Selective Catalysts Research Articles

Understanding Advanced Transition Metal-Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering.

Non-noble transition metal (TM)-based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction (2e- ORR) process. To efficiently drive this reaction, these TM-based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting-edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non-noble TM-based compounds for 2e- ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e- ORR performance (selectivity, activity, and stability) of TM-based catalysts, accompanied by an insightful exploration of the phase-performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non-noble TM-based electrocatalysts.

CO2 Electrolyzers.

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.

Overcoming limitations in propane dehydrogenation by codesigning catalyst-membrane systems.

Propylene production through propane dehydrogenation (PDH) is endothermic, and high temperatures required to achieve acceptable propane conversions lead to low selectivity and severe carbon-induced deactivation of conventional catalysts. We developed a catalyst-membrane system that removes the hydrogen by-product and can thus achieve propane conversions that exceed equilibrium limits. In this codesigned system, a silica/alumina (SiO2/Al2O3) hollow-fiber hydrogen membrane was packed with a selective platinum-tin (Pt1Sn1/SiO2) PDH catalyst on the tube side with hydrogen diffusing from the tube to the shell side. We demonstrate that the catalyst-membrane system can achieve propane conversions >140% of the nominal equilibrium conversion with a propylene selectivity >98% without deactivation of the system components. We also show that by introducing oxygen on the shell side of the catalyst-membrane system, we can couple the endothermic PDH reaction on the tube side with exothermic hydrogen oxidation on the shell side. This coupling results in higher rates of hydrogen transport, leading to further enhancements in the propane conversion as well as desired thermoneutral system operation.

A Simple Tool to Benchmark Reactivity in Asymmetric Catalysis

AbstractHerein, we report a simple and noninvasive experimental protocol in which a series of relative reaction rates may be obtained by way of single competition experiments. This approach permits a quantitative comparison of any given number of chiral catalysts relative to a ‘benchmarking’ chiral catalyst – a particularly useful tool since catalyst design and selection have remained largely dependent on chemical intuition. We apply this benchmarking approach towards an asymmetric N-heterocyclic carbene (NHC) catalyzed intramolecular Stetter reaction as a proof-of-concept study. In doing so, we demonstrate a rapid method to assess the complex interplay between catalyst reactivity and stereoelectronic effects – an analytical approach that has heretofore not been attempted for NHCs. To showcase the generality of this method, we apply it to an enantioselective Rh(I)-catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and aryl alkynes for a series of chiral phosphoramidite ligands. The results described herein demonstrate that this inexpensive and easily adoptable protocol can reveal complex yet subtle steric and stereoelectronic effects of vastly different chiral catalyst structures, which can further aid with catalyst development and selection for a clearly defined application.

Screening of borophene-supported highly active and selective single-atom catalysts for electrocatalytic nitrogen reduction reactions

Ammonia (NH3) is an ideal zero-carbon clean energy source because of its substantial hydrogen capacity, high-energy density and facile transportability. Compared to disadvantages of Haber–Bosch processes, such as demanding reaction conditions, high energy consumption and inefficiency, the electrocatalysis nitrogen reduction reaction (NRR) can achieve green synthesis of NH3 due to mild reactive conditions. Utilizing density functional theory (DFT), explored the potential of borophene-supported transition metals as single atom catalysts (SACs) for NRR. The NRR pathways and Gibbs free-energy (ΔG) of the selected V@Bβ12, Cr@Bβ12, Zr@Bβ12 and Mo@Bβ12 were studied in detail after rigorous screening processes. The limiting potentials of NRR in optimal path are -0.10, -0.27, -0.18 and -0.07 V, respectively, which are excellent catalysts for NRR. Under operating voltage conditions, TM@Bβ12 has excellent ability to resist surface oxidation and inhibit hydrogen evolution reaction (HER). In addition, V@Bβ12, Cr@Bβ12, Zr@Bβ12 and Mo@Bβ12 have good selectivity for NRR. Cr@Bβ12 and Mo@Bβ12 are also potential catalysts for HER. The source of TM@Bβ12 catalytic activity in NRR fully confirms the good conductive properties, and the transmission of the charge contribute to improve catalytical activity of NRR. This paper provides theoretical guidance on the synthesis of a new type of NRR catalyst.

