23-P-12 - Mechanistic study of aniline methylation over acidic and basic zeolites Y

Ivanova, I. I.; Pomakhina, E. B.; Ребров, А. В.; Kolyagin, Yu. G.; Hunger, Michael; Weitkamp, Jens

doi:10.1016/s0167-2991(01)81477-4

Cited by 4 publications

(6 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Preparation of Surface Methoxy Species on Zeolites H-Y and H-ZSM-5 and on the Silicoaluminophosphate SAPO-34 by the SF Method. In most of the former studies, ,,,− , surface methoxy groups were prepared on acidic zeolites by a treatment with gaseous methyl iodide or methanol vapor under batch conditions using a vacuum line. In the present work, surface methoxy groups were prepared applying the in situ SF method which is very convenient for the study of their further conversion with reactant molecules.…”

Section: Resultsmentioning

confidence: 99%

Role of Surface Methoxy Species in the Conversion of Methanol to Dimethyl Ether on Acidic Zeolites Investigated by in Situ Stopped-Flow MAS NMR Spectroscopy

2001

View full text Add to dashboard Cite

In situ continuous-flow (CF) MAS NMR experiments indicated that the investigation of the role of surface methoxy species in the conversion of methanol to dimethyl ether requires the preparation of pure methoxy groups on the catalyst surface. Applying the novel in situ stopped-flow (SF) MAS NMR technique, methoxy species were selectively retained on zeolites H-Y (n Si/n Al = 2.7) and H-ZSM-5 (n Si/n Al = 22.0) and on the silicoaluminophosphate H-SAPO-34 [n Si/(n Al + n Si + n P) = 0.088]. These pure methoxy species were obtained after conversion of 13CH3OH under CF conditions at 423 K and purging the catalyst materials with dry nitrogen at 473 K. For H-Y, H-ZSM-5, and H-SAPO-34, the 13C MAS NMR signals of selectively prepared methoxy species occurred at 56.2, 59.4, and 56.6 ppm, respectively. Application of cross polarization led to a strong enhancement of the above-mentioned signals accompanied by sideband patterns which indicates that these alkoxy species are rigidly bound on the catalyst surfaces. By conversion of methanol with 13C-isotopes in natural abundance (denoted 12CH3OH) on zeolite H-Y covered with 13C-enriched methoxy species, the formation of partially 13C-enriched dimethyl ether (13CH3O12CH3) was observed at 60.5 and 63.5 ppm. This finding gives experimental evidence for the formation of dimethyl ether on acidic zeolites by the reaction of methanol with surface methoxy species formed in a former reaction step.

show abstract

Section: Resultsmentioning

confidence: 99%

Role of Surface Methoxy Species in the Conversion of Methanol to Dimethyl Ether on Acidic Zeolites Investigated by in Situ Stopped-Flow MAS NMR Spectroscopy

2001

View full text Add to dashboard Cite

show abstract

“…Since the resonance position at 58 ppm may be indicative of carbon atoms bound to oxygen, the formation of surface methoxy groups (CH 3 OZ, Z denotes the zeolite framework) , was considered in more detail. However, an assignment of the signal at 58 ppm to surface methoxy groups could be ruled out for the following reasons: (i) The conversion of pure methanol on zeolite H−Y under the same continuous-flow conditions gave no 13 C MAS NMR signal at 58 ppm (Figure , left).…”

Section: Resultsmentioning

confidence: 99%

“…Thus, it is very likely that DME can react with aniline, although the reaction could have occurred via the conversion of dimethyl ether to methanol through trace quantities of water present in the catalyst. On the other hand, methoxy groups prepared by adsorption and conversion of 13 CH 3 I and 13 CH 3 OH under batch conditions can also react with aniline to NMA …”

Section: Resultsmentioning

confidence: 99%

“…Thus, the above-mentioned low-field shifts are most probably caused by a protonation of NMA and NNDMA (proton affinity of 916.6 and 941.1 kJ/mol, respectively) on the Brønsted acid sites of zeolite H−Y leading to N -methylanilinium and N , N -dimethylanilinium cations. Observing the low-field 13 C NMR shifts of aniline (proton affinity 30 of 882.5 kJ/mol) adsorbed on zeolite H−Y, Ivanova et al also suggested a protonation of these molecules. Furthermore, although there are still longstanding arguments on the preferred protonation site of aniline and substituted anilines in the gas phase, we believe that, according to their basic behavior in solution, the protonation of aniline or substituted anilines on zeolite H−Y occurs preferentially at the nitrogen atom rather than at carbon atoms of the aromatic ring.…”

