EPR and NMR Studies of Coke Induced Selectivation over H–ZSM-5 Zeolite during Ethylbenzene Disproportionation Reaction

Solid-state nuclear magnetic resonance investigations of the nature, property, and activity of acid sites on solid catalysts

“…14a, bottom) [179]. Two weak signals at d 13C ¼ 15 and 129 ppm are due to non-enriched carbon atoms of the methyl group and the aromatic ring, respectively [181,182]. The zeolite Al,Na-Y/63 used for this study was prepared via the same procedure like the material applied for investigating the formation of bridging OH groups according to the Hirschler-Plank mechanism (see 1 H and 27 Al MAS NMR spectra in Fig.…”

“…Due to the restricted pore size of zeolite ZSM-5, p-diethylbenzene is the most preferred product in the disproportionation and only few m-diethylbenzene are formed [178]. The 13 C MAS NMR signals of p-and m-diethylbenzene occur at d 13C ¼28.8 and 27.9 ppm, respectively [181,182]. The signals of these products are difficult to distinguish from the strong signal of A at d 13C ¼29 ppm.…”

“…Fig. 14b shows the 13 C MAS NMR spectra of ethyl[a-13 C]benzene-loaded zeolite Al,Na-ZSM-5/52 (cation exchange degree of 52%) recorded before (bottom) and after (top) thermal treatment at 483 K for 0.5 h. Before heating, 13 C MAS signals occur at d 13C ¼15, 29, and 129 ppm, which are assigned to the non-enriched methyl group, 13 C-enriched methylene group, and non-enriched aromatic ring of ethylbenzene, respectively [181,182]. Upon heating of ethyl[a-13 C]benzene-loaded zeolite Al,Na-ZSM-5/52 at 483 K for 0.5 h, the reaction starts as indicated by new 13 C MAS NMR signals at d 13C ¼14, 73, and 85-90 ppm.…”

“…After adsorption of A on ZSM-5, the aromatic ring is rapidly protonated to form the ethylcyclohexadienyl carbenium ion I with the low activation energy of E a ¼29 kJ/mol [111]. The proton is added to the carbon atom holding the ethyl group to form a s-complex [181,182]. At higher temperatures, the s-complex I is very unstable and splits off an ethyl cation from the aromatic ring to produce the benzene molecule G. The alkyl cation is stabilized by a nearby SiO À Al site and forms a more stable ethoxy group J [186,187].…”

Surface modification of nano-sized HZSM-5 and HFER by pre-coking and silanization

“…31 P MAS NMR experiments were carried out on a Bruker MSL-500P spectrometer operating at a Larmor frequency of 202.46 MHz and typically under a sample spinning rate of 10-12 kHz. Detailed description of the related experiments can be found elsewhere [34,35].…”