Binary Co-catalyst Research Articles

Hollow core-shell LDH@N-HCS/CN S-scheme photocatalyst with the enhanced visible-light activity

It is a great challenge to effectively increase the charge separation and active sites of earth-abundant graphitic carbon nitride (CN) semiconductors to improve the photocatalytic performance. Looking for a highly active cocatalyst has attracted attention because of their potential to resolve the issues of low charge separation and low specific surface area of CN. A core-shell cocatalyst composed of nitrogen doped hollow carbon spheres (N-HCS) as the core and LDH nanoplates as the photoactive shell has been designed to increase the pristine CN active sites and charge separation. N-HCS acted as the support for LDH nanoplates to prevent particle agglomeration and served as the fast electron transfer channels to enhance the photoinduced charge separation efficiency. The ternary nanocomposites exhibited superior activity for nonyl phenol and Acid Blue 92 degradation compared to the unmodified CN under the visible light. The optimized deposition of LDH@N-HCS (15 wt%) on the CN surface resulted in 7-fold higher activity than without the cocatalyst. The improved photocatalytic activity of the ternary composite compared to CN could be attributed to two factors: efficient electron-hole pair separation due to LDH nanoplates and CN interface, and the presence of the N-HCS as an electron collector. The porous hollow structure of the cocatalyst exposes the numerous surface-active sites that favor visible light photocatalytic performance and supplies multiple reflection of photons into the cavity, increasing the usage ratio of light. This work will supply a novel strategy to rationally fabricate a noble metal-free binary cocatalyst for efficient visible light activity.

Pd-Sn promoted NbOx/TiO2 catalysts for hydrogen photoproduction: Effect of Pd-Sn interaction on charge handling and reaction mechanism

Enhanced performance of Pd in the photocatalytic production of green hydrogen from methanol:water mixtures is achieved through the use of a sn-containing binary co-catalyst. For a Pd:Sn molar ratio of 1:1, the binary co-catalyst leads to an outstanding enhancement of activity under UV, visible and sunlight illumination, rendering a quantum efficiency value of 4 % in the latter case. A core–shell type interaction occurs between Pd metal nanoparticles and Sn oxo-hydroxyde nanoentities, resulting in an electronic modification of both components. The chemical effects of the binary co-catalyst were explored under reaction conditions using infrared spectroscopy. Overall, this study provides evidence that the electronic interaction between Pd and Sn promotes the adsorption and attack of the charge carrier species on the methanol molecule and controls the reaction mechanism, favoring the generation of hydrogen. This new system appears to be a strong candidate in the contribution to the new hydrogen economy through a green and eco-efficient process using renewable energy and reagents.

Construction and performance of CdS/MoO2@Mo2C-MXene photocatalyst for H2 production

Nowadays, photocatalytic technologies are regarded as promising strategies to solve energy problems, and various photocatalysts have been synthesized and explored. In this paper, a novel CdS/MoO2@Mo2C-MXene photocatalyst for H2 production was constructed by a two-step hydrothermal method, where MoO2@Mo2C-MXene acted as a binary co-catalyst. In the first hydrothermal step, MoO2 crystals with an egged shape grew on the surface of two-dimensional (2D) Mo2C MXene via an oxidation process in HCl aqueous solution. In the second hydrothermal step, CdS nanorods were uniformly assembled on the surface of MoO2@Mo2C-MXene in ethylenediamine with an inorganic cadmium source and organic sulfur source. The CdS/MoO2@Mo2C-MXene composite with MoO2@Mo2C-MXene of 5 wt% exhibits an ultrahigh visible-light photocatalytic H2 production activity of 22,672 µmol/(g·h), which is ∼21% higher than that of CdS/Mo2C-MXene. In the CdS/MoO2@Mo2C-MXene composite, the MoO2 with metallic nature separates CdS and Mo2C MXene, which acts as an electron-transport bridge between CdS and Mo2C MXene to accelerate the photoinduced electron transferring. Moreover, the energy band structure of CdS was changed by MoO2@Mo2C-MXene to suppress the recombination of photogenerated carriers. This novel compound delivers upgraded photocatalytic H2 evolution performance and a new pathway of preparing the low-cost photocatalyst to solve energy problems in the future.

