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| - Synthesis and Characterization of Acidic High-Silica Faujasite-Type Gallosilicates
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| - Ultrastabilization of a (rare-earth-loaded) faujasite (FAU)-type gallosilicate appears to be the only viableroute for synthesizing a gallosilicate with an acid site density comparable to that of ultrastable FAU-typealuminosilicates. Neither gallium insertion into a FAU-type silica nor substitution of framework gallium bysilicon using ammonium hexafluorosilicate appears feasible. The ultrastable FAU-type gallosilicate showsno sites with enhanced Brønsted acidity. According to the shift observed by IR spectroscopy when CO isadsorbed, the acid site strength of FAU-type gallosilicates is weaker than that of high-silica FAU-typealuminosilicates but stronger than that of FAU-type silicoaluminophosphates. Although the ultrastable FAU-type gallosilicate is (hydro)thermally stable in an oxidizing atmosphere up to 1150 K, it releases its galliumin a reducing atmosphere (starting at 525 K) and loses structural integrity increasingly rapidly above 635 K.This severely limits the potential use of catalysts based on gallosilicate framework structures in hydrocarbonhydroconversion reactions.
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