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

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⁺ 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.

SUBMITTER: LiBretto NJ

PROVIDER: S-EPMC8055657 | biostudies-literature | 2021 Apr

REPOSITORIES: biostudies-literature

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Publications

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

LiBretto Nicole J NJ Xu Yinan Y Quigley Aubrey A Edwards Ethan E Nargund Rhea R Vega-Vila Juan Carlos JC Caulkins Richard R Saxena Arunima A Gounder Rajamani R Greeley Jeffrey J Zhang Guanghui G Miller Jeffrey T JT

Nature communications 20210419 1

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+ 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 Zn ...[more]

PMID: 33875664

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Project description:The production of linear alpha-olefins (α-olefins) is a practical way to increase the economic potential of the Fischer-Tropsch synthesis (FTS) because of their importance as chemical intermediates. Our study aimed to optimize Na-promoted Fe1Zn1.2O x catalysts such that they selectively converted syngas to linear α-olefins via FTS at 340 °C and 2.0 MPa. The Fe1Zn1.2O x catalysts were calcined at different temperatures from 350 to 700 °C before Na anchoring. The increase in the size of the ZnFe2O4 crystals comprising the catalyst had a negative effect on the reducibility of Fe oxides and the particle size of Fe5C2 during the reaction. The Na species in the catalyst restrained the reduction of Fe1Zn1.2O x but facilitated the formation of Fe5C2. When pure Fe1Zn1.2O x was calcined at 400 °C, the corresponding catalyst (i.e., Na0.2/Fe1Zn1.2O x (400)) exhibited higher catalytic activity and stability than the other catalysts for a 50 h reaction. Compared to the other catalysts, Na0.2/Fe1Zn1.2O x (400) enabled a higher number of active Fe carbides (Fe5C2) to intimately interact with the Na species, even though the catalyst had a lower total surface basicity based on surface area. The Na0.2/Fe1Zn1.2O x (400) showed a maximum hydrocarbon yield of 49.7% with a maximum olefin selectivity of 61.3% in the C1-C32 range. Examination of the reaction product mixture revealed that the Na0.2/Fe1Zn1.2O x catalysts converted α-olefins to branched paraffins (13.9-19.5%) via a series of isomerization, skeletal isomerization, and hydrogenation reactions. The Na0.2/Fe1Zn1.2O x (400) catalyst had a relatively low consumption rate of internal olefins compared to other catalysts, resulting in the lowest selectivity for branched paraffins. The Na0.2/Fe1Zn1.2O x (400) showed a maximum α-olefin yield (26.6%) in the range C2-C32, which was 27.9-50.0% higher than that of other catalysts. The α-olefin selectivity in the C5-C12 range for the Na0.2/Fe1Zn1.2O x (400) was 37.5% relative to the total α-olefins.

Dataset Information

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

Publications

Olefin oligomerization by main group Ga<sup>3+</sup> and Zn<sup>2+</sup> single site catalysts on SiO<sub>2</sub>.

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