Number Of Active Centers Research Articles

Polymerization of six-membered propylene oxalate

Ring-opening polymerization (ROP) of the six-membered cyclic propylene oxalate was studied for the first time. The reaction proceeded with a high limiting conversion of about 96 % at 100 °C in the presence of tin(II) octoate. Linear macromolecules, Mw of 20–30 × 103, Ð ∼ 2, represented 86 % of the product, 4 % came from the equilibrium concentration of monomer, while the rest 10 % were cyclic oligomers consisting of 3–10 repeat units. ROP was accompanied by partial (about 30 %) conversion of the catalyst into the insoluble tin(II) oxalate in the course of polymer cross-linking reaction. The kinetics of polymerization obeyed first-order law, indicating typical for ROP constant number of active centers during the process. Polymerization without catalyst was 2000 times slower and also resulted in formation of polymer with Ð ∼ 2. Addition of benzyl alcohol to the polymerization mixture resulted in its inclusion into linear macromolecules and a decrease in their molecular weight. The results point to the possibility of synthesizing propylene oxalate block copolymers using macroinitiators with hydroxyl end groups.

Adsorption removal of copper(II) from water by zero valent iron loaded dendritic mesoporous silica

The object of research is synthesized dendritic mesoporous nanoscale silica (DMSN) modified with zero-valent iron (Fe0@DMSN). This material exhibits a high adsorption capacity for heavy metal ions, in particular copper, whose increased content in the aquatic environment poses a threat to living organisms. In this regard, the main physicochemical features of the removal of copper cations from the aqueous medium using the obtained sample were investigated. The morphology of the obtained dendritic silicas was studied by electron microscopy and the presence of a layer of zero-valent iron was confirmed by X-ray diffraction analysis and infrared spectroscopy. The parameters of the porous structure of the synthesized materials were determined. It was found that after modification of mesoporous silica with particles of zero-valent iron, the value of its specific surface area decreased from 504 m2/g to 312 m2/g. This may be due to the formation of a Fe0 layer not only on their surface but also in the channels of the inorganic matrix, which has a unique dendritic structure characteristic of this type of particles. At the same time, the number of active centers increases due to the enrichment of the silica surface with functional modifier groups that show a high affinity for metal cations. The adsorption capacity of Fe0@DMSN towards Cu2+ ions has been studied and it has been shown that the maximum adsorption value is 39.8 mg/g, which is significantly higher than that of the initial synthesized DMSN sample (0.7 mg/g). The experimental data obtained indicate that the obtained sorption material based on dendritic mesoporous silica nanoparticles with a layer of reactive zero-valent iron can be used for the purification of water contaminated with metal ions. In addition, the magnetic properties of such materials, known and proven by various scientists, will make it easy to separate the solid phase in the processes of sorption water purification using magnetic separation.

Nano-MnOx prepared by redox method for toluene oxidation removal from air

Catalytic oxidation is an efficient VOCs removal technology with great potential and development advantages. The key to the oxidative elimination of VOCs lies in the development and application of the catalyst with high efficiency. In this work, the nano-MnOx catalysts were prepared by redox method and the catalytic oxidation performance of toluene was studied. The calcination temperature could effectively change the surface chemical composition and the nano-MnOx catalyst structures, which could effectively regulate the number of active centers on the catalyst surface to improve the adsorption, activation, and oxidation ability of the nano-MnOx catalysts for toluene molecules. The nano-MnOx catalyst dominated by the MnO2 phase, which was prepared at the calcination temperature of 400 °C, had a high specific surface area, developed porosity, abundant reactive oxygen species, and oxygen vacancies. The structural characteristics are conducive to the adsorption, activation, and oxidation of toluene molecules, and thus exhibited excellent toluene catalytic oxidation activity. At the reaction temperature of 140 °C, the toluene oxidation conversion was as high as 99.4 %, and the toluene conversion remained above 96.6 % after experiencing a 690 min stability test.

