Mesoporous mordenites obtained by desilication: Mechanistic considerations and evaluation in catalytic oligomerization of pentene

Abstract

Desilication of mordenite crystals previously enriched in silica by dealumination has been investigated in order to better understand the process of mesopore formation. Pentene oligomerization in the liquid phase in the presence of an alkane solvent has been used to evaluate the catalytic activity of the desilicated zeolite. Relevant physico-chemical characteristics such as texture, porosity, acidity and composition of zeolite samples desilicated at 80 °C in NaOH solutions at different base concentrations were analyzed quantitatively. The generation of mesoporosity is due to the hydrolysis and dissolution of the surface of the crystals, probably initiated by the formation of etch pits at low coordination atoms, followed by surface roughening, formation and growth of internal mesopores, fragmentation and, ultimately, by a complete dissolution of the crystal. Such a process which is similar to the one involved in the chemical weathering of rocks, results in a severe loss of crystalline material and of the strong acidity associated to it. The oligomerization catalyst prepared from desilicated mesoporous mordenite proved highly stable and selective for the production of C15–C30 oligomers from pentene.