Catalytic System Research Articles

Enhanced electroreduction of low-concentration nitrate using a Cu-Pd bimetallic cathode system: Performance evaluation, mechanism analysis, and potential applications

Copper (Cu) is a widely recognized cathode for the electrochemical reduction of nitrate (NO3-). Nevertheless, its practical applications are currently restricted due to limited activity and selectivity, particularly at low NO3- concentrations. Herein, a Cu-Pd bimetallic cathode system was designed for NO3- reduction reaction with low NO3- concentrations (≤40 mg-N L−1). In this system, a Cu nanowire array cathode was utilized for NO3- reduction, while a Pd/C particle cathode was employed for NO2- reduction with H2 generated in situ from a polypyrrole electrode. Due to the improved mass transfer and active sites derived from Pd/C particle cathode, along with the synergistic effects of NO3- reduction and NO2- reduction, the constructed Cu-Pd bimetallic cathode system achieved a 7.32-fold increase in NO3– removal rate and a 1.70-fold increase in NH4+ selectivity compared to the traditional Cu cathode. This performance surpassed that of many other state-of-the-art Cu-based cathodes under similar conditions. Moreover, the Cu-Pd bimetallic cathode system displayed high reusability, and extremely low Cu and Pd leaching. Additionally, it showed strong resistance to environmental factors and can adapt to a wide pH range (3−9) and various NO3- concentrations (10–40 mg-N L−1). The electron spin resonance and scavenger experiments confirmed that both direct electron transfer and indirect reduction by atomic H* were involved in the NO3- removal process, with indirect reduction playing a more significant role. Overall, our findings guide the design of superior catalytic systems for NO3- removal to enhance the activity and selectivity of NO3- reduction for efficient water purification.

A highly efficient N-rich Cu-MOF heterogeneous catalyst based on N,N-bis(1H-tetrazole 5-yl)amine in the A3 coupling reaction

The preparation of propargylamines using metal-organic frameworks (MOFs) with high yields in short reaction times is a new method in organic chemistry. A N-rich Cu-MOF catalyst, [Cu(BTA)2]n, with N,N-bis(1(2)H-tetrazol-5-yl)amine (BTA) ligand has been prepared and characterized using FT-IR, XRD, SEM, EDX, and ICP-AES techniques to investigate its performance as a recyclable catalyst in aldehyde-alkyne-amine (A3) reaction for the synthesis of propargylamine derivatives. This catalytic system offers various advantages such as simplicity, high efficiency, short reaction time, and environmental friendliness.

Low-temperature activated porous carbon with functional groups derived from waste tea powder as a potential catalyst for CO2 fixation into cyclic carbonates

The globe is currently confronted with two main environmental problems: environmental solid waste and greenhouse gases. Thus, it is urgent to mitigate these issues and convert them into value-added products. In this context, this work demonstrated the mitigation of two global issues with a single approach. This work established a facile process for a hierarchical porous carbon from abundant bio-waste, such as waste tea powder, and employed it as a heterogeneous catalyst for CO2 fixation into cyclic carbonate. Derived porous carbon catalysts, WTC-1 (Waste tea carbon), WTC-2, AWTC-2-400 (Activated waste tea carbon), AWTC-2a-400, AWTC-2-600, and AWTC-2-800, were produced without the use of solvent by acid-free washing and KOH-free activation. These WTC catalysts were characterized by several standard techniques: XRD, FTIR, XPS, SEM, BET, and TPD. Among the low-temperature activated carbon catalysts, AWTC-2a-400 with potassium-based salt, KI exhibited excellent conversion of propylene oxide (98 %) and ≥ 99 % selectivity of propylene carbonate without solvent under mild conditions of 2.5 MPa, 120 oC, and 2 h. It was observed that the catalytic activity of the WTC catalyst was attributed to the presence of Lewis acidic and basic sites, CaO/CaCO3, MgO, -COOH/OH, and -NH, which are capable of activating the CO2 molecule. Further, the developed catalytic system (AWTC-2a-400/KI) demonstrated superior catalyst versatility for various epoxides under optimized conditions. Moreover, AWTC-2a-400 showed good stability and reusability. Importantly, all reactions were conducted on a gram scale, and the proposed catalyst was effective, which might be favorable for future industrial applications.