Ni2P–Ni2P4O12 enhanced CdS nanowires for efficient visible light photocatalytic hydrogen production

Intrinsic charge carrier recombination, narrow visible light absorption and poor durability restrain the photoactivity for solar-to-H2 production. Here, noble-metal-free binary co-catalyst Ni2P–Ni2P4O12 was synthesized by a simple one-step thermal phosphorylation method for enhancing CdS nanowires in visible-light-driven hydrogen generation, where the CdS nanowires are uniformly dispersed on the surface of Ni2P–Ni2P4O12 through in-situ solvothermal strategy. The photocatalytic hydrogen production rate of 5 ​wt% Ni2P–Ni2P4O12/CdS nanowires can reach 5093 ​μmol ​g−1 ​h−1 using Na2S–Na2SO3 as sacrificial agent under the irradiation of visible light (λ ​> ​420 ​nm), which is about 16 times for CdS nanowires (316 ​μmol ​g−1 ​h−1). In the cycling experiments, the composite catalyst shows good stability and the hydrogen production rate remains about 83% of the initial value. The interface structure construction between CdS nanowires and Ni2P–Ni2P4O12 result in the excellent photocatalytic activity, broaded visible light absorption and stability. Specifically, Ni2P–Ni2P4O12 can effectively promote the separation of electron hole pairs in space, in which Ni2P4O12 can accept H+ ions and Ni2P can reduce the over potential of H+ reduction, resulting in the synergically promotion in the photocatalytic activity. The cost-effective ternary photocatalyst exhibits great potential for sustainable and high-efficiency photocatalytic water splitting, and Ni2P–Ni2P4O12 may be suitable to modify a wider variety of semiconductor photocatalysts.

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Three α‐diimine Ni (II) catalysts (Cat.1, Cat.2 and Cat.3) were synthesized and investigated for ethylene polymerization using alkyl aluminum and organoboron compounds as binary cocatalyst. The effects of different alkyl aluminum and boron complexes on ethylene polymerization catalyzed by Cat.1, Cat.2, and Cat.3 were studied. The sodium tetrakis[3,5‐bis (trifluoromethyl)phenyl]borate (NaBArF) was found to have best promotion for the catalytic activity of Cat.1, compared to negative effect of dimethylanilinium tetrakis (pentafluorophenyl)borate (TTB) and trityl tetrakis (pentafluorophenyl)borate (AB). All the three catalysts showed higher catalytic activity when NaBArF was introduced into the catalytic system, especially for Cat.3 (increased by 41.3% at 70°C). There was still minor increase of the catalytic activity for Cat.2 which have much better thermostability than Cat.3. The charging sequence of NaBArF and the [B]/[Ni] ratio have significant effects on the catalytic activity. The better catalytic performance of Cat.1/AlEt2Cl/NaBArF could be explained by its ability to raise the number of active centers. Namely, the molar percentage of active centers of Cat.1/AlEt2Cl/NaBArF was still above 30%, which was 1.7 times that of Cat.1/AlEt2Cl even if polymerization ran up to 30 min based on 2‐thiophenecarbonyl chloride (TPCC) quench‐labeling method. Lower [Al]/[Ni] ratio but more active centers and longer active centers lifetime of this binary cocatalyst is promising for improving the activity of ethylene polymerization industrially at elevated temperature.

Binary Ni2P/Ti3C2 Multilayer Cocatalyst Anchored TiO2 Nanocomposite with Etchant/Oxidation Grown TiO2 NPs for Enhancing Photocatalytic H2 Production

Ternary nickel phosphide (Ni2P) and titanium carbide (Ti2C2) MXene supported titanium dioxide nanoparticles (TiO2 NPs) to construct a Ni2P/TiO2 NPs/Ti3C2 MXene hybrid composite for stimulating photocatalytic hydrogen production has been investigated. The performance comparison of two-dimensional (2D) Ti3C2 MXene multilayers with in situ grown TiO2 NPs synthesized through etching and atmospheric calcination methods was conducted and promising separation of charge carriers was observed. TiO2 NPs embedded over 2D Ti3C2, synthesized through both methods, were found to have promise in promoting photoactivity, whereas 2.89 times more H2 yield was attained with TiO2 NPs embedded through the oxidation (ox) approach. Using the Ni2P/TiO2/Ti3C2-ox heterostructure, a rate of 9425 ppm g–1 h–1 of H2 was reached, 2.77, 4.81, and 8.28 times more than those using Ni2P/TiO2, TiO2/Ti3C2 and TiO2 samples, respectively. This obviously augmented H2 production rate can be ascribed to a binary cocatalyst with efficient charge carrier separation, higher light absorption, and more attachment of water molecules. Among different alcohols, glycerol was a promising reagent to yield more hydrogen in addition to having higher photostability in consecutive cycles. This study provides a new approach to construct a ternary nanocomposite with proficient charge carrier separation and would be beneficial for other energy applications.

