Redox behaviour of transition metal ions in zeolites. Part 8.—Characterization of a ruthenium metal phase in NaY zeolite

Abstract

RuNaY zeolite was prepared by ion exchange with Ru³⁺-hexammine. This complex was decomposed and the ions reduced to the metal state. The influence of water present during the reduction and the sintering of the metal in oxygen was investigated at different temperatures.

Temperature programmed oxidation experiments allow an overall characterization and the detection of possible bidisperse systems of metal particle sizes. Ruthenium is held very easily in the zeolite supercages. When water is present during reduction Ru agglomerates are built up in holes of the zeolite crystals. In the presence of oxygen excessive sintering occurs and large crystals are formed outside the zeolite. This picture is obtained using transmission electron microscopy, microprobe analysis and X-ray line broadening techniques. Chemisorption of hydrogen and its desorption during a temperature programmed run indicate that the metal particles absorb subsurface hydrogen. The determination of Ru-particle sizes from the latter measurements is not straight-forward.