Alkylation of benzene with methanol on zeolites: Infrared spectroscopy studies

Rakoczy, Jan; Romotowski, T.

doi:10.1016/0144-2449(93)90003-l

Cited by 38 publications

(30 citation statements)

References 12 publications

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“…This constitutes a clear indication of methylation by methoxy groups. Similar experiments were reported by Rakoczy and Romotowski [43]. By dosing methanol into an FTIR cell containing samples of H-Y, characteristic methoxy bands were seen and found to be stable until 260°C.…”

Section: Insights From Spectroscopic Studiessupporting

confidence: 71%

“…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 .…”

Section: Insights From Spectroscopic Studiesmentioning

confidence: 99%

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

et al. 2011

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Alkylation and methylation are important reactions in industrial zeolite catalyzed hydrocarbon transformation processes. This contribution compiles the present knowledge concerning the reaction mechanism of zeolite catalyzed methylation of alkenes and aromatics, based on insights obtained using spectroscopy, quantum chemistry, and kinetic measurements. A central issue is to discuss the potential role surface bound methoxy group intermediates.

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Section: Insights From Spectroscopic Studiessupporting

confidence: 71%

Section: Insights From Spectroscopic Studiesmentioning

confidence: 99%

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

et al. 2011

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“…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].…”

Section: Introductionmentioning

confidence: 80%

“…5. The spectra are presented in the following order from top to bottom: H-ZSM-5 (14); H-ZSM-5 (45); H-beta (44); H-beta (220). The peaks with maxima at 3735 cm -1 arise from the m(OH) mode of various weakly acidic silanol groups, predominantly located on the external surface of the zeolite crystallites.…”

Section: Surface Sites: Ft-ir Spectra Of the Dehydrated Zeolitesmentioning

confidence: 99%

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

et al. 2011

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The methylation of aromatics is a reaction step that occurs in several petrochemical processes. Here, we have investigated the methylation of benzene by methanol over H-ZSM-5 and H-beta catalysts by conducting kinetic measurements and in situ FT-IR spectroscopy at comparable reaction conditions. A lower rate of methylation per Brønsted acid site is seen for H-beta, and this is linked to the formation of fairly persistent cationic species, as observed with FT-IR.

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“…However, at higher temperature the equilibrium is shifted towards the methoxy species [55], which acts as the electrophylic alkylating agent on alkylaromatics [56,57].…”

Section: Catalyst Activity and Deactivation Ratementioning

confidence: 99%

Methylation of phenol over high-silica beta zeolite: Effect of zeolite acidity and crystal size on catalyst behaviour

Bregolato

Bolis

Busco

et al. 2007

Journal of Catalysis

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A systematic investigation has been carried out, aiming at elucidating several aspects of the gas/solid methylation of phenol over high Si/Al ratio BEA-structured zeolite in protonated form. The catalysts have been characterized by several techniques, such as XRD, SEM, BET, ICP, FT-IR, TGA, micro-calorimetry and modelling by ab initio calculations. The correlation between these characteristics and kinetics and mechanistic features of the catalytic reaction, as well as of catalyst deactivation, showed that these zeolites are very active for the present reaction, leading to cresols and anisole as primary products. As catalyst deactivation proceeds, the selectivity to cresols and anisole increases substantially, together with a rapid decrease of selectivity to poly-alkylated species. Catalyst surface acidity is prevalently made of medium-to-low-strength silanolsbased acid sites of Brønsted type. High-strength Lewis acid sites are either almost absent, especially when metal cations partially substitute for protons, or play a role essentially in catalyst deactivation. Stacking faults in the zeolite framework, generated by the 2 intergrowth of at least two BEA polymorphs, lead to an increase of the concentration of silanols-based acid sites. Deactivation is essentially due to the interaction of phenol and oxygenated products with the strong Lewis acid sites. For time-on stream values longer than a few hours, self oligomerisation-cyclisation of methanol to olefins and aromatics, followed by further alkylation to aromatic C atoms, contributes more significantly to catalyst deactivation. At higher temperature all the zeolites deactivate at a comparable rate, whereas at lower temperature initial catalytic activity is higher for larger crystal size zeolite, due to the longer diffusion time of bulkier coke precursors within zeolite pores. At any conversion level and at any temperature the anisole/cresols ratio is systematically lower for the larger crystal size zeolite, since the secondary transformations of anisole to cresols, by both intra-molecular rearrangement and inter-molecular alkylation of phenol, is favoured by the longer residence time of anisole within the zeolite pores.

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Alkylation of benzene with methanol on zeolites: Infrared spectroscopy studies

Cited by 38 publications

References 12 publications

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

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

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

Methylation of phenol over high-silica beta zeolite: Effect of zeolite acidity and crystal size on catalyst behaviour

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