Carbon Supports for NP Catalysts

The Pd is leaching and is redeposited at the end of the reaction, which provides an excellent recovery of the precious metal from the reaction mixture. The precipitation of the catalyst at the end of the reaction significantly changes its state and decreases its activity, however, making its re-use unattractive. Kohler et al. also showed that optimization of the Pd/C catalyst (temperature, solvent, base and Pd loading) allows turnover frequencies (TOFs) of up to 9000 to be reached and Pd concentration down to 0.005 mol% to be developed for the Heck reaction of unac-tivited bromobenzene at 140 °C [44]. The turnover numbers (TONs) are surpassed, however, by those of the best homogeneous catalysts. 

AuNPs occupy a special place given their great success and present developments. Thus, four chapters of the book are devoted to the various aspects of AuNP catalysis. In the AuNP-catalyzed CO oxidation to CO2 by O2 that can occur down to 200 K 

HAuChaq + NaOH [Au(OH)4] Na aq (pH 6-10) Au(OH)3/Support wash, dry then calcinate at 563-673 K - AuNP/Support (optimal AuNP size 3 nm, stable hemispherical NPs, the size being controlled by the calcination temperature whose optimum is 570 K, optimal support Ti02 for which the addition of Mg citrate is necessary during or after co-precipitation for a good dispersion of hny AuNPs). 

It has been shown that oxidation of CO by O2 to CO2 can also be catalyzed by the cluster Aug in the gas phase (Fig. 1.14) [45c], and calculations with Au,o predict CO oxidation by O2 below room temperature [45dj. Recent studies by Haruta s 

AppUcations are expected in both the catalytic removal of CO produced at ambient temperature by engines and the removal of CO traces from dihydrogen streams feeding the fuel cells. There is a tremendous recent increase in the number of reports focusing on this area of supported AuNP-catalyzed CO oxidation, Ti02 becoming the dominant support [45]. 

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