Synthesis and characterization of acidic high-silica faujasite-type gallosilicates

Ultrastabilization of a (rare-earth-loaded) faujasite (FAU)-type gallosilic ate appears to be the only viable route for synthesizing a gallosilicate wi th an acid site density comparable to that of ultrastable FAU-type aluminos ilicates. Neither gallium insertion into a FAU-type silica nor substitution of framework gallium by silicon using ammonium hexafluorosilicate appears feasible. The ultrastable FAU-type gallosilicate shows no sites with enhanc ed Bronsted acidity. According to the shift observed by IIE spectroscopy wh en CO is adsorbed, the acid site strength of FAU-type gallosilicates is wea ker than that of high-silica FAU-type aluminosilicates but stronger than th at of FAU-type silicoaluminophosphates. Although the ultrastable FAU-type g allosilicate is (hydro)thermally stable in an oxidizing atmosphere up to 11 50 K, it releases its gallium in a reducing atmosphere (starting at 525 K) and loses structural integrity increasingly rapidly above 635 K. This sever ely limits the potential use of catalysts based on gallosilicate framework structures in hydrocarbon hydroconversion reactions.