Enhancement of hydrogen-rich gas production by acetic acid steam reforming: characterization of Ni–Co modified biochar-based catalysts

Abstract The development of cost-effective and highly efficient biochar-based catalysts is essential for the catalytic steam reforming process of bio-oil. In this study, pickling peanut shell biochar was used to prepare biochar-supported Ni/Co monometallic catalyst and biochar-supported nickel-Co bimetallic catalyst through the impregnation method. The catalytic effect of these catalysts on acetic acid (a bio-oil model compound) steam reforming was investigated. It was found that Co could enhance the dispersion of metal particles. The catalyst exhibited the best catalytic effect and significantly improved resistance to carbon deposition with a loading of 8 wt% and a Ni-to-Co ratio of 6:2. At the temperature of 600 °C and the S/C ratio of 3, the selectivity of H2 reached 84.48 %, and the conversion of acetic acid reached 95.49 %. A synergistic effect was observed between Ni and Co, leading to increased metal dispersion, enhanced reducibility, and a higher number of active centers. Co facilitates water dissociation and promotes the oxidation of C–H and mobile O, resulting in a faster decarbonization rate. The effective utilization of biochar-based catalysts and the rational utilization of bio-oil contribute to the timely achievement of carbon emission reduction targets.

The promotion of rare earth on Pt-SiO2-Al2O3 catalyst for NO oxidation in diesel exhaust

The effective oxidation of NO is the key to the catalytic treatment of diesel vehicle exhaust. Improving the NO oxidation ability is mainly to optimize the chemical state of the active site (Pt), followed by increasing the number of active centers. Considering that the atoms with electronegativity weaker than Pt can provide electrons to change the chemical state of Pt, rare earth elements with weak electronegativity are selected as additives to obtain Pt/M-SiO2-Al2O3 (M = Sc, Y, La, Ce, Pr, Nd, Sm, Eu) catalysts by co-impregnation method. Among them, the Pt/La-SiO2-Al2O3 catalyst has the best NO oxidation performance, compared with the Pt-SiO2-Al2O3, the NO conversion rate increased by 28 %. Due to the special outer electron arrangement of La, its electronegativity is the smallest in rare earth, which makes its outer electrons easy to transfer to Pt atoms, and has the strongest electron interaction. Thus, the highest content of Pt0 was detected in CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS). In addition, CO chemisorption and transmission electron microscopy (TEM) confirmed that the introduction of La in the catalyst can significantly improve the dispersion of precious metals. Notably, this simple approach of affecting electron interaction by introducing weakly electronegative elements provides a reference for the design of noble metal catalysts with different valence states to solve complex problems.

The surface modification of the silica-coated magnetic nanoparticles and their application in molecular diagnostics of virus infection

The study presents a series of examples of magnetic nanoparticle systems designed for the diagnosis of viral diseases. In this interdisciplinary work, we describe one of the most comprehensive synthetic approaches for the preparation and functionalization of smart nanoparticle systems for rapid and effective RT-PCR diagnostics and isolation of viral RNA. Twelve different organic ligands and inorganic porous silica were used for surface functionalization of the Fe3O4 magnetic core to increase the number of active centres for efficient RNA binding from human swab samples. Different nanoparticle systems with common beads were characterized by HRTEM, SEM, FT-IR, XRD, XPS and magnetic measurements. We demonstrate the application of the fundamental models modified to fit the experimental zero-field cooling magnetization data. We discuss the influence of the nanoparticle shell parameters (morphology, thickness, ligands) on the overall magnetic performance of the systems. The prepared nanoparticles were tested for the isolation of viral RNA from tissue samples infected with hepatitis E virus—HEV and from biofluid samples of SARS-CoV-2 positive patients. The efficiency of RNA isolation was quantified by RT-qPCR method.

Convenient construction of electrocatalysts via combustion-assisted corrosion engineering for efficient water oxidation

Developing an efficient strategy for the universal synthesis of electrocatalysts is crucial for advancing the industrialization of water splitting, yet it remains a significant challenge. In this study, we propose combustion-assisted corrosion engineering as a rapid method to fabricate electrocatalysts for the oxygen evolution reaction (OER) within seconds. By utilizing a three-dimensional framework composed of nickel foam and the unique structure of the active species, we enable swift electrolyte diffusion and gas release. Consequently, the optimized S–NiO/NF exhibits remarkable OER catalytic activity, requiring a low overpotential of 236 mV to achieve a current density of 50 mA cm−2 in 1.0 M KOH solution. Notably, the reconfiguration during the OER process leads to the formation of actual catalytic active species, enhancing the number of active centers and thereby improving the catalyst's performance. This research presents a versatile method for industrially fabricating non-noble metal self-supporting electrodes with high efficiency, offering a practical solution for energy conversion and storage.

