PNNL

Abstract

Nickel- and alkali-earth-modified LTA based zeolites catalyze the dimerization of 1-butene in the absence of Bronsted acid sites. The catalyst reaches over 95% selectivity to n-octenes and methylheptenes. The ratio of these two dimers is markedly influenced by the parallel isomerization of 1-butene to 2-butene, shifting the methylheptene/octene ratio from 0.7 to 1.4 as the conversion increases to 35%. At this conversion, the thermodynamic equilibrium of 90% cis- and trans-2-butenes is reached. Conversion of 2-butene results in methylheptene and dimethylhexene with rates that are 1 order of magnitude lower than those with 1-butene. The catalyst is deactivated rapidly by strongly adsorbed products in the presence of 2-butene. The presence of pi-allyl-bound butene and Ni-alkyl intermediates was observed by IR spectroscopy, suggesting both to be reaction intermediates in isomerization and dimerization. Product distribution and apparent activation barriers suggest 1-butene dimerization to occur via a 1'-adsorption of the first butene molecule and a subsequent 1'- or 2'-insertion of the second butene to form octene and methylheptene, respectively. The reaction order of 2 for 1-butene and its high surface coverage suggest that the rate-determining step involves two wealdy adsorbed butene molecules in addition to the more strongly held butene. This work was funded by EVONIK Performance Materials GmbH. J.L. acknowledges support for this contribution by the U.S. Department of Energy (DOE) (CN 269409), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences, for exploring transition metal cations for C-C bond forming reactions. R.B.-D. acknowledges the Alexander von Humboldt foundation for financial support