An INS study of entrapped organic cations within the micropores of zeolite RTH.

Two different organic cations (structure directing agents, SDAs) have been selected because of their ability to drive the synthesis of zeolites towards the same microporous material, RUB-13 (RTH), both being organophosphorous compounds. These P containing structure directing agents are characterized by a high concentration of positive charge on the phosphorus atom. Then, in the presence of fluoride anions used in these syntheses, a strong P(+)F(-) electrostatic contribution competes with the van der Waals short range SDAzeolite interaction that drives the zeolite formation. The rotation of the methyl groups present in the SDA is expected to be nearly free if van der Waals interactions dominate, but they will be hindered if the Coulombic P(+)F(-) term forces a closer approach to the SDA towards the zeolite framework. SDAs can be designed a priori to tune which interactions dominate. The rotational mobility of the SDAs, as well as certain related bending modes, has been well tackled by inelastic neutron scattering (INS) in order to test this hypothesis. The INS results provide valuable information for the design of specific SDAs for the synthesis of zeolites.

Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication.

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends.

Synthesis and structure determination of a new microporous zeolite with large cavities connected by small pores.

A new small-pore germanosilicate zeolite, named as ITQ-49, has been synthesized using a new ditetraalkylphosphonium dication as an organic structure-directing agent, and its structure has been solved by direct methods applied to the powder X-ray diffraction pattern of the calcined solid. This new zeolite crystallizes in the space group Immm with cell parameters a = 19.6007(8) Å, b = 18.3274(7) Å, and c = 16.5335(6) Å. The pore topology of ITQ-49 consists of large, nonspherical cavities that are connected to each other through small eight-membered-ring windows, resulting in a unidirectional small-pore zeolite that has a relatively large adsorption capacity. Also, ITQ-49 contains double four-membered-ring units where Ge is preferentially located, and fluoride anions are placed inside these units.