Dual Catalyst System Research Articles

Riboflavin‐Catalyzed Photoinduced Atom Transfer Radical Polymerization

AbstractThe photoATRP of methyl acrylate (MA) is investigated using riboflavin (RF) and CuBr2/Me6TREN as a dual catalyst system under green LED irradiation (λ ≈ 525 nm). Both RF and CuBr2/Me6TREN enhanced oxygen tolerance, enabling effective ATRP in the presence of residual oxygen. High molar mass polymers (up to Mn ≈ 129 000 g·mol−1) with low dispersity (Đ ≤ 1.16) are prepared, and chain‐end fidelity is confirmed through successful chain extension. The molecular masses of the obtained polymer increased linearly with conversion and showed high initiation efficiency. Mechanistic studies by laser flash photolysis reveal that the predominant activator generation mechanism is reductive quenching of RF by Me6TREN (83%, under [CuBr2]/[Me6TREN] = 1/3 condition), supported by polymerization kinetics and thermodynamic calculations.

Upcycling of polyethylene/polypropylene mixtures promoted by well-controlled multiblock olefin copolymers

Polyethylene (PE) and isotactic polypropylene (iPP) are two of the most widely used polymer materials, whose huge consumptions urge people to tackle their recycling problem. The incompatibility of PEs and PPs has resulted in their waste streams being recycled into low-value products with poor mechanical properties. Herein, a series of iPP-based olefin block copolymers (OBC) with up to five alternating hard/soft blocks were prepared via coordinative chain transfer polymerization. The facile synthetic strategy of multiblock OBCs not only overcame the inefficiency and diseconomy of living coordination polymerization, but also avoided the critical requirements of complex dual-catalyst systems for chain shuttling polymerization, making it suitable for low-cost and large-scale production of OBCs. These well-designed OBCs provided excellent elastomeric properties combining high strength, high elongation, and high elastic recovery. More importantly, they also demonstrated a strong ability in the upcycling of PE/PP mixtures, transforming brittle blends into tough materials. The PE/PP blends compatibilized with OBCs exhibited greatly improved interfacial adhesion and mechanical properties, with up to 25 times higher elongation at break compared to uncompatibilized blends. It was further demonstrated by the extruding-blow-molded bottles prepared using post-consumer PE/PP products, where recycled bottles containing OBCs exhibited much better mechanical properties than those without OBC. The synthetic strategy of OBCs and the upcycling route of PE/PP blends in this work are not only of great academic value, but also of substantial economic and environmental significance, providing insights into the sustainable development of plastics.

Value-Added Upcycling of PET to 1,4-Cyclohexanedimethanol by a Hydrogenation/Hydrogenolysis Relay Catalysis.

We present an innovative process for directly transforming poly(ethylene terephthalate) (PET), a polymer extensively used in food and beverage packaging, into trans-isomer-enriched 1,4-cyclohexanedimethanol (CHDM), a key ingredient in advanced specialty polymers. Our approach leverages a dual-catalyst system featuring palladium on reduced graphene oxide (Pd/r-GO) and oxalate-gel-derived copper-zinc oxide (og-CuZn), utilizing hydrogenation/hydrogenolysis relay catalysis. This method efficiently transforms PET into polyethylene-1,4-cyclohexanedicarboxylate (PECHD), which is then converted into CHDM with an impressive overall yield of 95 % in a two-stage process. Our process effectively handles various post-consumer PET plastics, converting them into CHDM with yields between 78 % and 89 % across different substrates. Additionally, we demonstrate the applicability and scalability of this approach through a temperature-programmed three-stage relay process on a 10-gram scale, which results in purified CHDM with an isolated yield of 87 % and a notably higher trans/cis ratio of up to 4.09/1, far exceeding that of commercially available CHDM. This research not only provides a viable route for repurposing PET waste but also enhances the control of selectivity patterns in multistage relay catalysis.

