Catalysis of Organic..

Auten, Crump, Singh and Chandler 321have E app values within experimental error of 32 kJ/mole. The high temperatureoxidation and delayed low temperature oxidation treatments are only slightly higher(36 and 40 kJ/mole, respectively). The observation that the E app values from the lessactive B catalysts do not change substantially from the freshly prepared and activatedcatalyst, and are similar to the catalyst treated with high temperature (300 ºC)oxidation, indicates that the active sites on all these catalysts are at least qualitativelysimilar. This, in turn, suggests that the primary activity differences from sample tosample are not due to intrinsic activity difference associated with different types ofactive sites. Rather, the differences observed in catalytic activity are likely to be dueto differences in the number of active sites present on each catalyst.In order to better understand changes to the catalyst surface during activation,infrared spectroscopy was used to monitor the dendrimer decomposition process. IRspectra of intact Au-DENs/TiO 2 areAbsorbanceTiO 216571540 153814500.6SiO 2 (x4)12201155170015001300Wavenumbers (cm -1 )Figure 4. IR spectra of (top) Pt-DENs/SiO 2 and (bottom) Au-DENs/TiO 2compared with a spectrum of Pt-DENs/SiO 2 in Figure 4. The spectrum of Pt-DENs/SiO 2 shows the amide I and II bands at 1657 and 1538 cm -1 . These values areconsistent with free PAMAM dendrimers in solution and with previous reports forunactivated dendrimer templated catalysts on SiO 2 .(3,7,9) The TiO 2 supported DENsare strikingly different, with 2 prominent peaks from the dendrimer visible at1540cm -1 and 1440 cm -1 . Two additional smaller peaks at 1220 cm -1 and 1155 cm -1 -are also apparent on the TiO 2 support.