Multicomponent Reductive Coupling for Selective Access to Functional γ-Lactams by a Single-Atom Cobalt Catalyst.

Despite their significant importance to numerous fields, the difficulties in direct and diverse synthesis of α-hydroxy-γ-lactams pose substantial obstacles to their practical applications. Here, we designed a nitrogen and TiO2 co-doped graphitic carbon-supported material with atomically dispersed cobalt sites (CoSA-N/NC-TiO2), which was successfully applied as a multifunctional catalyst to establish a general method for direct construction of α-hydroxy-γ-lactams from cheap and abundant nitro(hetero)arenes, aldehydes, and H2O with alkynoates. The striking features of operational simplicity, broad substrate and functionality compatibility (>100 examples), high step and atom efficiency, good selectivity, and exceptional catalyst reusability highlight the practicality of this new catalytic transformation. Mechanistic studies reveal that the active CoN4 species and the dopants exhibit a synergistic effect on the formation of key acid-masked nitrones; their subsequent nucleophilic addition to the alkynoates followed by successive reduction, alkenyl hydration, and intramolecular ester ammonolysis delivers the desired products. In this work, the concept of reduction interruption leading to new reaction route will open a door to further develop useful transformations by rational catalyst design.

An improved immobilized molybdenum oxidative catalyst bearing an amino acid-derived bifunctional chelator

Herein we introduce a new glycine-bisphenol molybdenum(VI) complex, SBA@AP-GDC-Mo, immobilized on ordered mesoporous silica SBA-15 (Santa Barbara Amorphous) as an efficient and selective heterogenous catalyst. SBA@AP-GDC-Mo was fully characterized by Fourier transform-infra red (FT-IR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), field emission-transmission electron microscopy (FE-TEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES) and Barrett–Joyner–Halenda (BJH) and Brunauer–Emmett–Teller (BET) adsorption isotherms. The catalytic performance of SBA@AP-GDC-Mo was evaluated in the chemoselective oxidation of sulfides to sulfoxides and sulfones and found to be superior to our previously reported diamine–bisphenol molybdenum(VI) catalyst. The advantages of SBA@AP-GDC-Mo include high activity and better chemoselectivity under mild and eco-friendly conditions (e.g., ambient temperature using aqueous or aqueous–ethanolic solutions), recyclable for at least four cycles and easier overall synthesis in good yields including tethering of the ligand to the support.

Enhancing H2O2 Electrosynthesis at Industrial-Relevant Current in Acidic Media on Diatomic Cobalt Sites.

Electrocatalytic synthesis of hydrogen peroxide (H2O2) in acidic media is an efficient and eco-friendly approach to produce inherently stable H2O2, but limited by the lack of selective and stable catalysts under industrial-relevant current densities. Herein, we report a diatomic cobalt catalyst for two-electron oxygen reduction to efficiently produce H2O2 at 50-400 mA cm-2 in acid. Electrode kinetics study shows a >95% selectivity for two-electron oxygen reduction on the diatomic cobalt sites. In a flow cell device, a record-high production rate of 11.72 mol gcat-1 h-1 and exceptional long-term stability (100 h) are realized under high current densities. In situ spectroscopic studies and theoretical calculations reveal that introducing a second metal into the coordination sphere of the cobalt site can optimize the binding strength of key H2O2 intermediates due to the downshifted d-band center of cobalt. We also demonstrate the feasibility of processing municipal plastic wastes through decentralized H2O2 production.

Constructing Highly Efficient ZnO Nanocatalysts with Exposed Extraordinary (110) Facet for CO2 Electroreduction.

