Study on Carbon Cycle of Hydrogen Supply System over Supported Pt Catalyst: Methylcyclohexane-Toluene-Hydrogen Cycle
Owing to the importance of carbon cycle and universality of carbon loss in sustainable hydrogen supply system, Pt based catalysts were designed carefully for reversible methylcyclohexane-toluene-hydrogen (MTH) cycle. Through adjusting activity of Pt species toward C-H bonds to a middle level, higher selectivities of liquid organic hydrogen carriers (LOHCs) were achieved, which making MTH cycle closer to a closed carbon cycle. Specifically, in hydrogen generation process, we tried to enhance coking resistance as well as inhibit side-reactions such as disproportionation, de-alkylation and hydro-isomerization by Cu doping in Pt/S-1. Experimentally, selectivities of H2-rich and H2-lean LOHCs in MTH cycle reached to 99.9% with almost coke free. Moreover, Pt based catalysts exhibited excellent activity and durability in catalyzing MTH cycle. Hydrogen release rate reached to 445.3 mmol/gPt/min with 92.26% methylcyclohexane (MCH) conversion and hydrogen storage rate achieved to 1271 mmol/gPt/min with greater than 99.9% toluene conversion. Finally, through further investigating the geometric configuration and electronic environment of Cu and Pt species, we found that Pt was co-located and interacted with Cu by forming alloy. And the unique electron structure of Cu-Pt alloy facilitated electron transfer from Pt to Cu, decreasing electron density of Pt. As a consequence, over-dehydrogenation and hydrogenolysis in MTH cycle were inhibited.