Characterization of Cr-MCM-41 and Al,Cr-MCM-41 Mesoporous Catalysts for Gas-Phase Oxidative Dehydrogenation of Cyclohexane
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- 作者：Maria Lezanska ; Grzegorz S. Szymanski ; Piotr Pietrzyk ; Zbigniew Sojka ; Johannes A. Lercher
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：February 1, 2007
- 年：2007
- 卷：111
- 期：4
- 页码：1830 - 1839
- 全文大小：231K
- 年卷期：v.111,no.4(February 1, 2007)
- ISSN：1932-7455
文摘
The effects of the Cr concentration in hydrothermally synthesized Cr-MCM-41 and the impact of variouspostsynthesis treatments including grafting with alumina were investigated. Using physicochemicalcharacterization by XRD, diffuse reflectance UV-vis spectroscopy, EPR spectroscopy, 29Si MAS NMRspectroscopy, H2 TPR, and acidity measurements, formation of mono- and dichromate surface species aswell as CrV, dispersed CrIII, and clustered CrIII was detected, confirming the high speciation and valenceversatility of the surface chromium. The roles of each species in the preparation stage, calcination, leaching,and grafting are discussed. Leaching resulted in removal of all isolated CrIII species, suggesting that CrIII isattached to the MCM-41 surface via silanol groups. The resulting materials exhibited low acidity, with bothLewis and Br
nsted acid sites being present. The oxidative dehydrogenation (ODH) of cyclohexane wascatalyzed by Cr-MCM-41 with a conversion of up to 25.7% in the temperature range of 533-633 K. TheCrIII sites have been concluded to be responsible for cyclohexane ODH, but total activity was influenced bythe presence of easily reducible CrVI at the beginning of the reaction. During the reaction, high-valence Crions were reduced to clustered Cr2O3 species.
nsted acid sites being present. The oxidative dehydrogenation (ODH) of cyclohexane wascatalyzed by Cr-MCM-41 with a conversion of up to 25.7% in the temperature range of 533-633 K. TheCrIII sites have been concluded to be responsible for cyclohexane ODH, but total activity was influenced bythe presence of easily reducible CrVI at the beginning of the reaction. During the reaction, high-valence Crions were reduced to clustered Cr2O3 species.