Subnanometer Bimetallic Platinum–Zinc Clusters in Zeolites for Propane Dehydrogenation

Propane dehydrogenation (PDH) has great potential to meet the increasing global demand for propylene, but the widely used Pt-based catalysts usually suffer from short-term stability and unsatisfactory propylene selectivity. Herein, we develop a ligand-protected direct hydrogen reduction method for encapsulating subnanometer bimetallic Pt-Zn clusters inside silicalite-1 (S-1) zeolite. The introduction of Zn species significantly improved the stability of the Pt clusters and gave a superhigh propylene selectivity of 99.3 % with a weight hourly space velocity (WHSV) of 3.6-54 h^-1 and specific activity of propylene formation of 65.5 mol <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow></mml:mrow> <mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mn>3</mml:mn></mml:msub> <mml:mi>H</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mn>6</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:math> g_Pt ^-1 h^-1 (WHSV=108 h^-1 ) at 550 °C. Moreover, no obvious deactivation was observed over PtZn4@S-1-H catalyst even after 13000 min on stream (WHSV=3.6 h^-1 ), affording an extremely low deactivation constant of 0.001 h^-1 , which is 200 times lower than that of the PtZn4/Al₂ O₃ counterpart under the same conditions. We also show that the introduction of Cs⁺ ions into the zeolite can improve the regeneration stability of catalysts, and the catalytic activity kept unchanged after four continuous cycles.