Co-condensation method

An alternative method to synthesize organically functionalized mesoporous silica phases is the co-condensation method (also called one-pot synthesis or direct synthesis). Historically, the classical co-condensation reaction involved tetraalkoxysilane [(RO Si (predominantly TEOS or TMOS)] and a terminal organotrialkoxysilane of the type (R 0)3Si-R in the presence of structure-directing agents (Fig. 3.9, top). Meanwhile, not only bis- and multi-silylated precursors are used, that is, precursors of the type [(R 0)3Si]mR, m > 2 (Fig. 3.9, bottom), together with TMOS/TEOS, but... 

Figure 3.9 Co-condensation method (direct synthesis) employing TEOS and a terminal organotrialk-oxysilane (top) or TEOS and an organo-bridged silsesquioxane (bottom) as mixed precursors for the organic modification of mesoporous pure silica phases. R = organic functional group.

Figure 3.16 Possible transformations of iodopropyl groups integrated into mesoporous silica phases via the co-condensation method.

This method, unlike the co-condensation method, does not require a very high temperature calcinat to produce spinel structure from co-precipitated double hydroxides. Usually a temperature of 700 to 800°C and 2 to 3 hours of calcination is sufficient to convert the co-precipitated double hydroxide to spinel. The characteristic X-Ray diffraction patterns of MgAl204 and Mg2Al205 are presented in Figure 3. It may be... 

Figure 1. X-Ray Diffraction Patterns of MgAI O Prepared by Thermal Co-Condensation Method. A=Incomplete (1000°C, 7h) B=Complete.

TGA Test of a CeC>2/MgAl204 Catalyst Prepared by Co-Condensation Method. 

The physical properties of the spinels prepared by this method (Table I) are very different from those prepared by the co-condensation method. The spinels prepared by this method have a very high surface area (-150 m2/g). 

When impregnated with Ce(N03)3 solution and calcined the resulting catalysts are extremely active towards SOx abatement (Table I, Figure 4). The solid solution spinel catalyst is nearly 25% more active than the stoichiometric spinel catalyst. This can be explained by assuming that -MgO- structural fragments of the spinel are the chemisorption active sites (1). There are more active sites in Mg2Al20c than in MgA1 04. We also see that the catalyst prepared by co-precipitation method is 4 times more active than the catalyst prepared by the thermal co-condensation method. In Zone D we see that the sulfated catalyst is very effectively reduced by H. Nearly 70% of the absorbed species is reduced within 2 min. of reduction. 

It is very apparent from this work that coprecipitation and co-gel formation methods for the preparation of spinels provide very active catalysts for FCC SOx reduction whereas the co-condensation method produces very dense ceramic type spinels with low activity. The high magnesium spinel catalyst is more active than the stoichiometric spinel catalyst. 

Fig. 5. Arene complexes of low-valent lanthanide elements obtained by co-condensation methods...

CONTROL OF PARTICLE MORPHOLOGY OF ORGANICALLY FUNCTIONALIZED MSNS BY INTERFACIAL DESIGNED CO-CONDENSATION METHOD... 

Incorporation of the Cu(II) complex to the mesopore surface was accomplished by the aforementioned co-condensation method using a methanolic solution of Cu(II) complex as a precursor. The solution was prepared by mixing copper(II) bromide and N-(2-aminoethyl)-aminopropyltrimethoxysilane (AAP-TMS). The measurements of... 

Radu, D. R. Lai, C.-Y Huang, J. Shu, X. Lin, V. S. Y, Fine-tuning the degree of organic functionalization of mesoporous silica nanosphere materials via an interfacially designed co-condensation method. Chemical Communications (10), 1264-1266, 2005. 

The imprinted materials were prepared via a co-condensation method with aminopropyltriethoxysilane (TEOS), and monomers containing 8-hydroxyquino-line (8-HQ) moieties, in the presence of proper metal ion (Zn or Cd " ). 

Figure 1. Comparison of argon and nitrogen adsorption-desorption isotherms measured at - 196 °C for vinyl-functionaUzed FDU-1 silica studied (A) and (B), respectively calcined silica (FDU-1), extracted vinyl-functionaUzed silica obtained via co-condensation method (FDU-1 Vo), vinyl-functionahzed sihca obtained via post-synthesis modification (FDU-lVm) and calcined vinyl-functionahzed sihca obtained by one-pot synthesis (FDU-1 Vo-c). The corresponding pore size distributions (PSDs) calculated according to the KJS method [17] from adsorption branches (C) and (D).

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