Heterogeneous Nickel Catalysts Research Articles

Heterogeneous Nickel Catalysts for the Synthesis of Ethylene-Based Polyolefin Elastomers

Heterogeneous Nickel Catalysts for the Synthesis of Ethylene-Based Polyolefin Elastomers

Lewis acid-induced homo- and heterogeneous nickel catalysts for ethylene polymerization and copolymerization with polar monomers

By introducing soluble and supported Lewis acids, homogeneous and heterogeneous nickel-catalyzed ethylene (co)polymerization was designed and studied.

Heterogenization Strategies for Nickel Catalyzed Synthesis of Polyolefins and Composites

ConspectusPolyolefin is one of the most common synthetic polymers. However, most polyolefins are nonpolar materials, which leads to poor compatibility with polar materials, thus limiting their application in some fields. Polar functionalized polyolefins can lead to significantly improved dyeability, adhesiveness and compatibility with polar fillers, and can realize customized properties of polyolefin materials. Transition-metal-catalyzed coordination copolymerization of olefin and polar functionalized comonomers represents a direct and potentially economic route to synthesize polar-functionalized polyolefin materials, which has attracted great attention in recent decades. Literally hundreds of nickel and palladium catalysts have been synthesized and investigated in olefin-polar monomer copolymerization to achieve high copolymerization efficiency by tuning the molecular structures of the catalysts. In particular, earth-abundant and low-cost nickel-based catalysts hold great potential for industrial applications. However, most research efforts focus on homogeneous copolymerization catalysts, while the industrially preferred heterogeneous systems have remained largely unexplored. With the objective of bridging this gap, our group has recently developed a series of heterogenization strategies for the synthesis of high-performance heterogeneous nickel catalysts taking advantage of hydrogen bond anchoring, ionic anchoring, coanchoring, cocatalyst, and ionic cluster formation. These strategies involve known or easily accessible catalysts, can be easily adapted to various catalytic systems, and can lead to simultaneous enhancement in all copolymerization parameters such as thermal stability, activity, comonomer incorporation ratio, and copolymer molecular weight versus the homogeneous counterparts. In addition, the performance of the catalysts can be tuned by changing the type of the support, thereby facilitating the discovery of high-performance heterogeneous nickel catalysts. Most importantly, great product morphology control can be achieved. This is desirable for industrial polymerization processes because it avoids reactor fouling and results in significant improvements in the safety and operational efficiency of the polymerization processes. Finally, these heterogenization strategies give access to high-performance polyolefin materials (polar-functionalized polyolefins, polar-functionalized polyolefin in-reactor blends and polyolefin-based functional composites) with custom-made properties. Compared with melt blending, polyolefin composites obtained by heterogeneous catalytic in situ polymerization have better material properties. By using functional fillers, customized polyolefin composites with high performance can be prepared in situ. These polyolefin-based materials have potential applications in many fields, such as electrical and thermal conductivity, photodegradation, flame retardancy, barrier, etc. It is expected that the continuous research on the copolymerization mechanism/catalysts, heterogenizatioin strategies and material properties of polar functionalized polyolefins and their composites will eventually achieve commercialization of nickel-catalyzed production of polyolefins and composites.

Heterogenization of nickel catalysts with ionic liquid‐modified supports for ethylene polymerization and copolymerization

AbstractThe preparation of heterogeneous catalysts by loading homogeneous metal complexes on the supports is an effective strategy preferred by the polyolefin industry. In this contribution, we synthesize a series of heterogeneous nickel catalysts using the supporting strategy of ionic liquid‐modified supports. These supported catalysts have polymerization activities up to 1.68 × 107 g mol−1 h−1, polymer molecular weights up to 224.1 × 104 g mol−1, and significantly, higher melting points compared to homogeneous systems. The polyolefin materials prepared by this supporting strategy possess a wide range of tunable mechanical properties, from thermoplastics to elastomers. These heterogeneous nickel catalysts can catalyze the copolymerization of ethylene and methyl 10‐undecenoate.