Synergistic effect of Ru embedded 2D Ti3AlC2 binary cocatalyst with porous g-C3N4 to construct 2D/2D Ru-MAX/PCN heterojunction for enhanced photocatalytic H2 production

Developing engineering advanced semiconductor materials with low cost and high efficiency have great importance in solar assisted hydrogen production. In this work, well-designed Ru modulated oxygen defective Ti3AlC2 MAX multilayers binary cocatalyst with porous g-C3N4 has been fabricated through ultrasonic approach. Synergistic effect of Ru/Ti3AlC2 enabling proficient charge carrier transportation for significantly enhanced H2 production. The optimized 3Ru-15Ti3AlC2/g-C3N4 exhibited 1445 µmol g−1h−1 of H2 evolution rate which is 7.67 and 16.35 times more than using 15Ti3AlC2/CN and CN samples. The obvious augmented H2 production can be attributed to efficient charges separation with higher light absorption due to Ru/Ti3AlC2 binary cocatalyst. The catalyst loading and sacrificial reagents further confirms mass transfer and surface-active sites exposed to light irradiation. This study provides new approach to construct heterojunction of 2D/2D self-assembly, enabling synergistically improved quantum yield with higher cyclic stability and can be further explored in other solar energy assisted applications.

Novel titanium(IV) diolate complexes with additional O‐donor as precatalyst for the synthesis of ultrahigh molecular weight polyethylene with reduced entanglement density: Influence of polymerization conditions and its implications on mechanical properties

New alkoxo‐titanium(IV) complexes with diolate ligand containing additional donor oxygen atom have been synthesized from readily available and scalable precursors. The structure of complex 4 was established by X‐ray diffraction. Titanium atom adopts a distorted tetrahedral geometry formed by six oxygen atoms of ligands. The resulting complexes 3–4 are moderately or highly active in ethylene polymerization in the presence of {EtnAlCl3–n + Bu2Mg} binary cocatalysts. The influence of the nature of the solvent, the organoaluminum cocatalyst and the polymerization temperature on the activity of catalytic systems, and the properties of the resulting polymers were studied. The obtained polymers are linear polyethylene of ultrahigh molecular weight (up to 5.8·106 g mol−1) with a broad molecular weight distribution. The polymers are suitable for the modern methods of polymer processing—the solventless solid‐state formation of super high‐strength (breaking strength up to 2.8 GPa) and high‐modulus (elastic modulus up to 140 GPa) oriented films and film tapes. The possibility of scaling up the synthesis of ultrahigh molecular weight polyethylene (UHMWPE) without a significant drop in the productivity of the catalytic system and polymer properties is shown. UHMWPE samples have been investigated by small‐angle X‐ray scattering (SAXS) methods to study the structural changes induced by solid‐state drawing of nascent reactor powders.

Methylaluminoxane’s Molecular Cousin: A Well-defined and “Complete” Al-Activator for Molecular Olefin Polymerization Catalysts

