Nuclear magnetic resonance activation volume

The formation of complex ions is an important problem for the study of the structure and properties of molten salts. Several physicochemical measurements give evidence of the presence of complex ions in melts. The most direct methods are the spectroscopic methods which obtain absorption, vibration and nuclear magnetic resonance spectra. Also, the formation of complex ions can be demonstrated, without establishing the quantitative formula of the complexes, by the variation of various physicochemical properties with the composition. These properties are electrical conductivity, viscosity, molecular refraction, diffusion and thermodynamic properties like molar volume, compressibility, heat of mixing, thermodynamic activity, surface tension. 

The activation volume, obtained from the pressure dependence of the reaction rate, has become a well-established, and often decisive, criterion for the determination of the reaction mechanism, so that variable-pressure NMR has also become an important tool in the understanding of chemical reactions. High gas pressures can be used to produce increased concentrations of a gas in solution, leading to faster reaction rates, advantageous shifts in chemical equilibria, or even entirely new chemical species. High-pressure NMR is an obvious technique for the study of such reactions. Nuclear magnetic resonance has also proven to be a powerful technique in solid-state physics, where variable-pressure experiments can be used to study phase transitions, transport phenomena, and electronic properties. 

The most common characterization techn iques used in refineries to monitor the changes in catalyst activity during commercial operation are textural properties (surface area, pore volume, average pore diameter, and pore size distribution) determined by nitrogen adsorption/desorption metals content (mainly Ni and V) by atomic absorption and carbon content by combustion. There are more advanced characterizations techniques that are mostly employed by researchers for more detailed studies of catalyst deactivation such as Nuclear Magnetic Resonance (NMR), x-ray Photoelectron Spectroscopy... 

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