Catalysts for methane transformations into aromatics

Marczewski, Marek; Marczewska, H.; Mazowiecka, Katarzyna

doi:10.1007/bf02071184

Cited by 9 publications

(10 citation statements)

References 3 publications

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“…Previously, Wang et al (1993) reported that methane aromatization activity over Mo/HZSM-5 with SiO 2 /Al 2 O 3 ) 50 was higher than that over Mo/HZSM-5 with SiO 2 /Al 2 O 3 ) 25. This result was contradictory to the observation of Marczewski et al (1995) who used alternative catalysts of MnO x -Na/SiO 2 -HZSM-5 and CuO-FeO/HZSM-5 and found that the methane aromatization conversion increased upon decreasing the SiO 2 /Al 2 O 3 ratio over CuO-FeO/HZSM-5. The latter findings led to the conclusion of an acidity dependence, as the acidity of HZSM-5 is associated with the 3-coordinated Al sites.…”

Section: Introductioncontrasting

confidence: 90%

Bifunctional Behavior of Mo/HZSM-5 Catalysts in Methane Aromatization

Shu

Adnot

Grandjean

1999

Ind. Eng. Chem. Res.

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Catalytic functions of Mo/HZSM-5 toward methane aromatization are examined under various activation and reaction conditions. Molybdenum ions are necessary in the activation of methane. High benzene yields of around 7% are obtained with a selectivity of more than 96% at 973 K over a 2 wt % Mo/HZSM-5 catalyst in a tubular reactor. Pretreatment with hydrogen is found to be beneficial to the initialization of aromatization. The aromatization activity increases upon decreasing the Si/Al ratio in HZSM-5, indicating an acidity dependence. This is supported by the fact that a Mo catalyst supported on cesium-exchanged ZSM-5 losses its catalytic aromatization activity at all. The effective coordination between molybdenum ion sites and Brønsted acid sites in the framework of ZSM-5 is important in the activation of the stable C−H bonds in methane and the eventual aromatization to form benzene. The constant O1s binding energy in the XPS spectra of both fresh and used catalysts suggests that coke formation does not occur on the SiO4 tetrahedra but rather on the molybdenum sites supported on the external surface of ZSM-5.

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Section: Introductioncontrasting

confidence: 90%

Bifunctional Behavior of Mo/HZSM-5 Catalysts in Methane Aromatization

Shu

Adnot

Grandjean

1999

Ind. Eng. Chem. Res.

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“…[14] Furthermore, Mo 2 C and H-ZSM-5 alone were also reported to be poorly active. [5] In line with these findings, it has been reported that C 2 H 4 conversion on H-ZSM-5 zeolite led to a similar aromatics distribution than that obtained for CH 4 on Mo/H-ZSM-5, [15] whereas Marczewski et al obtained a direct correlation between the amount of framework Al and aromatic production, [16] further supporting the idea that the aromatisation step occurs entirely on the Brønsted acid sites of the zeolite. In contrast, titration experiments performed by Tessonier et al for the quantification of BAS after Mo exchange, revealed that regardless of the amount of BAS left, the catalysts had comparable yield to aromatics.…”

Section: Introductionsupporting

confidence: 69%

“…In line with these findings, it has been reported that C 2 H 4 conversion on H‐ZSM‐5 zeolite led to a similar aromatics distribution than that obtained for CH 4 on Mo/H‐ZSM‐5, whereas Marczewski et al . obtained a direct correlation between the amount of framework Al and aromatic production, further supporting the idea that the aromatisation step occurs entirely on the Brønsted acid sites of the zeolite. In contrast, titration experiments performed by Tessonier et al .…”

Section: Introductionsupporting

confidence: 59%

Implications of the Molybdenum Coordination Environment in MFI Zeolites on Methane Dehydroaromatisation Performance

et al. 2019

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The structure and activity of Mo/Silicalite‐1 (MFI, Si/Al=∞) were compared to Mo/H‐ZSM‐5 (MFI, Si/Al=15), a widely studied catalyst for methane dehydroaromatisation (MDA). The anchoring mode of Mo was evaluated by in situ X‐ray absorption spectroscopy (XAS) and density functional theory (DFT). The results showed that in Mo/Silicalite‐1, calcination leads to dispersion of MoO3 precursor into tetrahedral Mo‐oxo species in close proximity to the microporous framework. A weaker interaction of the Mo‐oxo species with the Silicalite‐1 was determined by XAS and DFT. While both catalysts are active for MDA, Mo/Silicalite‐1 undergoes rapid deactivation which was attributed to a faster sintering of Mo species leading to the accumulation of carbon deposits on the zeolite outer surface. The results shed light onto the nature of the Mo structure(s) while evidencing the importance of framework Al in stabilising active Mo species under MDA conditions.

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“…The molybdenum loading (2%) of the catalysts was the same and the SIO2/A1203 ratio exerted an influence on methane conversion. The acidity decreased with increasing SiOJAlzO3 ratio [7], The results show that the activity of methane conversion decreases with increasing SiOJAI203 ratio, This demonstrates that the activity of the catalysts shows some correlation with the Brtnsted acidity of the HZSM-5 zeolites, Pt/7-A1203 is well known as an industrial reforming catalyst, but Pt/HZSM-5 has a much lower activity for aromatization of methane as compared with Mo/HZSM-5 ( Table 2). Owing to the high temperature, the non-oxidizing atmosphere and the acid catalysis, significant coke formation occurs during methane conversion.…”

Section: Resultsmentioning

confidence: 68%