Preparation and characterization of ruthenium clusters on mesoporous supports

Ruthenium-containing MCM-41, MCM-48 and SBA-15 mesoporous molecular sieves were prepared employing various methods and different metal precursors, viz. RuCl3, Ru(NH3)(6)Cl-3 and Ru-3(CO)(12). The catalysts were characterized by X-ray powder diffraction, nitrogen adsorption, transmission electron microscopy and hydrogen chemisorption. The measurements reveal that small ruthenium clusters can be prepared inside the channel of the mesoporous support using ruthenium carbonyl or ruthenium hexammine chloride as precursors. Thermogravimetry coupled with mass spectrometry, UV-VIS spectroscopy and electron spin resonance spectroscopy were used to study the autoreduction of the Ru(NH3)(6)(3+) complex, which is distinctly different from the process observed on microporous materials (zeolites). Due to the low water content of the samples, the intermediate formation of [Ru(NH3)OH](2+) and Ru-red is suppressed, but the formation of nitrosyl complexes is evident from the UV-VIS spectra. A new intermediate is found. which is characterized by a sharp ESR signal with g(/) = 1.95 and g(perpendicular to) = 2.10 accompanied by the appearance of a broad UV-VIS band centered at 706 nm, which reflects the green-blue color of the sample. (C) 2001 Elsevier Science B.V. All rights reserved.