Emulsion Polymerization Strategy for Heterogenization of Olefin Polymerization Catalysts

Heterogenization of homogeneous metal catalysts on solid supports has been widely studied for product morphology control in ethylene polymerization. In this contribution, an emulsion polymerization strategy was introduced to achieve heterogenization of various imino-based nickel olefin polymerization catalysts. A series of polymeric microspheres were prepared through emulsion copolymerization of vinyl-functionalized imino ligands with comonomers such as styrene or methyl methacrylate. The corresponding heterogeneous nickel catalysts demonstrated superior properties in ethylene polymerization and copolymerization with methyl 10-undecylenate. Their catalytic properties can be controlled by tuning the comonomer type, composition, and particle size. Most importantly, this strategy can achieve product morphology control and avoid reactor fouling while generating polyethylene products with minimum inorganic contamination. In addition, the introduction of polymer microspheres can improve the mechanical properties and surface properties of polyolefin products.

Ethylene homo and copolymerization by phosphorus‐benzoquinone based homogeneous and heterogeneous nickel catalysts

AbstractThe low cost and high abundancy of nickel makes it highly attractive for both industrial and academic researchers in the field of polyolefin. However, the development of high performance nickel catalysts for ethylene homo and copolymerization is highly challenging. In this contribution, two novel cationic nickel catalysts with quinone backbone and sterically hindered aryl substituents on phosphine have been synthesized and supported on solid supports to prepare heterogeneous catalysts. The homogeneous catalysts showed high activity and high thermal stability in ethylene polymerization. After heterogenization of these catalysts, all the polymerization parameters (polymerization activity, thermal stability, and polymer molecular weight) were significantly improved. The heterogeneous catalyst can achieve activity of up to 3.26 × 106 g mol−1 h−1, along with polyethylene molecular weight of up to 81.8 × 104 g mol−1. More importantly, these homogeneous and heterogeneous catalysts can realize copolymerization of ethylene with a series of polar comonomers such as methyl 10‐undecenoate, 10‐undecenol, and 6‐chloro‐1‐hexene.

Influence of Silica-Supported Alkylaluminum on Heterogeneous Zwitterionic Anilinonaphthoquinone Nickel and Palladium-Catalyzed Ethylene Polymerization and Copolymerization with Polar Monomers

The development of the heterogeneous late transition metal-catalyzed olefin (co)polymerization is a challenge in current research. Here, we report the preparation of heterogeneous anilinonaphthoquinone nickel and palladium catalysts by the binding of SiO2-supported alkylaluminums to a quinone oxygen of the ligand (Mt-AlR3/SiO2). The heterogeneous nickel catalyst exhibited a very high activity (up to 10.4 × 106 g mol–1 h–1) for ethylene polymerizations to produce semicrystalline high-molecular-weight (Mn up to 54.3 × 104 g mol–1) polyethylenes with a low degree of branching (<11.1/1000 C), high Tm values (121–131 °C), and well-regulated particle morphologies. The polymerization behavior depended on the electron density of the metal center modulated by the Lewis acidity of the remotely bound alkylaluminum as can be analyzed and verified through model optimizations and density functional theory (DFT) calculations. Most importantly, these nickel catalysts were able to produce semicrystalline ethylene/5-hexene-1-yl copolymers with a high activity and high molecular weight. The heterogeneous palladium catalyst can promote the copolymerization of ethylene with commercial methyl acrylate or polar norbornene derivatives with a moderate activity, affording a polar functionalized polyethylene and a cyclic olefin copolymer.

A Convenient and Stable Heterogeneous Nickel Catalyst for Hydrodehalogenation of Aryl Halides Using Molecular Hydrogen.

Invited for this month's cover is the group of Matthias Beller at the Leibniz Institute for Catalysis in Rostock in collaboration with Muhammad Anwar and Sarim Dastgir at the Qatar Environment and Energy Research Institute in Doha. The image illustrates a hydrodehalogenation of polybrominated diphenyl ether (PBDE) using a heterogeneous nickel catalyst supported on titanium oxide and dihydrogen. The Research Article itself is available at 10.1002/cssc.202102315.

