Subnanometer Bimetallic Platinum-Zinc Clusters in Zeolites for Propane Dehydrogenation

摘要

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 molC3H6 g(Pt)(-1) h(-1) (WHSV=108 h(-1)) at 550 degrees 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/Al2O3 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.