Photocatalytic hydrogen production from alcohols to in-situ hydrogenation of nitrogen to ammonia by a dual-catalyst system

Haber-Bosch process to produce ammonia from hydrogenation of nitrogen is high energy intensive and non-sustainable due to substantial CO2 emissions primarily from the H2 generation. Herein, the nitrogen hydrogenation into ammonia is realized through a sustainable synthesis method by a biomimetic photocatalytic dual-catalyst system which used renewable alcohols as hydrogen source, a low redox potential H4SiW12O40 (SiW12) as photocatalyst and suspended Pt-on-carbon (Pt/C) particles as nitrogen hydrogenation catalyst. The SiW12 can quickly dehydrogenate alcohols using solar energy to produce electrons and protons. The produced electrons were stored in SiW12 anion and could be transferred by SiW12 to be released to reduce the nitrogen with protons into ammonia on the Pt/C. The synergistic effects between SiW12 and Pt can enhance electrons into [NNHn]+ and [NHn]+ species through an associative-distal pathway, resulting in the nitrogen hydrogenation with a very low activation energy, and further breaking the scaling theory relations.

Theoretical optimization of bed packing arrangement in cascade Dual-Catalyst system with side reactions

The performance of cascade dual-catalyst systems is highly related to the catalysts spatial arrangement within the bed layers. However, optimization tools for the cascade dual-catalyst layer arrangements are still in need of development. In this study, an optimization framework based on genetic algorithms (GA) and artificial neural networks (ANN) is developed for optimization while explore effects of side reaction on optimized arrangement. Further, a new descriptor as known as delta switch (DS) is introduced. Isolated analysis of the effects of the two types of side reactions shows that the solely side reaction on S0 results in a repeated S0-S1-S0 structure, while the introduce of side reactions on S1 disrupts this structural regularity and reduces the optimal length of the bed layer. Based on DS patterns, a simplified cascade dual-catalysts spatial optimization framework (≤3 layers) is employed, achieving ≥ 95 % performance of original GA.

Atomically dispersed copper-zinc dual sites anchored on nitrogen-doped porous carbon toward peroxymonosulfate activation for degradation of various organic contaminants

Single-atom catalysts (SACs) have been widely studied in Fenton-like reactions, wherein their catalytic performance could be further enhanced by adjusting electronic structure and regulating coordination environment, although relevant research is rarely reported. This text elucidates fabrication of dual atom catalyst systems aimed at augmenting their catalytic efficiency. Herein, atomically dispersed copper-zinc (Cu-Zn) dual sites anchored on nitrogen (N)-doped porous carbon (NC), referred to as CuZn-NC, were synthesized using cage-encapsulated pyrolysis and host–guest strategies. The CuZn-NC catalyst exhibited high activity in activation of peroxymonosulfate (PMS) for degradation of organic pollutants. Based on synergistic effects of adjacent Cu and Zn atom pairs, CuZn-NC (PMS) system achieved 94.44 % bisphenol A (BPA) degradation in 24 min. The radical pathway predominated, and coexistence of non-radical species was demonstrated for BPA degradation in CuZn-NC/PMS system. More importantly, CuZn-NC/PMS system showed generality for degradation of various refractory contaminants. Our experiments indicate that CuZn-N sites on CuZn-NC act as active sites for bonding PMS molecules with optimal binding energy, while pyrrolic N sites are considered as adsorption sites for organic molecules. Overall, this research designs diatomic site catalysts (DACs), with promising implications for wastewater treatment.

Efficient base- and ligand-free palladium catalysed O-arylation of phenols in choline chloride:triethanolamine as a reusable deep eutectic solvent.

In this paper, we present a novel and sustainable approach using choline chloride:triethanolamine as a green, efficient and reusable deep eutectic solvent (DES) for Pd-catalysed O-arylation reactions with Pd/BaSO4 (10%). By using the unique properties of DESs, we successfully achieved C-O bond formation without the need for additional solvents, bases and ligands. This solvent/catalyst system ([ChCl][TEA]2) functioned as a dual catalyst and solvent system, enabling fast and environmentally friendly C-O bond formation from phenol derivatives and electron-deficient aryl halides, leading to remarkable yields under mild reaction conditions. To identify and characterize this DES, we employed differential scanning calorimetry, thermogravimetric analysis, Fourier-transform infrared spectroscopy, refractive index, viscosity, the potential of hydrogen (pH) and conductivity measurements. One of the remarkable advantages of this DES system is its exceptional stability. This solvent/catalyst system exhibited high stability throughout the reaction cycles, showing no significant loss of activity. As a result, this DES and catalyst (Pd/BaSO4 (10%)) can be easily recycled and re-used for up to three consecutive cycles, making it an economically and environmentally attractive option for organic reactions. Our approach offers several key benefits, including simple catalyst preparation, quick reaction times and excellent production efficiency.

