Zeolite Pore Entrance Effect on Shape Selectivity in Naphthalene Isopropylation

Naphthalene alkylation with propylene was studied over various large-pore zeolites and also over amorphous aluminosilicate catalysts. Isomeric distribution of isopropylnaphthalenes and diisopropylnaphthalenes were compared at different temperatures. Surprisingly, higher α-selectivity in monoalkylation and higher concentration of bulky isomers in diisopropylation was observed in the products obtained over zeolites than over amorphous aluminosilicate catalysts. The explanation of such results was proposed to be a specific shape-selectivity effect of alkylation reaction occurring in the entrances to the pores of zeolite. This type of shape selectivity can be very significant and conceal other shape-selectivity effects such as β-selectivity of reactions occurring inside the pores. Results available from the literature, indicating this type of shape selectivity, were also discussed.