Preparation, characterization, and hydrogenation activity of new Rh0–MCM-41 catalysts prepared from as-synthesized MCM-41 and RhCl3

Abstract

Impregnation of as-synthesized MCM-41 silica by ethanolic solutions of rhodium(III) chloride was tested as an alternative to its introduction into the synthesis gel to get, after calcination and reduction by H 2 , highly dispersed metal(0) nanoparticles throughout the mesopores network. Rh(III) and Rh(0)–based solids thus obtained were analyzed by infrared spectroscopy, elemental analysis, transmission electron microscopy, N 2 sorption, and X-ray diffraction. Materials with 1.6 wt % of rhodium could be obtained as a result of CTA + /Rh 3+ exchange. The determining role of CTA + was emphasized through blank experiments. In a second series of materials, ethanol was also exploited for its ability to reduce Rh(III). All Rh(0)-based solids were tested as catalysts in the hydrogenation of styrene under mild temperature and pressure conditions. Catalysis performances of the most efficient sample (reduced by H 2 ) were further compared with those of a very similar material prepared by the introduction of Rh(III) directly into the synthesis gel of MCM-41 silica. Better cis selectivities in the hydrogenation of disubstituted arene derivatives were achieved with materials issued from the new preparation method. Ammonium template facilitates incorporation of Rh(III) in the as-synthesized MCM-41 in ethanol, thus affording, after an ex situ reduction step, catalytically active dispersions of Rh(0) with a high cis selectivity in the hydrogenation of disubstituted arenes. • The role of cetyltrimethylammonium in the uptake process of rhodium(III) was clearly demonstrated in ethanol. • Relationship between surfactant removal and rhodium incorporated was tested at different nominal molar Si/Rh ratios. • Ethanol can also be used as a reducing agent provided that the reaction is carried out ex-situ. • Differences were highlighted between the materials prepared according to this new path and that of direct hydrothermal synthesis. • Resulting materials lead to a better selectivity in cis hydrogenated compounds compared to samples prepared by DHT.