Co/Fe Dual Catalysis for Sequential Hydrosilylation–Isomerization: Access to Trisubstituted (E)‐Alkenyl Silanes from Terminal Alkynes

Comprehensive SummaryBy rational modification of electronic and steric properties of pincer ligands, a Co/Fe dual catalyst system is developed for one‐pot sequential Markovnikov alkyne hydrosilylation and stereoselective alkene isomerization. The protocol provides an atom‐economical and efficient approach to trisubstituted (E)‐alkenyl silanes from widely accessible terminal alkynes with high regio‐ and stereoselectivities under mild conditions. The utility of this reaction was demonstrated by gram‐scale synthesis and derivatization of bioactive molecules. The radical clock and trapping experiments indicated that radical pathway might be operative in the alkene isomerization step.

Highly selective production of light aromatics from co-catalytic fast pyrolysis of pre-deoxygenated biomass and hydrogen-rich polyethylene using a dual-catalyst system

Co-catalytic fast pyrolysis of torrefaction deoxygenated pine wood (PW) and high-density polyethylene (HDPE) in dual-catalyst (metal oxidize and zeolite) system is an effective technology to produce renewable bio-aromatics. In this work, the torrefaction deoxygenation pretreatment (TDP) was carried out to remove oxygen element from PW prior to catalytic fast pyrolysis (CFP). 56.90 % oxygen could be removed at TDP temperature of 300 °C, releasing in the oxygen carrier of CO2, CO, H2O, alcohols, acids, phenols, etc. Then, the synergistic effect between the metal oxide and the HZSM-5 in dual-catalyst system was also investigated. Among these metal oxides (Al2O3, MgO, CaO, ZnO, and Fe2O3) and hierarchical HZSM-5, the dual-catalyst of CaO and hierarchical HZSM-5 (treated by 0.2 M NaOH) was the optimal combination. The layout mode between feedstock and dual catalyst was also optimized. The highest yield of aromatics was produced in layout Mode 8, where the CaO was mixed with torrefied PW, but the hierarchical HZSM-5 and HDPE were laid in separated layers. The mixing of CaO and torrefied PW promoted the conversion of the macromolecular oxygenates into micromolecular oxygenates. Then, these small-molecular oxygenates could enter the hierarchical channel of HZSM-5, being converted into aromatics by undergoing the Diels-Alder reaction.

Direct additive-free N-formylation and N-acylation of anilines and synthesis of urea derivatives using green, efficient, and reusable deep eutectic solvent ([ChCl][ZnCl2]2)

In the current report, we introduce a simple, mild efficient and green protocol for N-formylation and N-acetylation of anilines using formamide, formic acid, and acetic acid as inexpensive, nontoxic, and easily available starting materials just with heating along stirring in [ChCl][ZnCl2]2 as a durable, reusable deep eutectic solvent (DES), which acts as a dual catalyst and solvent system to produce a wide range of formanilides and acetanilides. Also, a variety of unsymmetrical urea derivatives were synthesized by the reaction of phenyl isocyanate with a range of amine compounds using this benign DES in high to excellent yields. [ChCl][ZnCl2]2 showed good recycling and reusability up to four runs without considerable loss of its catalytic activity.

Study on ex-situ catalytic pyrolysis of poplar to produce aromatics over a dual-catalyst system of hydroxyapatite and HZSM-5

The ex-situ catalytic pyrolysis of poplar in a dual-catalyst system of hydroxyapatite (HAP) and HZSM-5 was performed using a bench-scale device to enhance the aromatics production. Results indicated that the introduction of HAP could effectively achieve the deoxygenation of macromolecular oxygenates, which were then converted into hydrocarbon precursors. The combination of HAP and HZSM-5 exceedingly promoted the production of aromatics especially monocyclic aromatics (MAHs) than single HZSM-5. The effects of operating conditions on aromatics yield and distribution were investigated. Under the catalyst layout of mode B, with the optimum conditions reaching the catalytic temperature of 500 °C, HAP to HZSM-5 ratio of 2:4, and catalyst to biomass ratio of 1:1, the maximum aromatics yield of 9.10 wt% was achieved, accompanied by the monocyclic aromatics/polycyclic aromatics ratio enhanced to 2.33. At this point, the synergistic effect for MAHs and total aromatics reached 170.09% and 214.14%, respectively. Compared to the conventional metal oxides, the HAP/HZSM-5 dual-catalyst system exhibited superior performance in aromatics production. Besides, the anti-coking capability of HZSM-5 in the dual-catalyst system was also better than that of pure HZSM-5. This research provided a new perspective for the efficient utilization of biomass energy.