Section: Resultsmentioning

confidence: 99%

“…No direct observation of the working catalyst, which is desirable for the formulation of more reliable and more sophisticated reaction mechanisms, has so far been achieved. Recently, in situ 13 C MAS NMR investigations of aniline methylation on zeolite H−Y under batch conditions using samples sealed in glass ampules were performed for the first time . With a molar methanol-to-aniline ratio of 1:3 at reaction temperatures between 373 and 523 K, the primary alkylation product was N -methylaniline (NMA), and the formation of surface methoxy groups was found to be the rate-limiting step of the overall reaction.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Formation and Decomposition of N,N,N-Trimethylanilinium Cations on Zeolite H−Y Investigated by in Situ Stopped-Flow MAS NMR Spectroscopy

et al. 2002

View full text Add to dashboard Cite

Methylation of aniline by methanol on zeolite H-Y has been investigated by in situ (13)C MAS NMR spectroscopy under flow conditions. The in situ (13)C continuous-flow (CF) MAS NMR experiments were performed at reaction temperatures between 473 and 523 K, molar methanol-to-aniline ratios of 1:1 to 4:1, and modified residence times of (13)CH(3)OH between 20 and 100 (g x h)/mol. The methylation reaction was shown to start at 473 K. N,N,N-Trimethylanilinium cations causing a (13)C NMR signal at 58 ppm constitute the major product on the catalyst surface. Small amounts of protonated N-methylaniline ([PhNH(2)CH(3)](+)) and N,N-dimethylaniline ([PhNH(CH(3))(2)](+)) were also observed at ca. 39 and 48 ppm, respectively. After increase of the temperature to 523 K, the contents of N,N-dimethylanilinium cations and ring-alkylated reaction products strongly increased, accompanied by a decrease of the amount of N,N,N-trimethylanilinium cations. With application of the in situ stopped-flow (SF) MAS NMR technique, the decomposition of N,N,N-trimethylanilinium cations on zeolite H-Y to N,N-dimethylanilinium and N-methylanilinium cations was investigated to gain a deeper insight into the reaction mechanism. The results obtained allow the proposal of a mechanism consisting of three steps: (i) the conversion of methanol to surface methoxy groups and dimethyl ether (DME); (ii) the alkylation of aniline with methanol, methoxy groups, or DME leading to an equilibrium mixture of N,N,N-trimethylanilinium, N,N-dimethylanilinium, and N-methylanilinium cations attached to the zeolite surface; (iii) the deprotonation of N,N-dimethylanilinium and N-methylanilinium cations causing the formation of N,N-dimethylaniline (NNDMA) and N-methylaniline (NMA) in the gas phase, respectively. The chemical equilibrium between the anilinium cations carrying different numbers of methyl groups is suggested to play a key role for the products distribution in the gas phase.

show abstract

Aniline methylation on modified zeolites with acidic, basic and redox properties

Ivanova

Ponomoreva

Pomakhina

et al. 2002

Studies in Surface Science and Catalysis

View full text Add to dashboard Cite

23-P-12 - Mechanistic study of aniline methylation over acidic and basic zeolites Y

Cited by 4 publications

References 1 publication

Role of Surface Methoxy Species in the Conversion of Methanol to Dimethyl Ether on Acidic Zeolites Investigated by in Situ Stopped-Flow MAS NMR Spectroscopy

Role of Surface Methoxy Species in the Conversion of Methanol to Dimethyl Ether on Acidic Zeolites Investigated by in Situ Stopped-Flow MAS NMR Spectroscopy

Formation and Decomposition of N,N,N-Trimethylanilinium Cations on Zeolite H−Y Investigated by in Situ Stopped-Flow MAS NMR Spectroscopy

Aniline methylation on modified zeolites with acidic, basic and redox properties

Contact Info

Product

Resources

About