Page 85 - Principles of Catalyst Development
P. 85
72 CHAPTER 4
• A1 3 +
0 0 2 -
0 OH-
3
Figure 4.17. Suggested scheme for acidic sites on r-AI20,.,,'71
Neutralization of the proton, H', by a base, B, occurs through the
reaction()5)
(4.6 )
in which the acid ionization constant is
(4.7)
with y's the appropriate activity coefficients. It 1S convenient to express
acid strength by
( 4.8)
so that strong acidity shows large negative values of pKa. Methods for
measuring pKa are discussed in Chapter 7. Distributions in y-A1 20 1 are
given in Fig. 4.18, which also shows how acidity increases with calcination
temperature as the surface becomes structured. Further heating above 400°C
causes dehydration and a decrease in acidity. (55)