Isobutane/1-butene alkylation on LaNaY catalysts modified by alkali and alkaline-earth cations

The effect of incorporating alkali and alkaline-earth cations into La exchanged NaY zeolites on the alkylation of isobutane with 1-butene has been investigated. The strength of the acid sites of the LaMNaY (M = Group I A and Group II A elements) catalysts do not change significantly, while the density of acidic sites decrease in the order of Na > K > Rb > Cs in the alkali Group I A elements and Ba > Mg > Ca > Sr in the alkaline-earth Group ii A elements. The LaBaNaY catalyst has a higher density of acid sites than expected based on the electronegativity of Ba among the Group II A elements. A higher yield of alkylation and oligomerization products and also a higher amount of carbonaceous deposit were observed on the LaMNaY catalysts with a lower density of acidic sites except for LaBaNaY. Thermal gravimetric and differential thermal analysis indicate that the carbonaceous material could be located on the pore mouth and inside the pores of the zeolite. The carbonaceous material on the pore mouth can be desorbed before 300 degrees C, while that in the zeolite pore is more difficult to be removed and a series of reactions such as dehydrogenation, aromatization and polymerization may take place during a temperature-programmed oxidation process. The diffusion of oligomerization products from the zeolite pore appears to be a slow step. The accumulation of these products in the zeolite pores is believed to be the main factor for the catalyst deactivation. (C) 2000 Elsevier Science B.V. All rights reserved.