Investigation of Coke Deposits on Al-MCM-41

Rozwadowski, M.; Lezanska, M.; Włoch, Jerzy; Erdmann, K.; Golembiewski, and R.; Kornatowski, J.

doi:10.1021/cm001147s

Cited by 49 publications

(60 citation statements)

References 42 publications

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“…Especially in the case of ethanol, bands arise at higher frequencies and the theoretical values listed in Table 3 suggest that these might also originate from larger aromatic compounds. This is accompanied by growth of the C=C band at 1607 cm −1 with shoulder at 1640 cm −1 for methanol and 1600 cm −1 with shoulder at 1660 cm −1 for ethanol (see Figure 8 (b) and (d)) which also demonstrate the formation of aromatic carbenium ions as suggested in literature earlier [36,35,92,93,94] and is in line with the calculated IR spectra of Figure 7 (b). Once formed, these bands remain rather stable throughout the entire period of reaction though the relative stronger intensity in the case of ethanol is evident.…”

Section: Formation Of Hydrocarbon Pool Speciessupporting

confidence: 90%

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Hemelsoet

Ghysels

et al. 2011

Catalysis Today

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Theoretical and experimental IR data are combined to gain insight into the methanol and ethanol conversion over an acidic H-SAPO-34 catalyst. The theoretical simulations use a large finite cluster and the initial physisorption energy of both alcohols is calculated.Dispersive contributions turn out to be vital and the final adsorption of ethanol is predicted to be stronger compared to methanol (difference of 14 kJ mol −1 ). Calculated IR spectra of the alcohols and of formed aromatic cations upon conversion are also analyzed and support the peak assignment of the experimental in situ DRIFT spectra, in particular for the C-H and C=C regions. Theoretical IR spectra of the gas phase compounds are compared with those of the molecules loaded in a SAPO cluster and the observed shifts of the peak positions are discussed. To get a better understanding of these framework-guest interactions, a new theoretical procedure is proposed based on a normal mode analysis.A cumulative overlap function is defined and enables the characterization of individual peaks as well as induced frequency shifts upon adsorption.

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Section: Formation Of Hydrocarbon Pool Speciessupporting

confidence: 90%

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Hemelsoet

Ghysels

et al. 2011

Catalysis Today

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“…The cyclohexene vapor mixed with a carrier gas (5% of C 6 H 10 , 95% of He) was passed at a rate of 0.5 g of C 6 H 10 per hour and gram of the catalyst for 12 h (Rozwadowski, 2001a(Rozwadowski, , 2001d.…”

Section: Coke Deposition Proceduresmentioning

confidence: 99%

“…A contact time of 1 ms, a recycle time of 5 s, and a 7-mm o.d. zirconia rotor spun at 4.5 kHz were used (Rozwadowski, 2001a). 27 Al MAS NMR spectra of the original and coked samples were recorded at 78.2 MHz.…”

Section: Ir and Uv-vismentioning

confidence: 99%

“…Superposition of the bands assigned to vibrations of the C C bonds in alkenes and aromatics made interpretation of the spectra difficult to some extent. However, differences in the band intensities within the short-wave regions of the spectra (C H stretching vibration range), occurring upon a change in the reaction temperature, indicated formation of paraffinic and olefinic compounds at the lower temperatures and of aromatic and some olefinic compounds at the higher ones (Rozwadowski, 2001a). This conclusion was confirmed by a shift of the band at 1600 cm −1 to 1590 cm −1 with the rise of the reaction temperature, associated probably with delocalization of the π bond.…”

Section: Cyclohexene Conversion Productsmentioning

confidence: 99%

“…The conversion of cyclohexene has commonly been accepted as a suitable reaction for testing the catalytic behavior of various materials (Cheng and Rajagopalan, 1989;Navio et al, 1996;Radwan and Selim, 1996;Bunjes et al, 1997;Fasi et al, 1997;Navio et al, 1998;Hunka et al, 1999). We have applied this process to characterize the Al-MCM-41 material modified by coking (Rozwadowski et al, 2000), determine the probable mechanism of the respective conversion reaction, describe the active sites, and find a correlation between the postulated mechanism and the nature of the sites (Rozwadowski et al, 2001a(Rozwadowski et al, , 2001b. Polar (water) and nonpolar (benzene, nitrogen) compounds were chosen as probe molecules for adsorption to learn more about both the lyophilic properties of the examined mesoporous solids and the adsorption process (Rozwadowski et al, 2001c).…”

Section: Introductionmentioning

confidence: 99%

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Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

2005

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There were investigated aluminosilicate MCM-41 samples in the as-prepared form and those modified by the deposition of carbonaceous compounds during conversion of cyclohexene for 12 h. The amount of the deposits decreased with the rising reaction temperature and increased with the Al content of the samples. The cyclohexene conversion followed mainly two mechanisms: cyclohexene skeletal isomerization and hydrogen transfer. The products with 6 carbon atoms in a molecule prevailed in all cases. The process of conversion, proceeding on the Brønsted acid sites, resulted in formation of both coke deposits and volatile products. The creation of coke caused a decrease in the effective concentration of both the Brønsted and the Lewis acid sites. Thermodesorption of pyridine showed that (i) the concentration of these sites before and after the conversion differed only slightly and (ii) the acidic strength of the Brønsted sites was practically independent of their concentration and the sample Si/Al ratio. The chemical composition of the deposits was insignificantly affected by the Al content of the materials and depended mostly on the temperature and duration of the reaction. At relatively low temperatures, both aliphatic and aromatic compounds were formed, being rather weakly bound to the surface of the material. After a longer (55 h) reaction period, some deposits appeared that were strongly bound to the surface. Isotherms of adsorption of water, benzene, and nitrogen were determined, from which a mechanism of this process was derived. It included most probably multilayer adsorption at lower relative pressures, followed by capillary condensation. The sorption capacities of the uncoked samples for benzene and nitrogen were relatively high and independent of the sample Al content. In the case of water, however, an observed reduction in the sorption capacity with the increasing Al content suggested that clusters of the adsorbed molecules formed around the Al centers and caused partial clogging of the material pores. The deposited coke strongly decreased both the surface area and the sorption capacity of the materials.

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Advanced Solid-State NMR Techniques for the Study of Molecular Sieves

Mafra

Klinowski

1996

eMagRes

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Investigation of Coke Deposits on Al-MCM-41

Cited by 49 publications

References 42 publications

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

Advanced Solid-State NMR Techniques for the Study of Molecular Sieves

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