Palladium clusters have been synthesized by the "ship-in-a-bottle" approach in the supercages of NaX and NaY faujasite zeolites. In comparison with CO adsorbed on a bulk Pd electrode, the same molecule adsorbed on the Pd clusters electrodes evoked an enhanced IR absorption (EIRA). The enhancement factors have been determined to be about 38 and 51 in NaX and NaY, respectively. IR band centers of linear-bonded CO, bridge-bonded CO, and multi-bonded CO in NaX are measured, respectively, 12, 14, and 11 cm(-1) lower than those of the corresponding adsorption modes in NaY. The adsorption of CO and the oxidation of adsorbed CO in NaX matrix are faster than that in NaY matrix. These results suggest that part of the Pd2+ ions in NaX are located in sites III and III' that are near the 12-ring window of the supercage of zeolite, which lead to the formation of small Pd clusters. The present study is of significant importance in exploring the dependence of catalyst properties on structures, as well as in understanding and predicting the locations and properties of metal clusters in zeolites.
Nano-scale zeolite Y crystals were synthesized, and palladium nanoparticles were prepared in the supercage of the zeolite by "ship-in-a-bottle" approach. A novel method to fabricate zeolite-modified electrode (ZME) loading Pd nanoparticles was developed, in which the zeolite Y loading Pd 2þ ions was self-assembled on (3-mercaptopropyl) trimethoxysilane-attached Au surface to form the stable and density packed multilayers (SAM-ZME). The structures of zeolite Y and the SAM-ZME were investigated by using TEM, XRD and SEM techniques. Pd 2þ ions in the SAM-ZME were converted into Pd nanoparticles (Pd n 0 ) by two steps consisting of the electrochemical reduction as well as the succeeding admission and release of CO. The redox couple [Fe(CN) 6 ] 3À/4À was used to probe the electron-transfer barrier properties during self-assembling process. Moreover, the special properties of the SAM-ZME loading Pd n 0 were studied by using cyclic voltammetry and CO-probe in situ FTIR spectroscopy. The results illustrated that Pd n 0 in the SAM-ZME exhibits higher electrocatalytic activity for oxidation of adsorbed CO than that of ZME prepared in our previous study by zeolite coating method. The present study is of importance in design and preparation of SAM-ZME, which poccesseses excellent properties for the immobilization of electrocatalysts or biomolecules.
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