The thermal, hydrothermal, and mechanical stabilities of a wide range of ordered mesoporous materials, in particular, the molecular sieves MCM-41, MCM-48, HMS, FSM-16, KIT-1, PCH, and SBA-15, have been studied in detail using X-ray diffraction (XRD) and nitrogen sorption. The thermal stability was found to be strongly related to the wall thickness and the silica precursor used during synthesis, and the following stability trend was observed: MCM-41 (fumed silica), MCM-48 (fumed silica), KIT-1 (colloid silica) > SBA-15 (TEOS) > FSM-16 (layered silicate), PCH (layered silicate) > MCM-41 (TEOS), MCM-48 (TEOS), HMS (TEOS). The hydrothermal stability is influenced by the wall thickness and the polymerization degree and decreases according to the following trend: KIT-1 > SBA-15 > MCM-48 (fumed silica and TEOS), PCH > FSM-16, MCM-41 (fumed silica and TEOS), HMS. The mechanical stability is little influenced by the nature of the mesoporous molecular sieves. All materials collapsed at a maximum pelletizing pressure of 450 MPa.

A synthesis route to mesoporous titania with remarkable thermal stability was developed using an amine or cetyltrimethylammonium-templating procedure. By a treatment of the titania hybrids in aqueous ammonia, a method has been developed to overcome the lack of thermal stability above 350 °C. As for most mesoporous titanias described in the literature, this thermal instability originates from the uncontrolled phase transformation of amorphous template-free titania into massive anatase grains. In situ Raman spectroscopy, X-ray Diffraction, Differential Scanning Calorimetry and Thermogravimetrical Analysis demonstrated that parts of the amorphous titania walls of the NH 3 -treated titania hybrids were transferred into walls built up of rutile nanobuilding blocks before the template was thermally removed. We further found that, after a subsequent increase of temperature to remove the template, the remaining amorphous particles were transformed into anatase in such a way that this crystallographic transformation is accompanied by a retention of the pore structure without massive segregation of anatase nuclei. This leads to ordered high surface area (up to 600 m 2 g -1 ) mesostructured titania having pore volumes up to 0.28 cm 3 g -1 . XRD and N 2 adsorption-desorption data showed an outstanding thermal stability; the mesoscale order of NH 3 -treated titanias was retained after thermal treatment up to 600 °C.

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.

Pure silica MCM-48 is prepared by a novel synthesis method, using the [C18H37N+(CH3)2−(CH2)12−N+(CH3)2C18H37]·2Br- surfactant, abbreviated as GEMINI 18-12-18. The MCM-48, obtained after careful calcination, is a highly crystalline, mesoporous material with the characteristics of the Ia3d cubic phase, a surface area exceeding 1000 m2/g, and a narrow mesoporous pore size distribution (r = 1.4 nm; fwhh < 0.2 nm). This MCM support is grafted with VO x species using a designed dispersion of VO(acac)2 in a gas-deposition reactor. In the first step, the complex is anchored to the support. In a subsequent step the adsorbed complex is thermolyzed to yield chemically bonded VO x surface species. The final material contains 1.7 mmol V/g (8.7 wt % V) and still has a narrow pore-size distribution and a surface area of 800 m2/g. It is observed that all silanols are consumed during the adsorption of the VO(acac)2 complex to the MCM support. Therefore, the maximum achievable number of surface V species is limited by the silanol number and not by the geometrical surface, which has a higher capacity. After calcination of the adsorbed complex, the supported VO x species are present in a strictly tetrahedral configuration, mainly as chains of linked tetrahedra and not as isolated species.

The reaction of Fe(acac)3 with the surface of zirconia has been studied for the first time using in situ infrared diffuse reflectance spectroscopy, photoacoustic spectroscopy, and Fourier transform Raman spectroscopy. The unstable Fe(acac)3 reacts readily with the surface of zirconia at room temperature in the liquid phase or at 110 °C in the gas phase, yielding grafted Fe−OH species and Zr−acac surface groups. We present evidence that the reaction occurs both with coordinatively unsaturated Zr sites and with the surface hydroxyls. The grafted Zr−acac groups are thermally unstable and form Zr−acetate groups after thermal treatment at 110 °C in ambient air. After removal of the organic ligands, noncrystalline iron oxide species are formed on the zirconia surface. The grafting of iron oxide on zirconia is a relevant procedure to form either redox catalysts or solid-state fuel cells.

The growth and thermal stability of an iron oxide overlayer on yttria-stabilized zirconia (YSZ) have been studied using atomic layer deposition (ALD), mainly in combination with low-energy ion scattering (LEIS). These techniques form a powerful combination, where ALD is designed for controlled (sub)monolayer deposition, while LEIS selectively probes the altered outermost atomic layer. The Fe(acac) 3 precursor reacts already at room temperature with YSZ. The reaction proceeds until saturation, which is characteristic for ALD. After the results of repeated ALD cycles, which consist of Fe(acac) 3 deposition followed by an oxidation treatment, have been studied, a model could be proposed which describes the growth mode of the iron oxide layer on YSZ. Oxidation at temperatures of 800 °C and higher causes a migration of Fe 2 O 3 into the bulk, limiting its usefulness in surface catalytic processes at these temperatures. At 800 °C the diffusion coefficient of Fe in YSZ is determined to be 10 -23 m 2 /s. The reaction mechanism of Fe(acac) 3 with the YSZ surface is studied using infrared diffuse reflectance. The results reveal more than one reaction mechanism, but there seems to be a preference for the reaction via coordinatively unsaturated sites.

Highly crystalline and porous vanadium-incorporated MCM-48 materials were prepared using gemini surfactants as structure-directing agents and vanadyl sulfate pentahydrate as the source of the heteroelements. Materials with Si/V ratios varying from 20 to 100 were synthesized without loss of the typical cubic MCM-48 structure. The synthesis conditions were optimized to yield reproducible V−MCM-48 materials of high quality. The resulting materials are thoroughly characterized by UV−vis diffuse reflectance, electron spin resonance, Raman, and Fourier transform infrared spectroscopies. It was proven that the V ions in the MCM-48 are present as isolated surface species and as incorporated species in the silica matrix. For the first time, both chemical and spectroscopic tools were employed to distinguish the incorporated V sites (which are present inside the silica walls) and species that are situated externally on the surface. A fairly low amount (1 wt %) of V species is really incorporated, but these species are extremely stable, and do not leach, whereas the surface species are easily lost in aqueous media.

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