Catalysis of Organic..

Singh and Chuang 103537373650Temp (°C)250Au/TiO x -SiO 2IR Intensity (A.U.)Au/TiO 2 -SiO 2250Au/TiO x -SiO 225Au/TiO 2 -SiO 22540003500 3000Wavenumber (cm -1 )25002000Figure 3. IR analysis of Au/TiO x -SiO 2 and Au/TiO 2 -SiO 2 .TPR results over Au/TiO 2 -SiO 2Fig. 4 shows IR spectra as a function of temperature during TPR study ofpropylene partial oxidation over Au/TiO 2 -SiO 2 . Exposure of the catalyst toAr/C 3 H 6 /H 2 /O 2 (28/4/4/4 ml/min) at 25 °C led to the decrease in the intensity of the3741 cm -1 (OH stretching) band and the formation of bands associated with gaseousand adsorbed propylene at 3104 cm -1 (υ as =CH 2 of gas phase propylene), 3079 cm -1(υ as =CH 2 of π-complexed propylene), 2983 cm -1 (υ s =CH 2 of π-complexedpropylene), 2954 cm -1 (υ s CH). 1633 cm -1 (C=C of π-complexed propylene on M n+ ),1475 and 1441 cm -1 (δCH of adsorbed propylene) (14). Adsorbed propylene speciesappears to interact with adsorbed oxygen on the Au surface and the OH on oxidesurface, producing the 1708 cm -1 (C=O of adsorbed propionaldehyde) band and the1666 cm -1 (C=O of adsorbed acetone) band. The decrease in the OH intensity at3741 cm -1 provides the direct evidence of interaction between OH and propylene andC 3 oxygenated products (i.e., propionaldehyde and acetone). (15).