Catalysis of Organic..

104 Propylene Partial Oxidation0.01IR Intensity (A.U.)374136883646T(°C)250175150125100755025IR Intensity (A.U.)31043079298329543375170816661633157514751441T(°C)2501751501251007550250.053800 3600Wavenumber (cm -1 )35003000 2500 2000 1500Wavenumber (cm -1 )1000Figure 4. In situ IR spectroscopy of TPR of partial oxidation of propylene overAu/TiO 2 -SiO 2 .Fig. 5 shows the calibrated MS profiles depicting flow rates of reactants andproducts during TPR over Au/TiO 2 -SiO 2 . The mass spectrometry analysis shows theconsumption of H 2 (m/e=2), O 2 (m/e=32) and C 3 H 6 (m/e=41) indicated by thenegative profiles as well as the formation of products indicated by the positiveprofiles for propionaldehyde (m/e=29), acetone (m/e=43), iso-propanol (m/e=45),PO (m/e=58), and CO 2 (m/e=44). The formation of propionaldehyde, acetone, isopropanol,and CO 2 reached a maximum at 160 °C. The occurrence of the maximumformation at the same temperature suggests the formation of these various C 3oxygenates may share a common rate-limiting step. It is important to note that them/e=58 profile behaved significantly differently from other C 3 oxygenates. Theformation of PO began to occur at temperatures above 160 o C where a 1575 cm -1emerged, as shown in Fig. 4. This 1575 cm -1 band is in good agreement withadsorbed acetate/formate which has been suggested to be formed from bidentatepropoxy species on Au/TiO 22 (19). Propylene oxide can further oxidize to give suchspecies. These observations further justified the assignment of m/e=58 to PO eventhough other C 3 oxygenates’s fragments contribute to m/e=58.