Study of the carbon cycle of a hydrogen supply system over a supported Pt catalyst: methylcyclohexane-toluene-hydrogen cycle

• Published in: Catalysis science & technology Vol. 1; no. 4; pp. 1171 - 1181
• Main Authors: Zhang, Xiaotong, He, Ning, Lin, Long, Zhu, Quanren, Wang, Gang, Guo, Hongchen
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2020
• Subjects: Alkylation; Carbon; Carbon cycle; Catalysts; Coking; Conversion; Copper; Dehydrogenation; Disproportionation; Electron density; Electron transfer; Electronic structure; Hydrogen; Hydrogen production; Hydrogen storage; Hydrogenolysis; Isomerization; Methylcyclohexane; Platinum base alloys; Selectivity; Toluene
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c9cy01999e

Owing to the importance of the carbon cycle and the universality of carbon loss in sustainable hydrogen supply systems, Pt-based catalysts were designed carefully for a reversible methylcyclohexane-toluene-hydrogen (MTH) cycle. Through adjusting the activity of the Pt species toward C-H bonds to a middle level, liquid organic hydrogen carriers (LOHCs) with higher selectivity were achieved, making the MTH cycle closer to a closed carbon cycle. Specifically, in the hydrogen generation process, we tried to enhance coking resistance as well as inhibit side-reactions such as disproportionation, de-alkylation and hydro-isomerization via Cu doping in Pt/S-1. Experimentally, the selectivities of H 2 -rich and H 2 -lean LOHCs in the MTH cycle reached 99.9% with almost coke free during these two processes. Moreover, Pt-based catalysts exhibited excellent activity and durability in catalyzing the MTH cycle. The hydrogen release rate reached 445.3 mmol g Pt −1 min −1 with 92.26% methylcyclohexane (MCH) conversion and a hydrogen storage rate of 1271 mmol g Pt −1 min −1 was achieved with greater than 99.9% toluene conversion. Finally, through further investigating the geometric configuration and electronic environment of the Cu and Pt species, we found that the Pt was co-located and interacted with the Cu by forming an alloy. Moreover, the unique electron structure of the Cu-Pt alloy facilitated electron transfer from the Pt to the Cu, decreasing the electron density of the Pt. As a consequence, over-dehydrogenation and hydrogenolysis in the MTH cycle were inhibited. Owing to the importance of the carbon cycle and the universality of carbon loss in sustainable hydrogen supply systems, Pt-based catalysts were designed carefully for a reversible methylcyclohexane-toluene-hydrogen (MTH) cycle.