Journal
INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES
Volume 22, Issue 14, Pages -Publisher
MDPI
DOI: 10.3390/ijms22147756
Keywords
benzene; partial hydrogenation; cyclohexene; reaction modifier; ZnSO4; MnSO4; FeSO4
Funding
- Key Science and Technology Program of Henan Province [192102210139]
- Training Plan of Young Backbone Teachers in Colleges and Universities of Henan Province [2019GGJS252]
- Innovation and Entrepreneurship Training Program for college students in Henan Province [202112949001]
- Key Scientific Research Projects of Colleges and Universities in Henan Province [18A150018]
- National Natural Science Foundation of China [21908203]
- China Postdoctoral Science Foundation [2019T120637]
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Zn2+ or Fe2+ can enhance the selectivity towards cyclohexene but hinder the catalytic activity towards benzene hydrogenation; the presence of ZnO in Ru-Zn catalyst leads to increased adsorption of Zn2+ and Fe2+, resulting in improved selectivity towards cyclohexene synthesis.
Nano Ru-based catalysts, including monometallic Ru and Ru-Zn nanoparticles, were synthesized via a precipitation method. The prepared catalysts were evaluated on partial hydrogenation of benzene towards cyclohexene generation, during which the effect of reaction modifiers, i.e., ZnSO4, MnSO4, and FeSO4, was investigated. The fresh and the spent catalysts were thoroughly characterized by XRD, TEM, SEM, XPS, XRF, and DFT studies. It was found that Zn2+ or Fe2+ could be adsorbed on the surface of a monometallic Ru catalyst, where a stabilized complex could be formed between the cations and the cyclohexene. This led to an enhancement of catalytic selectivity towards cyclohexene. Furthermore, electron transfer was observed from Zn2+ or Fe2+ to Ru, hindering the catalytic activity towards benzene hydrogenation. In comparison, very few Mn2+ cations were adsorbed on the Ru surface, for which no cyclohexene could be detected. On the other hand, for Ru-Zn catalyst, Zn existed as rodlike ZnO. The added ZnSO4 and FeSO4 could react with ZnO to generate (Zn(OH)(2))(5)(ZnSO4)(H2O) and basic Fe sulfate, respectively. This further benefited the adsorption of Zn2+ or Fe2+, leading to the decrease of catalytic activity towards benzene conversion and the increase of selectivity towards cyclohexene synthesis. When 0.57 mol center dot L-1 of ZnSO4 was applied, the highest cyclohexene yield of 62.6% was achieved. When MnSO4 was used as a reaction modifier, H2SO4 could be generated in the slurry via its hydrolysis, which reacted with ZnO to form ZnSO4. The selectivity towards cyclohexene formation was then improved by the adsorbed Zn2+.
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