Partial Incorporation of La3+ in Beta Zeolite for Isobutane/1-Butene Alkylation

Abstract

The incorporation of La3+ cations in different degrees in beta zeolite (Si/Al = 12.5) was studied in order to improve the selectivity and stability of the catalysts for the alkylation of isobutane with butenes in gas phase to obtain trimethylpentanes (TMPs). La/Al ratios between 0.04 and 0.20 were achieved, representing between 10 and 60 percent of the available exchange sites. The different amounts of lanthanum incorporated led to different quantities, strength and nature of acid sites, without extensive detriment to the structural properties. For a molar La/Al ratio of approximately 0.16, a catalyst with a suitable proportion of strong Brønsted sites was obtained, which favored hydride transfer and cracking reactions, thus allowing a faster desorption of TMPs and avoiding polymerization and multiple alkylation. As a result, deactivation by coke deposition was decelerated. Higher La/Al ratios led to lower acid strength and higher proportion of Lewis sites, which promoted polymerization, while lower ratios led to stronger sites which gave place to excessive cracking.