Conversion of Acetone Over Modified Y Zeolites, Sapo-5 and Alpo₄-5

The effect of acidity on the reactions of acetone at 350° C was studied with large-pore AlPO₄-5 and SAPO-5 phosphates and thermochemically modified Y zeolites, which contained Al in various concentration and distribution. It was shown that the catalytic activity of hydroxyls depends on their acid strength: it decreases in the sequence SiOHAl (bridging) > POH, (Al_n - non-skeletal Al) > SiOH. In contrast to mediumpore HZSM-5 zeolite, which yields mainly aromatics and aliphatics (most abundant is isobutene), large-pore molecular sieves yield also mesityloxide and phoroncs, especially at low conversion levels. The formation of the latter compounds over Y zeolites is enhanced by the non-skeletal Al species, which also increase the deactivation rate and add carbonylate-like species into the deposit. The discussion considers also steric constraints imposed by the zeolite structure.