Tuning structure and activity of propane dehydrogenation catalysts using tailored PtSn alloys

The emergence of shale gas reserves as feedstock has necessitated the development of active and stable dehydrogenation catalysts to produce light olefins through alkane dehydrogenation. While PtSn catalysts are the industrial benchmark for propane dehydrogenation (PDH) processes, their underlying structure remains elusive. In this work, we apply surface organometallic chemistry (SOMC), combined with a thermolytic molecular precursor (TMP) to prepare a family of bimetallic PtSn catalysts supported on SiO₂. We start with preparing isolated Sn/SiO₂ sites via grafting and thermolysis of Sn(OSi(O ^t Bu)₃)₄, and characterize them via Fourier Transform Infrared Spectroscopy (FTIR), ¹¹⁹Sn solid state NMR and X-ray absorption spectroscopy (XAS). These well-defined Sn/SiO₂ sites are subsequently used to prepare several bimetallic PtSn/SiO₂ propane dehydrogenation catalysts with varying Pt : Sn ratios via grafting of a Pt precursor on Sn/SiO₂, followed by temperature programmed reduction in hydrogen - yielding supported, alloyed Pt _x Sn _y nanoparticles exhibiting ordered Pt _x Sn _y phases as confirmed by powder X-ray diffraction (XRD). All prepared PtSn catalysts show remarkable PDH activity at a competitive weight hourly space velocity (WHSV) of 65 g_(C3H8)/g_(Cat)/h. The best catalyst, at a Pt : Sn ratio of 0.68, stabilizes at a productivity of 53 600 mol_(C3H6)/mol_(PtExposed) /h after 30 h on stream, and we observe that it is primarily composed of the Pt₁Sn₁ alloy. Overall, our findings provide a strategy for the preparation of well-defined, supported Pt _x Sn _y catalysts with tailored Pt : Sn ratios, while the formation of an alloyed Pt₁Sn₁ phase is identified to be key towards highly active and stable PtSn based PDH catalysts.