13.4.4 SEA IN WI AND DI MODES
A final note can be made in this section regarding the generality of the SEA method.
Strong electrostatic adsorption corresponds to the pH value which maximizes the
strength of the precursor-support interaction. For benchtop experiments, surface
loadings are generally held low (500–2000 m2/l) in order to minimize pH shifts for
the sake of convenience. There is nothing inherently incorrect in utilizing SEA at
much higher surface loadings. This is illustrated in the pH shift and adsorption
calculations shown in Figure 13.12, for the uptake of CPA by alumina as a function
of surface loading. The lowest loading, 500 m2/l, corresponds to a typical SL
employed in the laboratory, whereas 150,000 m2/l roughly corresponds to the SL at
DI conditions of typical γ-aluminas. Uptake curves at all SLs show the characteristic
volcano shape. The maximum obtainable uptake decreases at the highest SLs due
to the higher concentration of Pt, which must be employed to achieve the same
surface density. The higher ionic strength of the CPA solutions suppresses the
adsorption equilibrium constant of the Pt complex, which is not quite compensated
by the higher Pt concentration. For a 200 m2/gm alumina, a surface density of
1 µmol/m2 corresponds to a Pt loading of about 4 wt%, which is much higher than