Hollow Zeolite Single-Crystals Encapsulated Alloy Nanoparticles with Controlled Size and Composition

Standard chemical and physical methods to control the size of supported metallic nanoparticles are generally not compatible with the harsh conditions of applications (high temperature, presence of steam). Sintering of nanoparticles usually occurs, leading to particle growth and eventually to a degradation of physical properties. Here we describe a generic process for synthesizing nanoalloys of controlled size (2-10 nm) and composition encapsulated in zeolite nanoboxes. The originality of the synthesis design is that the nanoboxes act both as nanoreactors in which the bimetallic particles are formed and as protective ultra-microporous shells, which prevent sintering by coalescence even under harsh conditions. Moreover, the present process allows for control over the size and composition of the NPs, which are factors that ultimately determine the catalytic properties. A series of mono-(Au, Pd, Pt) or bi- (AuAg, PdAg, PtAg and PdPt) metallic nanoparticles individually encapsulated in hollow silicalite-1 single crystals have been prepared and characterized. The simultaneous presence of Ag and Au at the surface of Au161Ag22 NPs has been demonstrated by results of the catalytic activity for CO oxidation near room temperature.