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 mic
roscopy and hydrogen chemisorption. The measurements reveal that small ruth
enium clusters can be prepared inside the channel of the mesoporous support
using ruthenium carbonyl or ruthenium hexammine chloride as precursors. Th
ermogravimetry coupled with mass spectrometry, UV-VIS spectroscopy and elec
tron spin resonance spectroscopy were used to study the autoreduction of th
e Ru(NH3)(6)(3+) complex, which is distinctly different from the process ob
served 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 s
uppressed, but the formation of nitrosyl complexes is evident from the UV-V
IS 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 t
he 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.