Tungsten Oxide-Based Z-Scheme for Visible Light-Driven Hydrogen Production from Water Splitting

The stoichiometric water splitting using a solar-driven Z-scheme approach is an emerging field of interest to address the increasing renewable energy demand and environmental concerns. So far, the reported Z-scheme must comprise two populations of photocatalysts. In the present work, only tungsten oxides are used to construct a robust Z-scheme system for complete visible-driven water splitting in both neutral and alkaline solutions, where sodium tungsten oxide bronze (Na0.56WO3–x) is used as a H2 evolution photocatalyst and two-dimensional (2D) tungsten trioxide (WO3) nanosheets as an O2 evolution photocatalyst. This system efficiently produces H2 (14 μmol h–1) and O2 (6.9 μmol h–1) at an ideal molar ratio of 2:1 in an aqueous solution driven by light, resulting in a remarkably high apparent quantum yield of 6.06% at 420 nm under neutral conditions. This exceptional selective H2 and O2 production is due to the preferential adsorption of iodide (I–) on Na0.56WO3–x and iodate (IO3–) on WO3, which is evidenced by both experiments and density functional theory calculation. The present liquid Z-scheme in the presence of efficient shuttle molecules promises a separated H2 and O2 evolution by applying a dual-bed particle suspension system, thus a safe photochemical process

Highly Selective Transformation of Biomass Derivatives to Valuable Chemicals by Single-Atom Photocatalyst Ni/TiO2

Selective C-C cleavage of the biomass derivative glycerol under mild conditions has been recognised as a promising yet challenging synthesis route to produce value-added chemicals. Here, a highly selective catalyst is presented for the transformation of glycerol to the high-value product glycolaldehyde, which is composed of nickel single atoms confined to the titanium dioxide surface. Driven by light, the catalyst operates under ambient conditions using air as a green oxidant. The optimised catalyst shows a selectivity of over 60% to glycolaldehyde, resulting in 1058 μmol·gCat -1 ·h-1 production rate, and nearly 3 times higher turnover number than NiOx nanoparticle-decorated TiO2 photocatalyst. Diverse operando and in-situ spectroscopies (including operando XANES, in-situ XPS, O2 -TPD, EXAFS, etc.) unveil the unique function of the Ni single atom, which can significantly promote oxygen adsorption, work as an electron sink and accelerate the production of superoxide radicals, thereby improving the selectivity towards glycolaldehyde over other by-products. This article is protected by copyright. All rights reserved

Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and Wδ+

Direct solar-driven methane (CH4) reforming is highly desirable but challenging, particularly to achieve a value-added product with high selectivity. Here, we identify a synergistic ensemble effect of atomically dispersed copper (Cu) species and partially reduced tungsten (Wδ+), stabilised over an oxygen-vacancy-rich WO3, which enables exceptional photocatalytic CH4 conversion to formaldehyde (HCHO) under visible light, leading to nearly 100% selectivity, a very high yield of 4979.0 μmol·g-1 within 2 h, and the normalised mass activity of 8.5 × 106 μmol·g-1Cu·h-1 of HCHO at ambient temperature. In-situ EPR and XPS analyses indicate that the Cu species serve as the electron acceptor, promoting the photo-induced electron transfer from the conduction band to O2, generating reactive •OOH radicals. In parallel, the adjacent Wδ+ species act as the hole acceptor and the preferred adsorption and activation site of H2O to produce hydroxyl radicals (•OH), and thus activate CH4 to methyl radicals (•CH3). The synergy of the adjacent dual active sites boosts the overall efficiency and selectivity of the conversion process

Selective oxidation of methane to C2+ products over Au-CeO2 by photon-phonon co-driven catalysis.

