Regioselectivity and Reaction Mechanism of Ru‐Catalyzed Hydrogenolysis of Squalane and Model Alkanes

• Published in: ChemSusChem 2017-01, Vol.10 (1), p.189-198
• Main Authors: Nakagawa, Yoshinao, Oya, Shin‐ichi, Kanno, Daisuke, Nakaji, Yosuke, Tamura, Masazumi, Tomishige, Keiichi
• Format: Article
• Language: English
• Subjects: alkanes; Alkanes - chemistry; Bonding; Carbon-carbon composites; Catalysis; Catalysts; Hydrogen; Hydrogen - chemistry; Hydrogenolysis; Mathematical models; Methane; Models, Molecular; Molecular Conformation; Oxidation; Pressure; Reaction mechanisms; regioselectivity; ruthenium; Ruthenium - chemistry; Silicon Dioxide - chemistry; Squalene - analogs & derivatives; Squalene - chemistry; Stereoisomerism; Substrate Specificity; Surface Properties; surface species; Temperature
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201601204

The dependence of the C−C hydrogenolysis activity on reaction parameters and the structure of the substrate alkanes was investigated for Ru/CeO2 catalyst with very small (dispersion: H/Ru=0.89) Ru particles. The substrate concentration and reaction temperature did not have a significant effect on the selectivity pattern, except that methane production was promoted at high temperatures. However, the hydrogen pressure had a marked effect on the selectivity pattern. Ctertiary−C bond dissociation, terminal Csecondary−Cprimary bond dissociation, and fragmentation to form excess methane had negative reaction order with respect to hydrogen partial pressure, whereas Csecondary−Csecondary bond dissociation had an approximately zero reaction order. Therefore, a high hydrogen pressure is essential for the regioselective hydrogenolysis of Csecondary−Csecondary bonds in squalane. Ru/SiO2 catalyst with larger Ru particles showed similar changes in the product distribution during the change in hydrogen pressure. The reaction mechanism for each type of C−C bond dissociation is proposed based on reactivity trends and DFT calculations. The proposed intermediate species for the internal Csecondary−Csecondary dissociation, terminal Csecondary−Cprimary dissociation, and Ctertiary−C dissociation is alkyls, alkylidynes, and alkenes, respectively. Many routes, simple guide! Ru‐catalyzed C−C hydrogenolysis involves four types of reactions. Only the Csecondary−Csecondary bond dissociation has a positive reaction order with respect to H2. High hydrogen pressure increases the regioselectivity. The reaction mechanism for each type of C−C bond dissociation is proposed based on reactivity trends and DFT calculations