The effect of Ce promotor on catalytic performance of Zn/ZSM-5 in coaromatization of methanol and n-hexane

Ce modified Zn/ZSM-5 catalyst was prepared and the effect of Ce promotor on coaromatization of methanol and n-hexane was studied. The physical and chemical properties of Zn–Ce/HZ were tested by XRD, XPS, TEM, N2 adsorption-desorption and Py-FTIR. The loading of Ce tuned the acidity distribution and increased the LAS/BAS ratio, and mainly reduced the microporous specific surface area. Most of Zn and Ce elements entered the zeolite channels. The loading of Ce enhanced the interactions between Zn species and support and significantly increased the numbers of active centers of ZnOH+ species. Under the optimized conditions, the yield of aromatics was greatly improved from 25.2 % of HZ to 62.6 %. The reasons of deactivation were also analyzed. The higher the aromatization activity, the more the formed carbon deposit. The blockage of micropores and the greatly coverage of acid sites by carbon deposit thus resulted in poor catalytic performance.

Oxygen vacancy optimization of the titanium carbide MXene surface for enhanced electrochemical nitrogen reduction

Electrochemical N2 reduction reaction (NRR) provides a hopeful way for sustainable NH3 production. It is the key to realize efficient NRR reaction to optimize the structure and electronic configuration of catalyst materials. Increasing the number of active centers in Ti3C2Tx MXene allows for the development of effective NRR electrocatalysts. Herein, we rationally integrated defect engineering to create oxygen vacancy-rich Ti3C2-MXene (K-Ti3C2-400) as an efficient NRR catalyst with an NH3 yield of 32.25 ± 0.8 μg·h−1·mg−1cat. at − 0.55 V and a Faradaic efficiency of 12.85 % ± 0.26 % at −0.45 V versus reversible hydrogen electrode. According to the density functional theory, oxygen vacancies can prevent the hydrogen evolution reaction by delaying H adsorption, thereby activating absorbed N2 and encouraging *N2H synthesis. This research opens up new possibilities for creating MXene-based catalysts with surface reactivity and selectivity for electrochemical N2 fixation.

Fully dispersed cobalt diatomic site with significantly improved Fenton-like catalysis performance for organic pollutant degradation

A novel strategy for better catalytic performance in terms of precisely tuning the metal atom number of active centers is gradually getting attention. In this paper, the Co atom pair sites on N-doped porous carbon was engineered. The binuclear Co2 site structure was identified by aberration-corrected scanning transmission electron microscopy and X-ray absorption spectroscopy. As expected, the Co2NC display an outstanding Fenton-like catalysis activity in tetracycline degradation with turnover frequency exceeding 0.91 min−1 that is approximately 4 times higher than the conventional CoN4 site. The EPR tests indicated that the ROS strength stimulated by the binuclear site was much stronger than that of single site. Theoretical density functional theory calculations reveal that the optimized adsorption configuration is the O1 of peroxymonosulfate (PMS) interacting with two Co atoms, leading to stronger interaction effect and electron transfer for PMS comparing to single atom sites.

Highly Reliable Performance of Flexible Synaptic Devices Based on PVP-GO QD Nanocomposites Due to the Formation of Directional Filaments.

The metallic conductive filament (CF) model, which serves as an important conduction mechanism for realizing synaptic functions in electronic devices, has gained recognition and is the subject of extensive research. However, the formation of CFs within the active layer is plagued by issues such as uncontrolled and random growth, which severely impacts the stability of the devices. Therefore, controlling the growth of CFs and improving the performance of the devices have become the focus of that research. Herein, a synaptic device based on polyvinylpyrrolidone (PVP)/graphene oxide quantum dot (GO QD) nanocomposites is proposed. Doping GO QDs in the PVP provides a large number of active centers for the reduction of silver ions, which allows, to a certain extent, the growth of CFs to be controlled. Because of this, the proposed device can simulate a variety of synaptic functions, including the transition from long-term potentiation to long-term depression, paired-pulse facilitation, post-tetanic potentiation, transition from short-term memory to long-term memory, and the behavior of the "learning experience". Furthermore, after being bent repeatedly, the devices were still able to simulate multiple synaptic functions accurately. Finally, the devices achieved a high recognition accuracy rate of 89.39% in the learning and inference tests, producing clear digit classification results.

