In situ Fourier transform i.r. observation of methylating species in ZSM-5

Abstract

In situ Fourier transform i.r. spectra show that MeOH in ZSM-5 forms an AlOMe species above 473 K which correlates with the onset of hydrocarbon formation and which methylates benzene, ethene, propene, and cyclopentene; MeOMe is protonated by internal acid sites at l o w temperatures but forms the same methylating species at 473 K and above.

Neutron spectroscopy as a tool in catalytic science

“…14(e), while the methyl stretch, deformation and rock are at similar positions to those in HY, the methanol O-H stretch and deformation modes have vanished. These observations suggest that complete conversion of methanol to framework methoxy has occurred, which is remarkable, as methanol was introduced at 298 K; thus methoxylation of the Brønsted acid sites, the first step in the MTH process, has occurred at room temperature contrary to studies using more conventional spectroscopy techniques [66][67][68] and modelling studies [69][70][71][72] which suggest a significant energy barrier to the process. INS spectroscopy has also been used to investigate the working catalyst.…”

In Situ FT-IR Mechanistic Investigations of the Zeolite Catalyzed Methylation of Benzene with Methanol: H-ZSM-5 versus H-beta

“…Several spectroscopic investigations have shown that methoxy groups may indeed be formed on various sites on zeolite surfaces from methanol at moderate temperatures and that these, in turn, may react with aromatics or other unsaturated species to yield methylation products in apparent agreement with a stepwise mechanism [11][12][13][14][15]. Experimental kinetic data, on the other hand, are more easily reconcilable with the direct reaction mechanism not involving an intermediate [16][17][18].…”

Mechanistic Aspects of the Zeolite Catalyzed Methylation of Alkenes and Aromatics with Methanol: A Review

“…Upon the introduction of benzene the methoxy bands were reduced, which is an indication of methylation. Also employing a setup where reactants were sequentially dosed, Howe and co-workers [39,42] were able to show that methoxy groups could methylate alkenes such as ethene and cyclopentene in addition to benzene. The importance of methoxy groups on Brønsted sites compared to methoxy groups on silanols was emphasized [42].…”

“…Also employing a setup where reactants were sequentially dosed, Howe and co-workers [39,42] were able to show that methoxy groups could methylate alkenes such as ethene and cyclopentene in addition to benzene. The importance of methoxy groups on Brønsted sites compared to methoxy groups on silanols was emphasized [42]. Further, Datka et al [41] studied not only the reaction of methanol followed by admission of benzene to the FTIR cell, but also admitted the two reactants simultaneously.…”

“…Extensive compilations of the spectral features characteristic for these species have been given by Jiang et al [38] and by Howe and co-workers [39,40]. The bulk of data suggests that methoxy groups on Brønsted sites give rise to two m(CH) bands, one most often seen at *2980 cm -1 and another seen in the range 2868-2850 cm -1 in the FTIR spectra [41][42][43][44][45], whereas methoxy groups on silanols give rise to bands at 2959 and 2855 cm -1 [39,42]. Thus, methoxy groups on Brønsted and silanol sites should be distinguishable based on the signals appearing close to 2980 and 2960 cm -1 .…”