Diffusion rates in porous catalysts

Abstract

Rates of diffusion of helium, nitrogen, and carbon dioxide through alumina pellets were measured a t atmospheric pressure and room temperature. The cylindrical pellets, 3/4 in. diameter and % in. in length, were prepared from a-alumina particles with a mean pore radius of 65 A.Surface area and pore volume data indicated that the corresponding mean pore radius of the micro and macropores in the whole pellet was 96 A.The results showed that Knudsen type of diffusion was the controlling transport process despite the large fraction of void volume in the macropores. Carbon dioxide diffused more rapidly than expected, suggesting the possibility of migration of physically adsorbed molecules along the pore walls.The diffusion rates were about 16% higher than predicted, with a mean pore radius (Wheeler model) based upon the void volume of both micro and macropores used. However there is no logical basis for using this mean pore radius for o pellet having widely separated, micro and macropore size distributions.

Laboratory characterization of the structural properties controlling dynamical gas transport in Mars-analog soils

“…The Wicke-Kallenbach method was used extensively throughout the 1960s and '70s in studies of a variety of materials of interest for industrial chemistry, and to validate physical models of gas transport (e.g., Weisz, 1957;Evans et al, 1961;Henry et al, 1961;Scott and Dullien, 1962;Foster and Butt, 1966;Cunningham and Fig. 1.…”

Measurement Technique of Oxygen Diffusion Resistance through Gas Diffusion Layer

“…A number of ways to measure the oxygen diffusion characteristics of PEFCs have been reported in conventional studies (1)(2)(3)(4). These measurement techniques require complicated systems and take a long time to measure oxygen diffusion resistance with high precision.…”

Measurement of effective oxygen diffusivity in microporous media containing moisture

“…For example, a diffusion method in which the effective diffusivity was measured directly, such as the measurement of diffusion flux, was performed by Kwon et al [2]. Furthermore, the diaphragm method was used by Kawazoe et al [3], Henry et al [4], and Masamune and Smith [5], a separation membrane method by Hamai and Mitani [6] and Gibilaro and Waldram [7], and a method with an yttrium-stabilized zirconia oxygen sensor was used by Mezedur et al [8]. A zirconia-type oxygen sensor is based on the principle that oxygen ion transfer in zirconia produces an electric current; however, this sensor is generally used at temperatures above 300 °C and it is difficult to obtain measurements of microporous materials under wet conditions where liquid water is present in some of the micropores.…”