Dehydrogenation of alkane to light olefin over PtSn/θ-Al2O3 catalyst: Effects of Sn loading

• The Sn addition to Pt0.5/θ-Al2O3 catalysts increased the specific Pt surface area.
• The Pt0.5Sn0.75 catalyst showed the highest metal dispersion.
• The optimized Sn/Pt ratio increased with an increase in carbon number of alkane.
• The Sn addition blocked the cracking sites mainly.
• Excessive addition of Sn resulted in the deactivation of the catalyst.

Pt0.5Snx.x/θ-Al2O3 catalysts with different amount of tin (0.5, 0.75, 1.0 and 1.5 wt%) were prepared by a co-impregnation method. Propane dehydrogenation was performed at 873 K and a GHSV of 53,000 mL/(gcat h). The Pt0.5/θ-Al2O3 catalyst showed severe deactivation in alkane dehydrogenation reaction. The Sn addition decreased the cracking products of C1–C2 and the Pt0.5Sn0.75 catalyst with the highest Pt dispersion showed the highest C3 yield and C3 selectivity. n-Butane dehydrogenation was performed at 823 K and a GHSV of 18,000 mL/(gcat h). Similarly to propane dehydrogenation, the Sn addition to the Pt0.5/θ-Al2O3 catalyst decreased the cracking products of C1–C3. However, the Pt0.5Sn1.0 showed the highest n-C4 yield and the catalyst was steadily deactivated even at 823 K differently from propane dehydrogenation at 873 K.The small amount of Sn addition improved the C3 and n-C4 selectivity by blocking the cracking sites of Pt catalyst. The PtSn alloy formed after the reduction at 500 °C. The PtSn formation can enhance the C3 and n-C4 selectivity. The Pt dispersion on the Pt0.5/θ-Al2O3 catalyst increased with the Sn addition up to 0.75 wt%. The highest Pt metal dispersion was observed on the Pt0.5Sn0.75 catalyst. The conclusion was given to the Sn effects on the increase of Pt dispersion to enhance the activity as well as on the electronic and geometric effect of PtSn alloy to increase the stability and olefin selectivity.

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