Direct methane conversion to high-value chemicals under mild conditions is attractive yet challenging due to the inertness of methane and the high reactivity of valuable products. This work presents an efficient and selective strategy to achieve direct methane conversion through the oxidative coupling of methane over a visible-responsive Au-loaded CeO2 by photon-phonon co-driven catalysis. A record-high ethane yield of 755 μmol h−1 (15,100 μmol g−1 h−1) and selectivity of 93% are achieved under optimised reaction conditions, corresponding to an apparent quantum efficiency of 12% at 365 nm. Moreover, the high activity of the photocatalyst can be maintained for at least 120 h without noticeable decay. The pre-treatment of the catalyst at relatively high temperatures introduces oxygen vacancies, which improves oxygen adsorption and activation. Furthermore, Au, serving as a hole acceptor, facilitates charge separation, inhibits overoxidation and promotes the C-C coupling reaction. All these enhance photon efficiency and product yield

Tungsten oxide-based Z-scheme for visible light-driven hydrogen production from water splitting

The stoichiometric water splitting using a solar-driven Z-scheme approach is an emerging field of interest to address the increasing renewable energy demand and environmental concerns. So far, the reported Z-scheme must comprise two populations of photocatalysts. In the present work, only tungsten oxides are used to construct a robust Z-scheme system for complete visible-driven water splitting in both neutral and alkaline solutions, where sodium tungsten oxide bronze (Na0.56WO3–x) is used as a H2 evolution photocatalyst and two-dimensional (2D) tungsten trioxide (WO3) nanosheets as an O2 evolution photocatalyst. This system efficiently produces H2 (14 μmol h–1) and O2 (6.9 μmol h–1) at an ideal molar ratio of 2:1 in an aqueous solution driven by light, resulting in a remarkably high apparent quantum yield of 6.06% at 420 nm under neutral conditions. This exceptional selective H2 and O2 production is due to the preferential adsorption of iodide (I–) on Na0.56WO3–x and iodate (IO3–) on WO3, which is evidenced by both experiments and density functional theory calculation. The present liquid Z-scheme in the presence of efficient shuttle molecules promises a separated H2 and O2 evolution by applying a dual-bed particle suspension system, thus a safe photochemical process

Improving CO2 photoconversion with ionic liquid and Co single atoms

Photocatalytic CO2 conversion promises an ideal route to store solar energy into chemical bonds. However, sluggish electron kinetics and unfavorable product selectivity remain unresolved challenges. Here, an ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate, and borate-anchored Co single atoms were separately loaded on ultrathin g-C3N4 nanosheets. The optimized nanocomposite photocatalyst produces CO and CH4 from CO2 and water under UV-vis light irradiation, exhibiting a 42-fold photoactivity enhancement compared with g-C3N4 and nearly 100% selectivity towards CO2 reduction. Experimental and theoretical results reveal that the ionic liquid extracts electrons and facilitates CO2 reduction, whereas Co single atoms trap holes and catalyze water oxidation. More importantly, the maximum electron transfer efficiency for CO2 photoreduction, as measured with in-situ μs-transient absorption spectroscopy, is found to be 35.3%, owing to the combined effect of the ionic liquid and Co single atoms. This work offers a feasible strategy for efficiently converting CO2 to valuable chemicals

Efficient methane oxidation to formaldehyde via photon–phonon cascade catalysis

The oxidation of methane to value-added chemicals provides an opportunity to use this abundant feedstock for sustainable petrochemistry. Unfortunately, such technologies remain insufficiently competitive due to a poor selectivity and a low yield rate for target products. Here we show a photon–phonon-driven cascade reaction that allows for methane conversion to formaldehyde with an unprecedented productivity of 401.5 μmol h−1 (or 40,150 μmol g−1 h−1) and a high selectivity of 90.4% at 150 °C. Specifically, with a ZnO catalyst decorated with single Ru atoms, methane first reacts with water to selectively produce methyl hydroperoxide via photocatalysis, followed by a thermodecomposition step yielding formaldehyde. Single Ru atoms, serving as electron acceptors, improve charge separation and promote oxygen reduction in photocatalysis. This reaction route with minimized energy consumption and high efficiency suggests a promising pathway for the sustainable transformation of light alkanes

Converting Glycerol into Valuable Trioses by Cu^{δ+}-Single-Atom-Decorated WO_{3} under Visible Light