Green Molecular Transformation in Dual Catalysis: Photoredox Activation of Vitamin B12 Using Heterogeneous Photocatalyst.

This concept focuses on dual-catalysis using metal complexes and heterogeneous photocatalysts. Vitamin B12 derivatives are sophisticated metal complexes that facilitate enzymatic reactions in the biological systems. The B12 enzymes inspired reactions catalytically proceed in dual-catalyst systems of B12 derivatives and heterogeneous photocatalysts, such as titanium oxide (TiO2) and metal-organic frameworks (MOFs), under light irradiation. The cobalt ions in B12 derivatives are effectively reduced by photoexcited photocatalysts, producing low-valent Co(I) species. The photoinduced nucleophilic Co(I) species react with an alkyl halide to form an organometallic complex with a Co-C bond. The Co-C bond dissociates during photolysis to generate alkyl radicals. Based on this mechanism, dual-catalysis effectively promotes various light-driven organic syntheses and light-driven dehalogenation reactions of toxic alkyl halides. The trends of the dual-catalyst system and recent progress in this field are discussed in this concept.

Bottom-Up Construction of Ni(II)-Incorporated Covalent Organic Framework for Metallaphotoredox Catalysis.

The construction of an all-in-one catalyst, in which the photosensitizer and the transition metal site are close to each other, is important for improving the efficiency of metallaphotoredox catalysis. However, the development of convenient synthetic strategies for the precise construction of an all-in-one catalyst remains a challenging task due to the requirement of precise installation of the catalytic sites. Herein, we have successfully established a facile bottom-up strategy for the direct synthesis of Ni(II)-incorporated covalent organic framework (COF), named LZU-713@Ni, as a versatile all-in-one metallaphotoredox catalyst. LZU-713@Ni showed excellent activity and recyclability in the photoredox/nickel-catalyzed C-O, C-S, and C-P cross-coupling reactions. Notably, this catalyst displayed a better catalytic activity than its homogeneous analogues, physically mixed dual catalyst system, and, especially, LZU-713/Ni which was prepared through post-synthetic modification. The improved catalytic efficiency of LZU-713@Ni should be attributed to the implementation of bottom-up strategy, which incorporated the fixed, ordered, and abundant catalytic sites into its framework. This work sheds new light on the exploration of concise and effective strategies for the construction of multifunctional COF-based photocatalysts.

The modern preparation of menthol and the burgeoning dual catalyst system - The three different synthesis pathways and one significant improvement of menthol

This paper will mainly focus on the modern preparation pathway of menthol, which involves Takasago and BASF, these two traditional pathways. Besides, the unique dual catalyst system will also be talked about in this work. This paper will give the introduction of them, their advantages and disadvantages, moreover, their actual application will also be brought to notice. Menthol is a salient chemical substance that plays an important role in perfume manufacture, and it is actually the source of the special and pleasant smell of many herbs, especially mint. In addition, menthol is also a fundamental raw material in many parts of chemical synthesis due to its unique structure. This research can give summative conclusions about this basic but noteworthy domain.

Tandem Conversion of Fructose to Bio‐diketones Using a Multifunctional Pd‐POPs‐CF3SO3H Catalyst

AbstractTandem conversion of biomass to value‐added fine chemicals is a significant challenge. For instance, the production of fine chemicals from fructose involves conversion to 5‐hydroxymethylfurfural (5‐HMF), followed by another reaction and purification. Dual catalyst systems have been used in nearly every study on the tandem conversion of fructose to bio‐diketones. Therefore, a sole multifunctional heterogeneous catalyst was developed in this study for the tandem conversion of fructose to bio‐diketones, which has not been reported previously. Instrument corrosion and the separation or purification of 5‐HMF were avoided using the multifunctional heterogeneous catalyst, which contained integrated active sites of acid, metal, and anions. The multifunctional CF3SO3H‐functionalized porous‐organic‐polymers(POPs)‐supported Pd catalyst (Pd‐POPs‐CF3SO3H) was prepared using a series of modifications. A bio‐diketone yield of 51.0 % was achieved using Pd‐POPs‐CF3SO3H in the tandem conversion of fructose with an excellent TOF of 88.3 h−1 which is much more efficient than catalyst reported in literatures. Pd‐POPs‐CF3SO3H could be reused at least three times with stable performance. Control experiments and characterization results proved that the high specific surface area, hierarchical pore structure, abundance of CF3SO3−1 anions, and proximity of Pd moieties and acid sites (“The closer the better” principle) led to the decent performance for bio‐diketone.

