Pseudo-liquid phase

They also found that Dawson HP2W is more active than Keggin HP As and attributed the higher activity to the fact that Dawson HP2W has a less rigid structure and weaker acidity than Keggin HPW, which gives rise to a faster absorption - desorption rate of polar solvents in the pseudo-liquid phase of the HPA. 

On the one hand, these complete and rapid one-step solid-state reactions are due to the pseudo-liquid phase properties of solid-state HPAs. On the other hand, suitable crystal water of HPAs is important to the synthesis of POM nanoparticles. The HPA precursors with about twenty crystal water molecules are the best candidate for the preparation of uniform nanoparticles as observed in the TEM images (Figure 1). HPAs with excessive or lacking crystal water could not become the appropriate precursor. 

At a relatively low temperature (e.g., near OX), some gases undergo capillary condensation and become liquid occupying the pores. The associated transport is then governed by pseudo-liquid phase diffusion. When other gases do not dissolve in the condensed component(sX separation of gases occurs. Two examples are SO2/H2 [Barrer, 1965] and H2S/H2 [Kameyama, et al. 1979] systems in which SO2 and H2S, respectively, condense in the pores and diffuse across the membrane while H2 in both cases is blocked from the pores as it does not dissolve in either liquid SO2 or H2S. 

As mentioned above, H3PW12O40 (HTP) is very active solid acid for various reactions. It is also known that polar molecules are absorbed in the solid bulk phase and the polar reactants undergo chemical transformations in the solid bulk as well as on the surface. This behaviour of heteropoly compounds is called a pseudo liquid phase phenomenon. 

The behaviour of Dawson and Keggin-type heteropolycids has been studied over surface-type and bulk-type reactions. Both heteropolyacids have shown similar activity for all the reactions investigated, with the biggest differences found for t-BuOH dehydration and isobutene polymerisation. It is possible for t-BuOH dehydration that the pseudo-liquid phase is responsible for the higher peformance of the Dawson, as suggested by Misono for MTBE synthesis. However this does not explain why the Dawson, which is the most selective catalyst at low temperature for 1-BuOH and 2-BuOH dehydration, suddenly becomes the less selective for f-BuOH dehydration. 

Another promising class of compoimds are the heteropolyacids. Depending on the reaction conditions, they can act according to three basic mechanisms as normal surface catalysts, with involvement of the entire volume, or as pseudo-liquid phase catalysts. They have so far mainly been used in lapan for hydrogenation/dehydro-genation, selective oxidation, and acid/base reactions. 

Monteagudo et al characterized the asphaltenes as a continuous ensemble for which the distribution function was taken from the fractal aggregation theory. The asphaltene family was discretized in pseudo-components by the Gauss-Laguerre quadrature. Only the asphaltene polydispersity was taken into account. All other components were represented by as solvent whose properties (molar volume and solubility parameter) were calculated form a cubic equations of state. Aggregation of asphaltenes was considered to be a reversible process. And it was assumed the phase equilibrium was between a liquid phase and a pseudo-liquid phase containing only asphaltenes. 

The kinetics of adsorption and the amount of polar (alcohols) and nonpolar molecules, Keggin type compounds, was extensively studied through IR spectroscopy and thermogravimetric analysis [16,31,32,34,35]. Misono and coworkers [31] established that the rate of alcohol adsorption depends on the size of the probe molecule, and that the amount of adsorbed molecules in H3PW12O40 is an integral multiple of the number of protons. The observation of the diffusion coefficients and adsorption of polar molecules into the bulk structure of the HPAs proved unequivocally the pseudo-liquid phase behavior of those compounds. 

Owing to the flexible nature of the secondary structure of the acid forms and group A salts, polar molecules such as alcohols and amines are readily absorbed into the solid bulk by substituting water mol ciiles and/or by expanding the interdistance between polyanions. Heteropoly acids which have absorbed a significant amount of polar molecules resemble in a sense a concentrated solution and are in a state between solid and solution. Therefore, this state is called the pseudo-liquid phase . Some reactions proceed mainly in this bulk phase. The tendency to form a pseudoliquid phase depends on the kind of heteropoly compound and the molecules to be absorbed and on the reaction conditions. 

The bulk-type catalysis has been proved by several experiments such as i) a transient response analysis of the dehydration of 2-propanol, ii) a phase transition of the pseudo-liquid phase, and iii) the reactivity order of alcohols which was reversed depending on the partial pressure. Unusual pressure dependence as well as direct observation by MAS-NMR of reaction intermediates such as protonated alcohol and alkoxide have been reported for pseudo-liquid phase. ... 

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