Selective Hydrogenation of Benzene to Cyclohexene over Ru-Zn Catalysts: Investigations on the Effect of Zn Content and ZrO<sub>2</sub> as the Support and Dispersant

Haijie Sun; Zhihao Chen; Lingxia Chen; Huiji Li; Zhikun Peng; Zhongyi Liu; Shouchang Liu

doi:10.3390/catal8110513

Catalysts (Nov 2018)

Selective Hydrogenation of Benzene to Cyclohexene over Ru-Zn Catalysts: Investigations on the Effect of Zn Content and ZrO<sub>2</sub> as the Support and Dispersant

Haijie Sun,
Zhihao Chen,
Lingxia Chen,
Huiji Li,
Zhikun Peng,
Zhongyi Liu,
Shouchang Liu

Affiliations

Haijie Sun: Institute of Environmental and Catalytic Engineering, College of Chemistry and Chemical Engineering, Zhengzhou Normal University, Zhengzhou 450044, Henan, China
Zhihao Chen: Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou 450001, Henan, China
Lingxia Chen: Institute of Environmental and Catalytic Engineering, College of Chemistry and Chemical Engineering, Zhengzhou Normal University, Zhengzhou 450044, Henan, China
Huiji Li: Institute of Environmental and Catalytic Engineering, College of Chemistry and Chemical Engineering, Zhengzhou Normal University, Zhengzhou 450044, Henan, China
Zhikun Peng: College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, Henan, China
Zhongyi Liu: College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, Henan, China
Shouchang Liu: College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, Henan, China

DOI: https://doi.org/10.3390/catal8110513
Journal volume & issue: Vol. 8, no. 11
p. 513

Abstract

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m-ZrO2 (monoclinic phase) supported Ru-Zn catalysts and unsupported Ru-Zn catalysts were synthesized via the impregnation method and co-precipitation method, respectively. The catalytic activity and selectivity were evaluated for selective hydrogenation of benzene towards cyclohexene formation. Catalyst samples before and after catalytic experiments were thoroughly characterized via X-ray diffraction (XRD), X-ray Fluorescence (XRF), transmission electron microscopy (TEM), N2-sorption, X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), and a contact angle meter. It was found that Zn mainly existed as ZnO, and its content was increased in Ru-Zn/m-ZrO2 by enhancing the Zn content during the preparation procedure. This results in the amount of formed (Zn(OH)2)3(ZnSO4)(H2O)3 increasing and the catalyst becoming more hydrophilic. Therefore, Ru-Zn/m-ZrO2 with adsorbed benzene would easily move from the oil phase into the aqueous phase, in which the synthesis of cyclohexene took place. The generated cyclohexene then went back into the oil phase, and the further hydrogenation of cyclohexene would be retarded because of the high hydrophilicity of Ru-Zn/m-ZrO2. Hence, the selectivity towards cyclohexene formation over Ru-Zn/m-ZrO2 improved by increasing the Zn content. When the theoretical molar ratio of Zn to Ru was 0.60, the highest cyclohexene yield of 60.9% was obtained over Ru-Zn (0.60)/m-ZrO2. On the other hand, when m-ZrO2 was utilized as the dispersant (i.e., employed as an additive during the reaction), the catalytic activity and selectivity towards cyclohexene synthesis over the unsupported Ru-Zn catalyst was lower than that achieved over the Ru-Zn catalyst with m-ZrO2 as the support. This is mainly because the supported catalyst sample demonstrated superior dispersion of Ru, higher content of (Zn(OH)2)3(ZnSO4)(H2O)3, and a stronger electronic effect between Ru and ZrO2. The Ru-Zn(0.60)/m-ZrO2 was reused 17 times without any regeneration, and no loss of catalytic activity and selectivity towards cyclohexene formation was observed.

Published in Catalysts

ISSN: 2073-4344 (Online)
Publisher: MDPI AG
Country of publisher: Switzerland
LCC subjects: Technology: Chemical technology; Science: Chemistry
Website: https://www.mdpi.com/journal/catalysts

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