Highly Active and Stable Pt–Sn/SBA-15 Catalyst Prepared by Direct Reduction for Ethylbenzene Dehydrogenation: Effects of Sn Addition

Abstract

A series of Pt−Sn/SBA-15 catalysts (Sn/Pt nominal ratios: 0−3) prepared by direct reduction were applied to ethylbenzene dehydrogenation to styrene. The characterization by X-ray diffraction, X-ray absorption fine structure, CO adsorption, transmission electron microscopy, and X-ray photoelectron spectroscopy revealed the formation of highly dispersed and stable Pt−Sn alloy particles [Pt x Sn y (x/ y ≥ 3) and Pt−Sn alloys having Sn-rich surfaces] on SBA-15. Nonalloyed Sn existed as highly dispersed SnO 2 . 1Pt−1Sn/ SBA-15 (Sn/Pt nominal ratio = 1) exhibited the highest activity, on which Pt 3 Sn alloy nanoparticles were mainly formed. In contrast, PtSn alloy was dominant on Pt−Sn/SBA-15 catalysts whose Sn/Pt nominal ratios were larger than 1, and the activity was decreased. Furthermore, 1Pt−1Sn/SBA-15 exhibited a higher stability than Pt/SBA-15 and 1Pt−1Sn/SiO 2 . The addition of Sn not only inhibits C−C bond cleavage and improves selectivity toward styrene but also enhances the "drainoff" effect, allowing coke precursors to migrate from the active metals to SBA-15 with large surface area.

Effect of Direct Reduction Treatment on Pt–Sn/Al2O3 Catalyst for Propane Dehydrogenation

“…As shown in Figure 7, the SR catalysts showed the first peak at 417-454 • C, and the second peak occurred at 482-503 • C during coke oxidation. It has been reported [24] that the first peak near 417 °C can be attributed to coke combustion on either Pt or Pt-Sn alloy sites, whereas the second peak near 494.4 °C is due to the "drain-off'" effect. Here, drain-off is the case of the coke on metal sites migrating to the oxide support.…”

Effect of Reduction of Pt–Sn/α-Al2O3 on Catalytic Dehydrogenation of Mixed-Paraffin Feed

“…Peaks at 39 • and 45.5 • correspond to Pt 3 Sn alloy phase, whereas peaks at 41.7 • and 44 • in 2θ value correspond to the PtSn alloy phase [14,20]. Further, it was also reported that the Pt 3 Sn alloy phase was only formed at Pt/Sn molar ratios greater than 1 [14]. In the current experimental studies, the nominal Pt/Sn molar ratio was 0.4.…”

“…For PtSn alloys, the characteristic peaks must be between 36 • and 48 • in 2θ value [30,33]. Peaks at 39 • and 45.5 • correspond to Pt 3 Sn alloy phase, whereas peaks at 41.7 • and 44 • in 2θ value correspond to the PtSn alloy phase [14,20]. Further, it was also reported that the Pt 3 Sn alloy phase was only formed at Pt/Sn molar ratios greater than 1 [14].…”

“…The promoters like Sn, In, Ga, and Pb have been widely used to reduce the deactivation of the catalyst as a result of sintering of noble metal clusters and suppress the secondary reactions like hydrogenalysis (refer to Equations (3) and (4) and coking (Equation (5)) [7,11,12]. Among those, Pt promoted with Sn was reported to be the most efficient catalyst for paraffin dehydrogenation [13][14][15][16]. The Sn donates an electron to Pt, which reduces the adsorption of alkenes (products of dehydrogenation) and increases the barrier for dissociative adsorption of light alkanes [17].…”

“…Considering the superior cleaving of the C-H bond compared with the C-C bond and stability, the Pt-Sn based catalysts were identified to be excellent catalysts for dehydrogenation [10,18]. Al 2 O 3 , SiO 2 , SBA-15, and zeolites were widely used as catalyst supports for dehydrogenation [14,17,[19][20][21]. Among the supports studied, Al 2 O 3 has been reported to be a good support for the Pt-Sn catalyst owing to its high thermal stability and uniform pore size.…”