M.T. Navarro

Preparation and properties of Ti-containing MCM-41

Publisher Summary The new policies on environment preservation are directing the chemical processes to not only avoid the use of unfriendly reactants and catalysts but also to find more selective catalysts that minimize product waste and/or expensive separations and recycling. Zeolites doped with V and Zn can selectively oxidize n-butane to maleic anhydride. Pd/Cu–Y zeolites can replace the homogeneous Pd and Cu salts for the oxidation of short-chain olefins to carbonyl compounds using molecular oxygen. Metal phthalocyanine complexes entrapped in zeolites have also shown great activity and selectivity for the oxidation of alkanes, cycloalkanes, olefins, and alcohols using iodosobenzene and air as oxidants. An important advance in oxidation catalyst was given when Ti and V containing zeolites were shown to be active and selective to carry out the oxidation of different hydrocarbons with H 2 O 2 . Thus, the isomorphous substitution of Si by Ti and/or V into the framework of MFI and MEL zeolite structures leads to materials that show good activity and selectivity for the oxidation of phenol to catechol and hydroquinone, olefins to epoxides, and alkanes to alcohol and ketones using H 2 O 2 at relatively low temperatures. However, in the field of fine chemicals, it is sometimes required to oxidize large molecules that cannot penetrate in the narrow pores of the MFI structure.

Strategies to improve the epoxidation activity and selectivity of Ti-MCM-41

Two strategies to improve the catalytic activity of Ti-MCM-41 materials in the epoxidation of olefins are described; the first approach involves silylation of the surface of Ti-MCM-41 which produces a very hydrophobic catalyst whereas the second approach is based on removal of water from the reaction media; the increase in activity is not due to a change in the intrinsic activity of the Ti sites, but rather to a decrease of the catalyst deactivation by reducing the formation of diols produced by ring opening of the epoxide.

Influence of silylation on the catalytic activity of Ti-MCM-41 during epoxidation of olefins.

Abstract Ordered mesoporous titanium containing MCM-41 type materials have been silylated with a suite of organosilanes. We found that catalytic activity for epoxidation of cyclohexene using tercbutylhydroperoxide as oxidant as well as the selectivity to the desired epoxide strongly depend on the hydrophobic properties and on the number of free silanol groups of Ti-MCM-41 catalysts, which can be nicely controlled by modifying the number and/or the nature of the organosilane groups bounded onto the walls of Ti-MCM-41 catalysts.

Design of optically active nanoclusters of gold particles with mesostructured silica coating

Monodispersed, nanosized gold-mesoporous silica nanospheres in the size range 80–280 nm with specific optical properties are prepared in two steps: i) controlled aggregation of gold nanoparticles (GNP) in nanoclusters embedded in a uniform coating of amorphous silica, and ii) development of a porous regular and ordered silica shell by pseudomorphic transformation of the external layer. By careful manipulation of the synthesis variables, i.e., the concentration of co-solvent, surfactant and alkali, it is possible to obtain nanoparticles with controlled morphological and textural characteristics and desired optical behaviour. An optimized sample with most of the nanoparticles containing a multinucleus core made of 10 or more GNP shows a strong absorption cross-section in the near-infrared (NIR) region and a significant photothermal effect when irradiated with a λ = 808 nm laser diode module.

Sn-MCM-41—a heterogeneous selective catalyst for the Baeyer–Villiger oxidation with hydrogen peroxide

A new heterogeneous catalyst, Sn-MCM-41, is described for the Baeyer-Villiger reaction with hydrogen peroxide which selectively activates the carbonyl function for the nucleophilic attack by the oxidant, with high chemoselectivities when double bonds are present in the molecule.

The investigation of beta polymorphs by 19F nuclear magnetic resonance

Abstract ITQ-16 (polymorphs A, B and C of beta zeolite) with different Ge content (Si/Ge=4-30) have been synthesised in fluoride medium using 4-Aza, 1-azoniabicyclo[2,2,2]octane, 1-benzyl (BzD+) as organic structure directing agent (SDA). The X-ray diffraction (XRD) patterns, present the peaks characteristic of polymorph C (zeolite ITQ-17) and (A+B) (zeolite beta) which allows to determine the percentage of the former in every sample. F− anions are incorporated into the [43 54] and double four member ring (D4R) cages of polymorphs A and B, and of polymorph C, respectively, compensating the positively charged SDA. Since the 19F nuclear magnetic resonance (NMR) chemical shift depends on the number of Ge and Si atoms and the geometry of the lodging cage, the spectra of samples ITQ-16 change, with the relative amounts of polymorphs (A+B) and C, and the Si/Ge molar ratio. The percentage of polymorph C calculated from the relative area of the 19F NMR peaks show a good, agreement with those obtained by XRD. Moreover, the detailed analysis of the spectra indicates an enrichment in Ge of the D4R units of polymorph C. The general trend observed is that the relative amount of polymorph, C increases as the Ge content in the sample increases.

Direct Synthesis of a Photoactive Inorganic–Organic Mesostructured Hybrid Material and its Application as a Photocatalyst

A photoactive, hexagonally structured mesoporous material (Tyl-MCM41) is produced through co-hydrolysis of SiO(2) and a trialkoxysilane-functionalized trityl cation as photoactive species. The formation of the corresponding triphenylmethanol precursor in the material is confirmed by spectroscopic techniques. The hybrid material has an ordered structure with a narrow pore size distribution typical of ordered mesoporous MCM-41-type materials. The triarylcarbinol molecules incorporated into this hybrid structure (Triphol-MCM41) generate trityl cations under acidic conditions, which are photoactive and able to promote the photosensitized dimerization of 1,3-cyclohexadiene in a heterogeneous solid-liquid system. The material is stable and can be recycled without loss of the photochemical activity.

11-P-29 - New hydrophobic Ti-beta catalyst obtained by silylation and its catalytic performance for olefin epoxidation

Publisher Summary This chapter presents new hydrophobic Ti-Beta catalyst obtained by silylation and its catalytic performance for olefin epoxidation. Silylated Ti-Beta materials show a superior selectivity for epoxidation reactions than analogous fluoride synthesized Ti-Beta. This enhanced yield to the desired epoxide is attributed to the synergetic effect of the basic amine adsorbed on the Ti sites and the presence of silyl groups anchored on the silanol or titanol groups of the precursor Ti-Beta catalyst, which prevents the oxirane-ring opening reaction.