Catalytic activity in olefin polymerization depends not only on the catalyst but also, crucially, on activator/alkylator/scavenger “packages.” Along with binary mixtures containing Lewis or Brønsted acids and Al-alkyl systems, methylaluminoxane (MAO), a still ill-defined oligomeric compound, is the only single-component cocatalyst known to fulfill all three roles effectively and simultaneously. Herein, we report a simple molecular alternative, Al-H-Al+[B(C6F5)4]−, an unusual borate salt containing a homodinuclear Al-cation (Al-H-Al+ = [iBu2(DMA)Al]2(μ-H)+). Unlike the simpler [AliBu2]+[B(C6F5)4]−, this species is easily synthesizable and stable at room temperature. Importantly, Al-H-Al+[B(C6F5)4]− can be used as a stand-alone cocatalyst for molecular olefin polymerization catalysis, representing an unprecedented molecular activator able to completely activate dichloride metallocene and prototypical post-metallocene precatalysts. Furthermore, spectroscopic and polymerization studies suggest that Al-H-Al+ is the true activating species formed in situ in the binary cocatalyst [PhMe2NH]+[B(C6F5)4]−/AliBu3. As little as 50 equiv of Al-H-Al+[B(C6F5)4]− are required for efficient catalyst activation and impurity scavenging, orders of magnitude below the amounts usually required with MAO or AliBu3. The high, yet “tamed,” Lewis acidity of cationic Al-H-Al+ is likely responsible for the increased scavenging ability. Unlike MAO, the well-defined structure of Al-H-Al+[B(C6F5)4]− offers easy avenues for further tuning, making it the prototype of a promising cocatalyst family.

A genuine H-bond donor and Lewis base amine cocatalyst in ring-opening polymerizations

Hydrogen bond donor (HBD) and organic base binary cocatalyst established a gold standard in organocatalytic ring-opening polymerizations (ROPs). In depth probe of the mechanisms revealed that proton abstraction of the acidic H on the HBDs by the bases do occur frequently. A truly simple HBD and Lewis base (LB) cocatalysis, however, was elusive. We proposed genuine HBD/LB cocatalyst for ROPs by introducing 3-amino-1,2,4-benzothiadiazine-1,1-dioxide (ABTD) as a bidentate H-bond donor and triethylamine (TEA) as a mild Lewis base. ROPs of lactide (LA) and trimethylene carbonate (TMC) in solutions at room temperature were success. The mild ROPs produced polylactide (PLA) of predictable molecular weights (from 1.6 to 26.7 kg mol−1) and extremely narrow dispersities (Đ 1.01 to 1.06). Furthermore, well-defined diblock copolymers PTMC-b-PLA were synthesized. NMR titration experiments verified exclusive H-bond donor activation of the monomer and TEA activation of the hydroxyl chain end without trace of proton abstraction.

Integrating Ru-modulated CoP nanosheets binary co-catalyst with 2D g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution activity

Developing high-efficient and low-cost photocatalysts is of great significance yet challenging for photocatalytic hydrogen evolution. Herein, we report a 2D/2D Ru-modulated CoP nanosheets (Ru-CoP-x, where x refers the Ru-to-Co molar ratio)/g-C3N4 nanosheets (GCN NSs) ternary hybrid as a photocatalyst for hydrogen evolution under visible light. The optimal photocatalyst 25% Ru-CoP-1:8/GCN NSs exhibits an excellent hydrogen evolution rate of 1172.5 µmol g−1 h−1 under visible light with a high apparent quantum efficiency (AQE) of 3.49% at 420 nm, which is close to Pt/g-C3N4 photocatalytic system and higher than most reported transition metal phosphides (TMP)/g-C3N4 photocatalytic system. Experimental results indicate that the higher photocatalytic hydrogen evolution performance can be mainly attributed to the binary Ru-CoP-x co-catalyst with efficient charge separation and promoted surface water reduction kinetics, and the 2D/2D self-assembly structure with strong interface Schottky effect and short charge transport distance. This study provides a new approach to develop cost-effective Pt-alternative co-catalysts for photocatalytic hydrogen evolution by incorporating a small amount of ruthenium into the transition metal phosphides.

MAO‐free copolymerization of ethylene and 1-hexene with Ti (IV) complexes supported by fluorinated 2-hydroxymethylphenol derivatives

Ethylene/1-hexene copolymerization was carried out with a new Ti (IV) complexes stabilized by fluorinated 2-hydroxymethylphenol derivatives and activated by MAO-free binary cocatalysts—{alkyl aluminum chloride + Bu2Mg}. Structures and properties of the obtained copolymers were measured by DSC, GPC and 13C NMR. The effects of the ligand structure and the nature of organoaluminum activator on the polymer yield, comonomer incorporation, polymer composition, molecular weight, polydispersity index and stress–strain behavior have been investigated. The results indicated that the complex with adamantyl substituent was the most active in this series. The obtained copolymer exhibited the highest 1-hexene incorporation content of 18.9 mol%