High-concentration hydrogen peroxide production by solar interfacial catalysis

Solar-driven catalytic synthesis of H2O2 is an ideal alternative to the anthraquinone method, but current photocatalysts still suffer from low activity and inefficient solar energy utilization. Here we presented an economic and efficient solar interfacial catalysis system (SICS) that incorporated photothermal–photocatalytic materials into commercial sponge to simultaneously generate the required heat and carriers for H2O2 production. We demonstrated its superiority over conventional particulate photocatalysis (PC) in photocatalytic H2O2 production. The SICS, located at the air–water interface, remarkably improve the activities of photocatalysts by efficient utilization of solar-converted heat. The produced H2O2 from SICS was reserved in the sponge and resulted in an ultrahigh concentration of 46 mM for per gram catalyst after 1 h solar irradiation. As thus, our application experiments confirmed that the SICS presented great advantages in organic pollutant (e.g. phenol and tetracycline) degradation compared with conventional PC. This work paves a new way for the industrialization of solar-driven catalysis.

High-entropy oxide based biomimetic catalysis system enables robust oxidative desulfurization with an excellent regeneration ability

Sulfur-containing compounds from the usage of fossil fuel have severe impacts on the ecological environment and human health. To eliminate sulfur species in fuels, oxidative desulfurization is served as an effective technology, whose core lies in constructing an efficient catalytic system under mild conditions. High-entropy oxides (HEOs) with maximized conformational entropy normally generates abundant catalytically active sites, which are beneficial for the enhancement in catalytic performance. On this basis, a biomimetic catalytic system coupling HEO with deep eutectic solvent (DES) was designed for oxidative desulfurization with molecular O2 oxidant by following the electron transfer mechanism. This catalytic system not only exhibited excellent sulfide removal with O2 oxidant under the ambient pressure, but also can resist the adverse effects of naphthalene and indole in an appropriate concentration range. Uniquely, this HEO was capable to be recovered from the DES phase, ensuring a good recycling and regeneration ability. During the whole catalytic process, the electron was transferred in the sequence of sulfide → DES → HEO → O2. These extraordinary features make it to be an alternative candidate for industrial applications under mild conditions.

Electron transfer mediated photo-Fenton-like synergistic catalysis of Fe,Cu-doped MIL-101 coupled with Ag3PO4: Quantitative evaluation and DFT calculations

Widespread use of tetracycline (TC) results in its persistent residue and bioaccumulation in aquatic environments, posing a high toxicity to non-target organisms. In this study, a bimetal-doped composite material Ag3PO4/MIL-101(Fe,Cu) has been designed for the treatment of TC in aqueous solutions. As the molar ratio of Fe/Cu in composite is 1:1, the obtained material AP/MFe1Cu1 is placed in an aqueous environment under visible light irradiation in the presence of 3 mM peroxydisulfate (PDS), which forms a photo-Fenton-like catalytic system that can completely degrade TC (10 mg/L) within 60 min. Further, the degradation rate constant (0.0668 min−1) is 5.66 and 7.34 times higher than that of AP/MFe and AP/MCu, respectively, demonstrating a significant advantage over single metal-doped catalysts. DFT calculations confirm the strong adsorption capacity and activation advantage of PDS on the composite surface. Therefore, the continuous photogenerated electrons (e−) accelerate the activation of PDS and the production of SO4•−, resulting in the stripping of abundant photogenerated h + for TC oxidation. Meanwhile, the internal circulation of FeⅢ/FeⅡ and CuⅡ/CuⅢ in composite also greatly enhances the photo-Fenton-like catalytic stability. According to the competitive dynamic experiments, SO4•− have the greatest contribution to TC degradation (58.93%), followed by 1O2 (23.80%). The degradation intermediates (products) identified by high-performance liquid chromatography-mass spectrometry (HPLC/MS) technique indicate the involvement of various processes in TC degradation, such as dehydroxylation, deamination, N-demethylation, and ring opening. Furthermore, as the reaction proceeds, the toxicity of the intermediates produced during TC degradation gradually decreases, which can ensure the safety of the aquatic ecosystem. Overall, this work reveals the synergy mechanism of PDS catalysis and photocatalysis, as well as provides technical support for removal of TC-contaminated wastewater.

