Platinum clusters confined in FAU-LTA hierarchical porous composite with a core-shell structure
Résumé
Hierarchical porous composite with a core-shell structure possessing FAU-type zeolite core (zeolite X) and LTA-type zeolite shell (zeolite A) has been prepared. The intimate growth of zeolite shell is achieved by in situ crystallization of the LTA zeolite crystals with size of 1 mu m on large single FAU-type crystals with size of about 60-90 mu m. Direct visualization of the core-shell material is provided by X-ray microbeam measurements using synchrotron radiation on a single crystal complemented with field emission scanning electron microscopic study. The nitrogen sorption data confirmed that the access to large single FAU-type core is controlled by the defect-free LTA-type shell. Sorption measurements showed that about 98% of core crystals are covered by the LTA shells. Further the FAU-LTA core-shell material is used as a host for the stabilization of platinum clusters. The Pt location, mean size and distribution have been studied by CO chemisorption followed by FT-IR spectroscopy. High loading of platinum accessible to CO molecules in the core-shell material is achieved. The use of the FAU-LTA matrix allowed the stabilization of two different sizes of Pt clusters. Additional advantage of the core-shell material is the protection of the clusters from thermal sintering and poisoning, which is of significant importance for future catalysts. (C) 2010 Elsevier B.V. All rights reserved.