Electrochemical reduction of CO2 to highly valuable products is a promising way to reduce CO2 emissions. The shape and facets of metal nanocatalysts are the key parameters in determining the catalytic performance. However, the exposed crystal facets of ZnO with different morphologies and which facets achieve a high performance for CO2 reduction are still controversial. Here, we systematically investigate the effect of the facet-dependent reactivity of reduction of CO2 to CO on ZnO (nanowire, nanosheet, and flower-like). The ZnO nanosheet with exposed (110) facet exhibited prominent catalytic performance with a Faradaic efficiency of CO up to 84% and a current density of -10 mA cm-2 at -1.2 V versus RHE, far outperforming the ZnO nanowire (101) and ZnO nanoflower (103). Based on detailed characterizations and kinetic analysis, the ZnO nanosheet (110) with porous architecture increased the exposure of active sites. Further studies revealed that the high CO selectivity originated from the enhancement of CO2 adsorption and activation on the ZnO (110) facet, which promoted the conversion of CO2 toward CO. This study provides a new way to tailor the activity and selectivity of metal catalysts by engineering exposed specific facets.

CaH2-Assisted Molten Salt Synthesis of Zinc-Rich Intermetallic Compounds of RhZn13 and Pt3Zn10 for Catalytic Selective Hydrogenation Application

Zinc-included intermetallic compound catalysts of RhZn, PtZn, and PdZn with a molar ration of Zn/metal = 1/1, which are generally prepared using a hydrogen reduction approach, are known to show excellent catalytic performance in some selective hydrogenations of organic compounds. In this study, in order to reduce the incorporated mounts of the expensive noble metals, we attempted to prepare zinc-rich intermetallic compounds via a CaH2-assisted molten salt synthesis method with a stronger reduction capacity than the common hydrogen reduction method. X-ray diffraction results indicated the formation of RhZn13 and Pt3Zn10 in the samples prepared by the reduction of ZnO-supported metal precursors. In a hydrogenation reaction of p-nitrophenol to p-aminophenol, the ZnO-supported RhZn13 and Pt3Zn10 catalysts showed a higher selectivity than the RhZn/ZnO and PtZn/ZnO catalysts with the almost similar conversions. Thus, it was demonstrated that the zinc-rich intermetallic compounds of RhZn13 and Pt3Zn10 could be superior selective hydrogenation catalysts compared to the conventional intermetallic compound catalysts of RhZn and PtZn.

Construction of ternary alloy Cu-Ni-Co catalysts with highly active sites to enhance the initial adsorption process of nitrate reduction to ammonia

Ammonia, an exceptional carbon-free hydrogen source, holds significant promise as a product of electrocatalytic nitrate reduction to ammonia (ENRA) processes. Nonetheless, developing efficient ENRA catalysts remains a formidable challenge due to the intricacies of the eight-electron transfer process that generates a range of complex intermediates, impeding the desired ammonia formation. By offering multiple adsorption sites for various intermediates, multicomponent metal catalysts effectively regulate the processes of proton and electron transfer, providing a viable solution. To address this, CuNiCo alloy catalysts, denoted as CuNiCo/CP, are synthesized via co-deposition, employing salicylic acid as a complexing agent. The CuNiCo/CP alloy catalyst exhibits an ammonia yield of up to 303.49 μmol h–1cm–2 at –0.25 V vs. RHE, Faraday efficiency of up to 96.3 %, and excellent stability. Notably, a battery utilizing Zn-NO3− and CuNiCo/CP as the cathode exhibits an impressive peak power density of 9.678 mW cm–2. Experiment and DFT calculations demonstrate that CuCoNi/CP can provide more active sites and effective modulation of the initial adsorption energy. This work will inspire further Cu-based alloy ENRA catalyst development to optimize the adsorption of multiple intermediates to enhance catalyst activity and selectivity.

