Miguel A. Camblor

Synthesis of a titaniumsilicoaluminate isomorphous to zeolite beta and its application as a catalyst for the selective oxidation of large organic molecules

The isomorphous substitution of Si by Ti in the zeolite Beta framework by direct hydrothermal synthesis gives rise to useful catalysts for the selective oxidation of small and large organic compounds.

Synthesis of titanoaluminosilicates isomorphous to zeolite Beta, active as oxidation catalysts

Isomorphous replacement of Si by Ti in the low aluminum-containing zeolite Beta framework has been achieved by direct synthesis. The crystallization must be carried out in the absence of alkali cations, as they promote the precipitation of amorphous titanosilicate. The incorporation of Ti to the framework has been characterized by XRD, i.r., and thermal analysis. Ti is believed to perform a stabilizing role of the Beta framework similar to that of Al. The large pores of [Al, Ti]-Beta compared to TS-1 allow the use of this material as a catalyst in the selective oxidation of cyclododecane with hydrogen peroxide.

Synthesis of all-silica and high-silica molecular sieves in fluoride media

Recent advances in the synthesis of all-silica and high-silica crystalline molecular sieves in fluoride media, with special regard to low framework density phases, are presented. The fundamental differences between the synthesis in hydroxide and fluoride media with respect to the properties of the materials obtained and the phase selectivity of the crystallization are discussed.

Crystallization of zeolite beta: effect of Na and K ions

Crystallization of zeolite Beta has been studied in the whole range of K/(K + Na) molar ratios. Chemical changes of both solid and liquid phases have been related to the crystallization curves and crystal-size distributions of the final products. The role of the alkali cations in regulating the aluminum concentration in the liquid phase and modifying the nucleation events leading to the zeolite crystals is discussed.

Infrared spectroscopic investigation of titanium in zeolites. A new assignment of the 960 cm–1 band

The formation of Si–O–defect groups due to the incorporation of Ti in the framework of zeolites is evidenced by means of solid-state tetraethylammonium (TEA) cation exchange; a new assignment for the infrared (IR) band in both β-Ti and TS-1 is presented.

Synthesis in fluoride media and characterisation of aluminosilicate zeolite beta

Zeolite beta has been synthesised for the first time in a wide range of initial Al/(Al+Si) ratios (0–0.14) in the presence of F– and TEA+ at near neutral pH. The samples have been characterised by a number of techniques and compared to those synthesised in basic medium. An increase in crystal size and crystallinity as the Si/Al ratio increases together with an enhanced resolution of the XRD pattern and of the IR and 29Si MAS NMR spectra are apparent. This is attributed to an enhanced local order as Si substitutes for Al in the zeolite framework. IR and 27Al MAS NMR demonstrate dealumination is more severe the lower the Si/Al ratio. The presence of F– in the as-made samples induces significant changes in the IR spectrum in the region of characteristic framework vibrations (500–650 cm–1) probably due to a distortion of the framework. The determination of the micropore volume has been carried out using different methods, the t-plot method giving the more reliable results. Apparently, thermal analysis allows one to distinguish between TEA+ cations compensating for F– anions from those compensating for framework Al, as the latter appear to be oxidised at a higher temperature.

Influence of the synthesis conditions on the crystallization of zeolite Beta

Crystallization rate, average crystal size, and crystal-size distribution of zeolite Beta have been studied as a function of TEAOH/SiO 2 (TEAOH = tetraethylammonium hydroxide) and SiO 2 /Al 2 O 3 ratios, concentration of the gel, and agitation during crystallization. The influence of these parameters on the nucleation and crystal growth rates and on the chemical composition of the final crystalline material is discussed.

Synthesis of nanocrystalline zeolite beta in the absence of alkali metal cations

Contrarily to previous reports, pure aluminosilicate zeolite Beta can be synthesized in the complete absence of alkali cations without the use of seeds. Thus, the presence of alkali cations is not necessary for the nucleation and crystal growth to occur, although they greatly affect the crystallization kinetics. By this synthesis method stable suspensions of colloidal zeolite Beta particles in the nanoscale size (100 to 10 nm) were prepared. It is also possible to synthesize 100% crystalline zeolite Beta with up to 7.6 framework Al atoms per unit cell (Si/Al=7.4).

High silica zeolites with three-dimensional systems of large pore channels

Abstract Several high silica zeolites with three-dimensional systems of large pore channels have been prepared in aqueous fluoride media: Beta, ITQ-7, ITQ-10 and ITQ-14. Pure silica beta can crystallize using up to 17 organic cations considerably different in size, shape, rigidity and C/N ratios. There are clear differences in the powder X-ray diffraction patterns of calcined beta materials prepared with different cations, suggesting structural differences between them. However, this technique cannot be readily used to get further insights into these differences. 19 F MAS NMR spectroscopy shows the existence of fluoride occluded in double four ring cages in most of the different betas, thus demonstrating for the first time the real occurrence in these intergrown materials of polymorphs different from A and B. Double four ring cages are also present in ITQ-7 and in the new ITQ-10 and ITQ-14 zeolites.

Unseeded synthesis of Al-free Ti-β zeolite in fluoride medium: a hydrophobic selective oxidation catalyst

Al-free Ti-β zeolite spontaneously nucleates and grows in a reaction mixture containing tetraethylammonium and fluoride ions at near neutral pH, and shows an enhanced crystallinity and thermal and hydrothermal stability as well as a significant hydrophobic character.