ABSTRACT
The effectiveness of porous catalysts depends on the reaction rate constants and diffusion coefficients and is low when the latter coefficients are small. The effect of the nonuniform distribution on the rate of formation has been calculated when the amount of zeolite is in that range. The composite-center distribution has a better performance than both the uniform distribution and composite-surface distribution. P. J. Nandapurkar and E. Ruckenstein extended the above considerations to the catalytic cracking of hydrocarbons by the zeolite/silica-alumina catalysts. In this case, some steps of the reaction occur in the more porous (silica-alumina) medium. They again concluded that the diluted catalyst pellets can be more active than the pellets of the same size consisting of only zeolite and that there exists an optimum volume fraction of diluent (silica–alumina) for which the rate of formation of the desired compound is maximum.
