Effect of potassium addition on bimetallic PtSn supported θ-Al2O3 catalyst for n-butane dehydrogenation to olefins

• Sn addition suppressed the cracking sites on the Pt catalysts.
• Potassium addition blocked the isomerization sites (acid sites) on the Pt catalysts.
• K doped (PtSn)1.5/θ-Al2O3 catalyst gives stable n-C4= selectivity with time.
• K0.95(PtSn)1.5 catalyst was optimized showed the better n-C4= yield as well as stability.
• Distribution of Pt, Sn and K particles were clearly visible by HAADF STEM-EDS mapping.

PtSn/θ–Al2O3 catalysts with different amount of potassium (0.4, 0.7, 0.95, 1.2 and 1.45 wt.%) were prepared by an impregnation method, and their catalytic activity in n-butane dehydrogenation was investigated at 823 K, an atmospheric pressure and a GHSV of 18,000 mL(gcat h)−1. The compositions listed in order of n-C4= yields at 823 K were as follows: K0.95(PtSn)1.5 > (PtSn)1.5 > K0.4(PtSn)1.5 > K0.7(PtSn)1.5 > K1.2(PtSn)1.5 > K1.45(PtSn)1.5 > K0.9(Pt)1.5. The K0.9(Pt)1.5 and K0.95(Sn)1.5 catalyst severely deactivated in n-butane dehydrogenation. The (PtSn)1.5 (without K) catalyst showed the highest n-butane conversion, while K0.95(PtSn)1.5 did the highest n-C4= yield. The small amount of potassium on bimetallic PtSn/θ-Al2O3 catalyst improved n-C4= selectivity, but slightly decreased n-butane conversion, resulting in the increase of n-C4= yield. The effect of potassium was caused by blocking the acid sites of Pt catalyst. The TPR and HAADF STEM-EDS study suggested the reduction procedure of the Pt, Sn and K species. However, the higher loaded potassium (1.2 and 1.45 wt.%) doped (PtSn)1.5 catalysts were rather highly deactivated because the sizes of Pt particles were increased by weakening the interaction between Pt and Sn. The n-C4= selectivity of the (PtSn)1.5 catalyst increased with respect to the reaction, while that of the potassium doped catalysts maintained the high n-C4= selectivity from the beginning of the reaction. Also, different alkali metals (Ca, Na and Li) were tested for the comparison with K. The potassium doped catalyst showed the highest n-C4= yield among the other alkali metals for n-butane dehydrogenation.

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