In Situ Spectroscopic Analysis of Nanocluster Formation

Abstract

The importance of small metal clusters in catalysis and the problems in understanding the clustering process in solution are outlined. A new analysis method for UV/Vis spectra is presented and applied to monitor the kinetics of ion reduction and cluster formation in situ. This method, which is based on a combination of two chemometric techniques, takes into account the entire UV/Vis spectrum and offers better interpretation possibilities than the traditional "band-assignment" approach. This is particularly true for nanoclusters because these have significant spectral contributions also outside the broad plasmon band that is usually associated with them. The reduction of palladium, gold, and silver ions and the formation of the corresponding clusters is monitored in the presence of two different reducing agents, sodium borohydride and tetraoctylammonium acetate. While Pd2+ is found to reduce and cluster directly, the spectral decomposition of the Au3+ reduction profiles shows two species corresponding to the Au+ intermediate and the Au0 clusters. The rates of reduction and clustering for Pd, Au, and Ag are compared and the possibilities of synthesising multimetallic clusters of these metals by coreduction are discussed.

Highly porous chitosan microspheres supported palladium catalyst for coupling reactions in organic and aqueous solutions

“…The wetness impregnation allows for a uniform dispersion of a high weight loading of bivalent Pd 2þ species over the entire surface area of the supported matrices. In situ reduction of the bivalent Pd 2þ species usually results in high active reduced Pd 0 species with a nanocluster structure [14]. We have demonstrated that the Pd 2þ species could be readily converted into the reduced Pd 0 species in alcohol solutions [6,15].…”

Nanocluster nucleation and growth kinetic and mechanistic studies: A review emphasizing transition-metal nanoclusters

“…Among these are metal ions, solvent, reductant, and added stabilizers. This problem has also been addressed [43,44]; the results are presented in Section 4.6.…”

“…To deal with this problem, Rothenberg et al devised a system, called the "net analyte signal/principle component analysis" (NAS/PCA), in which the spectra of the interfering species are essentially subtracted out of the spectrum, leaving a difference spectrum that they assume is only the spectrum of the nanoclusters [43]. These authors used the NAS/PCA method to study the formation of Pd, Au, and Ag nanoclusters, as well as to study the possibility of forming bimetallic nanoclusters using combinations of those metals.…”

Speciation of Pd(OAc)2in ligandless Suzuki–Miyaura reactions

“…9), which is attributed to the nucleation of Pd(0). 55,56 Based on these observations, we can deduce that the reduction of palladium(II) acetate is accelerated by water, which first induces a rapid dissociation to monomer 7 (Scheme 4). Water then exchanges with acetate anions to form palladium(II) hydroxide species, 57 which undergoes transmetalation with Scheme 3 Reaction between Pd 3 (OAc) 6 and water.…”