Negative comonomer effect induced by TiCl3-like clusters in MgCl2-based Ziegler-Natta catalysts

The comonomer effect of ethylene/α-olefin copolymerization in the Ziegler-Natta (Z-N) catalytic system, remaining largely elusive and less understood at the molecular level, has been of huge industrial importance and absorbing research interest for decades. Herein, four catalysts with similar physical structures but different polymerization activities and comonomer effects were synthesized by using n-butanol in combination with different secondary electron donors. By tracking catalyst formation, it was found that altering the secondary donor changes the ν(O-H) stability and in turn the MgCl2 facet growth, to influence the polymerization activity. In situ diffuse reflectance Ultraviolet–visible spectra show that different types of active Ti centers are in function in the ethylene polymerization and the ethylene/1-butene copolymerization. Tracing further the microscopic structures of active species upon triethylaluminium (TEA) activation by using Extended X-ray Absorption Fine Structure, it is found that: (i) for the catalysts with negative comonomer effect, the enhanced donor migration promotes the aggregation of active species and leads to the formation of TiCl3-like clusters; (ii) by contrast, for the catalysts with positive comonomer effect, the less mobile donors hinder the aggregation of active species, thus inducing the formation of isolated Ti3+ sites. Our work reveals an evident correlation between the active center and the comonomer effect, which may be strongly modified by the aggregation of the former.

Research on Low Concentration Gas Catalytic Oxidation Power Generation System

In response to the difficulties in direct utilization of low concentration gas in coal mines and the slow development of industrial application of catalytic oxidation technology, a new mode of direct utilization of low concentration gas with a methane concentration of 1.0% in coal mines in catalytic oxidation gas turbine power generation is explored. And based on the development of a 30kW low concentration gas catalytic oxidation gas turbine power generation system, this paper introduces the design process of key equipment such as catalytic oxidation burners, low-temperature and low-pressure turbines, and countercurrent regenerators, providing a technical reference for the utilization of low concentration gas catalytic oxidation.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In SituEvolved Ligand Defects.

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05:1-4.3:1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Plasma‐Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal‐Organic Frameworks Featuring In Situ Evolved Ligand Defects

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal‐based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma‐driven catalytic system for mild production of pure syngas over porous metal‐organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma‐activated intermediate species of CO2 molecules. Specially, the Cu‐based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05:1‐4.3:1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu‐containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas‐production potential‐determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Unlocking the Fluorine-Free Buoy Effect: Surface-Enriched Ruthenium Polypyridine Complexes in Ionic Liquids.

Controlling the local concentration of metal complexes at the surface of ionic liquids (ILs) is a highly sought-after objective due to its pivotal implications in supported ionic liquid phase (SILP) catalysis. Equally important is to avoid per- and polyfluorinated substances due to environmental concerns. Herein, we investigate the surface enrichment of Ru polypyridyl complexes with fluorine-free alkylic side groups of varying lengths and shapes, using the hydrophilic IL [C2C1Im][OAc] as solvent. Additional charged carboxylate groups are included into the polypyridyl ligands to increase the solubility of the complex in the IL. When the ligand system is functionalized with long and hydrophobic alkyl side chains, the complex predominantly localizes at the IL/vacuum interface, as deduced from angle-resolved X-ray photoelectron spectroscopy. Conversely, in the presence of short or more bulky substituents, no surface enrichment is observed. This buoy-like behaviour with fluorine-free side groups is explored for 0.05 %mol to 1 %mol solutions. Intriguingly, surface saturation occurs at approximately 0.5 %mol, which is beneficial to the efficient operation of catalytic systems featuring high surface areas, such as SILP catalysts.

Catalytic Properties of [PSiP] Pincer Cobalt(II) Chlorides Supported by Trimethylphosphine for Alkene Hydrosilylation Reactions.

