Influence of preparation conditions on physicochemical properties and catalytic activity of stabilized zeolites

Abstract

Highly decationized zeolite NH4NaY, stabilized by water vapour under steaming conditions at 1030 K, was characterized by its lattice constant, sorption capacity, quantity of extralattice Al, number and character of OH groups present after dehydration in vacuum at 670 K. The catalytic activity and the effect of Lewis and Broensted type acid centers were tested by oligomeration of ethylene and propylene at 310 K and isotopic exchanges of ethylene-d4 + OH and propylene-d6 + OH at 570 K. The properties of this zeolite were compared with zeolites stabilized under selfsteaming conditions at 1040 and 820 K. Structural changes caused by the stabilization process are more pronounced with the steamed zeolite than with the selfsteamed one; in the latter case they diminish with stabilization temperature. Accordingly, the results of catalytic measurements reveal the effect of strong Broensted acid centers in the case of low-temperature selfsteamed zeolite; these centers apparently originate from remainders of the original decationized zeolite. The high-temperature self-steamed zeolite is essentially inactive, whereas the activity of the high-temperature steamed zeolite suggest the presence of catalytically active electron-acceptor centers.