Nickel catalysts for the preparation of functionalized polyolefin materials

<p indent="0mm">As the largest class of thermoplastic polymers, polyolefin materials have wide applications and huge annual production. The introduction of even a small amount of polar functional groups into the polyolefins could excise great control over important material properties. As the most direct and economic strategy, the coordination-insertion copolymerization of olefin with polar-functionalized monomers can enable molecular-level control of the copolymer microstructures. This represents one of the biggest challenges in this field, and is recognized as one of the last “holy grails” in this field. Late transition metal catalysts have attracted much attention in the direct copolymerization of olefin with polar monomers for the synthesis of functionalized polyolefin materials. In this field, research efforts have been devoted to palladium catalyst systems, which have been investigated thoroughly in the past few decades. In contrast, the utilization of less-expensive and earth-abundant nickel catalysts has received much less attention and is much more challenging, mainly due to the higher oxophilicity and lower polar group tolerance of the nickel metal versus palladium metal. However, the field of nickel-catalyzed copolymerization of olefins with polar monomers has witnessed rapid developments in recent years. This perspective mainly focuses on the work concerning nickel-catalyzed olefin copolymerization and summarizes the following subjects: First, we summarize the design and development of different nickel catalyst systems for the copolymerization of olefins with polar monomers, including α-diimine nickel, salicylaldimine nickel, various [N,O] nickel, phosphine-sulfonate nickel, phosphine-phenolate nickel and [P,C/N/P=O] nickel systems. We focus on their ligand design and catalytic properties (activity, copolymer molecular weight, comonomer incorporation, etc.) in these copolymerization reactions. In addition to the above-mentioned homogeneous nickel systems, we also summarize various heterogeneous nickel catalysts for the copolymerization of ethylene with polar monomers. Heterogeneous catalysts offer many distinct advantages, such as controlling the morphology of the copolymer product and preventing reactor fouling in the copolymerization processes. Second, we discuss some of the unique properties of the polar-functionalized polyolefin materials bearing various polar functional groups. These polar-functionalized polyolefin materials show great mechanical properties along with excellent antioxidant, self-healing, flame retardant properties, etc. Notably, there have been very few studies on the properties of functionalized polyolefins prepared by nickel catalysts, due to the inferior properties of nickel catalysts in the copolymerization reactions. Considering the recent developments of various high-performance nickel catalyst systems, more efforts should be directed towards this research field. Finally, we discuss problems and challenges in this field, and propose some promising research directions: (1) The design of new nickel catalysts with further improved catalytic properties, with special focus on expanding the scope of applicable olefins and polar monomers (ethylene, propylene, carbon monoxide, various polar monomers); (2) the development of new heterogeneous nickel catalysts and new supporting methods that could achieve product morphology control and enable continuous polymerization process by preventing reactor fouling; (3) the systematic studies on the properties of functionalized polyolefin materials with the aim of developing high-end applications. Although the research history of nickel-catalyzed copolymerization to access functionalized polyolefin materials is relatively short, we believe that it will become an important leading direction in the field of polyolefins.

Heterogeneous Electro-Fenton-like Designs for the Disposal of 2-Phenylphenol from Water

The hunt for efficient and environmentally friendly degradation processes has positioned the heterogeneous advanced oxidation processes as an alternative more interesting and economical rather than homogenous processes. Hence, the current study lies in investigating the efficiency of different heterogeneous catalysts using transition metals in order to prevent the generation of iron sludge and to extend the catalogue of possible catalysts to be used in advanced oxidation processes. In this study, nickel and zinc were tested and the ability for radical-generation degradation capacity of both ions as homogeneous was evaluated in the electro-Fenton-like degradation of 2-phenylphenol. In both cases, the degradation profiles followed a first-order kinetic model with the highest degradation rate for nickel (1 mM) with 2-phenylphenol removal level of 90.12% and a total organic reduction near 70% in 2 h. To synthesise the heterogeneous nickel catalyst, this transition metal was fixed on perlite by hydrothermal treatment and in a biochar or carbon nanofibers by adsorption. From the removal results using the three synthesized catalysts, it is concluded that the best catalysts were obtained by inclusion of nickel on biochar or nanofibers achieving in both with removal around 80% before 1 h. Thus, to synthetize a nickel electrocatalyst, nickel doped nanofibers were included on carbon felt. To do this, the amount of carbon black, nickel nanofibers and polytetrafluoroethylene to add on the carbon felt was optimized by Taguchi design. The obtained results revealed that under the optimised conditions, a near-complete removal was achieved after 2 h with high stability of the nickel electrocatalyst that open the applicability of this heterogeneous system to operate in flow systems.