In this paper, six silyl [PSiP] pincer cobalt(II) chlorides 1-6 [(2-Ph2PC6H4)2MeSiCo(Cl)(PMe3)] (1), [(2-Ph2PC6H4)2HSiCo(Cl)(PMe3)] (2), [(2-Ph2PC6H4)2PhSiCo(Cl)(PMe3)] (3), [(2-iPr2PC6H4)2HSiCo(Cl)(PMe3)] (4), [(2-iPr2PC6H4)2MeSiCo(Cl)(PMe3)] (5), and [(2-iPr2PC6H4)2PhSiCo(Cl)(PMe3)] (6)) were prepared from the corresponding [PSiP] pincer preligands (L1-L6), CoCl2 and PMe3 by Si-H bond activation. The catalytic activity of complexes 1-6 for alkene hyrdosilylation was studied. It was confirmed that complex 1 is the best catalyst with excellent regioselectivity among the six complexes. Using 1 as the catalyst, the catalytic reaction was completed within 1 h at 50 °C, predominantly affording Markovnikov products for aryl alkenes and anti-Markovnikov products for aliphatic alkene substrates. During the investigation of the catalytic mechanism, the Co(II) hydrides [(2-Ph2PC6H4)2MeSiCo(H)(PMe3)] (8) and [(2-iPr2PC6H4)2MeSiCo(H)(PMe3)] (9) were obtained from the stoichiometric reactions of complex 1 and 5 with NaBHEt3, respectively. Complexes 8 and 9 could also be obtained by the reactions of preligands L1 and L5 with Co(PMe3)4 via Si-H bond cleavage. More experiments corroborated that complex 8 is the real catalyst for this catalytic system. Under the same catalytic conditions as complex 1, using complex 8 as a catalyst, complete conversion of styrene was also achieved in 1 h, and the selectivity remained unchanged. Based on the experimental results, we propose a plausible mechanism for this catalytic reaction. The addition of B(C6F5)3 to catalyst 1 can reverse the selectivity of styrene hydrosilylation from the Markovnikov product as the main product (b/l = 99:1) to the anti-Markovnikov product as the main product (b/l = 40:60). Further study indicated that using the (CoCl2 + L1) system instead of complex 1, the selectivity was changed from Markovnikov to anti-Markovnikov product (b/l = 1:99.7). Therefore, the selectivity for the substrate styrene is influenced by the presence of a PMe3 ligand. The different selectivities may be caused by different active species. For the system of complex 1, a cobalt(II) hydride is the real catalyst, but for the (CoCl2 + L1) system, a cobalt(I) complex is proposed as active species. The molecular structures of Co(II) compounds 5 and 9 were resolved by single-crystal X-ray diffraction.

Synergistic One‐pot Tandem Combination of Cu and Proline Catalysis: Stereodivergent Synthesis of Chiral Aldols from Primary Alcohols

AbstractA new stereodivergent one‐pot tandem protocol, which granted diastereo‐ and enantioselective access to chiral aldols by starting from simple primary alcohols, is presented as a proof‐of‐concept. The synergistic combination of a chemoselective Cu(II)‐catalyzed oxidation of primary alcohols into the corresponding aldehydes (without the expected overoxidation into the corresponding carboxylic acids and using simple aerial O2 as co‐oxidant), followed by a concomitant organocatalyzed enantioselective aldol coupling promoted by the system (S)‐proline/HTBD‐BF4 [TBD=1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene], was achieved after fine‐tuning and compatibilizing the conditions required for the successful performance of both catalytic systems. Here, we demonstrated that selection and pairing of both catalysts needs to be extremely judicious to avoid orthogonality, kinetic, concentration or reciprocal poisoning issues. Refinement of the overall tandem protocol allowed us to design a synergistic and stereodivergent protocol which affords comparable or even better diastereoselective results than the organocatalytic system by itself. Finally, the following key factors (from a sustainable point of view) should be highlighted: i) no external VOC solvents are needed during our one‐pot tandem synthetic protocol (by working under neat conditions); and ii) isolation/purification of any intermediate is not required, thus reducing the chemical waste and energy/time costs, simplifying the practical aspects of our synthetic methodology.

