Pure silica MCM-48 and MCM-41 materials were prepared using GEMINI surfactants, with the general formula [C n H2 n +1N+(CH3)2−(CH2) s −N+(CH3)2C m H2 m +1].2Br-, abbreviated as GEM n-s-m. The alkyl chain length (n,m) determines the pore size, whereas the length of the spacer (s) influences the crystallographic phase formed. A spacer length of 10−12 C yields the cubic MCM-48; smaller spacers favor the hexagonal MCM-41 phase. A hydrothermal treatment is introduced as an intermediate synthesis step, which strongly improves the quality and stability of the calcined materials. The hydrothermal treatment reduces the synthesis time of high-quality MCM-48 to only 2 days. Both GEM 18-12-18 and GEM 16-12-16 yield excellent MCM-48, with a surface area in the range 1200−1600 m2/g and pore volumes exceeding 1.2 mL/g. The maxima of the very narrow pore size distributions are found at r p = 13.1 and 12.2 Å, respectively. The GEM 16-10-16 and GEM 18-10-18 surfactants also yield MCM-48, but the quality of these materials is lower. The GEM 16-8-16 finally yields MCM-41.

TiO x -VO x mixed oxides supported SBA-15 catalysts were prepared in a very controlled way by the designed dispersion method (MDD) using acetylacetonate complexes. The Ti and V active centers are generated by the MDD of the TiO(acac) 2 and VO(acac) 2 . The process consists of the adsorption and subsequent thermolysis of the Ti-V complexes. A careful selection of synthesis conditions allows us to modify the mutual interaction of the Ti and V centers and the interaction of the active centers with the silica support. The decomposition of the anchored complexes and the conversion of the physisorbed species toward covalently bonded TiO x -VO x surface groups have been studied by using a home-built in-situ IR transmission cell. IR seems to be the most suitable technique to follow the calcination process that is required to understand the reaction mechanism. During the thermal conversion, the Ti-V/acac precursor is converted toward supported mixed oxide. Additional characterization was done by FTIR-PAS, TGA, chemical analysis, as well as XRD, FT-Raman, and N 2 adsorption measurements.

Hydrothermal stability of SAPO-34 is greatly improved by the treatment of the acidic form of the SAPO-34 with NH3.

SAPO-34 has been modified by silanation and disilanation reactions. The acidic properties of these modified SAPOs have been characterized by IR measurements. The bands of the bridging hydroxyls at 3600 and 3625 cm -1 show a gradual decrease in intensity with increasing silane or disilane loading. The band intensity of the P-OH group at 3675 cm -1 remains unaffected. The silanation process can be monitored (i) spectroscopically through the characteristic IR band of Si-H at 2250 cm -1 and (ii) analytically by the changes in the H 2 /SiH 4 ratio during the modification. CD 3 CN has been used as an IR spectroscopic probe to elucidate the changes in Brønsted and Lewis acidity of the modified SAPO-34. The intensity of the CtN absorption band at 2320 cm -1 , which is attributed to CD 3 CN adsorbed on Lewis acid sites, increases relative to the band at 2290 cm -1 (Brønsted acidity). This indicates that Brønsted acid sites are irreversibly transformed into Lewis acid sites after silanation reactions on the SAPO-34. 1 H and 29 Si MAS NMR confirm that the silanes react with the Brønsted acid sites resulting in silicon incorporation and silanol formation. Methanol adsorption capacity measurements indicate that silanation and disilanation reactions cause a significant reduction of the void volume of the SAPO-34 cages without creating diffusion limitations. The ethylene/ethane and propylene/ propane selectivity ratios in the MTO reaction (methanol-to-olefins) increase as a function of the (di)silane loading, while the amount of coke on the SAPO-34 decreases linearly with increasing (di)silane loading.