A Small Paramagnetic Platinum Cluster in an NaY Zeolite: Characterization and Hydrogen Absorption and Desorption.

Abstract

A Small Paramagnetic Platinum Cluster in an NaY Zeolite: Characterization and Hydrogen Absorption and Desorption. -A well-defined cluster containing 12 equivalent Pt atoms is prepared by ion-exchange of NaY zeolite with aqueous [Pt(NH3)4]Cl2 solution at 343 K (about 48 h) followed by reduction in flowing H2 at 473 K (1 h). The samples are characterized by EPR, hyperfine sublevel correlation, and DFT calculations. The likely structure of the cluster is icosahedral Pt 13 H m (m ≤ 30). The adsorbed H on the Pt cluster surface can be exchanged reversibly at room temperature. The H2 binding energy of 1.36 eV is clearly larger than that for a (111) Pt single crystal surface, revealing a finite size effect. Evidence of an interesting magnetic behavior with high-spin states playing a prominent role is given. Pt clusters dispersed in zeolites are highly active catalysts for the oxidation of CO and residual hydrocarbons in automotive exhaust catalysts and for hydrogenation in petrochemical reactions and other commercial applications. -(LIU, X.; DILGER, H.; EICHEL, R. A.; KUNSTMANN, J.; RODUNER*, E.; J.