Zeolite-NaY-supported Ir/Sn catalysts derived from single- and dual-source organometallic precursors. Preparation and characterization of highly selective dehydrogenation catalysts

Zeolite-NaY-supported Ir/Sn catalysts (1 wt% Ir, 0.6 wt% Sn; 1:1 molar ratio) were prepared by adsorption of the organometallic precursors Ir(CO)(2)(acac) and SnMe3OH or (COD)(2) Ir-SnMe3 (COD = 1,5-cyclooctadiene) from hexane solutions followed by activation in H-2 up to 773 K. The Ir/Sn/NaY catalysts displayed high selectivity for the dehydrogenation of propane to propene at ca. 773 K and, in the presence of H-2, maintained thermodynamic conversion levels for up to 24 h. After activation, the catalyst derived from the dual-source precursors (Ir + Sn/NaY) appeared homogeneous in composition, whereas the catalyst derived from the single-source precursor (Ir-Sn/NaY) appeared heterogeneous with distinct regions of visible particles. Scanning transmission electron microscopy revealed that the nanoscale metal particles present were small and uniform in size (ca. 1 nm) in the Ir + Sn/NaY catalyst but ranged in size from 1 to 10 nm in the Ir-Sn/NaY catalyst. Energy-dispersive X-ray analysis showed that bimetallic particles were formed for both catalysts. Temperature-programmed reaction of chemiosorbed carbon monoxide indicated that the Ir/Sn/NaY catalysts were electronically modified by the presence of tin in comparison with analogously prepared Ir/NaY catalysts.