Molecular Dynamics of iso-Butyl Alcohol Inside Zeolite H-ZSM-5 as Studied by Deuterium Solid-State NMR Spectroscopy

Investigating the Interaction between Methanol and the Heulandite-type Zeolite using First Principle Molecular Dynamic

The interaction between methanol and the Heulandite-type zeolite has been unveiled to give an atomic scale detail regarding the catalytic activity of this zeolite for methanol conversion. The study was carried out by first principle molecular dynamics to get an insight into the structure and electronic behaviour of methanol inside the zeolite structure at different temperatures. The behaviour of methanol was studied when the location of the proton of Bronsted acid sites was varied to give both possible direct and less interaction with methanol. The results show that methanol interacts with the proton from zeolite to give a cationic species of [CH3OH2]+ both in 300K and 573K conditions. However, when the proton is located at different location far from possible interaction with methanol, the formation of a cationic species is hindered. This study provides an insight into the design of Heulandite type zeolite to give a catalytic activity toward methanol transformation.

2H-solid state NMR and DSC study of isobutyric acid in mesoporous silica materials

Solid state deuterium NMR has been used to study the molecular motion of d(6)-isobutyric acid (d(6)-iBA) in the pure (unconfined) state and confined in the cylindrical pores of two periodic mesoporous silica materials (MCM-41, pore size 3.3 nm and SBA-15, pore size 8 nm), and in a controlled pore glass (CPG-10-75, pore size ca. 10 nm). The line shape analysis of the spectra at different temperatures revealed three rotational states of the iBA molecules: liquid (fast anisotropic reorientation of the molecule), solid I (rotation of the methyl group) and solid II (no rotational motion on the time scale of the experiment). Transition temperatures between these states were determined from the temperature dependence of the fraction of molecules in these states. Whereas the solid I-solid II transition temperature is not affected by confinement, a significant lowering of the liquid-solid I transition temperature in the pores relative to the bulk acid was found for the three matrix materials, exhibiting an unusual dependence on pore size and pore morphology. Complementary DSC measurements on the same systems show that the rotational melting (solid I-liquid) of d(6)-iBA in the pores occurs at a temperature 20-45 K below the thermodynamic melting point. This finding indicated that the decoupling of rotational and translational degrees of freedom in phase transitions in confined systems previously found for benzene is not restricted to molecules with non-specific interactions, but represents a more general phenomenon.

Molecular dynamics of tert-butyl chloride confined in CPG studied by NMR

The molecular dynamics of tert-butyl chloride (TBC) confined to Controlled Pore Glass matrices of 25 and 7.5 nm were investigated by measuring NMR linewidths, lineshapes, and 1H and 2H spin--lattice relaxation times. The behaviour of confined TBC can be explained assuming that the guest molecules form two distinct phases; the surface-affected phase, composed of molecules located at the pore surface, and the bulk-like phase located at the centre of the pores. The bulk-like component of confined TBC, at the temperatures corresponding to the phase III, is characterized by two dynamically different subphases.