Origin of the Increase in the Selectivity of Ru Catalysts with the Addition of Amines in the Presence of ZnSO4 for the Selective Hydrogenation of Benzene to Cyclohexene

The synthesis of nylon 6 and nylon 66 can be performed, starting with the selective hydrogenation of benzene to cyclohexene, which is deemed to be environmentally friendly and cost-saving and to have higher atom efficiency. Nano-Ru catalyst was synthesized via a precipitation method. The prepared catalyst was evaluated in the selective hydrogenation of benzene toward cyclohexene generation in the presence of ZnSO4 in a liquid batch reactor. The promotion effect of the addition of amines, i.e., ethylenediamine, ethanolamine, diethanolamine, and triethanolamine, was investigated. The fresh and spent catalysts were thoroughly characterized by XRD, TEM, AES, N2-sorption, FT-IR, and TPR. It was found that the addition of amines could significantly improve the catalytic selectivity toward cyclohexene formation in the presence of ZnSO4. This was attributed to the formation of (Zn(OH)2)5(ZnSO4)(H2O)x (x = 0.5, 3 or 4) through the reaction between ZnSO4 and the amines, which could be chemisorbed on the Ru surface. This led to retarding the formation of cyclohexane from the complete hydrogenation of benzene and, thus, increased the catalytic selectivity toward cyclohexene synthesis. Therefore, with the presence of ZnSO4, the amount of chemisorbed (Zn(OH)2)5(ZnSO4)(H2O)x increased with increasing amounts of added amines, leading to a decline in the catalytic activity toward benzene conversion and selectivity toward cyclohexene generation. When 7.6 mmol of diethanolamine and 10 g of ZrO2 were applied, the highest cyclohexene yields of 61.6% and 77.0% of benzene conversion were achieved over the Ru catalyst. Promising stability was demonstrated after six runs of catalytic experiments without regeneration. These achievements are not only promising for industrial application but also beneficial for designing other catalytic systems for selective hydrogenation.

Potential of (La-)NiCu catalysts for the hydrodeoxygenation of 4-(2-furanyl)-3-buten-2-one into fuels: Investigation of support and La addition

Aiming at the valorization of furfural-derived compounds, the potential of (La-)NiCu catalysts for the hydrodeoxygenation of 4-(2-furanyl)-3-buten-2-one has been assessed. The impact of support acidity and the effects of modifying the support with La have been explored. While catalysts with non-acidic supports solely lead to hydrogenation, the acid sites enable furanic ring opening. Additionally, changing the support alters the metal-support interaction strength, with stronger interactions reducing the NiCu alloy particle size and increasing activity. Furthermore, according to Density of States calculations, La further enhances the hydrodeoxygenation activity by increasing the adsorption strength. Also, for the acidic supports, it increases the relative abundance of NiCu alloy on the support surface, further increasing the specific activity. The La-NiCu-Al catalyst demonstrated was the best performing catalyst at 200 °C and 40 bar H2, achieving a high conversion rate of 77 mol kgcat−1 h−1 with a combined selectivity of 29 % towards octane and BTHF at 99 % conversion, and stability over 5 hours Time-On-Stream. Additionally, isopropyl alcohol proved to be an excellent hydrogen donor, as the external H2 pressure does not substantially impact the catalyst activity and selectivity, but H2 itself proved to be important for the catalyst stability.

Comparative study and screening of Single-Atom and homonuclear Dual-Atom catalysts for NO reduction via electrocatalysis

Electrocatalytic technology offers a promising solution to address environmental pollution and resource scarcity. The development of high-stability and selective catalysts is crucial in this regard. This paper focuses on single-atom catalysts (SACs) and homonuclear dual-metal catalysts (DACs) constructed using transition metal atoms as active centers. Catalytic activity and selectivity of these catalysts in the nitric oxide reduction reaction (NORR) process are systematically investigated through first-principles calculations, while exploring the influence of adjacent metal atoms on their characteristics. Using a four-step screening approach, we identify Ti2-N6 as a standout candidate catalyst with a low applied voltage (-0.24 V) for selective NO catalysis and significant inhibition of competitive responses. Homonuclear DACs inherit the advantages of SACs while disrupting the inherent linear relationship, resulting in reduced applied voltage requirements and enhanced catalytic performance. This work presents an efficient catalyst screening method and highlights the unique characteristics and advantages of homonuclear DACs over SACs.