AlxSr1-xTiO3 perovskites with enhanced hydroxyl radicals and anions are highly reactive and break down organic dye molecules forming nontoxic by-products like H2O and CO2

AlxSr1-xTiO3 (x = 0, 0.005, 0.01, 0.05, 0.09) photocatalysts were prepared by solid state technique. The synthesized materials were characterized using various analytical techniques like PXRD, UV–visible and SEM etc. To study the phase purity, composition, surface morphology and bandgap. The bandgap was estimated to be 3.2 eV, and the crystalline structure is identified to be perovskite from PXRD results. The photocatalytic behaviour of AlxSr1-xTiO3 (x = 0, 0.005, 0.01, 0.05, 0.09) nanoparticles was tested by the photocatalytic degradation of methylene blue (MB) under ultraviolet light irradiation. These results demonstrated good photocatalyst efficiency of AlxSr1-xTiO3 (x = 0, 0.005, 0.01, 0.05, 0.09) which may be attributed to the bandgap, high adsorbing of the dye molecules on the surface, large surface area, availability of large number of active centres on the surface and possibly low electron-hole (e−/h+) recombination probability. AlxSr1-xTiO3 (x = 0, 0.005, 0.01, 0.05, 0.09) in addition, showed excellent stability against photocatalytic degradation even after repeated cycles of reusability. The degradation percentage was more than 90 %, at the natural pH of the solution. Based on the results a suitable photocatalytic degradation mechanism has been proposed. Thin films of AlxSr1-xTiO3 (x = 0, 0.005, 0.01, 0.05, 0.09) nanoparticles were deposited on a substrate and I-V measurements are carried to confirm the degradation of MB dye. These results reveal possible use of the material in large scale applications.

A bioinspired iron-peroxy species of feroxyhyte for micropollutants oxidation with ultrahigh peroxymonosulfate utilization efficiency

Efficient purification of water is essential to remove organic micropollutants for human and environmental health. The development of catalysts with high activity and peroxymonosulfate (PMS) utilization efficiency for removal of organic micropollutants remains challenging. Inspired by natural enzymes, we designed δ-FeOOH nanosheets with abundant 5-coordinated iron sites, which are responsible for the formation of iron-peroxy (FeIII-O-O-FeIII) species with PMS. The iron-peroxy species can directly oxidize and degrade electron-rich micropollutants (e.g. BPA) with an ultra-high PMS utilization efficiency of 78.4%. A laminar membrane constructed from a stack of δ-FeOOH nanosheets, replete with an abundance of 5-coordinated iron sites. The laminar membrane can degrade multiple micropollutants by almost 100% due to nonlinear transport between the δ-FeOOH nanolayers, compared with the dispersed catalyst. This work would motivate the community to focus more on the diversified behavior of the coordination number of active centers in the design of efficient catalysts for water purification.

Physicochemical and Electrochemical Properties of Materials Based on Titanium Suboxides

The influence of the synthesis conditions on the surface morphology, phase composition, and electrocatalytic activity of materials in oxygen and hydrogen evolution reactions was investigated. For instance, the slopes in the potential vs the logarithm of the current density dependencies during oxygen evolution were 221 and 109 mV/dec for TiO2 nanotubes and platinum-coated layers, respectively. In the latter case, small deviations may be attributed to the structural heterogeneity of the material or the developed surface of the coating. As for pristine TiO2 nanotubes, an atypical Tafel slope was observed, almost twice the theoretical value, indicating the presence of a semiconductor component in the electrode capacitance. Studies showed that the materials are n-type semiconductors. The cathodic polarization stage leads to the formation of titanium suboxides in the nanotube recovery phase, contributing to an increase in the material electrical conductivity. This also allows for the creation of a porous developed surface matrix for the electrodeposition of catalytic metal layers. Tafel slopes were calculated for the investigated materials in the hydrogen evolution reaction. For TiO2 nanotubes, a slope of 175 mV/dec was observed. The material surface was partially blocked by hydroxides, resulting in a low num-ber of active centers for the hydrogen evolution, and the polarization curve had a steep slope. In the case of TiO2 nanotubes coated with a platinum layer, a high number of cationic vacancies in the matrix and a deficit of oxygen ions facilitated the mobility of platinum atoms, leading to the emergence of a large number of active centers for the hydrogen evolution. As a result, the Tafel slope of the polarization curve was found to be 30 mV/dec.

