关键词: 多孔介质, 可控设计, 反应-扩散耦合, 硬球-拟颗粒, 分子模拟

Abstract: Most catalysts have complicated pore structures, and the coupling of reaction and diffusion processes in the pores determines the overall performance of catalysts. Understanding the reaction-diffusion coupling in the pores is important for better design of catalysts to improve their performance. In this work, the coupling of reaction and diffusion of reactants and products in catalyst pore structures was simulated by using the hard-sphere/pseudo-particle modeling (HS-PPM) approach which is combined with a simplified lumped reaction model for the C4 olefin cracking process. A controllable approach was proposed to construct more realistic model for the pore structure in catalyst materials, with which the effect of porosity, pore diameter and pore volume ratio could be studied independently and quantitatively. In addition to the effectiveness factor ?, a quantitative parameter JC was proposed to characterize the coupling of reaction and diffusion processes. The results showed that JC tended to be zero, which indicated that the overall diffusion process was significantly limited due to the competition between reactant diffusion and product diffusion in the complex pores. The reactant molecules were mainly diffused into the catalyst through the larger pores, and the larger product molecules were also mainly diffuse out of the catalyst through the larger pores. The competition between these two processes made it difficult for the reactants to diffuse into the pore, and the products to diffuse out of the pore, which led to the decrease of the overall performance of the catalyst albeit the potentially high reaction rate allowed by the intrinsic kinetics. The simulation approach used in this study could be helpful for the design of pore-scale structure of catalyst materials.

Key words: porous media, controllable design, reaction-diffusion coupling, HS-PPM, molecular simulation