Precipitation-deposition reduction step

For the preparation of gold nanopartides supported on insoluble solids, the most widely used procedure is the precipitation-deposition method [32-36]. Starting from an aqueous solution of HAuCh, addition of a base leads to precipitation of a mixture of Au(OH)3 and related oxy/hydroxides that adsorbs into the solid and is then reduced to metallic gold by boiling the adsorbed species in methanol or any other alcohol. In this procedure, it has been established that the pH of the precipitation and the other experimental conditions (nature of the alcohol, temperature and time of the reduction, calcination procedure, etc.) can provide a certain control of the particle size of the resulting nanoparticles [3j. Figure 12.2 illustrates the steps required in the formation of supported gold nanoparticles. 

Mechanisms for the electrochemical processes at mercury electrodes in solutions of [Ni(cyclam)] + and CO2 have been proposed (see Scheme 5.1 ). Scheme 5.1 shows the formation of a carbon-bonded Ni(II) complex by reaction of CO2 with Ni(cyclam)+. The formation of such a complex is considered to be a fundamental step in the mechanism of the [Ni(cyclam)] +-catalyzed electrochemical reaction. The overall process for the transformation of CO2 into CO also involves inner-sphere reorganization. Scheme 5.1 includes the formation of sparingly soluble complex containing Ni(0), cyclam and CO which is a product of the reduction of [Ni(cyclam)] + under CO. Depositation of a precipitate of the Ni(0) complex on the mercury electrodes inhibits catalysis and removes the catalyst from the cycle. The potential at which the [Ni L-C02H] + intermediate (see lower left hand of Scheme 5.1) accepts electrons from the electrode. This potential is not affected by substitution on the cyclam ring, as shown by comparison of [Ni(cyclam)] + and [Ni(TMC)] " (TMC = tefra-iV-methylcyclam)... 

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