Abstract
Mesoporous silica encapsulated Pt (Pt@mSiO(2)) and PtSn (PtSn@mSiO(2)) nanoparticles (NPs) are representatives of a novel class of heterogeneous catalysts with uniform particle size, enhanced catalytic properties, and superior thermal stability. In the ship-in-a-bottle synthesis, PtSn@mSiO(2) intermetallic NPs are derived from Pt@mSiO(2) seeds where the mSiO(2) shell is formed by polymerization of tetraethyl orthosilicate around a tetradecyltrimethylammonium bromide template, a surfactant used to template MCM-41. Incorporation of Sn into the Pt@mSiO(2) seeds is accommodated by chemical etching of the mSiO(2) shell. The effect of this etching on the atomic-scale structure of the mSiO(2) has not been previously examined, nor has the extent of the structural similarity to MCM-41. Here, the quaternary Q(2), Q(3) and Q(4) sites corresponding to formulas Si(O(1/2))(2)(OH)(2), Si(O(1/2))(3)(OH)(1) and Si(O(1/2))(4), in MCM-41 and the mesoporous silica of Pt@mSiO(2) and PtSn@mSiO(2) NPs were identified and quantified by conventional and dynamic nuclear polarization enhanced Si-29 Magic Angle Spinning Nuclear Magnetic Resonance (DNP MAS NMR). The connectivity of the -Si-O-Si-network was revealed by DNP enhanced two-dimensional (29)Si-(29)Si correlation spectroscopy.