Unlocking high-efficiency decontamination by building a novel heterogeneous catalytic reduction system of thiourea dioxide/biochar

Herein, we reported a new contaminant purification paradigm, which enabled highly efficient reductive denitration and dechlorination using a green, stable reducing agent thiourea dioxide (TDO) coupled with biochar (BC) over a wide pH range under anoxic conditions. Specifically, BC acted as both activators and electron shuttles for TDO decomposition to achieve complete anoxic degradation of p-nitrophenol (PNP), p-nitroaniline, 4-chlorophenol and 2,4-dichlorophenol within 2 h. During this process, multiple strongly reducing species (i.e., SO22-, SO2•- and e-/H•) were generated in BC/TDO systems, accounting for 13.3%, 9.7% and 75.5% of PNP removal, respectively. While electron transfer between TDO and H+ or contaminants mediated by BC led to H• generation and contaminant reduction. These processes depended on the electron-accepting capacity and electron-conducting domains of biochar. Significantly, the BC/TDO systems were highly efficient at a pH of 2.0–8.0, especially under acidic conditions, which performed robustly in common natural water constituents.

A Comprehensive Review on Synthesis of Thiazoles: Research on Magnetically Recoverable Catalysts

In chemistry, thiazoles and their derivatives constitute a significant class of biologically active molecules that are thought to be the fundamental building blocks of numerous other biologically active compounds. Many synthetic pharmaceuticals, including fungicides, dyes, antimicrobials, and anticonvulsants, are made using thiazoles and their derivatives as an intermediary. Thus, one of the main areas of organic synthesis research is the presentation of effective and environmentally acceptable catalytic methods for the synthesis of thiazole derivatives. Over the past ten years, organic synthesis in chemistry has been completely transformed by the use of magnetic nanocomposites as catalysts. Magnetic nanoparticles are very stable and easily manipulated on the surface, which can result in the creation of an efficient catalyst. The main feature of magnetic nanocatalysts is their ability to be easily separated from the reaction mixture using only an external magnet. In recent years, several magnetic nanocatalysts have been reported to produce various thiazole compounds. We will look at these methods and talk about the characteristics of these catalytic systems in this post. This review will be helpful for synthetic chemists who are interested in magnetic nanocatalysts and working in the field of thiazole synthesis.

Frustrated Lewis pairs on facet-engineered CeO2 boost the conversion of low-concentration CO2 into cyclic ureas with assistance of diamine platforms

The development of efficient processes for value-added utilization of low-concentration CO2 is an on-going challenge. In this work, we present a sequential system based on diamine platforms for the direct utilization of low-concentration sources of CO2 (≤15%) in the production of cyclic ureas. Specifically, the low-concentration CO2 is captured by ethylenediamine to form ethylenediamine carbamate (EDA-CA), which subsequently undergoes the intramolecular dehydration to give ethyleneurea (EU) in the presence of frustrated Lewis pairs (FLPs) on the facet-engineered CeO2. Remarkably, the productivity of EU obtained from EDA-CA in the sequential system (9.5 mmol·gcat−1·h−1) is ∼4 times higher compared to the traditional catalytic system (2.4 mmol·gcat−1·h−1) using ethylenediamine and pure CO2 (3 MPa). Density functional theory calculations demonstrated that the FLPs on facet-engineered CeO2 significantly reduce the energy barrier for the nucleophilic attack of N-containing segment towards the carbonyl carbon in EDA-CA (rate-limiting step), ultimately optimizing the intramolecular cyclization efficiency of EDA-CA. This work not only provides an innovation tandem approach that enables the production of cyclic ureas from low-concentration CO2, but also opens up a promising avenue for the direct utilization of low-concentration CO2 for value-added applications in the future.

Photocatalytic regeneration of nicotinamide cofactor biomimetics drives biocatalytic reduction by Old Yellow enzymes

A key approach in developing green chemistry involves converting solar energy into chemical energy of biomolecules through photocatalysis. Photocatalysis can facilitate the regeneration of nicotinamide cofactors during redox processes. Nicotinamide cofactor biomimetics (NCBs) are economical substitutes for natural cofactors. Here, photocatalytic regeneration of NADH and reduced NCBs (NCBsred) using graphitic carbon nitride (g-C3N4) was developed. The process involves g-C3N4 as the photocatalyst, Cp*Rh(bpy)H2O2+ as the electron mediator, and Triethanolamine as the electron donor, facilitating the reduction of NAD+ and various oxidative NCBs (NCBsox) under light irradiation. Notably, the highest reduction yield of 48.32 % was achieved with BANA+, outperforming the natural cofactor NAD+. Electrochemical analysis reveals that the reduction efficiency and capacity of cofactors relies on their redox potentials. Additionally, a coupled photo-enzymatic catalysis system was explored for the reduction of 4-Ketoisophorone by Old Yellow Enzyme XenA. Among all the NCBsox and NAD+, the highest conversion ratio of over 99 % was obtained with BANA+. After recycled for 8 times, g-C3N4 maintained over 93.6 % catalytic efficiency. The photocatalytic cofactor regeneration showcases its outstanding performance with NAD+ as well as NCBsox. This work significantly advances the development of photocatalytic cofactor regeneration for artificial cofactors and its potential application.

