suppress CO2 generation using a gas-phase photoelectrochemical (GPEC) system with a cell coated with a Pt/YSZ powder catalyst on an oxygen ion-conductive YSZ pellet, where the reaction was assisted by light irradiation. As a result, SRM proceeded stoichiometrically and the production of CO2 was suppressed. We expect the findings obtained by the GPEC system will be useful in providing design guidelines for photocatalysts.

Fundamentals and applications of photo-thermal catalysis

Photo-thermal catalysis has recently emerged as an alternative route to drive chemical reactions using light as an energy source.

Photocatalytic Methane Reforming: Recent Advances

Methane reforming is an important potential technology for solving both environmental and energy problems. This technology is important because methane is counted as a greenhouse gas, but on the other hand, it can be reformed into industrially valuable compounds. More research has focused on photocatalytic methane reforming, which has a higher activity than thermal catalysts under dark conditions. The reaction selectivity toward specific products in photocatalytic methane reforming is sometimes different from thermal catalyst systems. Herein, we discuss recent advances in photocatalytic methane reforming to provide various strategies for reforming.

Site-Selective Nanoreactor Deposition on Photocatalytic Al Nanocubes

Photoactivation of catalytic materials through plasmon-coupled energy transfer has created new possibilities for expanding the scope of light-driven heterogeneous catalysis. Here we present a nanoengineered plasmonic photocatalyst consisting of catalytic Pd islands preferentially grown on vertices of Al nanocubes. The regioselective Pd deposition on Al nanocubes does not rely on complex surface ligands, in contrast to site-specific transition-metal deposition on gold nanoparticles. We show that the strong local field enhancement on the sharp nanocube vertices provides a mechanism for efficient coupling of the plasmonic Al antenna to adjacent Pd nanoparticles. A substantial increase in photocatalytic H₂ dissociation on Pd-bound Al nanocubes relative to pristine Al nanocubes can be observed, incentivizing further engineering of heterometallic antenna-reactor photocatalysts. Controlled growth of catalytic materials on plasmonic hot spots can result in more efficient use of the localized surface plasmon energy for photocatalysis, while minimizing the amount and cost of precious transition-metal catalysts.

3D structured materials and devices for artificial photosynthesis

Artificial photosynthesis is an effective way to convert solar energy into fuels, which is of great significance to energy production and reduction of atmospheric CO₂ content. In recent years, 3D structured artificial photosynthetic system has made great progress as an effective design strategy. This review first highlights several typical mechanisms for improved artificial photosynthesis with 3D structures: improved light harvesting, mass transfer and charge separation. Then, we summarize typical examples of 3D structured artificial photosynthetic systems, including bioinspired structures, photonic crystals (PC), designed photonic structures (PC coupling structure, plasmon resonance structure, optical resonance structure, metamaterials), 3D-printed systems, nanowire integrated systems and hierarchical 3D structures. Finally, we discuss the problems and challenges to the application and development of 3D artificial photosynthetic system and the possible trends of future development. We hope this review can inspire more progress in the field of artificial photosynthesis.

Carbon Sphere Template Derived Hollow Nanostructure for Photocatalysis and Gas Sensing

As a green and preferred technology for energy crisis and environmental issues, continuous research on photocatalysis and gas sensing has come forth at an explosive rate. Thus far, promising synthetic methods have enabled various designs and preparations of semiconductor-based nanostructure which have shown superior activity. This review summarized various synthetic routines toward carbon sphere template derived hollow nanostructures and their successful attempts in synthesize doping, solid solution, heterostructure, and surface modified nanostructures for heterogeneous photocatalysis and gas sensing. Moreover, the challenges and future prospects are briefly discussed. It is eagerly anticipated that this review may broaden the view and in-depth understanding of carbon sphere template derived hollow nanostructures while expected to have further progresses in heterogeneous photocatalysis, gas sensing and other related fields which will make great contributions to their application.

Visible-light-driven dry reforming of methane using a semiconductor-supported catalyst

Dry reforming of methane (CH₄ + CO₂ → 2H₂ + 2CO) was efficiently proceeded using Rh/TaON under visible light at low temperature.

Metal Carbide as A Light-Harvesting and Anticoking Catalysis Support for Dry Reforming of Methane

Dry reforming of methane (DRM) is one of the most attractive chemical reactions, since it converts global-warming gases into valuable syngas including hydrogen and carbon monoxide. Numerous previous studies used metal oxides catalysis supports, such as Al2O3, but their operating temperature was very high and severe coking occurred and deteriorated their catalytic activities. The present study reports that a metal carbide like tantalum carbide (TaC) acts as a multifunctional catalyst support for the DRM reaction, including light-harvesting properties for saving energy operation as well as an anticoking property for long-term stability. Nickel nanoparticles loaded on tantalum carbide (Ni/TaC) are prepared by impregnation and reductive hydrogen treatment. TaC particles act as a light-harvesting support to promote the DRM reaction by photon irradiation through plasmonic photothermal energy conversion in TaC. Furthermore, Ni/TaC exhibits an excellent long-term anticoking property, as compared to Ni loaded on conventional metal oxide supports such as Al2O3 or Ta2O5. According to the sole gas condition's experiment, and secondary ion mass spectroscopy, the oxy-carbide layer near the interface between TaC and Ni plays an essential role in imparting the efficient anticoking property of Ni/TaC.

Modifications of heterogeneous photocatalysts for hydrocarbon C–H bond activation and selective conversion

This feature article summarizes the recent progress in the modification of heterogeneous photocatalysts for photocatalytic hydrocarbons’ C–H bond activation.

Interlayer Photoelectron Transfer Boosted by Bridged RuIV Atoms in GaS Nanosheets for Efficient Water Splitting

Photocatalytic water splitting over layered nanosheet (NS) catalysts has caught a lot of attention for renewable hydrogen fuel production. However, the weak van der Waals interlayer interactions make it a great challenge to realize an effective dissociation of photogenerated excitons and efficient charge transfer across the interior of layered catalysts during the photocatalysis process. Here, we propose an intercalation strategy of high-valence Ru^IV atoms to render two-dimensional GaS NS photocatalysts with rapid electron-hole dissociation and long photocarrier lifetime in visible-light-driven water splitting. Experimental and theoretical results unravel that the intercalated single-site Ru, confined in interlayer of GaS NSs, with a hexagonal structural configuration of "Ru₁-S₆", can serve as an electron-trapped high-speed channel toward simultaneously accelerating electron-hole pairs dissociation and promoting photoelectron transportation through the van der Waals interlayer. Consequently, the as-developed Ru-intercalated GaS NSs can give a notable H₂ production rate of 340 μmol g^-1 h^-1 under visible-light irradiation and an apparent yield of 7% at 420 nm, 38 times that of pure GaS NSs. This study opens up a feasible way for a new design of highly active layered photocatalysts toward high-efficiency solar energy conversion.