Spectroscopic and XRD Characterisation of Zeolite Catalysts Active for the Oxidative Methylation of Benzene with Methane
(2004) Spectroscopic and XRD Characterisation of Zeolite Catalysts Active for the Oxidative Methylation of Benzene with Methane. Spectrochimica Acta Part A: Molecular and Bimolecular Spectroscopy 60(4):pp. 791-799.
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Abstract
The benzene methylation with methane over zeolite catalysts was previously shown in our laboratory to require the presence of oxygen. Thus, a two-step mechanism involving the intermediate formation of methanol by partial oxidation of methane followed by the methylation of benzene with methanol in the second step, was postulated. This paper now reports the results of the characterisation of the zeolite catalysts used for the oxidative benzene methylation reaction in order to provide some information about their composition, structure, properties and their behaviour before and after the reaction. The catalysts were characterised by XRD, ICP-AES, XRF, FTIR and solid state NMR. XRD results indicate that the crystalline structures of all the ZSM-5 and H-beta catalysts remained unchanged after batch reaction of benzene with methane over the catalysts in agreement with the observation that the catalysts recovered from the reactor could be reused without loss of activity. Elemental analyses and FTIR data show that as the level of metal ion exchange increases, the Brönsted acid concentration decreases but this metal ion exchange does not totally remove Brönsted acidity. FTIR results further show that only a small amount of acid sites is actually necessary for a catalyst to be active since used catalysts containing highly reduced Brönsted acidity are found to be reusable without any loss of their activity. 29Si and 27Al MAS NMR together with FTIR spectra also show that all the active zeolites catalysts contain some extra-framework octahedral aluminium in addition to the normal tetrahedral framework aluminium. The presence of this extra-lattice aluminium does not, however, have any adverse effect on the crystallinity of the catalysts both before and after oxidative benzene methylation reaction. There appears also to be no significant dealumination of the zeolite catalysts during reaction since their catalytic performance was retained after use.
| Item Type: | Journal Article |
|---|---|
| Status: | Published |
| Keywords: | Catalysts characterisation, oxidative benzene methylation, spectroscopic techniques, X-ray diffraction, zeolites |
| Subjects: | 250000 Chemical Sciences > 250100 Physical Chemistry (incl. Structural) > 250102 Chemistry of Catalysis 250000 Chemical Sciences > 250100 Physical Chemistry (incl. Structural) > 250104 Chemical Spectroscopy 250000 Chemical Sciences > 250200 Inorganic Chemistry > 250203 Solid State Chemistry 250000 Chemical Sciences > 250100 Physical Chemistry (incl. Structural) > 250103 Colloid and Surface Chemistry |
| ID Code: | 1618 |
| Deposited By: | Adebajo, Moses O |
| Deposited On: | 16 June 2005 |
| Alternative Locations: | http://dx.doi.org/10.1016/S1386-1425(03)00302-0 |
| Copyright Owner: | Copyright 2004 Elsevier |
| Copyright Statement: | Reproduced in accordance with the copyright policy of the publisher. |
| Additional Information: |