Photochemical Synthesis of Chiral Heterocycles via Asymmetric Carbon‐Heteroatom Bond Formation

Chiral heterocyclic compounds play a crucial role in the pharmaceutical science, materials science, and agrochemical industries. The critical step for synthesizing chiral heterocycles is the formation of asymmetric carbon‐heteroatom bonds, which can be achieved in a chiral environment under thermal or photochemical conditions. However, photochemical asymmetric transformation has become an area of immense growth in the past 15 years. In the drug discovery and development era, chiral photochemical transformations have drawn the attention of researchers to develop new synthetic strategies for chiral heterocycles via asymmetric carbon‐heteroatom bond formation. Chiral photochemistry in the pathway of asymmetric synthesis requires a chirality source which is transferred to the products. A catalytic chiral metal complexing agent or a chiral photosensitizer that generally follows a single electron transfer (SET) or oxidative and reductive quenching cycle has been widely exploited to achieve this goal. In this review, we have demonstrated the recent development of photochemical synthesis of chiral heterocycles via asymmetric carbon‐heteroatom bond formation by using a chiral metal catalyst, asymmetric organocatalyst, or dual catalytic system based on their plausible mechanism.

MOX-TiO2 (M=Pt, Pd, Ru) for alcoholysis reaction from furfuryl alcohol to ethyl levulinate

Simple noble metal oxides (PtOx, PdOx, RuOx) based titanium dioxide (Pt–TiO2, Pd–TiO2, Ru–TiO2) were prepared using a facile sol-gel method. The conversion of furfuryl alcohol (FAL) to ethyl levulinate (EL) was studied. Full characterizations were performed using XRD, XPS, Raman and in situ FT-IR. An in-depth study of acidic strength and sites distribution (Brønsted or Lewis) was conducted by NH3-TPD, pyridine-IR. The profiles of H2-TPR and O2-TPD suggested enhanced reducibility and optimum oxygen storage capacity in Pt–TiO2. Remarkable FAL conversion (94.4%), EL yield (89.6%) with productivity (21.3 × 103 molEL/mmolPt h) and TOF (22.5 × 103 molFAL/mmolPt h) were obtained. Metal productivity follows the order: Pt (21.3 × 103 molEL/mmolPt h) > Ru (11.5 × 103 molEL/mmolRu h) > Pd (3.6 × 103 molEL/mmolPd h). Two different reaction pathways were proposed. From computational calculations of charge density differences and Ead value, a robust electron transfer capacity was found in Pt–TiO2, as well as an advantageous FAL adsorption as compared to other catalytic systems.

Tandem photocatalysis of nitrate to nitrogen on Cu@CN/TiOx S-scheme heterojunction

The persistent challenge of nitrate (NO3–) pollution in water systems, profoundly impacting ecosystems and human health, demands effective remediation strategies. Here, we present an innovative S-scheme Cu@CN/TiOx heterojunction for high-efficiency photocatalytic denitrification (PCDN). Evaluation of its performance demonstrates exceptional NO3– removal efficiency (99.5%) and remarkable N2 selectivity (95.5%), with 13.7 and 4.1 times higher rate constants of NO3– removal than the individual Cu@CN and TiOx components. Notably, this catalyst exhibits impressive stability across multiple cycles, maintaining consistent high conversion rates and selectivity. Mechanistic insights unveiled a tandem reaction pathway where Cu@CN selectively reduced NO3– to NO2–, followed by the TiOx-mediated CO2•– generation, enabling highly selective NO2– to N2 conversion. This unique catalytic system, featuring spatially separated redox-active sites, presents a promising avenue for efficient, selective, and stable denitrification processes, offering significant potential in addressing water pollution challenges and advancing tandem catalytic systems.