Generation and Properties of Bronsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

作者：Obenaus Utz; Dyballa Michael; Lang Swen; Scheibe Matthias; Hunger Michael^*

来源：Journal of Physical Chemistry C, 2015, 119(27): 15254-15262.

DOI：10.1021/acs.jpcc.5b03149

In the present work, the generation and properties of Bronsted acidic bridging OH groups (Si(OH)Al) in Rh-, Pd-, and Pt- containing zeolites Y were quantitatively investigated by multinudear solid-state NMR spectroscopy. The number of Si(OH)Al groups formed per noble metal atom upon their reduction was found to be 0.3 to 1.3 instead of the theoretically expected values of 2 (Pd2+, Pt2+) or 3 (Rh3+, Ir3+). For zeolites Y with low noble metal loadings, a significantly lower acid strength of Si(OH)Al groups in comparison with those of H,Na-Y zeolites occurred. Interestingly, noble metal-containing zeolites Y with lower acid strength have a significant content of not completely reduced noble metal atoms with partially cationic character. The spatial distribution of Si(OH)Al groups in noble metal-containing zeolites Y was found to differ significantly from that in H,Na-Y zeolites. This effect is explained by the migration of a significant content of noble metal atoms into the sodalite cages of zeolites Y already upon calcination of their noble metal complexes. Therefore, a much higher content of Si(OH)Al groups generated by the reduction of noble metal species in zeolites Y are located in sodalite cages compared to those in H,Na-Y zeolites.

• 出版日期2015-7-9