Heterogeneous Nickel Catalyst Promotes Indole Formation via Dehydrogenative Coupling

Key words indoles - heterogeneous catalysis - nickel catalysis - dehydrogenative coupling

Hydrogen-Bonding-Induced Heterogenization of Nickel and Palladium Catalysts for Copolymerization of Ethylene with Polar Monomers.

The practical synthesis of polar-functionalized polyolefins using transition-metal-catalyzed copolymerization of olefins with polar monomers is a challenge; the use of heterogeneous catalysts is little explored. Herein, we report the synthesis of heterogeneous naphthoquinone-based nickel (Ni/SiO2 ) and palladium (Pd/SiO2 ) catalysts through hydrogen bonding interactions of the ligands with the silica surface. Ni/SiO2 exhibits high activities (up to 2.65×106 g mol-1 h-1 ) during the copolymerization of ethylene with 5-hexene-1-yl-acetate, affording high-molecular-weight (Mn up to 630 000) polar-functionalized semicrystalline polyethylene (comonomer incorporation up to 2.8 mol %), along with great morphology control. The resulting copolymers possess improved surface properties and great mechanical properties. Pd/SiO2 can mediate ethylene copolymerization with polar monomers with moderate activity to produce high-molecular-weight copolymers with tunable comonomer incorporation.

Heterogeneous Nickel Catalysts Derived from 2D Metal-Organic Frameworks for Regulating the Selectivity of Furfural Hydrogenation.

Hydrolysis of the biomass platform compound furfural can produce a bulk of fine chemicals because of its multiple functional groups. Developing an efficient catalytic system to regulate the process toward some desirable products has always been a hot research area. Herein, the novel Ni-based catalysts (Ni-MFC-X, X = 300, 400...800) synthesized by pyrolysis of the 2D Ni-based metal–organic framework (MOF) in the temperature range 300–800 °C show good performance for selective hydrogenation of furfural (FUR). Interestingly, the calcination temperature of the MOF precursor plays an important role in hydrogenation of furfural with controllable selectivity toward furfuryl alcohol (FOL) and tetrahydro FOL (THFOL). Ni-MFC-500 affords us 92.5% conversion of furfural and 59.5% selectivity of FOL. Ni-MFC-700 can promote hydrogenation of furfural with 91.8% conversion and 51.0% selectivity of THFOL. Furthermore, the stability of as-obtained Ni-MFC-500 and Ni-MFC-700 was also very impressive in this reaction system.

Selective cleavage of lignin and lignin model compounds without external hydrogen, catalyzed by heterogeneous nickel catalysts.

Selective hydrogenolysis of the Caryl-O bonds in lignin is a key strategy for the generation of fuels and chemical feedstocks from biomass. Currently, hydrogenolysis has been mainly conducted using hydrogen, which is flammable and not sustainable or economical. Herein, an external hydrogen-free process for aryl ethers hydrogenolysis in lignin models and dioxasolv lignin over nickel nanoparticles supported on Al2O3, is reported. Kinetic studies reveal that the transfer hydrogenolysis activity of the three model compounds decreased in the following order: benzyl phenyl ether (α-O-4), 2-phenylethyl phenyl ether (β-O-4) and diphenyl ether (4-O-5), which linearly corresponds to their binding energies and the activation energies. The main reaction route for the three model compounds was the cleavage of the ether bonds to produce aromatic alkanes and phenol, and the latter was further reduced to cyclohexanol. Dioxasolv lignin depolymerization results exhibit a significant Caryl-O decrease over the Ni nanoparticles supported on Al2O3 with iso-propanol as the hydrogen source through 2D-HSQC-NMR analysis, which confirmed the transfer hydrogenolysis conclusion in the model study. This work provides an economical and environmentally-friendly method for the selective cleavage of lignin and lignin model compounds into value-added chemicals.

