Catalyst design accounting for the fractal surface morphology

Abstract

Fractal geometry can be used in the development of porous catalysts with higher conversions and selectivities for desirable products. The fractal surface morphology, which can be tuned by changing the preparation conditions, has an influence on the Knudsen diffusivities and on the intrinsic reaction rates per unit catalyst mass. Depending on the catalyst and the operating conditions, the effective reaction rate of a first-order reaction can either increase or decrease with the fractal dimension of the surface. The simulation of an industrial unit for the catalytic reforming of naphtha is used as an example of how the design of the fractal catalyst surface can influence iso-paraffins, aromatics and hydrogen yields. The hydrogen yields exhibit a maximum of around 3.6 wt.% for an intermediate fractal surface dimension, D s ads = 2.6. The highest isoparaffins yield is obtained for a smooth surface (23 wt.%), while surfaces with a high D x ads lead to the highest aromatics yields (up to 76 wt.% for D s ads = 3).