Photocatalytic selective oxidation under visible light presents a promising approach for the sustainable transformation of biomass-derived wastes. However, achieving both high conversion and excellent selectivity poses a significant challenge. In this study, two valuable trioses, glyceraldehyde and dihydroxyacetone, are produced from glycerol over Cuδ+ -decorated WO3 photocatalyst in the presence of H2 O2 . The photocatalyst exhibits a remarkable five-fold increase in the conversion rate (3.81 mmol ⋅ g-1  ⋅ h-1 ) while maintaining a high selectivity towards two trioses (46.4 % to glyceraldehyde and 32.9 % to dihydroxyacetone). Through a comprehensive analysis involving X-ray photoelectron spectroscopy measurements with and without light irradiation, electron spin resonance spectroscopy, and isotopic analysis, the critical role of Cu+ species has been explored as efficient hole acceptors. These species facilitate charge transfer, promoting glycerol oxidation by photoholes, followed by coupling with OH- , which are subsequently dehydrated to yield the desired glyceraldehyde and dihydroxyacetone

Investigation of highly selective metal-oxide photocatalysts for glycerol oxidation into value-added chemicals

Glycerol is an important by-product in biodiesel production and is produced in large quantities, resulting in a huge surplus flooding the market with a very low price (US $0.11 per kg). It is also a highly versatile polyol which can be transformed into a plethora of different value-added chemicals. Despite many research efforts devoted to finding active catalysts to transform glycerol into valuable products, it remains a significant challenge to develop an efficient and highly selective catalyst for the transformation of glycerol into a specific product. Therefore, glycerol transformation is not only of great scientific significance but also of economic interest. Photocatalysis has been recognised as a promising strategy in glycerol conversion under very mild conditions. However, one barrier is that most semiconductor-based photocatalysts are either non-selective (particularly with the presence of water and/or oxygen) or ineffective to activate the C-C or C-O bond because of poor oxidative activity. To address the above issues, a highly selective catalyst was first synthesised for the transformation of glycerol to the high-value product glycolaldehyde, which is composed of nickel single atoms confined on titanium dioxide. Driven by light, the catalyst operates under ambient conditions using air as a green oxidant. The optimised catalyst shows a selectivity of over 60% to glycolaldehyde, resulting in a 1.06 mmol·g-1·h-1 production rate, and nearly 3 times higher turnover number than NiOx nanoparticle-decorated TiO2 photocatalyst. Diverse operando and in-situ spectroscopies unveil the unique function of the Ni single atoms, which can significantly promote oxygen adsorption, work as an electron sink and accelerate the production of superoxide radicals, thereby improving the selectivity towards glycolaldehyde over other by-products. Next a two-step co-catalyst modification strategy was applied by loading Au and Ag onto ZnO to significantly promote charge separation/transport, meanwhile generating H2O2 and glyceraldehyde simultaneously. Under light irradiation, the optimised catalyst shows a very high glyceraldehyde yield of 3.86 mmol·g-1·h-1, nearly 6 times higher than ZnO, with a remarkable 75% selectivity to glyceraldehyde. Furthermore, H2O2 yield reaches 4.64 mmol·g-1·h-1, 13 times higher than pristine ZnO, leading to a record AQY of 25%. Spectroscopic results and structure analysis unveil that AuAg alloy can effectively act as hole acceptors, improving the charge transfer and facilitating glycerol oxidation. O2•− radicals are facilely formed over Ag single atoms supported ZnO by photogenerated electrons and further reduced to H2O2. In addition, Ag single atoms over the ZnO surface can prevent the H2O2 decomposition and thus significantly enhance the H2O2 selectivity. As a result, nearly 100% atom economy and high charge utilisation have been achieved. Finally, two valuable trioses, glyceraldehyde and dihydroxyacetone, are converted from glycerol over Cuδ+-decorated WO3 photocatalyst with a five-fold enhancement in conversion (14.52 mmol·g-1) and a selectivity of 84%. In-situ spectroscopies and isotopic analysis confirm the function of Cu+ species, which efficiently serve as hole acceptors, enhancing charge transfer which in turn improving the photocatalytic activity. Moreover, it is found that the glycerol oxidation over Cuδ+-decorated WO3 is initiated by the photogenerated holes, followed by coupling with •OH radicals, and finally dehydrated into the target products