Question

The plot shown in Figure 8.1 was obtained for the Dubinin-Raduskevich analysis of CO2 adsorption ona zeolite. Sketch the expected micropore distribution for this material explaining your reasoning fully 8.2 1.0 0.8 0.7 log (p ip) Figure 8.1

Answer 1

0Statement of Dubinin: The process of adsorption in micropores(size of pore radii is less than 0.6-0.7 nm ) is thermodynamically analogs to the process of solution.

Dubinin equation $A=RTln(\frac{P_{0}}{P})$ ...... (1)

where A is molar work of adsorption. this equation state that the volume adsorbed at equilibrium pressure is dependent upon A.

Dubinin -Radushkevich equation as follows:

$log n=log n_{0}-B(\frac{T}{\beta })^{2}ln^{2}(\frac{P_{0}}{P})$

Where $B=2.303R^{2}/k$

the k is a structural parameter related to pore size distribution at adsorbent.

n=micropore volume.

Draw the graph between log(n) and log² (P₀/P)

intercept will be n₀(limiting value of adsorption space) and slope will be$B/\beta ^{2}$

Dubinin got a linear graph for a particular range adsorbent-adsorbate system.

Dubinin explains linearity deviation with the help of five graphs as follows:

(1D microbore g 0刈 Continouky Pore size lang er micro pores absent mi'cropore yste m Pore size tielol si Pressuso enhanches aol sorbtior Cause c Pore sice l Suermi crobores (b) meso p ores or acttvateate oli Hus ίον Pore size Systeun atean Pore diarrete

The plot as mention in the question resembles graph number (3).It signifies that the enhanced adsorption caused by filling of either mesopore (diameter of pores 2-50 nm) or supermicropores(diameter of pore 0.6-0.7 nm and 1.6 -1.7 nm). or formed a multilayer.