Achieving 78.2 % Faraday Efficiency for Electrochemical Ammonia Production Via Covalent Modification of CNTs with B4C

AbstractElectrochemical reduction of N2 to NH3 provides an alternative to the Haber‐Bosch process for sustainable NH3 production driven by renewable electricity. Here, we reported carbon nanotubes (CNTs) covalently modified with boron carbide (B4C) as a nonmetallic catalyst for efficient electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The structure of the catalyst was characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), elemental mapping, X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The catalyst held a superior selectivity for NRR with high Faraday efficiency of 78.2 % accompanying with NH3 yield rate of 14.0 μg mg−1cat. h−1 under the condition of 0.1 M Na2SO4 and −0.6 V vs. RHE. Electrochemical experiments including cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization curves were performed to explain the best electrochemical properties of B4C/CNTs among the samples. This work demonstrates that the strategy of covalent modification plays an important role to improve the selectivity of electrochemical NRR catalyst, thus allowing the reactions to proceed more efficiently.

Modulating the Catalytic Properties of Polyoxovanadates with Transition-Metal-Complex Units for Selective Oxidation of Sulfides.

Selective oxidation of sulfides to sulfoxides is of great significance in the synthesis of pharmaceuticals, desulfurization of fuels, and detoxification of sulfur mustard chemical warfare agents. Designing selective catalysts to achieve the efficient transformation of sulfides to sulfoxides is thus highly desired. Herein, we report three transition metal-complex-functionalized polyoxovanadates, [Zn2(BPB)2][V4O12]·0.5BPB·H2O (1), [Ni(BPB)(H2O)][V2O6]·2H2O (2), and [Co(HBPB)2][V4O12] (3) (BPB = 1,4-bis(pyrid-4-yl)benzene)), and explore their applications for selective oxidation of sulfides using H2O2 as an oxidant. All three compounds were catalytically effective for the oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide, with 1 being best-performing with complete conversion and a selectivity of 96.7%. In the selective oxidation of a series of aromatic and aliphatic sulfides to corresponding sulfoxides, 1 also showed satisfactory performance; in particular, the chemical warfare agent stimulant 2-chloroethyl ethyl sulfide can be completely and selectively oxidized to the nontoxic 2-chloroethyl ethyl sulfoxide within 20 min at room temperature. Catalyst 1 can be recycled and reused at least six times with uncompromised performance. The perfect performance of 1 is attributed to the synergistic effect of coordinatively unsaturated V and Zn sites in bimetallic oxide, as revealed by comparative structural and catalytic studies.

Selective hydroconversion of lignin-derived compounds over a Ni/hydroxyapatite

Catalytic hydroconversion (CHC) of lignin-derived compounds (LDCs) to cyclanes and cyclohexanol (CHII) promotes the value-added utilization of LDCs. Nevertheless, designing a highly active and selective catalyst for this purpose remains a challenge. Herein, Ni/hydroxyapatite (HAP) was fabricated by a slightly modified deposition–precipitation approach and employed for the CHC of benzyloxybenzene (BOB) and phenethoxybenzene (PEOB) under different conditions. Consequently, BOB was fully converted with CHII and methylcyclohexane (MCH) as the main products (MPs) in the yield of 94.8 and 100 % under the optimum conditions of 20 mg Ni15/HAP, 140 °C, 4 MPa H2, and 4 h, while complete conversion of PEOB to CHII and ethylcyclohexane (ECH) as MPs proceeded under initial hydrogen pressure of 4 MPa at 180 °C for 4 h. In addition, other lignin-related model compounds can also be selectively hydrogenated to cyclanes and CHII, suggesting the high activity and selectivity of Ni15/HAP. Meanwhile, based on the product distribution and Ni15/HAP characterization, relevant mechanisms were proposed. Specifically, BOB conversion to CHII and MCH via the >CH–O– bond cleavage induced by H− addition, abstraction of H+ by the resulting phenoxy anion from the catalyst surface, and benzene ring hydrogenation, whereas conversion of PEOB to CHII and ECH was similar to BOB. Furthermore, Ni15/HAP displays an excellent reusability.