A Titanium(IV) Complex with an OSO-Type Ligand as a Catalyst for the Synthesis of Ultrahigh-Molecular-Weight Polyethylene

Coordination compounds of titanium(IV) with OSO-type ligands have been prepared and characterized, and their catalytic activity in ethylene polymerization has been studied. It has been shown that in the presence of an {Et2AlCl + Bu2Mg} binary cocatalyst, the activity of the titanium-containing catalyst system reaches 1629 kgPE mol(Ti)−1 h−1 and leads to the preparation of ultrahigh-molecular-weight polyethylene (UHMWPE). The UHMWPE reactor powder has been processed by a solvent-free method to high-strength and high-modulus films (σ = 2.32 GPa, E = 125 GPa).

The influence of heteroatom on catalytic properties of heterobimetallic Ti(IV)–Ca and Ti(IV)–Ba complexes in the production of UHMWPE

New heterobimetallic Ti(IV)–Ca and Ti(IV)–Ba complexes stabilized with fluorinated ligand – 2-[bis-CF3-hydroxymethyl]-4,6-tert-butylphenol have been synthesized; their compositions and structures have been confirmed by NMR, IR-spectroscopy and elemental analysis. The solid-state structures of complexes 1–2 were established by X-ray analysis. These complexes catalyze ethylene polymerization in the presence of a binary cocatalyst {3Et2AlCl + Bu2Mg}. In the result of this reaction Ultra High Molecular Weight Polyethylene (UHMWPE) with a broad molecular weight distribution is obtained. UHMWPE samples were processed into high-strength (up to 2.4 GPa) and high-modulus (over 130 GPa) oriented film tapes by a solid-state uniaxial deformation. Such parameters of UHMWPE samples indirectly indicate a low degree of entanglements between the macromolecular chains. The effect of the pre-catalysts composition on the catalytic activity and properties of the obtained polymer has been investigated.

Solar-driven photocatalytic water oxidation of Ag3PO4/CNTs@MoSe2 ternary composite photocatalyst

Photocatalytic water splitting is a promising and effective way to simultaneously tackle energy requirement and environmental pollution. The fabrication of a novel and efficient non-metallic co-catalyst is increasingly essential for the improvement of photocatalytic oxygen production. Herein, a novel ternary composite based photocatalyst with high oxygen evolution activity was synthesized and fully characterized. The composite introduced here consists of CNTs and MoSe2 as a new cocatalyst in order to accelerate the activity of Ag3PO4 photocatalysis. The optimal oxygen generation rate of 102.3 μmol L−1 g−1 h−1 for the ternary Ag3PO4/CNTs@MoSe2 photocatalyst was achieved under the visible-light irradiation, which is higher than pure Ag3PO4 (2.88 times), Ag3PO4/CNTs (1.91 times) and Ag3PO4/MoSe2 (1.31 times) samples. The superior oxygen evolution is mainly attributed to CNTs@MoSe2 as binary co-catalysts which can bing about the effective separation and transportation of the photoexcited charge carriers and good electrical conductivity. The present work will set the foundations of designing high-performance Ag3PO4-based photocatalysts for energy and environmental applications.

Novel alkoxo-titanium(IV) complexes with fluorinated 2-hydroxymethylphenol derivatives as catalysts for the formation of ultra-high molecular weight polyethylene nascent reactor powders

A series of titanium (IV) complexes 3a–g stabilized by fluorinated derivatives of 2-hydroxymethylphenol have been synthesized; their composition and structure have been confirmed by NMR, IR-spectroscopy and elemental analysis. The structures of compounds 3c, 3f and 3g have been unambiguously established by X-ray diffraction study. The complexes in the presence of a binary cocatalysts {alkyl aluminum chloride + MgBu2} catalyze ethylene polymerization to afford Ultra High Molecular Weight Polyethylene (UHMWPE). The effects of substituents in the ligands on the catalytic activity and properties of the obtained polymer – molecular weight, DSC melting behavior, and morphology of nascent reactor powders have been investigated. UHMWPE samples were processed by a solid-state uniaxial deformation into high-strength (up to 2.65 GPa) and high-modulus (over 140 GPa) oriented film tapes, which indirectly indicates a low degree of entanglements between the macromolecular chains.

