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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Delgado, Juan Jose Alvaro, Mercedes Garcia, Hermenegildo Navalon, Sergio Martin, Roberto Calvino, Jose J. |
| Description | Author Affiliation: Martin R ( Instituto de Tecnología Química CSIC-UPV and Departamento de Química, Universidad Politécnica de Valencia, Av. De los Naranjos s/n, 46022 Valencia, Spain.) |
| Abstract | The catalytic activity of diamond-supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol $(50 g L^{−1})$ and $H_{2}O_{2}$ excesses $(100 g L^{−1})$ and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of $O_{2}$ evolved two different reactions of $H_{2}O_{2}$ decomposition (the Fenton reaction at acidic pH values and spurious $O_{2}$ evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and $35 kJ mol^{−1}).$ By using dimethylsulfoxide as a radical scavenger and N-tert-butyl-α-phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected $PBNOCH_{3}$ adduct was detected, supporting the generation of $HO^{.},$ characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as $H_{2}O_{2}$ decomposition at pH 4 (due to the barrierless attack of $HO^{.}$ to phenol), but increases the activation energy gradually up to about $90 kJ mol^{−1}$ at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 $(49 kJ mol^{−1}).$ |
| ISSN | 09476539 |
| e-ISSN | 15213765 |
| Journal | Chemistry - A European Journal |
| Issue Number | 34 |
| Volume Number | 17 |
| Language | English |
| Publisher | Wiley-VCH;ChemPubSoc Europe |
| Publisher Date | 2011-08-16 |
| Publisher Place | Germany |
| Access Restriction | Open |
| Subject Keyword | Chemistry |
| Content Type | Text |
| Resource Type | Article |
| Subject | Organic Chemistry Catalysis |
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