Shape-selective Isopropylation of Naphthalene over Hydrogen-Mordenite Catalysts. Effect of Mordenite Dealumination.

Abstract

An increasing demand for 2,6-dialkylnaphthalene has spurred interest in shape-selective naphthalene alkylation. This work deals with mordenite-catalyzed shape-selective naphthalene isopropylation to produce 2,6-diisopropylnaphthalene (2,6-DIPN). Effects of dealumination of mordenite on the structural and acidic characteristics and on the shape selectivity and activity were examined by physicochemical analysis, TPD, solid-state 27 Al and 29 Si MAS NMR, XRD, as well as catalytic alkylation reactions. Dealumination removes octahedral At species as well as tetrahedral At species, decrease the unit cell dimensions, and reduce the number of strong acid sites in mordenites. Proper dealumination can improve selectivity to 2,6-DIPN from 33 to 61% and significantly increases 2.6/2.7 ratio. Improved selectivity to 2,6-DIPN upon proper dealumination was attributed to decrease in mordenite acidity, reduction in unit cell dimension, and removal of some strong acid sites. However, neither the change in selectivity nor that in activity is a simple function of dealumination degree or SiO 2 /Al 2 O 3 ratio Some minor difference in the apparent framework SiO 2 /Al 2 O 3 ratio can result in major difference in activity or selectivity. There exist optimum conditions of dealumination as well as optimum reaction conditions for achieving higher selectivity to 2.6-DIPN.