Bronsted acids 834 INDEX

The hydrothermal deactivation of Y zeolite containing 0, 4, 7 and 12 wt.% of REO and its effects on catalytic activity, stability and selectivity were investigated. The Y zeolites were hydrothermally deactivated at 788°C in three consecutive cycles of two hours each. The fresh and deactivated zeolites were characterized by measuring Unit Cell Size (UCS) and surface area. The acidic properties were measured by the Temperature Programmed Desorption (TPD) of ammonia and IR-pyridine desorption. In order to correlate structural, textural and acid properties with catalytic behavior, the zeolites were evaluated in the conversion of cyclohexane. The Hydrogen Transfer Index (HTI) measured as a ratio of paraffins to olefins is a parameter of the selectivity. It was found that the REO was incorporated into zeolite structure up to high concentrations modifying to some extent XRD deflection, the acidic properties and the HTI ratio. After deactivation, the acidity and HTI were diminished and the Lewis/Bronsted acid ratio was modified. HTI decreased as REO concentration increased. 

Some of the earliest chemical studies of nonhydrocarbons, which resulted in the isolation of numerous strong acids and bases, were conducted at the University of Texas under the leadership of Lochte and Littman (I). This work used the classical extraction of petroleum with mineral acids and caustic followed by chemical identification (boiling point, refractive index, derivatives, etc.). Since only strong Bronsted acids and bases can be isolated by aqueous solvents, their identifications were limited to low-molecular-weight species aqueous solvents also do not isolate weak acids or bases (low pK values). 

The authors have found that the ROP of TeMC initiated with H2O or a primary alcohol (e.g., butyl alcohol) in the presence other Bronsted acids such as HCl Et20 proceeded without decarboxylation to give linear poly(TeMC) with Mn= 1000-10 000 and a narrow dispersion index ( 1.15). They postulated that the key feature of this polymerization is the appropriate acidity of the protonic acid, which should be not as high to polymerize the monomer by itself but sufficient to activate the monomer. ... 

Chatteijee, A. 2006. A reactivity index study to rationalize the effect of dopants on Bronsted and Lewis acidity occurring in MeAlPOs. J. Mol. Graphics Model. 24 262-270. 

There seems to be a close relation between this factor a and the index j8, in Bronsted s relation1 k = cK between the dissociation constant K of an acid and its catalytic activity k this had been suggested by Frumkin 2 the reader must consult the originals for further elaboration. 

The catalytic coefficients for all acids do not fall on the same Bronsted plot and Bronsted exponents from 0.56—0.71 are obtained depending upon the catalyst type. Observations like these may mean that the Bronsted exponent is not a precise index of transition state structure [183],... 

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