The effectiveness of mass fractal catalysts
The effectiveness of mass fractal catalysts
复制标题
质量分形催化剂的有效性
DOI：
--
复制
发表时间：
1997
期刊：
影响因子：
--
通讯作者：
G. Froment
中科院分区：
文献类型：
--
作者：
M. Coppens;G. Froment
许多多孔催化剂具有分形表面，但很少有分形体积，主要的例外是极其多孔的气凝胶。有人认为，它们的体积的分形形状是理想的，因为它每单位质量具有无限的面积，反应物很容易接近。本文通过将质量分形与非分形催化剂进行比较来研究质量分形的效率。研究发现，可比较的非分形催化剂的比表面积即使不高于质量分形催化剂的比表面积，也具有相同的数量级。尽管质量分形由于其活性位点非常容易接近而具有高效率，但非分形催化剂的产量通常高于质量分形催化剂，因为后者具有高孔隙率。对于一些强扩散限制的反应，特别是在介孔催化剂中，增加质量分形大孔性，具有有限的缩放范围，将提高产率，超出非分形催化剂所能达到的水平。尽管如此，当通过大孔中的粘性流传输非常快时，经典双峰催化剂中的有效反应速率高于具有高大孔率的分形催化剂。
Many porous catalysts have a fractal surface, but only rarely do they have a fractal volume, the main exceptions being extremely porous aerogels. It has been suggested that a fractal shape of their volume would be ideal, because it has an infinite area per unit mass that is easily accessible by the reactants. This paper investigates the efficiency of mass fractals by comparing them with nonfractal catalysts. It is found that the specific surface areas of comparable nonfractal catalysts are of the same order of magnitude, if not higher than those of mass fractals. Despite the high effectiveness factor of mass fractals due to the exceptionally easy accessibility of their active sites, production in a nonfractal catalyst is often higher than in a mass fractal, because of the high porosity of the latter. For some strongly diffusion limited reactions, especially in mesoporous catalysts, an added mass fractal macroporosity, with a finite scaling regime, would increase the yields beyond what is possible with a nonfractal catalyst. Nonetheless, when transport through viscous flow in macropores is very rapid the effective reaction rates in classical bimodal catalysts are higher than in fractal catalysts with their high macroporosity.