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MCM-41

About: MCM-41 is a research topic. Over the lifetime, 2355 publications have been published within this topic receiving 91416 citations.


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Journal ArticleDOI
TL;DR: In this paper, the formation of a lamellar phase and its transformation into hexagonal MCM-41 were studied by powder X-ray diffraction (XRD), 29Si magic-angle-spinning (MAS) NMR and transmission electron microscopy (TEM).
Abstract: Mesoporous silicates synthesized in strongly basic media from sodium silicate in the presence of cetyltrimethylammonium chloride, a cationic surfactant. The formation of a lamellar phase and its transformation into hexagonal MCM-41 were studied by powder X-ray diffraction (XRD), 29Si magic-angle-spinning (MAS) NMR and transmission electron microscopy (TEM). The gel mixture (pH>14) is transparent. Upon acidification, a layered phase with interplanar spacing d=35 A rapidly forms at pH=13 and gradually transforms into the lamellar phase with d=31 A. The 29Si MAS NMR spectrum of the layered phase is broad and dominated by the resonance from Si(OSi)3O–M+ (Q3) structural units (M stands for the surfactant cation). The spectrum of the lamellar phase is well resolved with a more intense line from the Si(OSi)4 (Q4) structural units, indicating a more regular atomic arrangement. The hexagonal phase is obtained at pH=11.5 upon acidification of the gel, or when the pH of the intermediate product containing the lamellar phase is adjusted to 7–9 and the hydrothermal treatment continued. The hexagonal phase gives a broad 29Si NMR spectrum dominated by the Q4 resonance, indicating a less ordered local atomic arrangement in comparison with the lamellar phase. We suggest that the transformation is driven by the increasing reactivity of the silicate species with increasing acidity of the gel, which facilitates further aggregation of uncondensed silicate between the layers.

47 citations

Journal ArticleDOI
TL;DR: In this article, a mesoporous MCM-41 silica was successfully synthesized and promoted with Pd nanoparticles through a microwave irradiation (MWI) approach.

47 citations

Journal ArticleDOI
TL;DR: A series of Al-MCM-41 mesoporous molecular sieves, with Si/Al ratio in the range 15-40, were synthesized and characterized by XRD, N 2 physisorption, DRIFT and 27 Al and 29 Si MAS NMR analysis as mentioned in this paper.

46 citations

Journal ArticleDOI
TL;DR: In this article, a series of chromium supported mesoporous MCM 41 silica catalysts (0.5 −6 wt% Cr) were used in the oxidative dehydrogenation of propane between 350 and 550°C.
Abstract: A series of chromium supported mesoporous MCM‐41 silica catalysts (0.5–6 wt% Cr) were prepared and tested in the oxidative dehydrogenation of propane between 350 and 550°C. The catalytic activity, observed at temperatures as low as 350 °C, can be well explained on the basis of the existence of highly dispersed and reducible chromium species.

46 citations

Journal ArticleDOI
TL;DR: In this article, a series of framework substituted Co-TUD-1 catalysts were characterized using X-ray diffraction, nitrogen physisorption, transmission electron microscopy and UV-vis and Raman spectroscopies.
Abstract: A series of framework substituted Co-TUD-1 catalysts, prepared by direct hydrothermal synthesis, were characterized using X-ray diffraction, nitrogen physisorption, transmission electron microscopy and UV–vis and Raman spectroscopies. These catalysts showed high conversion and selectivity towards trans -stilbene oxide in liquid phase trans -stilbene epoxidation with molecular oxygen as oxidant in the absence of a sacrificial reductant. The conversion and selectivity did not remarkably differentiate for fresh and recycled catalyst after four reaction runs. The unique pore structure of Co-TUD-1 catalyst is suggested to be beneficial for the epoxidation of bulky alkene molecules comparing with other well-established catalysts, e.g., Co-MCM-41 and Co 2+ -NaX. Microwave irradiation can significantly shorten the reaction time, whereas high conversion and epoxide selectivity remained.

46 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202334
202258
202172
202071
201993
201890