MCM-41

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

H3PW12O40 supported on MCM-41 molecular sieves: An effective catalyst for acetal formation

Abstract: Mesoporous Si-MCM-41 and Al-MCM-41 molecular sieves in four Si/Al ratios: 25, 50, 75 and 100, were synthesized under hydrothermal conditions. Ten weight percent, 15 wt.% and 20 wt.% H 3 PW 12 O 40 (PW) was supported on Si-MCM-41. They were characterized using powder X-ray diffraction (XRD), FT-IR, BET and TEM. The catalytic activity of these materials were tested for the acetalization of carbonyl compounds with 2,2-bis(hydroxymethyl)propane-1,3-diol at refluxing temperature using a Dean–Stark apparatus. The hydrophobic properties of catalyst and alcohols, and the steric properties of carbonyl compounds were suggested to play important roles in the acetalization. Fifteen weight percent PW/MCM-41 was found to be more active than other catalysts used and to have similar activity to that of HPA. TEM studies show that the high dispersion of HPA units, which was maintained through out the reaction, was lost when recycled even for shorter reaction cycle. The reaction was also studied over commercially available heteropolyacids, and zeolites (Hβ, HY, HM and ZSM-5). Occurrence of the reaction mainly within the pores was confirmed by running the reaction over the HPA loaded on an as-prepared catalyst that provides less product yield than the calcined material.

Pt/MCM-41 catalyst for selective catalytic reduction of nitric oxide with hydrocarbons in the presence of excess oxygen

Abstract: First results are reported on the use of MCM-41 mesoporous molecular sieve as the support for Pt for the selective catalytic reduction of NO by hydrocarbons in the presence of O2. MCM-41 provided the highest specific NO reduction rates for Pt as compared with all other supports reported in the literature, i.e., Al2O3, SiO2 and ZSM-5.

Sulfated zirconia catalyst supported on MCM-41 mesoporous molecular sieve

Abstract: Sulfated zirconia (SZ) was supported on siliceous hollow tubular MCM-41 mesoporous molecular sieve by using a one-step incipient wetness impregnation method with zirconium sulfate as the precursor. The SZ/MCM-41 catalyst was obtained by thermal decomposition of the precursor in air. The resultant catalyst was characterized with various techniques, such as nitrogen physisorption, X-ray diffraction, SEM, and TEM. It was shown that the well-ordered channels of MCM-41 support arranged in hexagonal arrays while the hollow tubular morphology was retained. Both tetragonal and monoclinic phases of zirconia were developed in the catalysts. With the addition of a proper amount of aluminum as a promoter, resulting in catalyst SZA/MCM-41, the transformation of zirconia from metastable tetragonal phase to monoclinic phase was retarded. The catalytic activity of SZA/MCM-41 catalyst in the isomerization of n-butane was dramatically improved in comparison to the activities of SZ/MCM-41 or SZA/silica.

Aqueous acidic hydrogen peroxide as an efficient medium for tungsten insertion into MCM-41 mesoporous molecular sieves with high metal dispersion

Abstract: Two sets of WOx/SiO2-MCM-41 precatalysts (A and B) were prepared and compared. Tungsten-containing MCM-41 mesoporous molecular sieves have been synthesized with tetraethyl orthosilicate and tungsten precursors, tungstic acid, 'H2WO4', or sodium tungstate, in the presence of cetyltrimethylammonium chloride (CTMACl) micelles as template in aqueous acid solution. In route A, H2O2 was added to avoid the formation of iso- (or hetero-) polyoxometalates in the counter-ion-mediated S+X−I+ pathway with oxo–peroxo species [S+ = quaternary ammonium ion surfactant, in this paper cetyltrimethylammonium (CTMA+), X− = Cl− and/or anionic peroxo species, I+ = inorganic silicate precursor generating silanols or their protonated forms]. This procedure is compared with methods involving or generating polyoxometalates without peroxo moieties (route B) to determine whether the metal loading and/or dispersion is improved by H2O2. The native materials were calcined in air (1 K min−1, isothermal at 920 K for 4 h) in order to decompose the organic template. The resulting molecular sieves have been characterized by chemical analysis, powder X-ray diffraction, UV-visible diffuse reflectance spectroscopy, nitrogen sorption isotherms, TEM and EDX analysis, and Raman spectrometry. High incorporation levels ((Si∶W)exp molar ratio ≈30∶1) with a nearly homogeneous distribution of the dopants can be obtained only by route A. The spectral differences between the materials are correlated with their catalytic reactivities for cyclooctene epoxidation with an anhydrous H2O2/t-BuOH mixture at room temperature. The results suggest that the novel preparation method (route A) has a marked effect on the dispersion of the WOx species on and into the silica matrix.