Adams aqueous colloidal

Considerably easier is the preparation of aqueous colloidal forms of transition metal oxides, which was optimized with the emergence of a straightforward method. The first example pertains to a water-soluble colloidal form of Adams catalyst (Pt02) [52]. 

The aqueous colloidal Adams catalyst can be immobilized conveniently on solid carriers such as AI2O3 by adding the calculated amount of solid material to the aqueous colloidal solution and stirring. However, prior reduction to the zerovalent form followed by immobilization is actually more efficient [54]. After washing with methanol several times to remove the surfactant, the heterogeneous catalysts were examined by TEM which showed that essentially no undesired agglomeration had occurred (1.9nm particles). 

Using the simple hydrolysis/condensation of metal salts under basic aqueous conditions in the presence of carbo- or sulfobetaines, respectively, colloidal Pt02 was obtained, the analytical data of which correspond to pure a-Pt02 and to commercial samples of Adams catalyst. Bi- and trimetallic colloidal metal oxides as precursors for fuel-cell catalysts, e.g., colloidal Pt/RuO and Pt/Ru/WO, have also been prepared this way [5If]. 

The SFB is a specialized apparatus, developed by Tabor and Winterton (50) and refined by Israelachvili and Adams (51), to study basic colloidal forces—specifically in this case to measure the interaction of orthogonally positioned hemicylinders (generally mica) as they are brought together (or separated) in aqueous solutions. Separations (D) can be measured with a precision of better than 5 A and forces (F) to a precision of 10 p,N. Data are presented in plots of F/R versus D where R is the radius of curvature of the cylinders. Force/distance curves have been measured in the presence of electrolytes, adsorbing surfactants, and, as mentioned in Chapter 2, polymers. Here we will briefly discuss some of the results obtained in four studies (52-55) concerned with the adsorption of conditioning polymer-type polyelectrolytes. 

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