Catalysis of Organic..

O’Keefe, Jiang, Ng and Rempel 373spectra are illustrated on the right side of Figure 5 as the temperature is increasedfrom ambient temperature to 200°C in discrete increments. Note that even at 200°C,the band intensities characteristic of adsorbed MIBK are evident indicating a stronginteraction between MIBK and the Pd/Al 2 O 3 catalyst. Similar experiments werecarried out for acetone and mesityl oxide pulse adsorbed on the Pd/Al 2 O 3 catalyst.The desorption spectra for acetone on Pd/Al 2 O 3 catalyst is given in Figure 6.3001705T: 25 to 250 o Crelative reflectance (%)2502001502965300029191648ΔT = 25 o C1368 12361425Pdd3des1003200 3000 2800 1800 1600 1400 1200wavenumber (cm -1 )Figure 6 DRIFT Figure 10. desorption Desorption spectra of acetone of acetone adsorbed on on Pd/Al 2 O 2 33 during reduced heating from25°C to 250°C at in 25°C H 2at 120 increments. o C for 1.5 h after The purged catalyst in He was at 25 first o C for reduced 1 h in H 2 at 120°Cfor 1.5 h and purged in He for 1h at 25°CThe ketone group in acetone also strongly interacts with the catalysts. WhenThe ketone group in acetone also interacts strongly with the catalysts. When mesityloxide adsorbed on the catalysts was subjected to thermal desorption in helium, it canbe converted to MIBK, most probably, due to the hydrogenation of C=C by theresidual hydrogen from the pre-treatment of the catalysts with hydrogen. Therefore,mesityl oxide adsorbed on the catalysts is not stable and the strongly adsorbedspecies are ketone groups. Previous experiments in which HPLC grade MIBK wasintentionally added to a mixture of mesityl oxide and acetone did not indicateproduct inhibition had occurred during the hydrogenations carried out in anautoclave (3). However, it is possible that the strong adsorption of MIBK may haveaffected the long-term catalyst performance in the CD reactor. DRIFT experimentswith MIBK on alumina alone without Pd resulted in essentially the same spectra asthat obtained with Pd/Al 2 O 3 . Therefore the DRIFT spectra could not provide aninterpretation of the mechanisms of the reaction. However, the DRIFT data suggest astrong interaction of ketone group of MIBK with the Lewis acid sites of the aluminasupport.