Synthesis impregnation

Vanadium has also been incorporated into raesoporous MCM-41 materials by hydrothermal synthesis, impregnation and CVD [167]. UV-VIS DR spectra reveal predominantly mononuclear vanadium( V) oxide and oligomeric clusters... 

Fig. 5.8 Synthesis of metal-doped organic and carbon aerogels (post-synthesis, impregnation).

The traditional approach used to embed iron oxide species into a mesostructured matrix, i.e. the post synthesis impregnation of the preformed porous material with an inorganic precursor like iron nitrate and followed by calcinations, presents a major drawback the inorganic salt tend to be adsorbed on the external surface of the silica, which usually leads to large agglomerates outside the mesopores, thus decreasing the specific advantages of... 

The traditional methods, such as hydrothermal synthesis, impregnation, and chemical vapor deposition (CVD), can be employed to incorporate heteroatom and metal/metal oxide nanoparticles as catalysts into the nanopores of MSs. The advances in this area have been well summarized in recent reviews [35 - 38]. Herein, we will mainly focus on the assembly of molecular catalysts in the nanopore of MSs and MOFs. Using the molecular chiral catalyst as a model, we will address the general strategies for incorporating molecular catalysts in the nanoreactor, including the covalent and noncovalent bonding methods. 

Promoters are sometimes added to the vanadium phosphoms oxide (VPO) catalyst during synthesis (129,130) to increase its overall activity and/or selectivity. Promoters may be added during formation of the catalyst precursor (VOHPO O.5H2O), or impregnated onto the surface of the precursor before transformation into its activated phase. They ate thought to play a twofold stmctural role in the catalyst (130). First, promoters facilitate transformation of the catalyst precursor into the desired vanadium phosphoms oxide active phase, while decreasing the amount of nonselective VPO phases in the catalyst. The second role of promoters is to participate in formation of a soHd solution which controls the activity of the catalyst. 

Iron impregnated on activated carbon was used as catalyst for the direct synthesis of phenol from benzene. The effect of Sn addition to the catalyst was studied. The prepared catalysts were characterized by BET, SEM and XRD analysis. The catalyst 5.0Fe/AC showed good activity in the conversion of benzene and addition of Sn seemed to improve the selectivity of phenol in the reaction. 

As expected, 7-AI2O3 (BET area 110 m /g) turned out to be the more stable support with a higher surface area than MgO (BET area 52 m /g). The BET area of RU/AI2O3 was found to be 104 m /g after NH3 synthesis at 773 K which decreased significantly to 70 m /g as a result of cesium impregnation. After NH3 synthesis at 773 K, the specific area of Ru/MgO was observed to be 25 m /g compared with 52 m /g found for the MgO support. Cesium impregnation caused a further decrease in specific area to 23 m /g. 

Figure 4. XPS Ru 3d data observed for the Ru/MgO catalysts. The Ru 3d spectra (from bottom to top) were obtained with the precursor after heating in high vacuum to 773 K, after reduction in 1 bar synthesis gas up to 773 K, and after impregnation with aqueous CsNOs solution and subsequent reduction in synthesis gas up to 673 K.

For many years, research efforts in materials chemistry have focused on the development of new methods for materials synthesis. Traditional areas of interest have included the synthesis of catalytic, electronic, and refractory materials via aqueous methods (sol-gel and impregnation) and high-temperature reactions [1-3]. More recent strategies have focused on the synthesis of materials with tailored properties and structures, including well-defined pores, homogeneously distributed elements, isolated catalytic sites, comphcated stoichiometries, inorganic/organic hybrids, and nanoparticles [4-13]. A feature... 

Figure 3. Schematic representation of the selective synthesis of metal nanowires and nanoparticles by the Sintering Controlled Synthesis approach, (a) Mesoporous silica, (b) impregnation of mesoporous silica with metal ions, (c) addition of water/alcohol vapors and UV-irradiation, or wet H2-reduction, (d) formation of metal nanowires, (e) dry H2-reduction, (f) formation of metal nanoparticles.

For the preparation of CoSalophen Y the Co—Y was impregnated by salicy-laldehyde, and 1,2-phenylenediamine in methanol was added slowly to the mixture.107 This was a successful encapsulation of a salen-type complex with larger diamine than the ethylenediamine, a successful preparation of an encaged metal-salen complex by the intrazeolite ligand synthesis method, and a successful intrazeolite synthesis using two different precursor molecules. 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

Abramoff B., Klein L.C., PMMA - impregnated silica gels synthesis and characterization, SPIE Proc. 1328, 241-248, (1990). 

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