Vacancy-rich, multi-heterostructured MXene/Fe3S4@FeSe2 catalyst for high performance lithium-sulfur batteries

Due to fast electron/ion transfer at interfaces, heterostructure catalysts can be used in lithium-sulfur (Li-S) batteries to boost sulfur-polysulfides-lihtium sulfide conversion and inhibit the polysulfides shuttle effect, thus giving rise to improved battery performance. However, traditional heterostructure catalysts still lack in the number of active centers that can guarantee high performance of Li-S batteries. Here, we designed and synthesized multi-heterostructured MXene/Fe3S4@FeSe2 catalyst through in-situ hydrothermal growth, sulfurization, and selenization steps. The resulting multi-heterostructure material is rich in vacancies and thus can provide more active centers than other heterostructured catalysts. Experiments and theoretical calculations show that MXene/Fe3S4@FeSe2 catalyst has a good synergistic conduction-adsorption-catalysis effect. Its high specific surface area and plural catalytic active centers can improve the conversion kinetics of LiPSs; the built-in electric field may reduce the energy barrier, and accelerate the electron/ion transfer. As a result, the Li-S battery assembled with MXene/Fe3S4@FeSe2 exhibits a high initial discharge capacity of 1185.6 mAh/g at 0.2 C (557.1 mAh/g at 5 C). Even at a high sulfur loading of 8.16 mg cm-2, the capacity retention rate is 82.4 % after 135 cycles. This work provides a new idea for the development of defect engineering in catalysts of Li-S battery.

STABILIZATION OF WATER-COAL COMPO­SITE FUELS USING CARBON MICRO-NANO­MATERIALS AND AMINO ALCOHOLS

The study investigated the potential of stabilizing composite water-coal fuel (CWCF) by adding carbon micro-nanomaterials obtained through the plasma-chemical conversion of organics-containing wastewater and amino alcohols. The study focused on systems based on anthracite with a solid phase concentration of 62%. Two amino alcohols, 2-amino-­2-methyl-1-propanol (AMP) and 2-amino-­2-ethyl-1,3-propanediol (AEPD) were used at concentrations of 0.25%, 0.5%, 1%, and 2.5% by weight of CWCF.
 The low stability and heterogeneity of coal particle distribution in organic liquids cause an increase in the viscosity of dispersed systems in combined systems. To regulate the rheological properties and stabilize the CWCF, chemicals such as dispersants, plasticizers, and stabili­zers are added. The CWCF 's properties can be improved by using additives such as sodium, calcium, and magnesium lignosulfonates, and naphthalene sulfonic acids. However, these reagents may not provide the desired properties of coal slurries in organomineral environments. Therefore, substitutes for these pro­ducts need to be found.
 Amino alcohols are commonly used as dispersants and stabilizers, especially in the production of water-based paints. They are low in cost, low in toxicity, and serve as anti-corrosive agents and pH stabilizers without causing excessive foaming. To strengthen the spatial structure, reactive particles such as carbon micro- and nanomaterials (CNM) can be introduced into the CWCF. Unlike polyelectrolytes and surfactants, CNM particles can have a varying number of active centers depending on the method of formation. By varying the properties of CNMs, it is possible to increase the number of contact centers and form a spatial grid without increasing the concentration of surfactants and polyelectrolytes. This is because contact interactions are activated during grinding, forming a new surface with energy-saturated active centers. As a result, the concentration of the system can be increased, and the calorific value of the fuel can be increased as well. However, the presence of an organic component can render mechanochemical activation ineffective by shielding active sites with large organic molecules. Therefore, identifying the most effective stabilizer reagents and deve­loping technology for their introduction into the dispersed system is a crucial and intricate problem in obtaining CWCF
 The study revealed that the ξ potential of anthracite particles is 40–45 mV in the pre­sence of amino alcohols. Sedimentation stabi­lity in the presence of highly dispersed carbon additives increases from 5–6 to 10–14 days, i.e., almost twice. The introduction of highly dispersed carbon leads to an increase in the effective viscosity of the systems and can be recommended for controlling the fluidity of the CWCF. The technical and operational requirements are best met by the CWCF containing 0.25% AMR and 1% highly dispersed carbon.

Heteroatom tuning in agarose derived carbon aerogel for enhanced potassium ion multiple energy storage

AbstractThe incorporation of heteroatoms into carbon aerogels (CAs) can lead to structural distortions and changes in active sites due to their smaller size and electronegativity compared to pure carbon. However, the evolution of the electronic structure from single‐atom doping to heteroatom codoping in CAs has not yet been thoroughly investigated, and the impact of codoping on potassium ion (K+) storage and diffusion pathways as electrode material remains unclear. In this study, experimental and theoretical simulations were conducted to demonstrate that heteroatom codoping, composed of multiple heteroatoms (O/N/B) with different properties, has the potential to improve the electrical properties and stability of CAs compared to single‐atom doping. Electronic states near the Fermi level have revealed that doping with O/N/B generates a greater number of active centers on adjacent carbon atoms than doping with O and O/N atoms. As a result of synergy with enhanced wetting ability (contact angle of 9.26°) derived from amino groups and hierarchical porous structure, ON‐CA has the most optimized adsorption capacity (−1.62 eV) and diffusion barrier (0.12 eV) of K+. The optimal pathway of K+ in ON‐CA is along the carbon ring with N or O doping. As K+ storage material for supercapacitors and ion batteries, it shows an outstanding specific capacity and capacitance, electrochemical stability, and rate performance. Especially, the assembled symmetrical K+ supercapacitor demonstrates an energy density of 51.8 Wh kg−1, an ultrahigh power density of 443 W kg−1, and outstanding cycling stability (maintaining 83.3% after 10,000 cycles in 1 M KPF6 organic electrolyte). This research provides valuable insights into the design of high‐performance potassium ion storage materials.

