Selective Adsorption onto Promoters

The steps to apply the SEA method for the synthesis of promoted metals are 

determination of support and promoter PZC (with bulk powders of each) 

metal uptake-pH surveys over each pure component (also recording pH shifts) 

an adsorption experiment at the optimal pH over a physical mixture of the two oxides, which can be identified separately in electron microscopy, to confirm the partitioning of the metal onto the desired oxide 

synthesis over the supported promoter oxide and characterization via scanning transmission electron microscope (STEM), EXAFS, and ultimately activity and selectivity testing to confirm the adsorption selectivity. 

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Several groups [87,210] claim that surfactants such as CTAB do not serve as soft tanplates but rather promote the formation of nanorods due to their adsorption onto selective planes on the seed surface. It was found that most of the metallic rods are composed of (100) side planes and (111) end planes, as presented in Figure 15.3. 

In many foods adhesion is an undesirable phenomenon, but in some food systems we need to promote adhesion between two phases. The surfactants play a key role in both the promotion and prevention of adhesion. If, upon adsorption, the selected surfactants will make the surfaces of the two phases more similar in nature and attractive to each other, the surfaces will have a chance to become colloidal and adhere to each other. If a polar solid has to be phase-adhered to a nonpolar hydrocarbon phase, a surfactant with a hydrocarbon chain should adsorb onto the polar solid, with its hydrophilic head oriented toward the polar solid and its hydrocarbon groups oriented away from it. This allows the polar solid surface to become hydrocarbon-like and thus more likely to adhere to the hydrocarbon phase. 

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