Dimerization of Linear Butenes and Pentenes in an Acidic Zeolite (H‐MFI)

Abstract

Quantum chemical evidence is produced to show that dimerization of linear butenes and pentenes at zeolitic Brønsted sites in H‐MFI yields alkanes featuring cyclohexane rings rather than branched alkenes. The absence of any C=C double bond in the formed cyclic alkane explains the observations that oligomerization stops at the dimer. The calculated reaction enthalpies for the dimerization of 2‐pentene in the gas phase are −84 kJ mol−1 for branched alkenes, but −153 and −154 kJ mol−1 for alkyl‐cyclopentane and ‐hexane, respectively. Together with calculated adsorption enthalpies of the dimers, −111 and −127 kJ mol−1, respectively, this implies surface dimer formation enthalpies of −264 and −281 kJ mol−1, respectively, in close agreement with the experimental value of −285 kJ mol−1. In contrast, the predicted enthalpy for formation of branched alkoxides, −198 kJ mol−1, deviates by 87 kJ mol−1 from experiment. Calculated IR spectra for the Brønsted OH group show the observed conversion of the band at approximately 3000 cm−1 (hydrogen bond with alkene) to a less intense band at approximately 3450–3500 cm−1 (interaction with alkane).

Synergy of Acidity and Morphology of Micro-/Mesoporous Materials in the Solid-Acid Alkylation of Toluene with 1-Decene

“…Figure d shows the DRIFT spectra of the catalyst 150-S1 surface in a flow of a toluene and 1-decene mixture, recorded at different temperatures in comparison with the model spectra of 1-decene, toluene, and para -ethyl-toluene. The 1645 cm –1 band of antisymmetric stretching CC (ν as ) of 1-decene in the DRIFT spectrum splits into two broad bands at 1660–1630 cm –1 (ν as ) and 1550–1520 cm –1 (ν s ), which is characteristic of conjugated delocalized double bonds . The symmetric stretching vibrations (ν s ) of olefinic hydrocarbons, usually lying in the range of 1550–1530 cm –1 , do not appear.…”

“…The 1645 cm −1 band of antisymmetric stretching CC (ν as ) of 1-decene in the DRIFT spectrum splits into two broad bands at 1660− 1630 cm −1 (ν as ) and 1550−1520 cm −1 (ν s ), which is characteristic of conjugated delocalized double bonds. 71 The symmetric stretching vibrations (ν s ) of olefinic hydrocarbons, usually lying in the range of 1550−1530 cm −1 , do not appear.…”

Selective recovery of light olefins from polyolefin catalyzed by Lewis acidic Sn-Beta zeolites without Brønsted acidity

“…Thus, zeolites have been used as catalysts for the conversion of light olefins. [41][42][43] Therefore, in the catalytic cracking of polymers, a decrease in the number of Brønsted acid sites is assumed to lead to an increase in the yield of light olefins. J. Lee et al prepared lanthanumcontaining zeolites and investigated the relationship between basicity and product distribution in C5 raffinate cracking.…”