Enantioselective Chemodivergent Three-Component Radical Tandem Reactions through Asymmetric Photoredox Catalysis.

Chemodivergent synthesis has been achieved in asymmetric photocatalysis. Under a dual catalyst system consisting of a chiral phosphoric acid and DPZ as a photosensitizer, different inorganic bases enabled the formation of two sets of valuable products from the three-component radical tandem transformations of 2-bromo-1-arylenthan-1-ones, styrenes, and quinoxalin-2(1H)-ones. The key to success was the distinct pKa environment, in which the radicals that formed on the quinoxalin-2(1H)-one rings after two radical addition processes underwent either single-electron oxidation or single-electron reduction. In addition, this work represents the first use of quinoxalin-2(1H)-ones in asymmetric photoredox catalysis.

Asymmetric Olefin Isomerization via Photoredox Catalytic Hydrogen Atom Transfer and Enantioselective Protonation.

Asymmetric olefin isomerization can be appreciated as an ideal synthetic approach to access valuable enantioenriched C═C-containing molecules due to the excellent atom economy. Nonetheless, its occurrence usually requires a thermodynamic advantage, namely, a higher stability of the product to the substrate. It has thus led to rather limited examples of success. Herein, we report a photoredox catalytic hydrogen atom transfer (HAT) and enantioselective protonation strategy for the challenging asymmetric olefin isomerization. As a paradigm, by establishing a dual catalyst system involving a visible light photosensitizer DPZ and a chiral phosphoric acid, with the assistance of N-hydroxyimide to perform HAT, a wide array of allylic azaarene derivatives, featuring α-tertiary carbon stereocenters and β-C═C bonds, was synthesized with high yields, ees, and E/Z ratios starting from the conjugated α-substituted alkenylazaarene E/Z-mixtures. The good compatibility of assembling deuterium on stereocenters by using inexpensive D2O as a deuterium source further underscores the broad applicability and promising utility of this strategy. Moreover, mechanistic studies have provided clear insights into its challenges in terms of reactivity and enantioselectivity. The exploration will robustly inspire the development of thermodynamically unfavorable asymmetric olefin isomerizations.

Catalytic Asymmetric Intermolecular [3 + 2] Photocycloaddition of Cyclopropylamines with Electron-Deficient Olefins.

An enantioselective intermolecular [3 + 2] cycloaddition of N-arylcyclopropylamines with 2-aryl acrylates/ketones and cyclic ketone-derived terminal olefins via asymmetric photoredox catalysis is reported. A dual catalyst system involving DPZ and a chiral phosphoric acid is effective for the transformations, leading to a wide array of valuable cyclopentylamines with high yields, ee's, and drs. Among them, elaborate modulation of the ester group of 2-aryl acrylates was shown to be effective in improving reactivity, thereby enabling the success of the transformations.

Nonstoichiometric Direct Arylation Polymerization of Octafluorobiphenyl with 2,7-Diiodofluorene for Regulating CH Terminals of π-Conjugated Polymer.

Nonstoichiometric direct arylation polycondensation of 2,2',3,3',5,5',6,6'-octafluorobiphenyl with excess of 2,7-diiodo-9,9-dioctyl-9H-fluorene is demonstrated. Pd/Ag dual-catalyst system under water/2-methyltetrahydrofuran biphasic conditions enables direct arylation under mild conditions and promotes the intramolecular transfer of a Pd catalyst walking through the fluorene moiety. The nonstoichiometric direct arylation polycondensation under the optimized reaction conditions produces the corresponding π-conjugated polymer with a high molecular weight and terminal octafluorobiphenyl units at both ends.

Photoexcited NiII-Aryl Complex-Mediated Giese Reaction of Aryl Bromides.

A Giese reaction of aryl bromides with electron-deficient alkenes was developed, enabled by a dual catalyst system containing NiII complex and IrIII photocatalyst. This protocol could accommodate a variety of aryl bromides and electron-deficient alkenes, delivering the conjugate adducts in up to 97% yield. The utilization of photoexcited (dtbbpy)NiII(aryl)Br intermediate as an aryl radical source allows this novel transformation of aryl halides, thus expanding the chemical space of excited nickel catalysis.