Catalytic parameters 222 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. 

The cyclohexene conversion to paraffins and olefins which is well known as the Hydrogen Transfer Index (HTl) ratio was used to evaluate the catalytic activity of the fi sh and deactivated materials at constant conversion (30 mol %) varying the contact time and at 250°C. The HTl results were related with the REO content, cell parameter and total acidity and are plotted in figures 5,6 and 7, respectively. 

The maximum A values measured so far in NEMCA studies utilizing YSZ are 3x10 3,5 shown in Table 1, which lists the catalytic reactions studied so far under EP conditions using conducting electrolytes. When the promoting ion does not react at all with any of the reactants (e.g., Na ) then, in principle, "infinite" values are expected. In practice A is always measurable (Table 2) due to a very slow consumption of Na to form surface oxides and carbonates. Nevertheless, in all cases the catalytically important parameter is the promotion index Pj defined below and also shown in Tables 1 and 2. 

From a catalytic point of view, a very important parameter which can be obtained via NEMCA is the promotion index Pj of the doping species defined from ... 

From a catalytic viewpoint, the promotion index P/ is the most important phenomenological parameter for quantifying the promoting or poisoning effect of a given coadsorbed species i (e.g., O ", F, Na", on the rate of a catalytic reaction. It is defined by... 

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