Metallocene supported core@LDH catalysts for slurry phase ethylene polymerisation

Thermal Degradation Kinetics Analysis of Ethylene-Propylene Copolymer and EP-1-Hexene Terpolymer

LLDPE is a less crystalline polymer with vast industrial and domestic applications. It is imperative to understand the synthesis, processing conditions, and thermal degradation mechanism of the co- as well as terpolymers. This paper reports the in-situ synthesis and thermal degradation studies of the ethylene-propylene copolymer and ethylene-propylene-1-hexene terpolymer and its nanocomposite with ZnAL LDH sheets. The 1-hexene dosing during the in-situ process influenced the product yield and immensely affected the thermal stability of the resultant polymer. One milliliter 1-hexene in-situ addition increased the product yield by 170 percent, while the temperature at 10 percent weight loss in TGA was dropped by about 60 °C. While only 0.3 weight percent ZnAL LDH addition in the terpolymer improved the thermal stability by 10 °C. A master plot technique and combined kinetics analysis (CKA) were deployed to access the thermal degradation mechanism of the synthesized polymers.

Synthesis of zirconocene complexes and their use in slurry-phase polymerisation of ethylene

A new family of zirconocene complexes of the type (^3-RInd^#)₂ZrX₂ (where Ind^# = C₆Me₅H and R = Me, Et and Ph) have been synthesised and fully characterised. Six new crystal structures have been reported (meso-(^3-EtInd^#)₂ZrBr₂, rac-(^3-EtInd^#)₂ZrCl₂, rac-(^3-EtInd^#)₂Zr(CH₂Ph)₂, meso-(^3-EtInd^#)₂Zr(CH₂Ph)₂, meso-(^3-MeInd^#)₂ZrBr₂ and meso-(^3-MeInd^#)₂Zr(CH₂Ph)₂). The complexes were studied for slurry-phase ethylene polymerisation when immobilised on solid polymethylaluminoxane (sMAO). Variation in the initiation group was found to have greater influence over polymerisation activity for meso-catalysts than rac-catalysts, with meso-alkyl catalysts showing higher polymerisation activities than meso-halide. Below 70 °C, polymerisation activity follows the order sMAO-meso-(^3-EtInd^#)₂Zr(CH₂Ph)_2, sMAO-meso-(^3-EtInd^#)₂ZrCl₂ and sMAO-meso-(^3-EtInd^#)₂ZrBr₂ (activities of 657, 561, and 452 kg_PE mol_M⁻¹ h⁻¹ bar⁻¹, respectively). sMAO-meso-(^3-EtInd^#)₂ZrBr₂ produces HDPE with the highest molecular weight, followed by sMAO-meso-(^3-EtInd^#)₂ZrCl₂ and sMAO-meso-(^3-EtInd^#)₂Zr(CH₂Ph)₂ (M_w of 503, 406, and 345 kg mol⁻¹, respectively, at 50 °C). sMAO-meso-(^3-MeInd^#)₂ZrBr₂ produced HDPE with almost identical molecular weights to sMAO-meso-(^3-EtInd^#)₂ZrCl₂ (395 kg mol⁻¹ at 50 °C).

A new family of zirconocene complexes of the type (^3-RInd^#)₂ZrX₂ (where Ind^# = C₆Me₅H and R = Me, Et and Ph) have been synthesised and fully characterised.

A facile synthesis of layered double hydroxide based core@shell hybrid materials

A simple and scalable co-precipitation method to obtain zeolite Z13X@Mg₂Al–CO₃-LDH and Mg-MOF-74@Mg₂Al–CO₃-LDH has been reported.