Oxygen vacancy based WO3/SnO2-x promote electrochemical H2O2 accumulation by two-electron water oxidation reaction and toxic uniform dimethylhydrazine degradation

The key to constructing an anodic electro-Fenton system hinges on two pivotal criteria: enhancing the catalyst activity and selectivity in water oxidation reaction (WOR), while simultaneously inhibiting the decomposition of hydrogen peroxide (H2O2) which is on-site electrosynthesized at the anode. To address the issues, we synthesized novel WO3/SnO2-x electrocatalysts, enriched with oxygen vacancies, capitalize on the combined activity and selectivity advantages of both WO3 and SnO2-x for the two-electron pathway electrocatalytic production of H2O2. Moreover, the introduction of oxygen vacancies plays a critical role in impeding the decomposition of H2O2. This innovative design ensures that the Faraday efficiency and yield of H2O2 are maintained at over 80 %, with a noteworthy production rate of 0.2 mmol h−1 cm−2. We constructed a novel electro-Fenton system that operates using only H2O as its feedstock and applied it to treat highly toxic uniform dimethylhydrazine (UDMH) from rocket launch effluent. Our experiments revealed a substantial total organic carbon (TOC) removal, achieving approximately 90 % after 120 mins of treatment. Additionally, the toxicity of N-nitrosodimethylamine (NDMA), a byproduct of great concern, was shown to be effectively mitigated, as evidenced by acute toxicity evaluations using zebrafish embryos. The degradation mechanism of UDMH is predominantly characterized by the advanced oxidative action of H2O2 and hydroxyl radicals, as well as by complex electron transfer processes that warrant further investigation.

A Closed-Loop Biorefinery Approach for the Valorization of Winery Waste: The Production of Iron-Sulfonated Magnetic Biochar Catalysts and 5-Hydroxymethyl Furfural from Grape Pomace and Stalks

In this work, a closed-loop strategy for the management and valorization of winery waste was proposed. The exhausted pomace and grape stalks that are typically obtained from white wine industries were used as a source of simple sugars, namely, glucose and fructose, and of lignocellulosic feedstock for the preparation of selective catalysts for the 5-hydroxymethylfurfural (5-HMF) production from fructose. A novel synthetic procedure was developed for the synthesis of iron-sulfonated magnetic biochar catalysts (Fe-SMBCs). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), BET surface area, porous structure analysis and determination of total amount of acid sites were performed in order to characterize the physico-chemical properties of the synthesized systems. Then, these heterogeneous catalysts were successfully tested via the dehydration of simple sugars into 5-HMF by using methyl isobutyl ketone (MIBK) and gamma valerolactone (GVL) as co-solvents. The optimum 5-HMF yield of 40.9 ± 1.1%mol with a selectivity of 59.8 ± 2.6%mol was achieved by adopting the following optimized conditions: 0.1 g of catalyst, volume ratio of GVL to H2O = 2 to 1, 403 K, 6 h. In addition, the catalyst was easily recycled using an external magnetic field and used for at least five reaction cycles without significant loss of catalytic activity.

Polyarene Oxides with Tunable Quinone Units for Photocatalytic CO2 Reduction: A Simple Strategy toward Effective and Selective Catalysts.

The photocatalytic transformation of carbon dioxide (CO2) into valuable chemicals is a challenging process that requires effective and selective catalysts. However, most polymer-based photocatalysts with electron donor-acceptor (D-A) structures are synthesized with a fixed D-A ratio by using expensive monomers. Herein, we report a simple strategy to prepare polyarene oxides (PAOs) with quinone structural units via oxidation treatment of polyarene (PA). The resultant PAOs show tunable D-A structures and electronic band positions depending on the degree of oxidation, which can catalyze the photoreduction of CO2 with water under visible light irradiation, generating CO as the sole carbonaceous product without H2 generation. Especially, the PAO with an oxygen content of 17.6% afforded the highest CO production rate of 161.9 μmol g-1 h-1. It is verified that the redox transformation between quinone and phenolic hydroxyl in PAOs achieves CO2 photoreduction coupled with water oxidation. This study provides a facile way to access conjugated polymers with a tunable D-A structure and demonstrates that the resultant PAOs are promising photocatalysts for CO2 reduction.