Heterogeneous Nickel Catalysts for Reductive Amination of Levulinic Acid

Key words atomic layer deposition - nickel catalysis - carbon nanotubes - reductive amination - levulinic acid

ChemInform Abstract: Robust Heterogeneous Nickel Catalysts with Tailored Porosity for the Selective Hydrogenolysis of Aryl Ethers.

AbstractSiC materials with tailored porosity and integrated Ni‐nanoparticles are synthesized and their catalytic activity for the hydrogenolytic cleavage of different phenyl ethers is examined.

Zinc inclusion to heterogeneous nickel catalysts reduces oligomerization during the semi-hydrogenation of acetylene

Isotopic labeling and density functional theory (DFT) were used to determine the mechanism for acetylene hydrogenation and oligomerization on well-defined intermetallic nickel–zinc catalysts. The primary benefit of adding zinc to nickel is a reduction in oligomeric species formation which leads to higher ethylene selectivity. The production of ethane is not highly dependent on zinc content; therefore, ethane production is not a good descriptor of ethylene selectivity since acetylene may also be converted to higher molecular weight products. Analysis using DFT and Langmuir–Hinshelwood kinetics shows that the large decrease in the adsorption energy of acetylene on intermetallic NiZn compared to pure Ni is responsible for the observed increase in ethylene selectivity. The adsorption energy of acetylene appears to be a descriptor for carbon–carbon bond formation since a high adsorption energy leads to an increased coverage of C2 species and an increased rate of carbon–carbon bond formation.

Robust Heterogeneous Nickel Catalysts with Tailored Porosity for the Selective Hydrogenolysis of Aryl Ethers

AbstractSiC materials with tailored porosity and integrated Ni NPs (Ni@SiC) were synthesized via microphase separation of polycarbosilane‐block‐polyethylene followed by its pyrolysis. Changing the length of organic block allowed the synthesis of micro, meso and hierarchical Ni@SiC materials which were characterized by PXRD, TEM, TGA, and nitrogen physisorption. Selective hydrogenolysis of aryl ethers mimicking the most abundant linkages of lignin was achieved in water avoiding the possible hydrogenation of aromatic rings.

An Investigation of the Partitioning of Dissociated H2 and D2 on Activated Nickel Catalysts

Heterogeneous nickel catalysts play an important role in numerous processes. In the past, a number of H/D isotopic labeling studies have probed catalytic mechanisms during specific associative and dissociative steps. The current work investigates the adsorption of hydrogen on Ni0 sites, the active surface where H-transfer reactions take place, to determine if preferential partitioning of H or D occurs on the metal surface. This is important for understanding whether differences in surface coverages between H and D could potentially impact KIE analyses. Overall, when H2 and D2 were added competitively to either H-activated NiO or Ni/alumina catalysts, no significant isotopic preference was identified. However, when the catalyst was pretreated with H2 (or D2) prior to flowing the equimolar mixture, a slight isotopic preference for H2 (or D2) was observed. This residual effect suggests that, in both cases, hydrogen exchange with hydroxyl groups on the support occurred. That is, in the case of hydrogen activated NiO, the resulting catalyst is likely a mixture of Ni and residual NiO, the latter presumably containing surface hydroxyl groups. The isotopic preference when H2 (or D2) pretreatment is conducted prior to running the H2/D2 (50–50 %) mixture is enhanced when alumina is used as a support due to greater OH/OD exchange. A similar, but even less pronounced effect, was observed previously with cobalt/alumina catalysts.

A Heterogeneous Nickel Catalyst for the Hydrogenolysis of Aryl Ethers without Arene Hydrogenation

A heterogeneous nickel catalyst for the selective hydrogenolysis of aryl ethers to arenes and alcohols generated without an added dative ligand is described. The catalyst is formed in situ from the well-defined soluble nickel precursor Ni(COD)(2) or Ni(CH(2)TMS)(2)(TMEDA) in the presence of a base additive, such as (t)BuONa. The catalyst selectively cleaves C(Ar)-O bonds in aryl ether models of lignin without hydrogenation of aromatic rings, and it operates at loadings down to 0.25 mol % at 1 bar of H(2) pressure. The selectivity of this catalyst for electronically varied aryl ethers differs from that of the homogeneous catalyst reported previously, implying that the two catalysts are distinct from each other.