Structure–Property Relationships of Pt–Sn Nanoparticles Supported on Al2O3 for the Dehydrogenation of Methylcyclohexane

Abstract

The structure–catalytic property relationships of Al2O3-supported Pt–Sn nanoparticles (Pt–Sn/Al2O3) in the dehydrogenation of methylcyclohexane (MCH) were investigated by varying the Sn/Pt ratios of the catalysts. The initial activity and the deactivation rate of the Pt–Sn/Al2O3 catalysts in the MCH dehydrogenation decreased in line with an increase in the Sn/Pt ratio from 0 to 3. The Pt–Sn/Al2O3 catalyst with a Sn/Pt ratio of 2 showed good activity, durability, and toluene selectivity in the MCH dehydrogenation among the series of catalysts. The dispersion of Pt in the Pt–Sn/Al2O3 catalysts was observed to decrease with an increase in the Sn/Pt ratio. Structural changes in the catalysts from Pt–Sn clusters to intermetallic Pt3Sn and PtSn nanoparticles were also observed using scanning transmission electron microscopy and X-ray diffraction. According to structural analysis using X-ray absorption fine-structure spectroscopy and infrared spectroscopy using carbon monoxide as a probe, the electron density of Pt increased, and the fraction of Pt–Pt adjacent sites decreased with an increase in the Sn/Pt ratio. Comparing the catalytic properties and the structures of the Pt–Sn/Al2O3 catalysts, their initial activities were correlated with the dispersion of Pt. In addition, the durability and selectivity of the catalysts were enhanced due to an increase in the electron density of Pt and a decrease in the number of Pt–Pt adjacent sites. Overall, the properties of the catalysts in the MCH dehydrogenation are determined by the local structure of Pt atoms rather than the crystal structure of the Pt–Sn alloy nanoparticles on Al2O3.