New Cocatalyst for Alkene Polymerization Reactions with Transition Metal Catalysts

The effect of a cocatalyst in alkene homo- and copolymerizations with transition metal catalysts of different types was studied. The results of studies of polymerizations of ethylene, propylene, and higher linear 1-alkenes and copolymerizations of ethylene with linear 1-alkenes using catalysts of different types in combination with a binary cocatalyst Al(C2H5)2Cl/Mg(C4H9)2 at [Al] : [Mg] > 2.5 were summarized. The traditional Ziegler–Natta catalysts (TiCl4, Ti(Oi-C3H7)4, and TiCl3 ) and titanium postmetallocene complexes with various organic ligands were studied. The binary cocatalyst significantly increased the activity of the traditional catalysts compared with that of Al(C2H5)2Cl and the activity of postmetallocene complexes compared with that of polymethylaluminoxane (MAO). The active centers of these catalytic systems differ in their kinetic parameters, stereospecificity, and copolymerization ability. The efficiency of the Al(C3H5)2Cl/Mg(C4H9)2 cocatalyst can be explained by the in situ formation of finely dispersed MgCl2 and immobilization of the cationic active centers on its surface.

Dual Cocatalysts in TiO2 Photocatalysis.

Semiconductor photocatalysis is recognized as a promising strategy to simultaneously address energy needs and environmental pollution. Titanium dioxide (TiO2 ) has been investigated for such applications due to its low cost, nontoxicity, and high chemical stability. However, pristine TiO2 still suffers from low utilization of visible light and high photogenerated-charge-carrier recombination rate. Recently, TiO2 photocatalysts modified by dual cocatalysts with different functions have attracted much attention due to the extended light absorption, enhanced reactant adsorption, and promoted charge-carrier-separation efficiency granted by various cocatalysts. Recent progress on the component and structural design of dual cocatalysts in TiO2 photocatalysts is summarized. Depending on their components, dual cocatalysts decorated on TiO2 photocatalysts can be divided into the following categories: bimetallic cocatalysts, metal-metal oxide/sulfide cocatalysts, metal-graphene cocatalysts, and metal oxide/sulfide-graphene cocatalysts. Depending on their architecture, they can be categorized into randomly deposited binary cocatalysts, facet-dependent selective-deposition binary cocatalysts, and core-shell structural binary cocatalysts. Concluding perspectives on the challenges and opportunities for the further exploration of dual cocatalyst-modified TiO2 photocatalysts are presented.

Binuclear and Hexanuclear Ti(IV) Complexes Supported by [OOOO]4–-type Ligand for Preparing Disentangled UHMWPE

Binuclear and hexanuclear titanium complexes stabilized by tetradentate [OOOO]4–-type ligand were active in ethylene polymerization in the presence of Et2AlCl/Bu2Mg binary co-catalyst, giving high molecular weight polyethylene. The binuclear complex showed significantly higher catalytic activity and thermal stability in comparison to mononuclear analogue. Ultra high molecular weight polyethylene (UHMWPE) samples were processed by a solid-state uniaxial deformation into high-strength (up to 2.5 GPa) and highmodulus (over 100 GPa) oriented film tapes, which indirectly indicates a low degree of entanglements between the macromolecular chains.

Pd-Pt bimetallic Nb-doped TiO2 for H2 photo-production: Gas and liquid phase processes

The performance of binary PtPd co-catalysts supported on Nb-TiO2 was tested in the gas and liquid phase photo-reforming of methanol. Co-catalyst formulations having Pt:Pd ratios from 2:1 to 1:4 were tested and the activity measured through the calculation of the quantum efficiency. Characterization of the initial and post-reaction materials showed that optimum activity is achieved in both processes by samples containing binary co-catalysts where Pd suffers an oxidation process and a PtPd alloying metallic phase is formed under reaction conditions. The analysis of catalytic output through an experimental design considering tree factors (methanol:water ratio, irradiance level, and catalyst volumetric concentration at liquid phase or surface concentration at gas phase) shows that the liquid phase process presents a rather high quantum efficiency value compared with the gas phase but the latter process displays higher atom efficiency as well as renders products with lower toxicity.