Hectogram-scale green synthesis of hierarchical 4A zeolite@CuOx(OH)(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures with Superb Congo red adsorption performance

Delicate design of hierarchical nanoarchitectures has become a highly effective strategy to develop novel adsorbents with improved adsorption capacity. Herein, hectogram-scale green fabrication of hierarchical 4A zeolite@CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures (4A-Cu-T, T was the calcination temperature) with terrific Congo red (CR) dye adsorption performance was achieved through a simple, template-free and surfactant-free hydrothermal approach. A series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction and photoelectron spectroscopy demonstrated that all resultant adsorbents featured a core–shell structure with 4A zeolite as core ingredients and CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies as shell components. The adsorption experimental results pointed out that 4A-Cu-300 with a maximum adsorption capacity of 512.987 mg g⁻¹ showed the best adsorption performance amongst all as-prepared adsorbents, and the adsorption capacity of shell component-CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies was calculated up to 3685.500 mg g⁻¹. The shell thickness and phase ratio of CuO and Cu(OH)₂ in CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies played key roles in improving the adsorption capacity. The successive tests suggested that the “carbon deposition” resulted in the decreased adsorption capacity of first-regenerated adsorbents, but little variance in adsorption performance among regenerated samples demonstrated the good stability of such adsorbents. This work unlocks a method for the rational design of high-performance adsorbents via delicate decoration of poor-performance materials with nanosheet assemblies, which will endow the non-active materials with enhanced adsorption properties.

The growth of CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies on the surface of 4A zeolite transforms poor-performance 4A zeolite adsorbents into high-performance 4A-Cu-300 adsorbents for Congo red study.

Group 4 permethylindenyl complexes for slurry-phase polymerisation of ethylene

Supported group 4 permethylindenyl based catalysts displayed extremely high ethylene polymerisation activity affording popcorn shaped low molecular weights polyethylenes.

Dendritic silica@aqueous miscible organic-layered double hydroxide hybrids

We present the synthesis of a series of hierarchical Silica@Layered Double Hydroxide (SiO₂@LDH) core@shell hybrid materials that have been post-treated using the Aqueous Miscible Organic Solvent Treatment (AMOST) method. The Silica@Aqueous Miscible Organic-Layered Double Hydroxide (SiO₂@AMO-LDH) hybrids exhibit composition flexibility with radially oriented AMO-Mg_yAl-CO₃-LDH nanosheets resulting in a new dendritic morphology.

Small-Sized Mg-Al LDH Nanosheets Supported on Silica Aerogel with Large Pore Channels: Textural Properties and Basic Catalytic Performance after Activation

Layered double hydroxides (LDHs) have been widely used as an important subset of solid base catalysts. However, developing low-cost, small-sized LDH nanoparticles with enhanced surface catalytic sites remains a challenge. In this work, silica aerogel (SA)-supported, small-sized Mg-Al LDH nanosheets were successfully prepared by one-pot coprecipitation of Mg and Al ions in an alkaline suspension of crushed silica aerogel. The supported LDH nanosheets were uniformly dispersed in the SA substrate with the smallest average radial diameter of 19.2 nm and the thinnest average thickness of 3.2 nm, both dimensions being significantly less than those of the vast majority of LDH nanoparticles reported. The SA/LDH composites also showed large pore volume (up to 1.3 cm3·g) and pore diameter (>9 nm), and therefore allow efficient access of reactants to the edge catalytic sites of LDH nanosheets. In a base-catalyzed Henry reaction of benzaldehyde with nitromethane, the SA/LDH catalysts showed high reactant conversions and favorable stability in 6 successive cycles of reactions. The low cost of the SA carrier and LDH precursors, easy preparation method, and excellent catalytic properties make these SA/LDH composites a competitive example of solid-base catalysts.

Silica@layered double hydroxide core-shell hybrid materials

A series of silica@layered double hydroxides (SiO₂@Mg₂Al-CO₃-AMO-LDHs) have been synthesised by in situ precipitation of Mg₂Al-CO₃-LDH at room temperature in the presence of amorphous spherical silica particles (∼500 nm). We have systematically investigated a number of synthetic parameters in order to evaluate their effects on the composition, morphological and physical properties of the isolated materials. Syntheses carried out at moderate stirring speeds (e.g. 500 rpm) were found to promote the formation of vertically aligned LDH platelets with respect to the silica surface. Addition rates of the metal solutions slower than 0.43 mmol h^-1 were found to create a thicker LDH shell consisting of vertically aligned LDH platelets. When the metal solutions were added rapidly (0.86 mmol h^-1), we observed that for both slow and fast stirring speeds the synthesised core-shell materials had thin LDH shells and the majority of the LDH precipitated independent of the silica, forming unbound "free" LDH.