(710b) Synthesis & Characterization of Novel Building Block Aluminosilicate Catalysts

A broadly applicable synthetic methodology has been developed for the synthesis of silica supported catalysts that are defined by a high density of isolated, single site, catalytic centers[1]. This nanostructuring strategy centers around the use of the Si₈O₁₂(OSnMe₃) building block. The building block reacts with a catalytic precursor (e.g. a metal chloride) to create a cross linked matrix wherein the catalytic sites are all the same and are all isolated from one another. The matrix can be further cross linked with chemically robust linkers such as siloxanes in order to create a more extensively networked system. Finally, remaining Sn centers are removed by reaction with excess Me₃SiCl. This methodology has been utilized to create a purely Lewis acidic aluminum site imbedded in silica (Fig. 1). This active sites should differ fundamentally from those found in typical aluminosilicate and zeolite catalysts and provides a unique starting place in solid acid chemistry. Characterization of the catalytic site has been carried out using gravimetric measurements, BET surface areas, FTIR pyridine adsorption studies as well as solid state NMR. TGA and TPD studies have also been carried out utilizing amine and alcohol substrates. Initial characterization of the catalyst by 27Al SSNMR surprisingly indicates that 4-, 5- and 6-coordinate aluminum sites are present in the as synthesized product. The possibility of adjacent oxygen atoms of corner Si-O-Si(CH₃)₃ groups binding to the Al centers in a dative fashion (Fig. 2) is being explored via POSS based molecular analogues of the catalyst. Furthermore, attempts to make the aluminum center more stable prior to insertion into the matrix have been carried out through use of AlCl₃*Py as a precursor. The prepared catalysts have been tested for activity in the dehydration of isopropanol. Results from these tests show the catalysts to be highly active and selective at relatively low temperatures comparable to known zeolites H-ZSM5 and H-Mordenite. Tests are now being carried out to explore the reactivity of the catalyst towards methanol .