scholarly journals Olefin oligomerization by main group Ga3+ and Zn2+ single site catalysts on SiO2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nicole J. LiBretto ◽  
Yinan Xu ◽  
Aubrey Quigley ◽  
Ethan Edwards ◽  
Rhea Nargund ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Equilibrium Distribution ◽  
Transition Metal Ions ◽  
Main Group ◽  
Single Site ◽  
Main Group Metal ◽  
Hydride Elimination ◽  
Single Site Catalysts ◽  
Olefin Oligomerization

AbstractIn heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+, while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.

scholarly journals Olefin Oligomerization by Main Group Ga3+ and Zn2+ Single Site Catalysts

2020 ◽  
Author(s):  
Nicole LiBretto ◽  
Yinan Xu ◽  
Aubrey Quigley ◽  
Ethan Edwards ◽  
Rhea Nargund ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Equilibrium Distribution ◽  
Transition Metal Ions ◽  
Main Group ◽  
Single Site ◽  
Main Group Metal ◽  
Hydride Elimination ◽  
Single Site Catalysts ◽  
Olefin Oligomerization

Abstract In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ions catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+; while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250°C where oligomerization is catalytically relevant. This work reports new chemistry for main group metal catalysts with potential for development of new olefin processes.

scholarly journals First Principles Analysis of Ethylene Oligomerization on Single-site Ga3+ Catalysts Supported on Amorphous Silica

2021 ◽  
Author(s):  
Yinan Xu ◽  
Nicole LiBretto ◽  
Guanghui Zhang ◽  
Jeffrey Miller ◽  
Jeffrey Greeley
Keyword(s):  
Amorphous Silica ◽  
First Principles ◽  
Main Group ◽  
Ethylene Oligomerization ◽  
Single Site ◽  
Local Geometry ◽  
Amorphous Oxides ◽  
Rate Determining Step ◽  
Main Group Metal ◽  
Olefin Oligomerization

Amorphous, single site, silica-supported main group metal catalysts have recently been found to promote olefin oligomerization with high activity at moderate temperatures and pressures (~250°C and 1 atm). Herein, we explore the molecular-level relationship between active site structures and the associated oligomerization mechanisms by developing amorphous, silica-supported Ga3+ models from periodic, first-principles calculations. Representative Ga3+ sites, including three- and four-coordinated geometries, are tested for multiple ethylene oligomerization pathways. We show that the three-coordinated Ga3+ site promotes oligomerization through a facile initiation process that generates a Ga-alkyl intermediate, followed by a Ga-alkyl-centered Cossee-Arlman mechanism. The strained geometry of a three-coordinated site enables a favorable free energy landscape with a kinetically accessible ethylene insertion transition state (1.7 eV) and a previously unreported β-hydride transfer step (1.0 eV) to terminate further C-C bond formation. This result, in turn, suggests that Ga3+ does not favor polymerization chemistry, while microkinetic modeling confirms that ethylene insertion is the rate-determining step. The study demonstrates promising flexibility of main group ions for hydrocarbon transformations and, more generally, highlights the importance of the local geometry of metal ions on amorphous oxides in determining catalytic properties.

Isospecific propylene polymerization with in situ generated bis(phenoxy-amine)zirconium and hafnium single site catalysts

2013 ◽  
Vol 42 (25) ◽  
pp. 9112 ◽  
Author(s):  
Haruyuki Makio ◽  
Aitha Vishwa Prasad ◽  
Hiroshi Terao ◽  
Junji Saito ◽  
Terunori Fujita
Keyword(s):  
Single Site ◽  
Propylene Polymerization ◽  
Single Site Catalysts

scholarly journals Sulfur Poisoning on Rh Nanoparticles but Sulfur Promotion on Its Single-Site Catalyst for Carbonylation

2021 ◽  
Author(s):  
Yun (J) Ding ◽  
Siquan Feng ◽  
Jiali Mu ◽  
Xiangsong Lin ◽  
Xiangen Song ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Role Reversal ◽  
Sulfur Poisoning ◽  
Single Site ◽  
Sulfur Resistance ◽  
Methanol Carbonylation ◽  
Flight Mass Spectrometry ◽  
Strong Adsorption ◽  
Single Site Catalysts

Abstract Sulfur poisoning is a challenge for most nanoparticle metal catalysts. A trace amount of sulfur contaminants could result in dramatic catalytic activity reduction or even irreversible deactivation1-5. Therefore, new approaches to enhance the catalyst sulfur-resistance have continuously attracted attention from academia and industry. Herein, a role reversal of sulfur from poison to promotor is presented for an Rh-based heterogeneous catalyst from supported Rh nanoparticles (NPs) to its single-site catalysts (Rh1/AC, AC: activated carbon) in methanol carbonylation, ethylene and acetylene hydrocarboxylic reaction with a feed containing 1000 ppm H2S (S-feed). In situ free-electron laser/time of flight mass spectrometry (In situ FEL/TOF MS) indicated that H2S could be quickly transformed into catalyst-friendly CH3SCH3 and/or CH3SH on the Rh1/AC, which coordinated with the Rh ions and promoted its methanol carbonylation reaction, possessing a lower energy barrier based on DFT calculations. On the contrary, strong adsorption of H2S on the surface of Rh NPs inhibited the reaction of reactants.

scholarly journals Activation and Functionalization of C–C σ-Bonds of Alkylidene Cyclopropanes at Main Group Centers

2020 ◽  
Author(s):  
Mark Crimmin ◽  
Richard Y Kong
Keyword(s):  
Bond Activation ◽  
Substrate Binding ◽  
Oxidative Addition ◽  
Main Group ◽  
Single Site ◽  
Mechanistic Studies ◽  
Metal Bond ◽  
Main Group Metal ◽  
Metal Metal ◽  
Group Center

Aluminum(I) and magnesium(I) compounds are reported for the C–C s-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C s-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to a- or b-alkyl migration steps that break the C–C s-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C s-bonds of alkylidene cyclopropanes.

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