Decomposition of styrene dimers on Al2O3–Cr and Al2O3–SiO2–Cr catalysts of acid and redox nature

Abstract

(allylic anion generation); c-Al 2 O 3 -Cr: Brønsted acid centers originating from chromium ions at high oxidation states (alkenyl chain protonation) and Cr 3? redox sites (allylic cation generation); SiO 2 -Al 2 O 3 (13 %)-Cr: Brønsted acid centers of silica-alumina (alkenyl chain and aromatic ring protonation) and Cr 3? redox sites (allylic cation generation). The protonation of styrene dimer at the alkenyl chain leads to b-cleavage to toluene and a-methylstyrene as well as to styrene and ethylbenzene. The allylic species formed react to the different styrene dimer isomers and through diphenylbutadiene intermediate to coke. The use of methylcyclohexane as solvent for the styrene dimers in the presence of chromium containing catalysts results in the aromatization reaction leading to toluene and hydrogen. The presence of the later reactant in the system causes styrene and a-methylstyrene hydrogenation to ethylbenzene and cumene.

The role of butylbenzene carbenium ions in the acid catalyzed cracking of polystyrene. Transformation of n-butylbenzene, sec-butylbenzene, iso-butylbenzene, tert-butylbenzene, 4-phenyl-1-butene, n-propylbenzene and n-hexylbenzene over silicaalumina and alumina acid catalysts

“…Due to the presence of a conjugated system of bonds, the latter can preferably successively detach H ? and H -ions to form coke deposit [11,19]. The protons and hydride ions formed can participate in hydrogen transfer reactions heading to the hydrogenation of styrene dimer to diphenylbutane.…”

“…The detailed mechanism of acid catalyzed styrene dimers transformation has already been proposed [10][11][12]. The main reaction pathways of thermally formed styrene dimers are presented below (Scheme 1).…”

Styrene and styrene dimer derivatives, cyclohexene, tert-butylbenzene and cumene as test reactions for acid strength measurements of crystalline and amorphous silica-aluminas, sulfated oxides and Amberlyst

“…All the studied catalysts were able to initiate diphenylmethane transformation and were classified as superacids. In our previous works [41][42][43][44], the acid properties of sulfated titania and alumina as well as sodium and chromium doped silica-aluminas and alumina were studied. A (1) and low (2) proton affinity semiquantitative test reaction method was applied since the minimal acid strength required for the reactions to proceed was not measured, but taken from the literature.…”

Diacetone alcohol decomposition and benzaldehyde Cannizzaro reaction as test reactions for the basic strength measurements of alumina, magnesia, Amberlyst type resins (A-15, XN 1010, A-26, A-21), Nafion NR 50 and solid sulfuric acid

“…In order to perform such a measurement, it is necessary to: (1) identify suitable substrates that react under the influence of the bases, (2) determine the experimental values of H_min for them, (3) apply them in (7) x = 1 − exp −k10 H_ t measuring the basicity of any specific catalyst. A similar approach has already been used successfully for acid strength measurements where, with various test reactions, we have determined the acid strength of a series of solid acids [5,6].…”