Mechanistic study on hydrogen effects in propylene polymerization with MgCl2-supported Ziegler-Natta catalysts: New evidences from active center counting and reaction kinetics

Propylene polymerizations catalyzed by MgCl2/Di/TiCl4-AlEt3/siloxane in the absence and presence of hydrogen were studied by determining the time-dependent changes of catalytic activity, number of active centers and active center distribution. Three types of active centers with high, medium and very low stereoselectivity were differentiated by fractionating the polymer into three parts. Chain propagation rate constant of each type of active centers was estimated by linear fitting/extrapolating the time-dependent change of apparent propagation rate constant. The centers with high (Ci*), medium (Cm*) and low (Ca*) stereoselectivity responded to addition of hydrogen differently. Adding hydrogen caused marked increase of Ci*, but its propagation rate constant (kpi) was evidently reduced. In contrast, numbers of Cm* and Ca* were only slightly affected, but their propagation rate constants were evidently enhanced by hydrogen. The different hydrogen responses of Ci* with those of Cm* and Ca* were explained by two kinds of hydrogen activation mechanisms.

Rational Design of a Copper Cobalt Sulfide/Tungsten Disulfide Heterostructure for Excellent Overall Water Splitting.

Integrating different components into a heterostructure is a novel approach that increases the number of active centers to enhance the catalytic activities of a catalyst. This study uses an efficient, facile hydrothermal strategy to synthesize a unique heterostructure of copper cobalt sulfide and tungsten disulfide (CuCo2S4-WS2) nanowires on a Ni foam (NF) substrate. The nanowire arrays (CuCo2S4-WS2/NF) with multiple integrated active sites exhibit small overpotentials of 202 (299) and 240 (320) mV for HER and OER at 20 (50) mA cm-2 and 1.54 V (10 mA cm-2) for an electrolyzer in 1.0 M KOH, surpassing commercial and previously reported catalysts. A solar electrolyzer composed of CuCo2S4-WS2 bifunctional electrodes also produced significant amounts of hydrogen through a water splitting process. The remarkable performance is accredited to the extended electroactive surface area, reasonable density of states near the Fermi level, optimal adsorption free energies, and good charge transfer ability, further validating the excellent dual function of CuCo2S4-WS2/NF in electrochemical water splitting.

Effects of Internal Electron Donor on Distribution and Reactivity of Active Centers in Ethylene/1‐Hexene Copolymerization with MgCl2‐Supported Ziegler‐Natta Catalyst

AbstractEthylene/1‐hexene copolymerization with two MgCl2‐supported Ziegler‐Natta catalysts containing no internal electron donor or diethylphthalate (DEP) is conducted for different polymerization time . Effects of DEP on active center distribution are studied by fractionating each copolymer sample into boiling n‐heptane soluble (C7‐sol) and insoluble (C7‐ins) fractions, and counting the number of active centers in the copolymer fractions . The main effect of introducing DEP in the catalyst are reduction in the Ti content and significant increase in the proportion of active centers producing C7‐ins fraction. The propagation rate constants of ethylene insertion (kpE) and 1‐hexene insertion (kpH) are respectively estimated by linear fitting/extrapolating the change of apparent propagation rate constants (kpi)a with polymer yield according to a simplified multi‐grain particle model. In both catalysts, kpE in the C7‐ins fraction is 9–12 times larger than that in the C7‐sol fraction, and kpH in the C7‐ins fraction is 3–4 times larger than that in the C7‐sol fraction. The two groups of active centers have distinctly different catalytic properties. Introducing DEP reduced the kpE and kpH values and the extent of diffusion limitation . In summary, addition of electron donor in MgCl2‐supported Z‐N catalyst significantly changed the active center distribution and catalytic properties of its two groups of active centers.