Atomically Precise Design of PtSn Catalyst for the Understanding of the Role of Sn in Propane Dehydrogenation

Propane dehydrogenation (PDH), an atom-economic reaction to produce high-value-added propylene and hydrogen with high efficiency, has recently attracted extensive attention. The severe deactivation of Pt-based catalysts through sintering and coking remains a major challenge in this high-temperature reaction. The introduction of Sn as a promoter has been widely applied to improve the stability and selectivity of the catalysts. However, the selectivity and stability of PtSn catalysts have been found to vary considerably with synthesis methods, and the role of Sn is still far from fully understanding. To gain in-depth insights into this issue, we synthesized a series of PtSn/SiO2 and SnPt/SiO2 catalysts by varying the deposition sequence and Pt:Sn ratios using atomic layer deposition with precise control. We found that PtSn/SiO2 catalysts fabricated by the deposition of SnOx first and then Pt, exhibited much better propylene selectivity and stability than the SnPt/SiO2 catalysts synthesized the other way around. We demonstrate that the presence of Sn species at the Pt-SiO2 interface is of essential importance for not only the stabilization of PtSn clusters against sintering under reaction conditions but also the promotion of charge transfers to Pt for high selectivity. Besides the above, the precise regulation of the Sn content is also pivotal for high performance, and the excess amount of Sn might generate additional acidic sites, which could decrease the propylene selectivity and lead to heavy coke formation. These findings provide deep insight into the design of highly selective and stable PDH catalysts.