The concept of active site in heterogeneous catalysis

The synthesis of hierarchically porous materials usually requires complex experimental procedures, often based around extensive trial and error approaches. One common synthesis strategy is the sol–gel method, although the relation between synthesis parameters, material structure and function has not been widely explored. Here, in situ 2D hard X‐ray ptychography (XRP) and 3D ptychographic X‐ray computed tomography (PXCT) are applied to monitor the development of hierarchical porosity in Ni/Al2O3 and Al2O3 catalysts with connected meso‐ and macropore networks. In situ XRP allows to follow textural changes of a dried gel Ni/Al2O3 sample as a function of temperature during calcination, activation and CO2 methanation reaction. Complementary PXCT studies on dried gel particles of Ni/Al2O3 and Al2O3 provide quantitative information on pore structure, size distribution, and shape with 3D spatial resolution approaching 50 nm, while identical particles are imaged ex situ before and after calcination. The X‐ray imaging results are correlated with N2‐sorption, Hg porosimetry and He pycnometry pore characterization. Hard X‐ray nanotomography is highlighted to derive fine structural details including tortuosity, branching nodes, and closed pores, which are relevant in understanding transport phenomena during chemical reactions. XRP and PXCT are enabling technologies to understand complex synthesis pathways of porous materials.

/pdf/evolution-of-hierarchically-porous-nickel-alumina-catalysts-3c49tko2.pdf

Evolution of Hierarchically Porous Nickel Alumina Catalysts Studied by X‐Ray Ptychography

https://pubs.rsc.org/en/content/articlepdf/2021/cy/d1cy00930c

Early-stage particle fragmentation behavior of a commercial silica-supported metallocene catalyst

Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts

Abstract PETRA III at DESY is one of the brightest synchrotron radiation sources worldwide. It serves a broad international multidisciplinary user community from academia to industry at currently 25 specialised beamlines. With a storage-ring energy of 6 GeV, it provides mainly hard to high-energy X-rays for versatile experiments in a very broad range of scientific fields. It is ideally suited for an upgrade to the ultra-low emittance source PETRA IV, owing to its large circumference of 2304 m. With a targeted storage ring emittance of $$20 \times 5\,\textrm{pm}^{2}\,\textrm{rad}^{2},$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>20</mml:mn> <mml:mo>×</mml:mo> <mml:mn>5</mml:mn> <mml:mspace /> <mml:msup> <mml:mtext>pm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> <mml:mspace /> <mml:msup> <mml:mtext>rad</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>,</mml:mo> </mml:mrow> </mml:math> PETRA IV will reach spectral brightnesses two to three orders of magnitude higher than today. The unique beam parameters will make PETRA IV the ultimate in situ 3D microscope for biological, chemical, and physical processes helping to address key questions in health, energy, mobility, information technology, and earth and environment. 

/pdf/the-synchrotron-radiation-source-petra-iii-and-its-future-3exj660f.pdf

The synchrotron radiation source PETRA III and its future ultra-low-emittance upgrade PETRA IV

Ziegler-type catalysts are the grand old workhorse of the polyolefin industry, yet their hierarchically complex nature complicates polymerization activity-catalyst structure relationships. In this work, the degree of catalyst framework fragmentation of a high-density polyethylene (HDPE) Ziegler-type catalyst was studied using ptychography X-ray-computed nanotomography (PXCT) in the early stages of ethylene polymerization under mild reaction conditions. An ensemble consisting of 434 fully reconstructed ethylene prepolymerized Ziegler catalyst particles prepared at a polymer yield of 3.4 g HDPE/g catalyst was imaged. This enabled a statistical route to study the heterogeneity in the degree of particle fragmentation and therefore local polymerization activity at an achieved 3-D spatial resolution of 74 nm without requiring invasive imaging tools. To study the degree of catalyst fragmentation within the ensemble, a fragmentation parameter was constructed based on a k-means clustering algorithm that relates the quantity of polyethylene formed to the average size of the spatially resolved catalyst fragments. With this classification method, we have identified particles that exhibit weak, moderate, and strong degrees of catalyst fragmentation, showing that there is a strong heterogeneity in the overall catalyst particle fragmentation and thus polymerization activity within the entire ensemble. This hints toward local mass transfer limitations or other deactivation phenomena. The methodology used here can be applied to all polyolefin catalysts, including metallocene and the Phillips catalysts to gain statistically relevant fundamental insights in the fragmentation behavior of an ensemble of catalyst particles.

Heterogeneity in the Fragmentation of Ziegler Catalyst Particles during Ethylene Polymerization Quantified by X-ray Nanotomography.

The invention relates to a catalyst composition for the polymerization of olefins, in which the catalyst is produced using a metal-containing compound having the formula (I): MeR n X 3-n (I), in which X is a halogen, Me is a metal of group III of Mendelejev's Periodic Table of Elements, R is a hydrocarbon moiety comprising > 2 carbon atoms, and n is 1 ≤n<3, or a dimer of a compound of formula (I); and the average particle size of the catalyst as reflected by D 50 (measured according to ISO13320) is between 0.5 and 4.5 μηη. The invention also relates to a process for production of said catalyst composition. The invention further relates to ultra-high molecular weight polyethylene produced via a polymerization process using said catalyst composition.

Catalyst composition for the polymerization of olefins

The present invention relates to a catalyst system for the production of polyethylene comprising: I) the reaction product obtained by reacting a) a hydrocarbon solution comprising: i. a magnesium-containing compound selected from an organic oxygen-containing magnesium compound and/or a halogen-containing magnesium compound; and ii. an organic oxygen-containing titanium compound wherein the molar ratio of magnesium: titanium is lower than 3:1; and b) an organo aluminium halide having the formula AlR n X 3-n in which R is a hydrocarbon moiety containing 1-10 carbon atoms, X is a halogen and 0 < n < 3; II) an aluminium compound having the formula AlR' 3 , in which R' is a hydrocarbon moiety containing 1-10 carbon atoms; and III) one or more of an electron donor selected from the group of 1,2-dialkoxy hydrocarbon compounds wherein the molar ratio of supplied organo aluminium halide I)b) to supplied titanium in I) a) in the preparation of I) is between 5.0 and 7.0; and the molar ratio of the electron donor III) to the titanium present in the reaction product I) is between 0.05 and 0.40 The production of polyethylene using said catalyst system results in a reduction of formation of ethane and a reduction of the hexane-extractable content of the polyethylene.

Catalyst system and process for the production of polyethylenes.

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Heterogeneity in the Fragmentation of Ziegler Catalyst Particles during Ethylene Polymerization Quantified by X-ray Nanotomography.

Catalyst composition for the polymerization of olefins

Catalyst system and process for the production of polyethylenes.