Example 7.1. Adsorption based on the BET equation. The following data have been obtained for the adsorption of nitrogen on TiO2 at 77 K: P/P 0.02 volume of gas (cm³ g¹) 1.2 0.05 1.5 0.1 0.2 0.3 0.4 0.6 0.8 0.9 1.9 2.4 2.7 3.0 3.8 4.6 6.7 1. Show that the adsorption isotherm is likely to be represented by the BET equation. 2. Estimate using the BET equation: a. the volume for monolayer coverage V,,, (in cm³ g'); b. the specific surface of solid TiO2 in m² g¹ if the area occupied by one nitrogen molecule is 16.2 x 10-20 m². Solution The V versus P/P, plot clearly shows that the adsorption of nitrogen on titanium oxide has the BET shape. 8 V (cm³/g) 2 0.4 1.2 0.8 PIP。 1. According to the BET theory, the plot of P/V(P.-P) versus P/P, should be linear. If we consider all the points provided in the above table, i.e. up to very high pressures, the resulting plot is not linear. However, the BET equation should be constructed based only on the points up to reduced pressures of about 0.4, i.e. up to sixth or seventh point. Indeed the plot of P/V(Po-P) versus P/P is linear up to reduced pressure 0.4 (approximately even up to the seventh point of reduced pressure 0.6). The straight line is shown in the plot below. How to find this value? 0.300 0.200 07/DX 0.100 0.000 0.6 0.0 0.2 0.4 PIP
Example 7.1. Adsorption based on the BET equation. The following data have been obtained for the adsorption of nitrogen on TiO2 at 77 K: P/P 0.02 volume of gas (cm³ g¹) 1.2 0.05 1.5 0.1 0.2 0.3 0.4 0.6 0.8 0.9 1.9 2.4 2.7 3.0 3.8 4.6 6.7 1. Show that the adsorption isotherm is likely to be represented by the BET equation. 2. Estimate using the BET equation: a. the volume for monolayer coverage V,,, (in cm³ g'); b. the specific surface of solid TiO2 in m² g¹ if the area occupied by one nitrogen molecule is 16.2 x 10-20 m². Solution The V versus P/P, plot clearly shows that the adsorption of nitrogen on titanium oxide has the BET shape. 8 V (cm³/g) 2 0.4 1.2 0.8 PIP。 1. According to the BET theory, the plot of P/V(P.-P) versus P/P, should be linear. If we consider all the points provided in the above table, i.e. up to very high pressures, the resulting plot is not linear. However, the BET equation should be constructed based only on the points up to reduced pressures of about 0.4, i.e. up to sixth or seventh point. Indeed the plot of P/V(Po-P) versus P/P is linear up to reduced pressure 0.4 (approximately even up to the seventh point of reduced pressure 0.6). The straight line is shown in the plot below. How to find this value? 0.300 0.200 07/DX 0.100 0.000 0.6 0.0 0.2 0.4 PIP
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Transcribed Image Text:Example 7.1. Adsorption based on the BET equation.
The following data have been obtained for the adsorption of nitrogen on TiO2 at 77 K:
P/P
0.02
volume of gas (cm³ g¹)
1.2
0.05
1.5
0.1
0.2
0.3
0.4
0.6
0.8
0.9
1.9
2.4
2.7
3.0
3.8
4.6
6.7
1. Show that the adsorption isotherm is likely to be represented by the BET equation.
2. Estimate using the BET equation:
a.
the volume for monolayer coverage V,,, (in cm³ g');
b. the specific surface of solid TiO2 in m² g¹ if the area occupied by one nitrogen molecule is 16.2 x
10-20 m².
Solution
The V versus P/P, plot clearly shows that the adsorption of nitrogen on titanium oxide has the BET shape.
8
V (cm³/g)
2
0.4
1.2
0.8
PIP。
1. According to the BET theory, the plot of P/V(P.-P) versus P/P, should be linear. If we consider all the
points provided in the above table, i.e. up to very high pressures, the resulting plot is not linear. However,
the BET equation should be constructed based only on the points up to reduced pressures of about 0.4, i.e.
up to sixth or seventh point. Indeed the plot of P/V(Po-P) versus P/P is linear up to reduced pressure 0.4
(approximately even up to the seventh point of reduced pressure 0.6).
The straight line is shown in the plot below.
How to find
this value?
0.300
0.200
07/DX
0.100
0.000
0.6
0.0
0.2
0.4
PIP
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