Platinum nanoparticles encapsulated in mesoporous silica: Preparation, characterisation and catalytic activity in toluene hydrogenation

Abstract

In this paper a novel route to prepare supported Pt catalyst is explored. Platinum nanoparticles were first prepared by hydrogen reduction of an aqueous solution of a platinum salt in the presence of a triblock copolymer as a capping agent. The Pt nanoparticles were characterised and described by TEM, UV–vis spectrometry and dynamic light scattering (DLS). The nanoparticles were quite uniform in size, in the range 6–10 nm. The nanoparticles were incorporated into the structure of mesoporous silica (SBA-15) during the synthesis. The same copolymer used as a capping agent in the preparation of the nanoparticles was used as a structure directing agent to synthesise the silica mesostructure. After incorporation of platinum into mesoporous SBA-15, the catalysts were characterised by N 2 adsorption–desorption, X-ray diffraction and (XRD) and transmission electron microscopy (TEM). The results indicate that at least part of the platinum was successfully incorporated into the pores of the silica mesoporous structure. The material was tested in toluene hydrogenation as a model reaction and the catalytic activity was compared with a conventional Pt supported on SBA-15, prepared using the incipient wetness technique. The conventional catalyst was considerably more active in the toluene hydrogenation due to a higher Pt dispersion, as measured by hydrogen chemisorption, but the turnover frequencies were comparable. There is some discrepancy between the Pt particle size as observed by TEM and the chemisorption data. This is probably caused by formation of agglomerates of Pt particles, or that the Pt active sites are blocked, e.g. by a remaining copolymer layer on the surface of the particles.