Photocatalytic activity of Ag/TiO(2) composites obtained by photoreduction treatment (PRT) was investigated. The composite materials, containing various ratio of silver nanoparticles (0.6-3.7 wt %) were obtained by depositing silver on the Evonic-Degussa P25 titania surface. Selected samples whose color varied between light rose and purple brown were examined by SEM, TEM, XPS, DRS, and BET techniques. Flat band potential was determined using Roy method. TEM analysis showed spherically shaped silver nanoparticles of the diameter 4-12 nm. The XPS measurements revealed that silver particles were obtained mainly in metallic form. DRS spectra and photovoltage measurements showed that silver nanoparticles modified the P25 spectral properties but they changed neither the band gap nor the location of flat band potential. The photocatalytic activity of Ag/P25 composite was compared to the photocatalytic activity of pure P25 in the photooxidation reaction of an important potable water contaminant humic acid (HA) and two model compounds, oxalic acid (OxA) and formic acid (FA). The photodecomposition reaction was investigated in a batch reactor containing aqueous suspension of a photocatalyst illuminated by either UV or artificial sunlight (halogen lamp). The tests proved that a small amount of silver nanoparticles deposited on the titania surface triggers the increase in photocatalytic activity; this increase depends, however, on the decomposed substance.

We investigate the distinctly different interaction of thiolate-protected cluster Au 38 (SC 2 H 4 Ph) 24 with two diverse support materials Al 2 O 3 and CeO 2 . The catalytic surfaces have been heated in different atmospheres, and the removal of the thiolate ligands has been studied. Thermogravimetry (TG), temperature-programmed process coupled with mass spectrometer (TPRDO-MS), and X-ray absorption spectroscopy (XAFS) studies were performed to understand the desorption of thiol ligands depending on conditions and support material. Depending on the atmosphere and the support material the fate of the thiol ligands is different upon heating, leading to metallic Au in the case of Al 2 O 3 and to cationic Au with CeO 2 . The thiolate removal seems to be a two-step procedure. The catalytic activity of these Au 38 -supported clusters was studied for the aerobic oxidation of cyclohexane. Conversion was higher for the gold clusters supported on CeO 2 . Surprisingly, a significant amount of cyclohexanethiol was found, revealing the active participation of the thiolate ligand in catalytic reactions. The observation also indicates that breaking and formation of C−S bonds can be catalyzed by the gold clusters. ■ INTRODUCTIONHeterogeneous catalytic processes by supported thiolateprotected clusters (Au n (SR) m ) represent an emerging field stimulated by reports showing higher activity and selectivity in several oxidation reactions 1−4 in comparison with metal nanoparticle catalysts. These clusters consist of a symmetric metal core protected by multiple gold−thiolate staples −SR− (Au−SR−) n (n = 1,2) that present size-dependent physical chemical properties, related with their quantized electronic structure and unique geometrical structure. In comparison to bulk gold, which has a face-centered cubic (fcc) structure, clusters of sizes <2 nm often show icosahedral structure. 5

The location of the Pd atoms in Pd2Au36(SC2H4Ph)24, is studied both experimentally and theoretically. X-ray photoelectron spectroscopy (XPS) indicates oxidized Pd atoms. Palladium K-edge extended X-ray absorption fine-structure (EXAFS) data clearly show Pd-S bonds, which is supported by far infrared spectroscopy and by comparing theoretical EXAFS spectra in R space and circular dichroism spectra of the staple, surface and core doped structures with experimental spectra.