Di Si | PubMed Health

PubMed2005

FTIR studies of zeolite matrix effects on the properties of palladium clusters confined in the supercages of NaX and NaY.

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.

Journal Article↗

PubMed2004

[Solid/liquid interfacial in situ IR microscope and step-scan time-resolved FTIR spectroscopy and applications in studies of nanomaterials].

Electrochemical in situ microscope IR reflection spectroscopy and step-scan time-resolved FTIR reflection spectroscopy were established by using an IR-plan advantage microscope and a Nexus 870 FTIR instrument, and a home-made signal synchronizer that harmonizes electrode polarization potential and step-scan spectral data collection sequence. These new techniques have been applied in studies of particular IR properties of 2-dimensional nanomaterials. By applying a treatment of fast potential cycling with different time (tau), a set of nanostructured Pt microelectrodes were prepared. CO adsorption was employed as a probe reaction together with in situ developed microscope FTIR spectroscopy. The results illustrated the variation of abnormal IR features with the nanostructure and the thickness (i.e., the size) of film formed on Pt microelectrode, i.e., following the increase of tau in fast potential cycling treatment, the direction of CO band was turned from absorption to antiabsorption direction, and the intensity and the width of CO band were increased. By taking the advantage of the abnormal infrared effects of nanostructured Pt microelectrode, the sensitivity of in situ IR reflection spectroscopy has been significantly improved, and spectra of time-resolution as fast as 50 micros have been recorded at solid/liquid interfaces. The current studies demonstrated not only the success of development of new techniques of in situ IR spectroscopy, but also the exploitation of the established techniques in studies of nanomaterials.

English Abstract↗